Chem220 Manual 2012

School of Chemistry
University of KwaZulu-Natal
Westville Campus

Chemistry 220
Organic Chemistry
2012

LABORATORY MANUAL
It is a legal requirement that

are worn in this room at all times.

Sunglasses (normal or prescription) are NOT to be worn as a substitute for safety glasses.

Prescription glasses (except sunglasses) are acceptable PROVIDED THEY COVER THE EYES COMPLETELY.

Some types of contact lens should not be worn in the laboratory. Check with your lens supplier.

All shoes MUST be closed. No high heels are allowed.

All headgear such as hats and scarves must be made safe.

Long hair MUST be tied back. Contents
This practical course consists of twelve laboratory sessions. The aim is to teach you some of the techniques required in an organic laboratory, to carry out syntheses that are discussed in the lecture course, and to familiarize you with the principles employed in identifying a simple organic compound.

Occupational Health and Safety Notices
The Elements 1. Nitration of acetanilide
2. Hydrolysis of p – nitroacetanilide and thin layer chromatography
3. Separation of a three – component mixture by extraction
4. Completion of experiments from day 1 to 4
5. NMR workshop
6. Sandmeyer Reaction: Preparation of p-chloronitrobenzene
7. Synthesis of benzilic acid from benzil
8. Aldol Condensation: Preparation of ethyl cinnamate
9. Isolation of caffeine from tea
10. Completion of isolation of caffeine from tea
11. Catchup day and completion of experiments

School of Chemistry
University of KwaZulu-Natal, Westville Campus

OCCUPATIONAL HEALTH AND SAFETY

You are WARNED that all substances handled and all operations performed in a laboratory can be hazardous or potentially hazardous. All substances must be handled with care and disposed of according to laid down procedures. All operations and manipulations must be carried out in an organised and attentive manner.

In order to assist you in developing good and safe laboratory techniques, a set of Laboratory Rules and Regulations is attached. You are required to read these and acknowledge that you have read and understood them. Additionally, in the laboratory manuals/practical books and/or pre-practical lectures your attention will be drawn to the correct and safe handling of specific chemicals/reagents/solvents and to the correct/safe manner in which specified laboratory operations must be carried out. These specific instructions and/or warnings must never be ignored.
Laboratory Rules and Regulations

Students must be present before the start of each scheduled practical session. Latecomers will be refused entry to the laboratory.
No student is permitted to work in the laboratory outside normal practical hours, except by express permission of the staff member(s) responsible for the practical.
Do not put anything into your mouth while working in the laboratory. NEVER taste a chemical or solution. Eating and drinking is PROHIBITED in all laboratories.
Students are not allowed to enter preparation and issue rooms.
Apparatus and chemicals are not to be removed from the laboratory.
Students will find the laboratory benches clean on arrival in the laboratory. The bench at which you work must be left clean when you leave the laboratory at the end of the practical session. Bench tops must be wiped clean. Glassware and other apparatus should be left clean and dry, unless otherwise indicated or instructed. Sinks and basins must be cleaned after each practical.
Work areas must at all times be kept clean and free from chemicals and apparatus that are not required. All glassware and equipment must be returned to its proper place, clean and dry and in working condition, unless otherwise indicated or instructed.
All solids must be discarded into the bins provided in the laboratory. Never throw matches, paper, or any insoluble chemicals into the sinks. Solutions and chemicals which are emptied into sinks must be washed down with water to avoid corrosion of the plumbing. Waste solvents must be placed into the special waste solvent bottles provided.
Before leaving the laboratory at the end of the practical session make sure that all electrical equipment is switched off, and that all gas and water taps are shut off.
Students who break or lose equipment allocated to them will be required to pay for replacements. All breakages or losses must be reported to the technician in charge.
Balances and other expensive equipment must be treated carefully and kept clean and tidy at all times.
Fumehoods must be used when handling toxic and fuming chemicals. Other operations, such as ignitions, are also carried out in fume-hoods. The only parts of the body that should ever be in the fumehood are the hands - never put your head inside a fume-hood!
Never leave a laboratory experiment unattended.
Reagent bottles must be re-stoppered immediately after use. It is ABSOLUTELY FORBIDDEN to introduce anything into reagent bottles - not even Pasteur pipettes! Solutions and reagents taken from bottles must NEVER be returned to the bottles. Do not place the stopper of a reagent bottle onto an unprotected bench top.
Laboratory reagents and chemicals must be returned to their correct places immediately after use. Spillage must be cleaned off bottles/containers. Labels must face the front.
The use of reagent bottle caps or filter paper as weighing receptacles is forbidden.
Liquids - whether corrosive or not - must be handled with care and spillage on the bench or floor should be avoided. Any spillage should be cleaned up at once. If the liquid is corrosive (acids or bases) call your demonstrator or staff members in charge. Never hold a container above eye level when pouring a liquid.
When carrying out a reaction, or boiling a liquid in a test tube, point the mouth of the test tube away from yourself and others in the laboratory.
Beware of hot glass and metal. Never handle any item that has been in a flame, hot oven, or a furnace without taking precautions. Use leather/asbestos gloves/tongs, or ask for advice.
Report all accidents, cuts, burns, etc., HOWEVER MINOR, to your demonstrator or the staff member in charge. Eyewash stations are located in various places in the laboratory. Ensure that you know where the nearest one to your bench is located.
A chemical laboratory is not a place for horseplay. Do not attempt any unauthorised experiments. Do not play practical jokes on your classmates - transgressors will be banned from the laboratory, with consequent refusal of a Duly Performed (DP) Certificate and refusal of a certificate of good conduct from the university on completion of your degree.

