Benghazi University Faculty of Science Chemistry Department             LABORATORY COURSE IN ORGANIC CHEMISTRY FOR CHEMISTRY STUDENTS COURSE NUMBER 5332& 5254     Professor. Mohamed EL-Fellah   Those  sciences are vain and full of errors which are not born from experiment, the mother of all certainty"

Table of CONTENTS TECHNIQUES EXPERIMENTS Page Introduction   TECHNIQUE 1 TECHNIQUE 2 TECHNIQUE 3 TECHNIQUE 4 TECHNIQUE 5 TECHNIQUE 6 TECHNIQUE 7 TECHNIQUE 8 TECHNIQUE 9 TECHNIQUE 10 TECHNIQUE 11 TECHNIQUE 12 TECHNIQUE 13 TECHNIQUE 14 TECHNIQUE 15 TECHNIQUE 16 TECHNIQUE 17 TECHNIQUE 18 Introduction to the Organic Laboratory            Experimental Method and Notebook               Distillation                                                      a)    Simple Distillation                                b)    Fraction Distillation                                                            c)    Steam Distillation                                d)    Vacuum Distillation                             Melting Points                                                Crystallization                                                Sublimation                           Chromatography                                            a)    Thin-Layer Chromatography b)    Column  Chromatography                                 Extraction                                                       Some Preparation of Organic Compounds    The Preparation of Aspirin                             The Preparation of Soap                               The Preparation of  2-Naphthyl Acetate      The Preparation of Dibenzalacetone The Preparation of Acetanilide   3 5 16 17 23 25 26 34 36 42 44 44 50 53 56 57 60 65 65 66

Introduction   LABORATORY COURSE IN ORGANIC CHEMISTRY   This laboratory course is designed to introduce students to the skills, methods, arts, and disciplines of experimental organic chemistry. Chemistry is one of the great experimental sciences and the successful chemist must be a skilled practitioner as well as being accomplished in theory.   Emphasis is placed on the areas of prime concern to the organic chemist: namely, the isolation of pure substances; the preparation of compounds; methods of purification and identification; the use of physical methods including spectroscopy; the interpretation of observations in terms of mechanism and theory. As you use this method to manipulate chemical compounds and observe the behaviour of chemical reactions, abstract concepts covered in lectures will become rooted in experience.   OBJECTIVES The main objective of these exercises is to teach students basic laboratory principles, techniques, and operations - the tools of the science. You will gain first-hand knowledge of some of the ideas previously encountered in lectures and books. And there will be opportunity to exercise and improve deductive and observational skills, and cultivate those habits of accuracy, neatness, and thorough inessential to good experimentation. We, as teachers, hope that during this course you will: 1.    Experience the process of discovery for yourself and see  the role played by                 experiment in scientific investigations . 2.    Become expert in isolating and purifying compounds by  extraction, distillation, crystallisation and in assessing  purity by physical measurement such as melting point, boiling point, chromatography. 3.    Practice some new techniques and handle as wide a variety of compounds as possible. 4.    Form a helpful working relationship with your demonstrator so that the opportunities for learning about chemistry during the laboratory sessions are exploited to the full.

DEMONSTRATORS Each class is assigned a group of a staff member whose function is to help the students as much as possible. Don't wait to be approached - if you need help - go to the staff member present. Demonstrators do not know all the answers but their greater experience in experimental chemistry will be a help to you. Student's problems in the laboratory are frequently those of lack of experience with a particular technique or lack ·of confidence or both. If you really do not know how to measure a melting point or how to do a distillation please tell your demonstrator and get his help. Also, don't be afraid of discussing your work with other members of your class, you may learn a lot from one another. However, report only your own work, not that of another   CONTINUOUS ASSESSMENT A scheme of continuous assessment will run throughout the course. This will count towards your final mark but, more importantly, it is to help you to assess how well you are progressing in your understanding and practice of chemistry. To this end, notebooks will be submitted at the end of each fortnight with samples. Each experiment will be assessed for a number of different points, some practical, such as the purity of your product, others theoretical, such as the answers to questions arising from a particular experiment. These points are listed for each experiment and your demonstrator will give you a mark for each as follows:   0          no result or no attempt 1          poor result 2          satisfactory result 3       very good result 4          Excellent.   The assessment areas have been chosen for their relevance to chemistry as it is professionally practised and the aim is to help you. For this reason, your demonstrators will discuss the assessment with you when they  mark your report sheet. The assessment areas are: Practical details (e.g. boiling point, melting point. yield of product. purity, appearance of sample); B Laboratory Technique, C Notebook; D Comprehension and answers to questions; The second part of the assessment will consist of two written, half-hour quizzes, one in the fourth week of the course covering general areas of laboratory practice and the second at the end of the course , based on the techniques and chemistry covered in the course.

EXPERIMENTAL METHOD AND NOTEBOOK An essential to success in laboratory work is proper preparation and planning. Read each experiment ahead of time; understand the chemistry of what you are to do before beginning the experiment. Study the parts of your organic chemistry textbook most closely related to the experiment you are about to perform. If you are able, track down the experiments in this course to primary or secondary sources of information in the library. You should, if you can, even go beyond this and find additional literature on the subject, or devise simple related tests or syntheses to widen the scope of the experiment. Incorporate the answers to questions at the end of an experiment into your notebook write-up. You must write a brief report on each experiment you do, and the sooner it is done the more accurate and useful it is likely to be Do not write lengthy reports, and do not copy out the detailed printed instructions for each experiment; these may be filed with your report. You must, of course, note where your procedure differs from that in the instructions and also where your observations differ from those expected. Your report must give details of the following: 1. A balanced equation for the reaction under study. 2. The quantities of materials used in the procedure. 3. The nature and size of the vessel used for the reaction. e.g. a 100 ml beaker, or a 10 ml round bottomed Quick fit flask. 4. A brief sketch of the essential experimental set-up employed. 5. The yields of all products of the reaction in grams and percentages, the calculation of percentage yields is shown below. 6. Melting points or boiling points of all products quoted as arrange. e.g. 141-l43oC, showing not the accuracy of the measurement but the range of temperature over which melting or boiling took place: 141.5oC or 14.2 oC is not acceptable. The close the melting points to the "correct" value, the smaller the range, is a general rule. Melting points will be checked by the demonstrator. 7. All significant observations and physical measurements. 8. Clear calculations of all derived quantities including an estimate of errors. 9. Answers to all questions at the end of each experiment.

YIELDS AND LOSSES - THEIR CALCULATION AND IMPORTANCE   In any chemical reaction the yield is limited by the stoichiometry; this can be demonstrated by reference to the formation of ethyl acetate in accordance with the following equation: This shows that 60 g of acetic acid cannot give more than 88 g of ethyl acetate. regardless of the amount of ethanol available, and conversely 46 g of ethanol can only give a maximum of 88 g of ethyl acetate, however much acetic acid is used. In practice, the yields obtained in organic preparations are usually less than the maximum theoretically obtainable. CALCULATION OF YIELDS Yields are conveniently expressed as a percentage of that theoretically possible. The yield theoretically obtainable is not always entirely clear. Reverting to the reaction in which ethanol is made to react with acetic acid, no problem would arise if equivalent quantities of all the reactants were used; if the reaction mixture simply contained 60 g of alcohol and 46 g of acetic acid, the equation shows that the theoretical yield of ethyl acetate is 88 g, regardless of whether one calculates by reference to the acetic acid or the ethanol. In practice, however, it is customary to use an excess of one or more of the reagents. In this example a substantial excess of alcohol is present, because it serves as a diluents' as well as a reactant, but the maximum possible yield of ethyl acetate is still limited by the acetic acid. Calculation of yields, both theoretical and actual, are always made with reference to the reactant which is not present in excess; this is one of the reasons for  recording not only the weights, but also the molar proportions of all the  components of the reaction mixture. The calculation of yield, which must take account of molecular weights of reactants and product, is based on the following: N.B. percentage yields are based on weight not volume   Calculate the Theoretical Yield Then calculate the theoretical yield based on the limiting reagent, which is the reagent present in the shortest supply. For following reaction of acetic acid, 3.0 g of the acid is treated with 3.3 g of ethanol and 2.0 ml of conc.H2SO4.   To calculate the theoretical yield: 1-                   1- Balance the reaction and calculate the moles of reactants. 2-          2- Calculate the molecular weights. 3-          3- Calculate the numbers of moles.                     MW:          60.05                           46.07                                                                        88.09           Weight:       3.00 g                          3.30 g                Moles:         0.050.07 4-    Determine the limiting reagent. The required amounts of ethanol to react with acid to form the ester. In this particular reaction, the acid is limiting reagents, while the alcohol is present in excess. 5-    Determine the theoretical number of moles of product possible. In this case, 0.05 mole of ethyl acetate is the maximum, or theoretical, yield (the same as the number of moles of acetic acid, one of the limiting reagents). 6-    Convert the theoretical yield of product to grams. 0.05 mole of ethyl acetate  = 0.05 mole   X   88.09 g/mol                                           =   4.41g (theoretical yield)