GENERAL FIRE ORDERS

Fire-fighting instructions are exhibited in individual laboratories. However, the following orders must always be obeyed.

In the event of a fire

Attack it at once using the appropriate fire fighting equipment and SHOUT for help.

On hearing a fire evacuation alarm

Stop normal work immediately.

Make safe any apparatus and material in use, shutting off any local gas taps/valves, electricity and other potentially dangerous services under your control.

Immediately leave the building.

Go to the Fire Evacuation Area outside the main entrance to the building; unless you have been given any other instructions.
Instructions to Students

Read the following instructions CAREFULLY. Make sure you understand the instructions, and then sign the declaration on the accompanying sheet and hand it your demonstrator.

Fire Extinguishers are provided in the laboratory. Make sure you know where they are situated and how to use them. NB. A SHOWER is situated in front of the lecturer's desk, as well as in the corridor outside. Make sure you know where they are!
Gas is highly flammable. It can form dangerous explosive mixtures with air when not controlled. GAS TAPS MUST BE TURNED OFF WHEN GAS IS NOT IN USE. Slow leaks can lead to dangerous concentrations.
Burners: students must provide their own matches or lighters. The use of paper spills is FORBIDDEN as it poses a fire hazard.
Flammable solvents such as ether, alcohol, hexane, benzene, acetone, etc. are used in the organic laboratory. Students must take care when handling these solvents. The following rules are important:
Flammable solvents are NOT TO BE HEATED IN OPEN CONTAINERS over a flame. These should be heated over a steam bath or under reflux conditions.
Solvents such as chloroform, hexane, and ether, which are immiscible with water, must be disposed of by carefully pouring them into the WASTE SOLVENT bottles located in the fume cupboards. They may NOT be poured down sinks or troughs.
Solvents that are miscible with water (e.g. alcohol and acetone) may be poured into the sinks, provided they are washed away with an ample volume of water.
Glassware with ground glass joints is expensive and must be treated with care. After use, glassware must be carefully cleaned, dried, and ground surfaces must be lightly smeared with petroleum jelly. This prevents the “freezing together" of the joints. The process of "freezing" is accelerated by the presence of any alkaline solid or solution left on the surfaces. The joints should NEVER be forced or heated with a flame. Disassemble ALL joints before leaving the laboratory.
Students must be careful when using balances. ALL SPILLAGES MUST BE CLEANED UP and balances must be left clean.
Laboratory benches must be looked after. Acid spillages must be neutralised with sodium bicarbonate and cleaned up immediately. Bunsen burners, hot glassware and steam baths must be placed on asbestos mats.
Refuse Bins are for SOLIDS only. No burning or smouldering materials may be placed in bins.
Sinks and troughs are for liquids only. Solid material will cause blockage of the drainage system.
Use of Fume Cupboards: The careless use of certain chemicals makes working in the laboratory extremely unpleasant. Brominations and the preparation of certain derivatives (e.g. benzoylations) must be done in the fume cupboard. Always check warnings on the reagent bottles BEFORE using them.
Practical Preparation: Before the practical class you are required to:
Familiarise yourself with the experimental procedures you are about to perform.
Read up the relevant section in your textbook.
Reactions will be discussed in lectures, practical work being examinable in your examination.
Important:

All SOLID products prepared must be submitted in neatly labeled sample tubes. Liquid products may not be handed in, but must be shown to your demonstrator for verification and then poured into the appropriate bottle on the demonstration bench.
The following information is required on the label:

Name of Student.
Name of compound.
Structural formula of compound.
Melting point of compound.

Marks for practical work will be assigned for:
Obtaining the correct products (verified by correct m.p./b.p.’s, tlc analysis etc.)
Quality of reports, including mechanisms, equations and/or any other relevant information;
Marks can (and will!) be deducted for:
Failing to follow the instructions given in your laboratory manual, and thereby endangering both yourself and those around you;
Failing to wear safety glasses at all times in the laboratory;
Failing to clean up properly any spillages which may occur on the floor, bench, or other working surfaces, especially on and around balances;
Behaving in an irresponsible manner while in the laboratory;
Not handing in practical reports on time. Each practical report must be handed in to your demonstrator at the practical session following the one in which it was scheduled to be completed, except those of the final practical, which must be handed in on Day 12 at the latest.

Important: If you do not finish the practical on the day it was scheduled to be completed, complete all the sections that you are able to, leaving space for the incomplete work and give your demonstrator to mark. Your demonstrator will mark your work in part and mark the rest when you have filled in the missing data and give you a final mark. It is your responsibility to ensure that your laboratory report is marked if your report is partially complete on the due date.

On day 5 any unfinished work for the first four practicals must be completed and on day 12 all unfinished work for the remainder of the practicals must be completed. All marks must be awarded and you must bring to the attention of your demonstrator any errors in the marking process or entering of marks.

Format of the Practical Report

Title of practical: e.g. The synthesis of 3,5-dihydroxychalcone

Aim: To synthesise the above chalcone at optimum yields

Reagents and chemicals
You must list all reagents and chemicals used in the practical.

Modifications to experimental Procedure
You must write down any modifications made to the experimental procedure.

Reaction mechanism:
You must include the mechanism in detail here using arrows.

mp of substance prepared from the literature: You must include the reference here as well.

mp of substance prepared:

expected yield: from the literature (include reference as well)

Calculation of yield:
Limiting reagent __________________ moles limiting reagent = mass / molar mass moles product = stoichiometric factor x moles mass product expected = moles x molar mass
% yield = mass product obtained / mass product expected

Short discussion
No more than 5 lines or one paragraph. You must comment on the crucial parts of the experiment, what to take careful note of in the procedure as well as any part of the experimental procedure that did not work well and give suggestions as to how you would change this if you repeated the experiment.

Please make every effort to type your report. If you come up against constraints, e.g. access to computers and printers then you can handwrite your report, however your handwriting needs to be legible. You can leave spaces for the melting point and calculation of the yield (if your sample is still drying), however the theoretical yield must be calculated.