SAFETY AND AVOIDING ACCIDENTS A chemistry laboratory can be a dangerous place. Accident prevention is everyone's responsibility, and if you work with care you (and your neighbours) ought to survive. Therefore: 1. Never work alone in the laboratory. 2. Do not smoke or eat in the laboratory. 3. You must wear safety glasses at all times. 4. Wear a laboratory coat and keep all books off the work bench except your notebook. 5. Never boil any liquids in the open laboratory or allow gases to escape; use the fume cupboard. 6. Use steam baths, heating mantle, or hot plate rather than open flames. If you need to use a Bunsen burner consult your demonstrator before lighting it and always extinguish it immediately after use. In no event should a flame be left unattended. Always point the mouth of a test-tube or flask away from yourself and others when conducting a reaction. 7. Never, but never taste anything in the laboratory; never allow any compound on your skin, or breathe in the dust from a solid or the spray or vapour of a liquid. Treat all compounds as potential hazards. Some compounds are particularly dangerous; carcinogenic compounds cause cancer; some apparently harmless compounds, like benzene, are very toxic indeed. All are lethal in sufficient quantity. Use rubber gloves to protect your hands. 8. Beware of fires. Know where the fire extinguishers are. Distill low-boiling flammable liquids with a steam bath and an efficient condenser. 9. Handle glassware carefully. Be particularly careful when connecting rubber tubing to a glass condenser as glass ware can easily fracture under pressure. Consult your demonstrator before assembling glass apparatus. 10. Report all accidents to your demonstrator. You may think that you are "all right" after an accident but it is not worth taking a chance. TECHNIQUES OF ORGANIC CHEMISTRY   The underlying theme of many of the experiments in this course isthe preparation for a reaction, the isolation of the product or products, their purification and identification, including the use of physical measurements. Next few pages show the equipment’s which most used in laboratories:   Typical glassware stored in a Laboratory.   Round-bottom flask, assorted sizes            2 and 3-neck round-bottom flask (used (for                                                                   reactions  distillations) with a reflux    condenser, stirrer, and                                                               dropping funnel)                  Erlenmeyer flask, assorted size Heavy-walled filter flask (for vacuum filtration)   Separator funnel                  dropping funnel                                         distillation head Claisen head (for extractions)             (for adding liquids to a reaction vessel)       (for distillations and reaction assemblies)                                                           Condenser, assorted kind    Beakers, assorted size      adapter  assorted size.   Receiver adapter         Vacuum distillation                                      Graduated cylinder ,

Hardware and other nonglass items typically found in Chemistry Laboratory.     Some typical laboratory heating devices. Back to Contents

PREPARATION FOR A REACTION   1. Assembling Equipment. Some of the equipment may be unfamiliar to you, but you will find drawings and charts in the laboratory of the standard glassware used. You will also find drawings in this manual of the appropriate experiments. In addition, at the beginning of each experiment the demonstrators will show the class how the necessary equipment should be assembled. 2. Is the glassware clean; are the joints mutually suitable and do you need to use grease? 3. Are all clamps in their proper place? There is a right and wrong way of using clamps. Watch the demonstrator. 4. Is the scale~ the apparatus suited to the scale of the experiment? A common mistake is that of using a flask which is much too large for the volume of material to be used.   EXPERIMENTS FOR ORGANIC CHEMISTRY I (5233)   A-  Purification of an organic compound   Experiment 1   Purification of Liquids by Distillation process involving the conversion of a liquid into vapour that is subsequently condensed back to liquid form. It is exemplified at its simplest when steam from a kettle becomes deposited as drops of distilled water on a cold surface. Distillation is used to separate liquids from non-volatile solids, as in the separation of alcoholic liquors from fermented materials, or in the separation of two or more liquids having different boiling points, as in the separation of gasoline, kerosene, and lubricating oil from crude oil. Other industrial applications include the processing of such chemical products as formaldehyde and phenol. Types of Distillation There are several types of distillation depending on the procedure and the instrument setup. Each of the distillation type is used for the purification of compounds having different properties. Following are the common types of distillation: Simple Distillation Simple distillation is practiced for a mixture in which the boiling point of the components differ by at least 70°C. It is also followed for the mixtures contaminated with in volatile particles (solid or oil) and those that are nearly pure with less than 10 percent contamination. Double distillation is the process of repeating distillation on the collected liquid in order to enhance the purity of the separated compounds.   Fractional Distillation Those mixtures, in which the volatility of the components is nearly similar or differs by 25°C (at 1 atmosphere pressure), cannot be separated by simple distillation. In such cases, fractional distillation is used whereby the constituents are separated by a fractionating column. In the fractionating column, the plates are arranged and the compound with the least boiling point are collected at the top while those with higher boiling point are present at the bottom. A series of compounds are separated simultaneously one after another. Fractional distillation is used for the alcohol purification and gasoline purification in petroleum refining industries. Steam Distillation Steam distillation is used for the purification of mixtures, in which the components are temperature or heat sensitive; for example, organic compounds. In the instrument setup, steam is introduced by heating water, which allows the compounds to boil at a lower temperature. This way, the temperature sensitive compounds are separated before decomposition. The vapors are collected and condensed in the same way as other distillation types. The resultant liquid consists of two phases, water and compound, which is then purified by using simple distillation. Steam distillation is practiced for the large scale separation of essential oils and perfumes. Vacuum Distillation Vacuum distillation is a special method of separating compounds at pressure lower than the standard atmospheric pressure. Under this condition, the compounds boil below their normal boiling temperature. Hence, vacuum distillation is best suited for separation of compounds with higher boiling points (more than 200°C), which tend to decompose at their boiling temperature. Vacuum distillation can be conducted without heating the mixture, as usually followed in other distillation types. For the separation of some aromatic compounds, vacuum distillation is used along with steam distillation.

1-   Simple Distillation.       SIMPLE distillation is a procedure by which two liquids with different boiling points can be separated. Simple distillation (the procedure outlined below) can be used effectively to separate liquids that have at least fifty degrees difference in their boiling points (if the boiling points do not have this degree of separation, see Fractional Distillation). As the liquid being distilled is heated, the vapours that form will be richest in the component of the mixture that boils at the lowest temperature. Purified compounds will boil, and thus turn into vapours, over a relatively small temperature range (2 or 3°C); by carefully watching the temperature in the distillation flask, it is possible to affect a reasonably good separation. As distillation progresses, the concentration of the lowest boiling component will steadily decrease. Eventually the temperature within the apparatus will begin to change; a pure compound is no longer being distilled. The temperature will continue to increase until the boiling point of the next-lowest-boiling compound is approached. When the temperature again stabilizes, another pure fraction of the distillate can be collected. This fraction of distillate will be primarily the compound that boils at the second lowest temperature. This process can be repeated until all the fractions of the original mixture have been separated.   Basic Procedure     Fill the distillation flask. The flask should be no more than two thirds full because there needs to be sufficient clearance above the surface of the liquid so that when boiling commences the liquid is not propelled into the condenser, compromising the purity of the distillate. Boiling chips should be placed in the distillation flask for two reasons: (1) they will prevent superheating of the liquid being distilled and (2) they will cause a more controlled boil, eliminating the possibility that the liquid in the distillation flask will bump into the condenser.  It the distillation flask slowly until the liquid begins to boil (see Figure 4). Vapours will begin to rise through the neck of the distillation flask. As the vapours pass through the condenser, they will condense and drip into the collection receiver (see Figure 5). An appropriate rate of distillation is approximately 20 drops per minute. Distillation must occur slowly enough that all the vapours condense to liquid in the condenser Many organic compounds are flammable and if vapours pass through the condenser without condensing  , they may ignite as they come in contact with the heat source. As the distillate begins to drop from the condenser, the temperature observed on the thermometer should be changing steadily. When the temperature stabilizes, use a new receiver to collect all the drops that form over a two to three degree range of temperature. As the temperature begins to rise again, switch to a third collection container to collect the distillate that now is formed. This process should be repeated; using a new receiver any time the temperature stabilizes or begins changing, until all of the distillate has been collected in discrete fractions. (note: All fractions of the distillate should be saved until it is shown that the desired compound has been effectively separated by distillation). Remove the heat source from the distillation flask before all of the liquid is vaporized. If all of the liquid is distilled away, there is a danger that peroxides, which can ignite or explode, may be present in the residue left behind. Also, when all of the liquid has evaporated, the temperature of the glass of the filtration flask will rise very rapidly, possibly igniting whatever vapours may still be present in the distillation flask. A. liquid left to stand in an open vessel, such as a beaker, will evaporate. Evaporation is the escape of molecules from the liquid phase to the gas phase. If a bell jar is placed over a beaker of an evaporating liquid, equilibrium is reached whereby the space above the liquid becomes saturated with molecules of the vapour. The molecules in the vapour exert a pressure on the walls of the bell jar. This pressure is characteristic of the liquid and is known as the equilibrium vapour pressure. As the term implies, it is the pressure exerted by a vapour  when in equilibrium with its liquid. Vapour pressure is a measure of the tendency of a liquid to pass into the gaseous state. It depends upon the nature of the liquid and the temperature. The greater the attractive forces between the liquid molecules, the lower the vapour pressure. Liquids composed of molecules having small mutual attraction have a high escaping tendency and hence a high vapour pressure. Vapour pressure increases with increasing temperatures. The temperature at which the vapour pressure is equal to the atmospheric (barometric) pressure is termed the boiling point of the liquid. It is a property of a pure liquid that it boils at a constant temperature at a constant pressure. Every pure liquid has its own characteristic boiling point and this serves as a useful criterion of identity and purity, Distillation is the process of heating a liquid to its boiling point, condensing the vapours, and collecting the liquid condensate. It is the most commonly used technique for the purification of organic liquids. Two liquids having widely different boiling points can be readily separated, The liquid boiling at the lower temperature will be collected in the receiver; the one that  boils at the higher temperature will remain behind in the distilling flask. In many cases a simple distillation is not satisfactory for the complete purification of miscible liquids. The first condensate of such a mixture will contain some of the higher-boiling liquid along with the lower-boiling component. If this initial condensate is redistilled, the first vapour sand condensate again will contain a greater percentage of the lower-boiling liquid. When this process of redistilling the condensate is repeated many times, a good separation of the mixture can be achieved. The necessity of performing these multiple distillations can be eliminated through the use of a fractionating column. The process is then termed a fractional distil/at ion.

Distillation of an Acetone-Water Mixture   In this experiment the efficiency of a simple distillation will be compared with that of a fractional distillation.   1- Set up a simple distillation apparatus as illustrated in Figure below. Be sure to check the following details:    2-   a.  The top of the thermometer bulb should extend just below the side arm of the  distilling flask so that the entire mercury bulb is bathed in the rising vapour. b.  The side arm should extend beyond the end of the cork into the top of the  condenser, and the tip of the condenser should extend beyond the Claisen adapter. c.  Clamp both the distilling flask and the condenser. The adapter need not be clamped. d. The lower end of the adapter is not connected to the receiver with a cork. If it were, a closed system would result and might lead to an explosion as the system was heated. e.  Circulate water through the condenser prior to distillation. Water enters  the lower portion of the condenser and exits from the upper position. f.  Add a few boiling chips (porous porcelain or tile chips) to the distilling  flask to prevent any major amount of superheating. These chips operate by supplying a surface on which bubble nuclei  can be formed, and thereby induce even boiling. When boiling is not uniform, bumping occurs. This term is used to describe the intermittent violent eruptions of the liquid mixed with its vapour.   3- Remove the thermometer with its cork and, by means of a long-stem funnel, add 20 ml of acetone and 45 ml of water into a 1-ml distilling flask.    4- Number and label five 50-ml Erlenmeyer flasks for collecting various fractions as follows: Apparatus for a simple distillation Gently heat the flask until the liquid begins to boil. When the liquid begins to drip into the receiver, so that the distillate collects steadily at the rate of approximately 1 drop every 2 seconds.   5- Change the receiving flasks rapidly at the specified temperature intervals shown in step4.    6-  Continue distilling until the temperature reaches 95oc, then shut off the heating mantle.    7- Measure with a graduated cylinder the volume of distillate obtained in each fraction and the residue remaining in the distilling flask. Record these five volumes in the table below. Graph a distillation curve by plotting the volume of distillate vs. the temperature range.

2- Fractional Distillation   A fractionating column is simply a glass column which contains a packing or condensing surface (e.g., glass helices, stainless steel sponges or indentations along the length of the column). The fractionating column functions as a combination of a number of miniature simple distilling assemblies. The rising vapours condense in the column, coat the surfaces of the packing, and start to flow back into the distilling flask. Before the liquid can return to the flask, it comes in contact with more of the rising hot vapours, and most of the liquid is revaporized by the heat of the hot vapours. This is the equivalent of a second distillation of the liquid and as this process occurs repeatedly in the column;  vapours of the lower-boiling component gradually make their way through the side arm of the column and into the condenser. The higher-boiling liquid again remains behind in the distilling flask. Table 1 Example of Azeotropic Mixtures     Azeotropic     Boiling  Point   Composition by Weight Ethanol- Water 78.1 ° 95% Ethanol Propanol- Water 87.3° 72 % Propanol Ethyl Acetate-Water 70.40 94 % Ethyl Acetate Ethyl Acetate-Ethanol 71.80 69 % Ethyl Acetate Carbon Tetrachloride     Methyl Alcohol 55.7° 80 % Carbon Tetrachloride Water-Hydrogen Chloride 1090 80% Water Occasionally liquids that may differ widely in their boiling points form Azeotropic mixtures of definite and constant composition (see Table 1). In these cases a mixture of fixed composition boils at a constant temperature and behaves, upon distillation, exactly as though it were a single pure liquid. The components of an azeotropic mixture cannot be separated by fractional distillation because the vapour in equilibrium with the liquid has the same composition as the liquid itself (as is the case for a pure substance). The formation of azeotropic mixtures is believed to be the result of loose intermolecular attractions between molecules of the liquid pairs. This is similar to water of crystallization, the attraction of water and a salt. A mixture of 95 % ethyl alcohol, and 5 % water boils at a temperature of 78.1 "c. (Pure ethyl alcohol boils at 78.4'C so that you would need a reliable thermometer to observe the difference.) Distillation of ethyl alcohol and water mixtures of less than 95 % alcohol results in separation into pure water and 95 % alcohol; mixtures containing more than 95 % alcohol are separable into pure (absolute) alcohol and 95 % alcohol.   The set-up employed for a fractional distillation is a slight modification of that used For a simple distillation.   1-    Fit a fractionating column into a 100-ml round-bottom flask (not a distilling flask). 2-    Add a few boiling chips, 20 ml of acetone, and 45 ml of water to the round- bottom flask and assemble the fractionating apparatus as illustrated in Figure below.   Apparatus for fractional distillation   3-    Proceed with the distillation in the same manner as before. 4-    Again measure and record the total volume of each fraction .     Fraction     Temperature Range (oC)   Volume Collected Simple Distillation Fractional Distillation I 55-64     II 65-71     III 75-84     IV 85-94     V. Residue -     Total Volume           Compare the volume of distillate obtained in each of the receivers by the two distillation methods. Which method was more efficient for the separation of an acetone-water mixture?

3- Steam Distillation Steam distillation is a process by which volatile organic compounds are separated from non-volatile inorganic salts. Most of the organic compounds break down at high temperatures. When steam is added to the distillation apparatus, the boiling point of the compounds comes down and this allows the organic compound to evaporate at lower temperature. Steam distillation is used for separating the liquid mixture which consists of compounds which are immiscible in water (i.e., that cannot undergo mixing or blending) but volatile in steam. The process is based on the principle that the vapour pressure above the mixture is equal to the sum of individual vapour pressure of the compounds. When vapour pressure is equal to atmospheric pressure, the liquid starts to boil. When steam is passed on to the mixture which contains the mixture of immiscible organic compounds, it gets heated by the steam and itself condenses into water. When vapour pressure above the mixture becomes equal to atmospheric pressure, the resulting mixture of organic compound and water starts to boil until one of the liquids completely distills out. The distillate which is a mixture of water and the organic compound separates into two layers because both the liquids are immiscible with respect to the other. These two layers are separated using a separating funnel. Process Steam is generated in a boiler by heating water. It then flows to a separate container through a tube. It is necessary to separate both the containers since the heat used to produce the steam can decompose the compound which is to be distilled. After the steam is added to the distillation apparatus, the steam then passes through a condenser and the vapours are collected. The condenser uses water to cool the steam. The resultant liquid is again purified using simple distillation to separate the compound. Apparatus for steam distillation

4- Vacuum Distillation   Many organic liquids cannot be distilled at atmospheric pressure because the temperature required causes decomposition. This frequently is the case with compounds boiling much above 200°C and sometimes at even lower temperatures. This difficulty can be overcome by distilling at a lower pressure. The vapour pressure of any substance is a function of temperature, and the lower the pressure within the distillation apparatus, the lower the boiling point. A plot of vapour pressure vs. temperature has the form shown in Figure 1. For simple organic compounds, reduction of the pressure from 750 to 20 mm causes a drop in boiling point of 90 to 120°C. A monogram for use in estimating boiling points of relatively nonpolar compounds at reduced pressures is given in Figure 1. This chart is less accurate for compounds that are highly associated in the liquid phase.    Figure 1 Boiling point-pressure monogram. To find the atmospheric pressure boiling point of a compound for which the boiling point is known at a reduced pressure (e.g., 700 at 1 mm), lay a straight-edge from the known boiling point (70°) on scale A to the pressure (1 mm) on scale C. The intercept on scale B gives' the boiling point at 760 mm (-240°). By connecting the atmospheric pressure boiling point on scale B (240°) with a different reduced pressure on scale C (e.g., 100 mm), the boiling point at this latter pressure can be read on scale A (165°). APPARATUS AND TECHNIQUE Distillation at reduced pressure is carried out in a set-up such as that shown in Figure 2. Pressures down to about 20 mm can be obtained with a good water aspirator; for lower pressure, an oil-sealed mechanical pump is used, and a cold trap must be placed in the system to protect the pump from vapours. To obtain a meaningful boiling point, a manometer must be included to measure the pressure. A Bunsen valve from a burner can be included to permit a controlled leak for distillation at an intermediate pressure. If several fractions are to be collected, some means of changing receivers without interrupting the distillation is required; this is usually advice (called a cow) which can be used to position different receivers under the outlet from the condenser (Fig. 2).   Figure 2 Vacuum distillation set-up.