Important:
Please make a copy of your report and keep it in your file. If your report goes astray, this will help you in your resubmission if allowed.
As soon as your report is returned, please verify your mark on student central.
Practical 1 _________________________________________________________________________________
Nitration reaction.
_________________________________________________________________________________
Note __________________________________________________________________________
All glassware must be completely DRY, as CONCENTRATED acids are being used.
Should you spill any acid on your skin, IMMEDIATELY wash with plenty of tap water, and only THEN tell your demonstrator/member of staff. The sooner it is washed off the less dead skin you will have!
______________________________________________________________________________
Nitration of Acetanilide

1. Cool a suspension of 5g acetanilide in 5 mL glacial acetic acid in a 50 mL Erlenmeyer flask in a mixture of ice and water. Measure out 10 mL conc. H2SO4 into a 10 mL measuring cylinder, and add this to the cooled suspension in 1 mL portions while swirling continously.
2. Carefully prepare a mixture of 2.0 mL conc. HNO3 and 1.5 mL conc. H2SO4, transfer to a separating funnel, and add this mixture dropwise with swirling to the cooled acetanilide suspension at such a rate that the temperature does not exceed 10C.
3. Remove the ice bath and let the mixture stand for 30 minutes at room temperature, then pour the mixture onto 20 mL crushed ice and filter off the solid product under vacuum on a Buchner funnel, washing the crude product with 2 x 10 mL icewater. Discard the filtrate in the waste bottle provided.
4. Recrystallise the crude product from MeOH and filter the crystals that have formed, washing with 2 x 10 mL icewater. Leave the crystals to dry on paper with your name on it. Your demonstrator will show you where to dry the crystals.

Recrystallisation
1. Add a bumping stone and just enough solvent to the product so that it just dissolves and heat to boiling on the steam bath.
2. Continue boiling until the first solid just reappears in the boiling solution, remove from the steam bath and allow to cool slowly to room temperature (RT), scratching the sides of the flask to initiate crystallisation.
3. Once the solution has reached room temperature and crystallisation appears complete, place the flask in an ice-water slurry until the solution is ice-cold, and then filter off the solid.
Practical Report
Follow the format on page ix.

Practical 2_______________________________________________________________
Hydrolysis of p-nitroacetanilide
Thin Layer Chromatography.
_________________________________________________________________________________
Hydrolysis of p-nitroacetanilide
1. Once dry, determine the mass and m.p. of the p-nitroacetanilide you prepared in practical 1, then, weigh out 1.00g for the hydrolysis. Hand in the remainder of the sample to your demonstrator. If you have less than 1.00 g, weigh out the entire sample and use all for the hydrolysis.
2. Prepare a 70% H2SO4 solution by adding 7mL conc. H2SO4 CAUTIOUSLY with cooling and stirring to 3mL water. Add the p-nitroacetanilide and 70% H2SO4 solution to a 50mL Quickfit RB flask fitted with a reflux condenser. Using a heating mantle, heat under reflux (Figure 1) gently for 15 min, then cool the flask in an icewater slurry. The hot solution should smell of acetic acid. Figure 1. Heating under reflux
3. Transfer three Pasteur pipette “squirts” of the solution to a 50 mL beaker, and add 4M NaOH until the solution is slightly alkaline.
4. Pour the mixture into 10mL icewater, and extract the solution with 2 x 10 mL portions of chloroform. Combine the chloroform extracts in a labeled 50 mL beaker and use for thin layer chromatography. You are not required to hand in a sample of the hydrolysed product.

Thin Layer Chromatography
This technique can be used to show a) whether two compounds are the same or not; b) the number of components in a mixture and c) changes taking place in a chemical reaction.
The method in general is rapid, (very) simple to carry out, requires very small quantities of sample and gives consistent results. Pre-coated thin-layer plates are used, which are coated with a thin (0.2mm) layer of 60 mesh silica gel containing a fluorescent indicator. (The layer is delicate and must not be disturbed in any way; the plates are best handled by holding the edges or resting them on the uncoated rear surface.)
1. Place a half sheet of filter paper into a clean and dry 250mL beaker as shown in Fig. 2, making sure that the “straight” edge of the paper rests on the bottom of the beaker. Prepare 10 mL of a solution of benzene:ethyl acetate, 9:1. Pour in a sufficient volume of this solution (called the eluant) to give a depth of 4-6mm of liquid in the beaker, and seal the container with a square of cling film. The filter paper serves to maintain an atmosphere saturated with vapour of the eluting solvents within the beaker.
2. Lightly mark four points across the narrow width of the plate 8mm apart and 1cm from the bottom (Figure 2), using the sharp point of a lead pencil. “Spot” the plate with solutions of each of the three isomers, o-, m-, and p-nitroaniline (these will be provided), and the extract of the hydrolysis reaction as follows:

Figure 2. Thin layer chromatography
a. Place the plate horizontally on the bench and use a capillary tube to draw up a small quantity from each solution and gently touch the silica gel layer at the appropriate point on the plate. The spot size should be kept as small as possible. b. When the spots are completely dry, carefully open the cover on the beaker to allow the prepared plate to be inserted, “spot end” down. Then re-seal the beaker again as soon as possible in order to maintain a saturated vapour atmosphere within the beaker.

Note __________________________________________________________________________
The liquid in the beaker must on no account cover the “spots” on the T.L.C. plate, i.e. the depth of the eluant must be kept within 4 and 6mm.
The eluant is selected by considering: polarity of the eluant; polarity of the sample; and activity of the silica gel.
______________________________________________________________________________

The eluant travels up the silica gel layer by capillary forces and will, if correctly chosen, dissolve and carry the solutes through the thin layer of silica gel. Since different compounds are selectively adsorbed on the silica gel, they will move up the plate at different rates. Thus, in an ideal case, the individual compounds in a multi-component sample will be separated into discrete “spots” when the eluant front has travelled some 80-90% of the plate length.
c. Allow the plate to remain in the sealed beaker until the solvent has traveled about 4-5cm up the plate. Remove the plate from the beaker. Mark the position of the solvent front and allow the plate to dry in the fume hood. The elution time required is about 15 minutes.
d. The plate is then examined to detect the position of the separated components and to determine which of the nitroaniline isomers are present. (If the recrystallisation was carried out correctly, only the p- isomer should be present. If not, traces of the other two should appear as well. If the spots are not visible, the plate can be examined either under a UV lamp, or sprayed in a fume cupboard, with a suitable reagent (please consult your demonstrator).
An important aspect of the technique is the reproducibility of the results provided all conditions (eluant composition, layer thickness, temperature, etc.) are maintained constant. A measure of this is provided by the Rf value for any given compound under standard conditions.
Rf = Distance travelled by compound spot (mm)/Distance travelled by solvent front (mm)

Practical Report
Write down the aim of the experiment and the mechanism of the hydrolysis reaction. Stick your TLC plate in your report and calculate the Rf of the standard compounds and your sample.
Comment on whether or not the hydrolysis worked and which of the nitrated products was present.
Practical 3 _______________________________
Separation of a Three Component Mixture by Extraction

Introduction

A mixture of m-nitroaniline (a base), benzoic acid (an acid), and naphthalene (a neutral substance) will be separated into its components by extraction.

Caution Ether is highly flammable: no flames are allowed in the laboratory when this practical is being carried out.

1. Weigh out 1.5g of the three component mixture and dissolve it in 14ml of ether. Pour the solution into a 100ml separating funnel. To extract the basic component (m – nitroanoline) from the mixture, add a solution of 1.5ml concentrated HCl (carefully) in 14ml of water to the solution in the funnel and shake the funnel thoroughly. Draw off the lower (aqueous) layer into a 100ml conical flask and repeat the extraction two more times. Finally, extract with 5ml water to remove excess HCl that may be dissolved in the ether layer. Combine the three acid extracts with the water extract and keep the ether extract for further separation.

2. Neutralise the combined acidic extracts by adding 10% NaOH until the solution is alkaline to litmus paper. (The proper way to test with litmus paper is to dip a clean glass rod into the solution and then touch it to the litmus paper. This prevents sample contamination.) Extract the alkaline solution twice with 14ml portions of ether, collecting and combining both extracts. Evaporate the ether solution on the steam bath. Weigh the residue (m- nitroaniline), place this in a labeled vial and determine its melting point.