Experiment 2   Melting Point   The melting point of a pure compound may be defined as that temperature at which the solid and liquid phases of the compound are in equilibrium at some particular pressure, usually taken as 1 atm. or 760 mm Hg. The melting point is an important criterion of identity of an organic solid and also a measure of purity, the preparation or purification of a cysteine solid is not complete until this value has been determined and recrystallization carried out until the melting point is no longer raised after further crystallisation. Very few substances melt instantaneously and a melting range (e.g., 135-137oC) should be recorded. This indicates that melting was first observed at l35oC and was complete at 137oC. Pure compounds have a very narrow melting range; impure compounds have a lowered melting point and a wider melting range. Equipment and Procedure The specimen to be examined is contained in a thin walled capillary tube about 1 mm. diameter. Suitable tubes are provided. A piece of clean capillary tube about 6 cm long is sealed at one end by heating in a small Bunsen flame. A small amount of the compound is powdered on a watch glass and some of the powder is introduced into the capillary tube. The capillary tube is then held vertically and gently tapped or rubbed with the milled edge of a coin which causes the material to settle to the bottom. The specimen is then placed in an electrically heated block close to the thermometer bulb and observed through the eye-piece. It: is heated slowly and the melting range, observed, When the approximate m.p., of the specimen is known care can he taken to heat at a rate of 2° per minute close to the m.p. so as to ensure that the specimen and the thermometer bulb are in thermal equilibrium. Prepare the melting point apparatus illustrated. The 150 ml beaker holds mineral oil or glycerine, and is provided with a loop stirrer made of heavy copper wire or glass. The thermometer must have a range of at least 250oC. When about three eighths of an centimetres of sample has been worked into the melting point capillary tube, fasten it to the thermometer with a narrow band or rubber tubing so that the sample is beside the thermometer bubble. Then mount the thermometer so that the bubble and the bottom of the sample tube are immersed in oil. Raise the temperature while stirring actively. Until the sample in the tube has melted. Does the sample melt sharply? Record the melting point or melting range.

Melting Points of a Mixture: It is usually possible to prove or disprove the identity of two solids of similar melting point by a mixture melting point determination. In general, a mixture of samples of non- identical compounds shows a melting point depression. When carrying out a mixture melting point determination, samples of each pure compound are first placed in separate capillary melting point tubes. Then approximately equal amounts of the two compounds are ground together on a watch glass and the mixture placed in a third capillary tube. The three samples are placed in the melting point apparatus and heated together whilst observing their behaviour. If the substances are identical, all three samples will melt at the same temperature. Otherwise the melting point of the mixture will be depressed and it will melt over a wide range of temperature. To prepare a sample for determination of mixture melting point, place approximately equal amounts of the two compounds on a watch glass and mix them together. Then crush the crystals to a powder and grind them thoroughly with a spatula. When the pile of crystals is spread out to a thin layer, scrape the powder together and grind again. Fill the melting point capillary in the usual way and fill other capillaries with samples of the two individual compounds that have been ground to the same degree of fineness. Place all three samples together, with the mixture in the middle, in the block and observe the melting point simultaneously. The temperature can be raised rapidly to about 20o below the expected melting point.

Experiment 3   Purification of Solids by Crystallization Techniques: Crystallisation, filtration, melting point determination. A highly effective and common method of purifying a solid substance consists of dissolving it in a suitable solvent at the boiling point of the solvent , filtering the hot solution by gravity to remove any  suspended insoluble particles and letting the solution cool naturally  while crystallisation proceeds. When the solution has reached room temperature it is chilled in in ice bath to promote further crystallisation. The process utilises the general principle that a solid which is soluble in the hot solvent becomes less soluble as the temperature decreases. Ideally, all of the desired compound should separate in a pure crystalline form and all the soluble impurities remain dissolved in the solution, usually referred to as the mother liquor. The crystals that have separated in this fist crop are collected by suction filtration and washed free of mother liquor with a little fresh, chilled solvent. If it is considered worthwhile, the combined mother liquor and washings can be concentrated in volume and let stand for separation of a second crop of crystals. The quality of each crop of crystals is ascertained by the melting point.   Decolourising Charcoal and Filtration Frequently a sample to be purified contains a soluble impurity that gives rise to solutions and crystals that are slightly coloured when they should be colourless. Such solutions are treated with decolourising (activated) charcoal. The fine carbon particles present a large active surface (300-2000 square metres per gram) for adsorption of dissolved substances, particularly polymeric, resinous by-products that appear in. traces in most organic reaction mixture. Decolourising charcoal is added to the hot solution prior to filtration, and the solution is kept hot for a few minutes) and. filtered. Hot solutions should be filtered through a fluted filter paper using gravity not a suction pump. Your demonstrator will show you bow to fold a fluted filter paper. The object fluting the paper is to decrease the area of contact of the filter with the funnel and so speed up the filtration process. If filtration is too slow, the solution will cool and may deposit crystals on the filter paper. It is advisable to heat the funnel before performing a hot filtration. The important steps in crystallisation are, therefore, the following: 1-    Dissolve the impure solid in the minimum volume of hot solvent. (In this course you will be told which solvent to use; if you were dealing with a. new compound or one of unknown composition it would be necessary by trial and error to find the most suitable solvent). 2-    If necessary, treat the solution with activated charcoal to remove traces of soIubIe coIoured impurities. 3-    Filter the hot solution, if necessary, to remove charcoal and/or Insoluble particles using gravity filtration and a fluted filter paper. 4-    Allow the clear solution to cool undisturbed to room temperature during which time crystallisation usually commences. Then cool further in an ice bath to complete   crystallisation. 5-    Filter the cooled mixture to separate the crystals from the mother liquor using a Buchner or Hirsch funnel and wash the crystals with the minimum amount of cold fresh solvent to complete the removal of dissolved impurities. 6-    Dry the crystals initially by drawing air through the funnel using the suction   pump. Solvents: The solubility of a solute in a particular solvent largely depends upon the temperature of the solvent see the table below. The most important consideration in performing a recrystallization is the choice of a suitable solvent. Solubility as a Function of Temperature     Solute     Solvent   Temperatureo C   Solubility (g/l00ml) Acetamide Ethanol 20° 60° 25.00 257.00 Acetanilide Water 25° 100° 0.56 5.00 Benzoic acid Water 18° 75° 0.27 2.20 Cholesterol Ethanol 17° 78° 1.00 11.00 Iodoform Ethanol 18° 78° 1.30 7.80 Succinic acid Water 20° 100° 6.80 121.00 Ideally, a good solvent for purification should have the following characteristics: (1) It does not react with the solute. (2) It dissolves considerably more of the desired product at high temperatures (usually the boiling point of the solvent) than at low temperatures (usually room temperature or ice temperature). (3) It dissolves contaminants at low temperatures and/or it does not dissolve them at high temperatures. (4) It has a relatively low boiling point to facilitate its evaporation from the wet crystals. Solvents commonly used for recrystallization purposes include water, methanol, ethanol, acetone, ethyl acetate, chloroform, carbon tetrachloride, benzene, hexane,and petroleum ether. These solvents are listed in a general order of decreasing polarity.   Crystallization of Acetanilide   1-    Weigh out a 2.5 g sample of impure acetanilide and place it in  a 125-ml Erlenmeyer flask. 2-    Add 50 ml of water and a small amount of decolorizing charcoal to the flask. 3-    Assemble the apparatus with a reflux condenser as illustrated in Figure 1.1. 4-    Circulate the water through the condenser in a slow, steady stream. 5-    Heat the water in the flask to boiling, adjusting the burner flame so that the waterrefluxes in a steady drip from the bottom of the condenser. 6-    Continue to heat the flask for about 10 min or until no more solid dissolvesWhile the mixture is being heated prepare a fluted filter paper see the figure below.                                       (a)                                       (b)                             (c)                       (d)

How to prepare fluted filter paper Step 1. Fold the paper in half, then in quarters, creasing the folds as you proceed. However, do not crease the very centre of the paper (the point), which might become weakened. Step 2. Open the quarters to a half-sized piece, and then fold the edges in to the centre fold. Step 3. Open the paper again to a half-sized piece, then accordian-pleat, using the existing fold lines as guides. (Again, do not crease the centre of the paper.) Step 4. Crease the folds (except at the point), then open the filter paper and place it in an appropriately sized funnel. The figure above, show preparing a fluted filter. (a) Fold the paper in half and then in half again. Bring each edge into the centre fold, making two additional creases in the same direction. This divides the paper into four equal sections. (b) Then divide each section by a crease still in the same direction. This gives eight equal sections') Divide each section in two by a crease in the opposite direction, thus making sixteen sections and thirty-two sections when the filter paper is opened (d). A stemless funnel and fluted filter paper are commonly used to speed up the gravity filtration of a hot solution. A fluted filter paper provides a maximum filter surface and a minimum of cooling and crystallization at the glass-paper interface. A stemless funnel prevents the filtrate from cooling in the stem accompanied by premature crystallization of the product. 1-    Place the stemless funnel containing the fluted filter paper in a beaker of appropriate size. The lower tip of the paper should project through the opening at the bottom of the funnel. 2-    Preheat the filter and funnel just prior to use by pouring a little boiling water through it. 3-    Carefully remove the reflux condenser from the flask. 4-    Using the flask clamp as a handle, pour the hot suspension through the  filter paper. Note: It is essential that this operation be completed as quickly  as possible in order that cooling be minimized. If all of the solution cannot be placed into the funnel at once, the remainder should be kept hot, by  heating over the Bunsen flame, until it can be transferred to the funnel. The charcoal and other insoluble impurities collect on the filter paper; the filtrate should be a clear solution. 1-    Allow the filtrate to cool to room temperature and then place it in an ice bath. 2-    Prepare a suction filtration apparatus using a Buchner funnel fig below. Buchner funnel and filter flask for suction filtration 13- Place the proper size filter paper in the funnel. Then attach the funnel  to  an aspirator with heavy-waned tubing. Turn on the aspirator and pour some distilled water through the funnel. This serves to moisten the filter paper, making it fit snugly to the funnel. 14-Decant, through the funnel, most of the mother liquor and then pour in the bulk of the crystalline acetanilide. Use a wash bottle containing cold distilled water to rinse out the remaining crystals from the beaker.  15-The residual liquid can be pressed out of the mat of crystals with a clean  rubber stopper.     16-Disconnect the suction flask and transfer the crystals to a clean watch glass or a large piece of filter paper to air-dry.  17-Weigh your dried crystals and calculate the percentage recovery of purified acetanilide. Then, determine the melting point. 18- Identified your unknown sample from the following table: Organic Compound Melting Point oC Dinitrobenzene Naphthalene Benzoic Acid Acetanilide 2 – Naphthol Benzanilide Urea Benzoin 89 – 90 79 – 80 121 – 122 113 – 114 120 – 121 160 – 161 132 – 133 132 – 133

Experiment 4   Purification of Solids by Sublimation Sublimation is a process whereby a solid is purified by vaporizing and condensing it without its going through an intermediate liquid state.  Solid compounds that evaporate (that is, pass directly from the solid phase to the gaseous phase) are rather rare; solid CO2(dry ice) is a familiar example of such a compound. Even though both solids and liquids have vapour pressures at any given temperature, most solids have very low vapour pressures. In order for a solid to evaporate, it must have an unusually high vapour pressure compared to othersolids. For a solid compound to exhibit such a high vapour pressure, it must have relatively weak intermolecular attractions. One factor that contributes to weak intermolecular attractions is the shape of the molecules. Many compounds that evaporate readily contain molecules that are roughly spherical or cylindrical shapes that do not lend themselves to strong intermolecular attractions. The table below show lists some solids that can be sublimed in the laboratory. Vapour pressures of some solids at their melting points Compound MP.(oC) Vapour pressure (mmHg) at the melting point Hexachloroethane 186 780.0 Camphor 179 370.0 Iodine 114 090.0 p-Dichlorobenzene 053 008.5 Naphthalene 080 007.0 Benzoic acid 122 006.0 Sublimation can be used to purify some solids just as distillation can be used to purify liquids. In sublimation, non-volatile solid impurities remain behind when the sample evaporates, and condensation of the vapour yields the pure solid compound. Sublimation has the advantages of being fast and clean because no solvent is used. Unfortunately, most solid compounds have vapour pressures too low for purification in this fashion. Also, sublimation is successful only if the impurities have much lower vapour pressures than that of the substance being purified. It would be practical to purify technical-grade iodine, which is contaminated with inorganic salts, by sublimation. It would not be practical to separate camphor from. isoborneol (from which commercial camphor is synthesized), however, because both compounds readily sublime.The vapour pressure of solid increases with temperature, just as it does for liquids. Therefore, evaporation can be facilitated by heating the solid, but not to its melting point. The rate of evaporation can also be increased by subliming the solid  under a vacuum; however, a very efficient cooling surface must be used for the condensation so that the solid's vapour is not lost into the vacuum system.   A sublimation apparatus using a filter flask, ice-filled test tube, and hotplate.

Experiment 5     Chromatography        1) Thin-Layer Chromatography Thin-layer chromatography (abbreviated TLC) is a variation of column chromatography. Instead of a column, a strip of glass or plastic is coated on one side with a thin layer of alumina or silica gel (sometimes mixed with plaster of Paris, CaSO4, a binder) as the adsorbent. Other adsorbents can also be used. The quality of the separation for a given mixture depends largely on the adsorbent. In a TLC analysis, few amount of a solution of the substance to be tested is placed ("spotted") in a single spot near one end of the plate, using a microcapillary. The plate is "developed" by placing it in a jar with a small amount of solvent. see the Figure 1  below) shows a tlc plate in a developing jar. The solvent rises up the plate by capillary action, carrying the components of the sample with it. Different com­pounds in the sample are carried different distances up the plate because of variations in their adsorption on the adsorbent coating. If several components are present in a sample, a column of spots is seen on the developed plate, with the more polar compounds toward the bottom of the plate and the less polar compounds toward the top. As an analytical tool, TLC has a number of advantages: 1-    It is simple, quick, inexpensive, and requires only small amounts of sample. 2-   TLC is generally used as a qualitative analytical technique, such as checking the purity of a compound or determining the number of components in a mixture. 3-   We can use TLC to follow the course of a reaction by checking the disappearance of starting material and the appearance of product. 4-   TLC is useful for determining the best solvents for a column chromatographic separation. 5-   It can also be an initial check on the identity of a sample (by spotting the plate with a known compound as well as with the sample). 6-   With calibration, TLC can be used as a quantitative technique. Preparative work can be carried out    with special thick-layered TLC plates.   Thin-layer chromatography. The spotted plate is placed in the developing jar with a piece of filter paper, which acts as a wick to saturate the atmosphere with solvent. Different compounds move up the plate at different rates: the less polar compounds move the fastest and are found closer to the solvent front. The RfV  is  the distance that the spot of a particular compound moves up the plate    relative to the distance moved by the solvent front is called the retention factor, or Rr value.                   The RfV     These distances are measured. When the developed tIc plate is removed from the developing jar, the solvent front is marked immediately with a pencil before the solvent evaporates. Assuming that the compound spots are colored, the spots are outlined with a pencil in case the color fades. The distance that a compound has travelled is measured from the original spot to the center of the new spot. If the spot is elongated, the "center" is estimated (usually closer to the leading edge). The distance that the solvent has travelled is measured from the original spot to the solvent front. The Rf value for a compound is a constant only if all variables are also held constant: temperature, solvent, adsorbent, thickness of adsorbent, amount of compound on the plate, and distance the solvent travels. Because it is difficult to duplicate all these factors exactly, an unknown sample is usually compared with a known compound on the same plate. A mixture containing compound A compares with pure A on the same plate. If two substances have the same Rf value, they are likely (but not necessarily) the same compound. A second tIc comparison with a different solvent may result in different Rf values, in which case the substances are not the same. If the second tIc analysis results in the same Rf value for the pair, the likelihood that the samples are identical increases. Even in this case, some other type of corroborating evidence should be sought.   Figure 2 The Rt value for compound A is the ratio of the distance it has travelled to the distance the solvent has travelled. The spot for A is not circular here, but shows "tailing"; therefore, the center of the spot is estimated. (Tailing is sometimes caused by too much sample in the original spot.)   A known and an unknown sample may be analyzed on the same plate at the same time.     1-Tlc Sheets and Plates. Commercial tic sheets are coated with silica gel (SiO2) or alumina (Al2O3). Choose the type that gives the best separation for your particular mixture. If commercial tic sheets are unavailable, plates can be made from micro­scope slides and a slurry of 1 g aluminum oxide G or silica gel G and 2 mL chloroform (CAUTION: toxic). A 2: 1 mixture by volume of dichloromethane and methanol (also toxic) may be substituted for the chloroform. Dip two slides, back-to-back, in the slurry. Allow the excess slurry to drain. Separate the slides and allow them to dry in a fume hood. Then wipe excess adsorbent from the backs and edges of the slides. Making satisfactory plates requires practice; therefore, prepare a number of plates and select the most evenly coated ones. Microscope slide plates are shorter than commercial sheets; conse­quently, the separation of components is not as clean. Pipets.Commercial 10-JLL disposable pipets are best. If commercial pipets are not available, draw out some soft glass tubing or melting-point capillary tubes in a flame. The diameter of the pipet should be about 1/4 of the diameter of a melting-point capillary. Developing jars.Developing chambers with the proper solvent system may be prepared in advance and kept in the fume hood. Any tall jar, such as an instant coffee jar or mason jar, with a lid or screw top, may be used for developing a tlc plate. The jar should be narrow enough to hold the plate upright inside, without the danger of its falling over . The lid of the jar should be  impervious to solvent fumes.   Steps in a TLC Analysis 1) Preparing the developing jar.Line the inside of the jar half-way around with a piece of filter paper, which will act as a wick to saturate the atmosphere in the jar with solvent vapor. Before inserting the tic plate, pour a small amount of the developing solvent into the jar to soak the filter paper and to cover the bottom of the jar to a depth of about 0.5-1.0 cm. The solvent level should cover the edge of the adsorbent on the plate, yet not reach the spots. Cap the jar and allow it to sit for at least 15 minutes to reach liquid-vapor equilibrium. Check that the solvent level is still about 0.5-1.0 cm, and add more solvent if necessary before inserting the plate. 2) Spotting the plate.Dissolve about 1 mg of the solid or liquid sample in a few drops of a volatile solvent such as methanol, CH3OH, or acetone, (CH3)2C=O. Dip the end of a fresh micropipet into this solution, which rises into the pipet by capillary action. At about 1.5 cm from the end of the plate, touch the end of the pipet gently and briefly to the adsorbent so that the solution runs out of the pipet and onto the adsorbent (Figure 4). Do not disturb the coating of adsorbent except where you are spotting. Make the spot as small as possible (1-3 mm in diameter) by allowing only a small amount of liquid to run out before lifting the pipet. As soon as the solvent evaporates, more sample may be added to the same spot. Depending on the concentration of the sample solution, one to three applications are usually sufficient. To determine the optimum number of applications, place three spots on one plate-the first spot containing 1-2 applications, the second spot containing 3 applications, and the third spot containing 4-5 applications. Spotting a tlc plate with solution from a micropipette