3. To separate the acidic component (benzoic acid) from the mixture, extract the remaining ether solution three times with 14ml of 10% NaOH and once with 5ml of water. Combine the alkaline (NaOH layer) and water layers and set them aside.

4. Neutralise the combined alkaline extracts by adding concentrated HCl drop by drop until the solution is acid to litmus paper. The solution can be kept cool in an ice bath during neutralisation. Filter off the precipitated benzoic acid (acidic component) by vacuum filtration using a Buchner funnel. Allow the sample to dry, weigh and place in a labeled vial. Determine the melting point of benzoic acid.

5. Pour out the remaining ether solution (which contains only the neutral component, naphthalene) through the top of the separating funnel into a 100ml beaker. Evaporate the ether on the steam bath in the fume hoods. Weigh the residue, place in a labeled vial and determine its melting point.

6. Hand in all your samples in clearly labeled vials.

Practical Report

In no more than half a page, discuss the principles of separating an acid, base and neutral substance. Use reactions and mechanisms where appropriate to illustrate your answer. Your report, including reactions and mechanisms should not exceed one page.

Report the percentage of each component recovered in the mixture and percentage of the sample lost during the experimental process.

_______________________________________ Catchup day
_______________________________________________________________________________

Use this day to weigh out all your dry samples and calculate your yields and percentage recovery if you have not done so already. You must also determine all your melting points.

You must ensure that any unfinished work is complete by the end of this practical session and that all your practical reports thus far are handed to your demonstrator to mark.

Practical 4_______________________________
NMR Workshop
________________________________________________________________________________

In this workshop you will be introduced to the following concepts:

chemical equivalence proton and carbon atoms in a similar environment will resonate with the same frequency and have the same splitting pattern.

splitting patterns
In essence, a proton is affected by other protons on an adjacent carbon atom. This follows the N+1 rule. If one proton is present on an adjacent carbon, the resonance will be split into a doublet; if two protons are present then it will split the resonance into a triplet; with four, a quartet etc.

chemical shift (shielding and deshielding)
Adjacent atoms affect the magnetic field experienced by the proton. In effect, methyl groups resonate around 1ppm, methylene groups between 1-2ppm and methine groups between 1.5 to 2.0 ppm (Note that there is overlap).

If there is an oxygen atom attached to the same carbon as the proton, the proton resonates between 3.0 to 3.5. Methoxy groups on aromatic rings resonate at between 3.7 to 4.0 ppm. A nitrogen atom attached to the carbon will also cause the proton to resonate between 2.6 to 3.4 ppm. This is because the electronegative atoms draw the electrons closer to it and are said to deshield the proton from the magnetic field. This will be explained further to you in the workshop and in lectures.

Due to diamagnetic anisotropy, protons on aromatic rings resonate between 6.5 and 8 and olefinic protons resonate between 5.5 to 6.5 ppm.

integration
The area under the peak gives one an indication of the number of protons that gave rise to the resonance. This can be used to ascertain which are methyl, methylene and methine groups as well as give an indication of equivalent resonances.

You will be shown how to work out examples in the workshop as well as given time to work out some examples on your own. You will be given a chance to interact with your demonstrators and fellow classmates.

Toward the end of the workshop you will be given a test to see how effective the workshop was. This will constitute your mark for the workshop and must be handed in to your demonstrator to mark.