It is important to spot the compounds high enough on the plate that they will be above the solvent level in the developing jar. If the spots are below the solvent level, they will be dissolved away from the plate by the solvent and you will have to prepare a fresh plate. If more than one sample is being analyzed on the same plate, space the spots well apart and at the same distance from the bottom of the plate. Samples that are spotted too close together may spread out and run together as they are developed; therefore, a maximum of 3-4 sample spots per 5-cm-wide plate is advised. Use a fresh micropipette for each sample and discard it after use. 3) Developing the plate. Prop the plate upright in the center of the jar (spots at the bottom) in such a way that the adsorbent side of the plate is visible through the side of the jar. Cap the jar and do not move it during the development. The solvent will rise rapidly up the adsorbent on the plate by capillary action. When the solvent front has risen almost to the top of the plate (about 1-2 cm from the end), open the jar, remove the plate, and quickly mark a line across the plate at the solvent front with a pencil. Check the plate for visible spots. Outline these carefully with the pencil, keeping your lines at the perimeters of the spots. A spot from a colorless organic compound will not be visible on the plate. Therefore, one or more visualization procedures may be followed.      A)   Column  Chromatography Principles and Applications Column chromatography is a simple, efficient method for separating the components of a mixture. It operates on the principle that different substances are adsorbed on the surface of a solid adsorbent (such as alumina) to an extent that depends on their polarity and other structural features. Since some compounds are more strongly adsorbed than others, they will be washed down a column of adsorbent at a slower rate and thus become separated from those less strongly adsorbed. The method discussed in this operation is classified as liquid-solid adsorption chromatography; other separation principles are also used in column chromatography. Liquid-solid adsorption chromatography involves the use of a solid stationary phase (such as alumina or silica) and a liquid mobile phase (such as hexane or chloroform), The stationary phase-usually called the adsorbent in adsorption chromatography-is packed firmly into a glass tube called the column. The sample, consisting of two or more components in a neat liquid or solution, is placed on top of the adsorbent in a narrow band and washed down the column (eluted) by a suitable mobile phase, also called the eluent. As the eluent passes down the column, the components of the sample spread out to form separate bands of solute, some passing down the column rapidly with the sol- vent, others lagging behind. Consider, for example, a separation of limonene and carvone on a silica adsorbent. At any given time, a molecule of one component will either be adsorbed on the silica (stationary phase) or dissolved in the mobile phase. While it is adsorbed, the molecule will stay put; while dissolved, it will move down the column with the eluent. A relatively polar molecule of carvone is strongly attracted to the polar absorbent and spends more time adsorbed on the silica than dissolved in a nonpolar eluent like petroleum ether. It will therefore pass down the column very slowly with this sol- vent. On the other hand, a nonpolar molecule of limonene is very soluble in petroleum ether and only weakly attracted to the adsorbent; it will therefore spend less time sitting still and more time moving than a carvone moleculee. As a result, the limonene pasass down the column rapidlyy and will soon separate from the slow-moving carvone, Ifa more polar solvent such as methylene chloride is then added, the carvone will spend a greater fraction of its time in solution and be washed down the column in turn. The kind of separation attained by column chromatography thus depends on a number of factors, including the quantity and kind of adsorbent used, the polarity of the mobile phase, and the nature of the components in the mixture. Experimental Considerations Adsorbents.A number of different adsorbents arc used for column chromatography, but alumina and silica are the most popular. Adsorbents are available in a wide variety of activity grades and particle-size ranges; alumina can be obtained in acidic, basic, or neutral forms as well. The activityof an adsorbent is a measure of its attraction for solute molecules, the most active grade of a given adsorbent being one from which all water has been removed. The most active grade is not always the best for a given application,since too active an adsorbent may catalyze a reaction or cause solute bands to move too slowly. Alumina is deactivated by mixing in 3-15% water (see Table I), whereas silica is generally deactivated with 10-20% water. Some mixtures should not be separated on certain kinds of adsorbents, For example, basic alumina would be a poor choice to separate a mixture containing aldehydes or ketones, which might undergo aldol condensation reactions on the column; it would also be unsuitable for carboxylic acids, which bond so strongly to alumina that they cannot be easily desorbed. Deactivated silica, although less active than alumina, is a good all-purpose adsorbent that can be used with most kinds of functional groups. The amount of adsorbent required for a given application depends on the sample size and the difficulty of the separation. If the components of a mixture differ greatly in polarity, a long column of adsorbent should not be necessary, since the separation will be easy. The more difficult the separation, the more adsorbent will be needed. About 20-50 grams of adsorbent per gram of sample is sufficient for most separations, but ratios of 200: 1 or higher arc occasionally required for problem cases. Eluents.In a typical elution process, the eluent acts primarily as a solvent to differentially remove molecules of solute from the surface of the adsorbent. In some cases, polar solvent molecules will also displace solute molecules from the adsorbent by becoming adsorbed themselves. If the solvent is too strongly adsorbed, the components of a mixture will remain largely in the mobile phase and will not separate efficiently. For this reason, it is generally best to start with a sol- vent of low polarity and then (if necessary) increase the polarity gradually to elute the more strongly adsorbed components. Table :2lists a series of common chromatographic solvents in order of increasing eluting power from alumina and silica. Such a listing is called an eluotropicseries. The eluotropic series for a nonpolar adsorbent like charcoal is nearly the reverse of the one for alumina; less polar sol- vents are the more effective eluents in this case. Elution TechniquesMany chromatographic separations cannot be performed efficiently with a single solvent, so several solvents or solvent mixtures arc used in sequence, starting with the weaker eluents near the top of the eluotropic series. These will wash down the most weakly adsorbed components while strongly adsorbed solutes remain near the top of the column. By adding more powerful eluents, the remaining solute bands can then be washed off the column one by one. In practice, it is best to change eluents gradually by using solvent mixtures rather than to change directly from one solvent to another. In stepwise elution the strength of the eluting solvent is changed in small stages by adding small portions of a stronger eluent to the weaker one. Because subsequent portions of the stronger eluent have less effect on elution power than the first one, the proportion of that eluent is increased more-or-less exponentially. For example, 5% methylene chloride in hexane may be followed by 15% and 50% mixtures of these solvents. One "rule of thumb" suggests that the eluent composition should be changed after three column volumes of the previous eluent have passed through; for example, if the packed volume of the adsorbent is 15 ml, then the eluent composition should be changed with every 45 ml or so of eluent.

Chromatography Column

Experiment 6 Extraction Extraction is the separation of a substance from one phase by another phase. The term is usually used to describe removal of a desired compound from a solid or liquid mixture by a solvent. In a coffee pot, caffeine and other compounds are extracted from the ground coffee beans by hot water. Vanilla extract is made by extracting the compound vanillin from vanilla beans. In the laboratory, several types of extraction techniques have been de­veloped. The most common of these is liquid-liquid extraction, or simply "extrac­tion." Extraction is often used as one of the steps in isolating a product of an organic reaction. After an organic reaction has been carried out, the reaction mixture usually consists of the reaction solvent and inorganic compounds, as well as organic products and by-products. In most cases, water is added to the reaction mixture to dissolve the inorganic compounds. The organic compounds are then separated from the aqueous mixture by extraction with an organic solvent that is immiscible with water. The organic compounds dissolve in the extraction solvent while the inorganic impurities remain dissolved in the water. The most commonly used device to separate the two immiscible solutions in an extraction procedure is the separatory funnel. Typically the aqueous mixture to be extracted is poured into the funnel first, and then the appropriate extraction solvent is added. The mixture is shaken to mix the extraction solvent and the aqueous mixture, and then is set aside for a minute or two until the aqueous and organic layers have separated. The stopcock at the bottom of the separatory funnel allows the bottom layer to be drained into a flask and makes possible the separation of the two layers. The result (ideally) is two separate solutions: an organic solution (organic compounds dissolved in the organic extraction solvent), and an inorganic solution (inorganic compounds dissolved in water). Unfortu­nately, often the water layer still contains some dissolved organic material. For this reason, the water layer is usually extracted one or two more times with fresh solvent to remove more of the organic compound. After one or more extractions and separations, the combined organic solutions are usually extracted with small amounts of fresh water to remove traces of inorganic acids, bases, or salts; treated with a solid drying agent to remove traces of water; and then filtered to remove the hydrated drying agent. Finally, the solvent is evaporated or distilled. The organic product can then be purified by a technique such as crystallization or distillation.

How to hold a separatory funnel              stopcock closed                                        While draining the lower layer. for shaking stopcock open  for shaking Two immiscible solutions can be separated with a separatory funnel. (The organic layer may be the upper or lower layer, depending on the relative densities of the two solutions.) When a compound is shaken in a separatory funnel with two immiscible solvents, such as water and diethyl ether (CH3CHzOCHzCH3), the compound dis­tributes itself between the two solvents. Some dissolves in the water and some in the ether. How much solute dissolves in each phase depends on the solubility of the solute in each solvent. The ratio of the concentrations of the solute in each solvent.

Natural Products: Caffeine ISOLATION OF CAFFEINE FROM TEA In this experiment you will extract caffeine with hot water from tea leaves, where it is present to the extent of about 5%. This treatment also extracts the tannins, another class of compounds present in tea~ It is therefore necessary to separate the caffeine from the tannins. You will do so by adding sodium carbonate to the solution. The tannins are acidic and remain in solution. The caffeine is extracted from the alka­line aqueous solution with methylene chloride. It can be purified by sublimation or recrystallization. Caffeine is described as a cardiac, respiratory, and psychic stimulant, and as a diuretic. It is reported to have a melting range of 235-236°C. Procedure. Place 125 ml of water in a 500-ml Erlenmeyer flask. Add 12.5 grams of tea and 12.5 grams of powdered calcium carbonate. Boil the contents of the flask with constant stirring for about 20 minutes. At this time, filter the hot mixture with suction, and press out the liquid from the tea leaves with a large cork. Transfer the filtrate to a 250-ml Erlenmeyer flask, Cool the aqueous solution to room temperature, transfer it to a separatory funnel,  and and extract three times with 30-mL portions of chloroform. Swirl or gently stir the two layers together for about 10 minutes (Note: More vigorous extraction procedures often result in very troublesome emulsions. Gentle stirring of the mixture with a magnetic stirrer is quite satisfactory).  and then separate them by means of a separatory funnel. Distill the chloroform layer until only about 10 ml remains, transfer the remaining solution to a tared (weighed) 25-ml Erlenmeyer flask (filtering if necessary), and evaporate to dryness on the steam bath. Recrystallize the solid residue of caffeine from 95% ethanol, using 5 ml per gram (One recrystallization from ethanol is sufficient and yields caffeine in the form of small needles. A reasonable expected recovery of recrystallized caffeine is about 25-50 % of the total present, depending upon the thorough­ness of the extraction. The greenish color that is present in the case of the tea extraction can be completely removed by careful washing of the crystals with ethanol).

A-        Organic Synthesis   Experiment 7    SYNTHESIS OF ASPIRIN (ACETYLSALICYLIC ACID)   Purpose:  To prepare an organic compound, determine its yield, purify it and test its purity. .   Materials: Salicylic acid C6H4 (OH) COOH, acetic anhydride (CH3CO)2O,  ethyl alcohol C2H5OH, 18 M H2S04.       The theoretical yield is calculated on the basis of salicylic acid, since excess acetic anhydride is used, and the percentage yield is calculated on the crude product. The instructor may direct you to take the melting range of this impure material before purifying it to get an idea of the effect of recrystallization. The solvent used for recrystallization is a mixture of alcohol and water in which aspirin is quite soluble when hot and only slightly soluble when cold. If desired, a second recrystallization can be carried out to see if there is further improvement of purity. A pure substance melts sharply at a characteristic temperature. The melting point of pure aspirin is 135oC. Any impurity lowers the melting point and usually spreads it into a melting range. To determine if the material prepared is really aspirin, a mixed melting point can be taken. A known sample of pure aspirin is mixed with the prepared sample by rubbing them together with a spatula, and the melting point is then taken. If the material is all aspirin the melting point will be that of aspirin, otherwise it will be much lower as on, substance acts as an impurity for the other. Procured: 1-    Place 2 g of salicylic acid in a 125-mL Erlenmeyer flask. 2-    Add 5 mL of acetic anhydride and 5 drops of 85% phosphoric acid. 3-    Stir well, and heat the flask in a boiling water bath for 5-10 minutes. Carefully remove the flask from the hot water and place it under the fume hood. Caution: The solution may start to boil from the heat generated by the decomposition of the excess acetic anhydride.) Handle the flask with great care. 4-    When the reaction subsides, add 40 mL of water and stir the solution until crystals begin to separate. Chill the flask in an ice bath to complete crystallization. 5-    Collect the product by suction filtration. Wash the crystals  on the filter with 5 mL of cold water, and continue to pull air through the filter until the product is dry.

Experiment 8 THE PREPARATION AND PROPERTIES OF SOAP   Introduction Although the family tradition of making soap has all but died out in modern times,  only a few generations ago people routinely made soap at home, usually outdoors, by boiling animal fat (a mixture of triacylglycerols) with lye (impure sodium hydroxide). After boiling for several hours, the mixture was allowed to cool, and the top layer, which had solidified, was cut into blocks of soap. Although this soap was rather irritating to the skin, it was inexpensive, easily made, and showed good cleaning action in soft water. In this experiment, you will make soap much in the same way as the traditional   method. You will saponify (make soap from) a vegetable oil by reacting it with sodium hydroxide according to the following equation: You will then mix the soap and glycerol with a saturated aqueous solution of salt (NaCl), which reduces the solubility of the soap and causes it to precipitate. Some of the properties of the purified soap can then be examined.    Materials Vegetable Oil. 95% Ethanol. NaOH. NaCl. Distilled Water. Phenolphthalein. Procedure Weigh a clean dry graduated cylinder to the nearest 0.1 g, and then pour 21 mL of    the vegetable oil supplied into the cylinder. Reweigh the cylinder to the nearest 0.1    g, and pour the oil into a clean 400-mL beaker. Rinse the graduated cylinder twice with10-mL portions of ethanol, pouring the rinses into the beaker. Next, add 25 mL of 20% sodium hydroxide (NaOH) to the beaker. (CAUTION: SODIUM HYDROXIDE IS ESPECIALLY HARMFUL TO LIVING TISSUE, PARTICULARLY THE EYES. IF YOU SPILL ANY ON YOURSELF, WASH IMMEDIATELY WITH COPIOUS QUANTITIES OF COLD WATER.) Place the beaker on a wire gauze supported on an iron ring over a Bunsen burner. Place an asbestos square, large enough to cover the beaker, in a convenient location nearby. Light the burner, adjust it for a low, cool flame, and heat the mixture in the beaker gently while stirring it with a glass rod. Continue heating the beaker just enough to allow the mixture to boil gently. If any foaming occurs, turn down the flame until the foam subsides and the mixture returns to a gentle boil. (Both ethanol and the oil are flammable, but the ethanol is much more volatile than the oil. Do not allow the flame to get near the upper part of the beaker, as the ethanol vapors in this vicinity might easily ignite. IF YOUR MIXTURE SHOULD CATCH FIRE, STAY CALM, TURN OFF YOUR BURNER, AND CALL YOUR INSTRUCTOR. ETHANOL BURNS WITH A LOW, EASILY CONTAINED FLAME, AND A FIRE IN THE BEAKER CAN BE EXTINGUISHED EASILY BY COVERING THE BEAKER WITH THE NEARBY ASBESTOS SQUARE. Continue heating the mixture until you do not detect any ethanol odor when you  gently fan (waft) the vapors from above the beaker toward your nose with your hand. Once the ethanol odor is gone (the ethanol will have evaporated), the reaction should be complete, and the beaker will contain a tan-colored, gummy solid that is a mixture of soap, glycerol, and impurities. Turn off the burner, and carefully remove the hot beaker from the wire gauze. Place the beaker on the asbestos square to allow it to cool. After the soap has cooled to the point that it is only slightly warm, pour into the beaker 100 mL of saturated aqueous sodium chloride, and stir the mixture thoroughly with a glass rod. The excess sodium hydroxide and glycerol will dissolve, and the purified soap will remain as a solid residue. Filter the soap from the solution by use of a Buchner ice to 50 mL of distilled water in a 100-mL beaker, and allow the water to chill. Then, turn off the vacuum, and use about half the cold water (no ice) to rinse any residue (scrape the soap off with a stirring rod) from the reaction beaker into the Buchner funnel. Stir the cold water-soap mixture in the Buchner funnel into a slurry, being careful not to tear the filter paper, and then turn on the vacuum to filter the mixture. Allow the vacuum to draw air through the soap for about 10 min to help dry it; during this time, remove a small sample for the following test. It is important that there be no residual sodium hydroxide in the soap, and it is necessary to test the soap for the presence of sodium hydroxide at this point. To do so, put about 0.5 g of soap in a large test tube and add 10 mL of 95% ethanol. Heat the mixture (turned away from yourself and others) carefully over a low flame, with constant shaking and swirling, until the soap dissolves. Allow the mixture to cool until it is just slightly warm, and add 3-5 drops of phenolphthalein solution. If the solution in the test tube turns pink, there is still sodium hydroxide in the soap, and you must wash it with salt water and cold water until additional tests with phenolphthalein give no pink color. Once the soap is shown to be free of sodium hydroxide, allow it to air-dry, and weigh it on a preweighed piece of weighing paper. Record the weight of the soap on the Data Sheet. Examination of Some Properties of Soap   1. Use some of your soap to wash your hands. If it was prepared properly, it should not make your hands feel greasy (a greasy feeling results from traces of oil or fat) or slippery (a slick, slippery feeling would be caused by sodium hydroxide). Record your observations on the Data Sheet. After drying your hands, put a few drops of oil in one hand and rub it with the other. Try to wash off the oil with tap water alone and then use some of your soap. Record your observations on the Data Sheet.   2. Soaps from insoluble salts with metal ions present in hard water, thus causing a scum to form in wash water. Typical metal ions in hard water are Ca2+ and Mg2+. To examine this property of soap, and to compare the behavior of soaps to that of detergents, first make a dispersion of about 1 g of your soap in 50 mL of distilled water in a 100-mL beaker; it may be necessary to stir and warm the contents of the beaker to disperse the soap uniformly. Cool the beaker by setting it in a large container of cold water, and make a similar dispersion of the synthetic detergent supplied. Label four small test tubes 1-4, and to tubes 1 and 2, add 0.5 mL of cooled soap dispersion and 1 mL of distilled water. To tubes 3 and 4, and 0.5 mL of detergent dispersion and 1 mL of distilled water. Then, to tubes 1 and 3, add drop wise approximately 20 drops of 0.1 % calcium chloride solution. Record your observations on the Data Sheet. To tubes 2 and 4, add drop wise approximately 20 drops of 0.1% magnesium chloride. Record your observations on the Data Sheet. Examination of Some Properties of Soap   1. Use some of your soap to wash your hands. If it was prepared properly, it should not make your hands feel greasy (a greasy feeling results from traces of oil or fat) or slippery (a slick, slippery feeling would be caused by sodium hydroxide). Record your observations on the Data Sheet. After drying your hands, put a few drops of oil in one hand and rub it with the other. Try to wash off the oil with tap water alone and then use some of your soap. Record your observations on the Data Sheet. 2. Soaps from insoluble salts with metal ions present in hard water, thus causing a scum to form in wash water. Typical metal ions in hard water are Ca2+ and Mg2+. To examine this property of soap, and to compare the behavior of soaps to that of detergents, first make a dispersion of about 1 g of your soap in 50 mL of distilled water in a 100-mL beaker; it may be necessary to stir and warm the contents of the beaker to disperse the soap uniformly. Cool the beaker by setting it in a large container of cold water, and make a similar dispersion of the synthetic detergent supplied. Label four small test tubes 1-4, and to tubes 1 and 2, add 0.5 mL of cooled soap dispersion and 1 mL of distilled water. To tubes 3 and 4, and 0.5 mL of detergent dispersion and 1 mL of distilled water. Then, to tubes 1 and 3, add drop wise approximately 20 drops of 0.1 % calcium chloride solution. Record your observations on the Data Sheet. To tubes 2 and 4, add drop wise approximately 20 drops of 0.1% magnesium chloride. Record your observations on the Data Sheet.

Experiment 9   THE PREPARATION OF 2-Naphthyl Acetate:         Dissolve 3 g. of pure 2-naphthol in 15 ml. of 10% sodium hydroxide solution, add 30 g. of crushed ice, and 3.5 ml. ofacetic anhydride. Shake the mixture vigorously for about 10-15 minutes; the 2-naphthyl acetate separates as colourless crystals. Filter at the pump, wash with water, drain, and dry thoroughly. Yield ofcrude material. Recrystallize from petroleum (b.p. 60-80°), from which, on cooling and scratching, the 2-napbthylacetate separates as colourless crystals, m.p. 71.   Experiment 10   THE PREPARATION OF Dibenzalacetone: The reaction of acetone with benzaldehyde in the presence of base is a classical aldol condensation.These reagents could be used to prepare either benzalacetoneor dibenzalacetone. This reaction done between two different carbonyl, which is one of them, has alpha - hydrogen and represented by acetone and the other did not has alpha - hydrogen and represented by benzaldehyde. The reaction carried with base which is sodium hydroxide.   Dissolve 2.5 g of NaOH in 25 ml water in a beaker. Add 25 ml of ethanol and cool the solution to 20oC. Place 3ml of benzaldehyde and 1 ml of acetone. Swirl the flask until a homogeneous solution is obtained. Add approximately one-half of the benzaldehyde solution to the hydroxide solution with vigorous stirring. Stir the mixture for 10 minutes, and then add the remainder of the benzaldehyde-acetone solution. Continue stirring for another 30 minutes. Filter the yellow solid with vacuum, press it as dry as possible, and then transfer it to a clean beaker. Add 100 mL of water. Stir the mixture into a thick paste. If the pasty mixture is strongly alkaline, refilter and rewash. If the paste is near-neutral, filter with vacuum to obtain the crude product. A typical crude yield is 2.8 g. Crystallize the crude product from 95% ethanol or ethyl acetate. Determine the melting point and per cent yield. (Reported m.p 120) .Write your data in the table below:   Weight of  the product before crystallization Weight after crystallization M.P. oC Theoretical Weight % yield                     Experiment 11   THE PREPARATION OF Acetanilide:   aniline, C6H7Nacetic anhydride acetanilide, C8H9NOacetic acid Heat a mixture of aniline ( 10ml) , acetic anhydride (10 m l ) and acetic acid ( 10 ml) in a conical  flask for about 45 minutes on a boiling water bath. Pour the content in a mixture of water and ice with stirring. The solid thus obtained is filtered under suction, air dried and recrystallized from water-alcohol mixture. Record the yield and m.p. (Reported m.p. 114o C).   Purpose:       a)   To synthesis acetanilide by reaction of aniline and acetic anhydride. b)    To purify acetanilide by crystallization method from water c)   Purity check by melting range    Compound  FW (g/mol)  MP (BP)  density  Hazards  Acetanilide  135.17  114 ºC  ---  Irritant. Harmful if inhaled/ingested.  Aniline  93.13  (184 ºC)  1.022 g/mL  Irritant (eyes/skin). Harmful if inhaled/ingested. Possible carcinogen.  Acetic Anhydride  102.09  (138 ºC)  1.082 g/mL  Irritant (eyes/skin). Toxic by inhalation, Flammable (fp 49 ºC).     Discussion:   Recrystallization is a widely-used technique to purify a solid mixture. The desired product is isolated from its impurities by differences in solubility. Insoluble impurities and colored impurities can be removed from hot solvent through the use of activated carbon and filtration. Soluble impurities remain in the cold solvent after recrystallization. The desired product should be as soluble as possible in hot solvent and as insoluble as possible in cold solvent. The selection of solvent is, therefore, critical to the successful recrystallization. Recrystallization is a purification procedure, which requires solubility of the impure solid in a heated solution and crystallization of the solid upon cooling. Clearly, this operation depends upon solute-solvent in traction involving a number of parameters including concentration, polarity of solute and solvent (like dissolves like), etc. Choice of a solvent or solvent pair for recrystallization experiments generally involves preliminary tests using a small sample and various solvent systems. To determine the proper solvent or solvent system, the following steps are commonly performed. I)             The crude crystals should have low solubility in the chosen solvent at room temperature. II)            The crude crystals should have high solubility in the chosen solvent when heated to boiling. III)           The crude crystals should not react with the solvent IV)          The solvent should boil at temperature below the solid melting point. V)           The solvent should moderately be volatile so crystals dried readily. VI)          The solvent should be non-toxic, non-flammable, and inexpensive     The procedure illustrated in this experiment involve recrystallization, gravity filtration, suction filtration, melting and mixture melting points, as well as calculations of theoretical and percentage yields. Gravity-filtration utilizes a “fluted” filter paper in the decolorizing or recrystallization step. In gravity filtration, generally the filtrate is the desired material, which is used further in the experiment. In suction filtration, a Buchner funnel is employed to collect the desired crystals resulting from a reaction or recrystallization attempt. Be sure to “wet the filter paper” with the solvent/solid mixture to be filtered. When performing a suction filtration, it is usually advisable to install a trap between the aspirator and the suction flask. In any case always break the vacuum before turning the water off. In this operation, the filtrate or “mother liquor”  may be concentrated to obtain a second crop, etc. ( or may be disposed- consult with you instructor). This experiment involves four functional groups common in organic chemistry. The substrate (reactants) are both liquids and one of the products is solid. The reaction of aniline with acetic anhydride is a transformation in which products, acetanilide and acetic acid, are obtained. A solid product is often desirable since it may be recrystallized and a melting point determined. Solids prepared in this manner serve a derivative, whose melting point may be correlated with known values and thus is a means of identification and serves as a test for homogeneity or purity.   Procedures Heat a mixture of aniline ( 10ml) , acetic anhydride (10 m l ) and acetic acid ( 10 ml) in a conical  flask for about 45 minutes on a boiling water bath. Pour the content in a mixture of water and ice with stirring. The solid thus obtained is filtered under suction, air dried . The product crystallized from water-alcohol mixture. with occasional stirring until the entire solid dissolved. Set the beaker aside to cool for 5-8 minutes and then chill it in an ice bath. When crystallization is complete, collect the product by vacuum filtration using a small Buchner funnel. Allow the sample to dry completely. Weigh the dry product, calculate the percentage yield and determine its melting point. Collect to product in a paper and write your name and submit it to your instructor. The aqueous filtrate may be flushed down the drain. Record the yield and m.p. (Reported m.p. 114o C).   Back to Contents