Practical 5_________________________________________________________
Sandmeyer reaction (preparation of diazonium salts)
_________________________________________________________________________________
Preparation of p-Chloronitrobenzene (Sandmeyer Reaction)

Part 1: Preparation of Cuprous chloride, CuCl
1. Add 14 g CuSO4.5H2O and 4.7 g NaCl to 50 mL water in a 250mL beaker and warm the mixture to 55-60 C, stirring with a glass rod until a clear solution is obtained.
2. IN THE FUME CUPBOARD, Add a solution of 7 g sodium bisulphite in 13 mL water to the solution. The mixture will become green rapidly, and the CuCl that forms separates as a white powder as the solution cools. Cool the solution to 10-15 C by standing in cold water to ensure the complete precipitation of the CuCl. (DO NOT cool below this temperature or crystals of Na2SO4 may separate and cause contamination). Allow the solution to stand in cold water while part 2 is being performed.
Part 2: Diazotization of p-Nitroaniline
3. Prepare a mixture of 20 mL conc. HCl and 20 mL H2O by SLOWLY adding the acid to the H2O, and then dissolve 5 g p-nitroaniline in it. Cool to 5 C, and SLOWLY add a solution of 7g NaNO2 in 15mL water. Leave the solution to stand at 5 C and return to the CuCl preparation.
4. Filter off the solid CuCl though a Buchner funnel under vacuum and wash with 2 x 10 mL DISTILLED water. Transfer the well-drained CuCl to a 400mL beaker containing a mixture of 10 mL conc. HCl and 10 mL water mixed as above. A brownish-coloured solution will form. Heat the solution on a water bath.
5. Add the diazonium solution, which must still be below 5 C, to the heated CuCl solution in small portions with vigourous stirring using a GLASS ROD. When the addition is complete, allow the mixture to stand for 10 minutes, followed by heating on a water bath for 15 minutes.
6. Cool, filter and wash the solid material with 2 x 10 mL portions of DISTILLED water. Suck dry for 5 minutes, then recrystallise from methanol. Transfer the crystals to a labeled, preweighed pill vial and hand in. If the sample is not completely dry, leave until the following week on paper with your name. Then take the mass and determine the melting point.

Practical Report: follow the format on page ix.
Practical 6________________________________
Synthesis of Benzilic Acid from Benzil.
_________________________________________________________________________________
Synthesis of Benzilic Acid from Benzil
When benzil is heated with potassium hydroxide solution, it undergoes a molecular rearrangement to form the potassium salt of benzilic acid, or diphenylglycollic acid.

This reaction applies to many 1,2-diketones, and is termed the Benzilic Acid Rearrangement. It provides a ready method for the preparation of disubstituted α-hydroxy-carboxylic acids.

1. Dissolve 5 g of benzil in 15 mL of boiling ethanol in a 50 mL round bottom flask fitted with a reflux condenser. Add a solution of 5 g of KOH in 10 mL water, and heat the mixture (which rapidly turns purple) in a heating mantle for 15 minutes.
2. Cool and stir the solution from which the potassium benzilate separates in fine crystals. Filter the product under vacuum, washing the crystals with a small quantity of ethanol to remove the purple colour and dry under suction for a further 5 minutes.
3. Dissolve the crystals in 50 mL cold water, filtering the solution if a small insoluble residue remains, and then boil the clear solution gently whilst dilute H2SO4 is added until separation of pale orange-coloured crystals of acid is complete. Cool the solution and filter under vacuum, washing with some hot water.
4. Transfer the crystals to a pre-weighed, labelled pill vial, and hand in. If the sample is not completely dry, leave until the following week on paper with your name. Then take the mass and determine the melting point.

Practical Report: follow the format on page ix.

Practical 7________________________________________________________________
Aldol condensation.
Vacuum distillation _________________________________________________________________________________
Preparation of ethyl 3-phenylpropenoate (ethyl cinnamate)
Note _________________________________________________________________________
Ethyl acetate and benzaldehyde are flammable; avoid exposure to heat or flames.
Sodium ethoxide and acetic acid are corrosive; rinse copiously with water if contact occurs
______________________________________________________________________________

1. In a 100 mL beaker clamped securely in an ice-water bath on top of a magnetic stirrer, place a Teflon-coated magnetic stirring bar, 20 mL ethyl acetate (previously dried over K2CO3) and 6.0 mL of 21% ethanolic solution of sodium ethoxide. Stir the solution and check the temperature to make sure it is below 10 °C.
2. Add 4.0 mL of benzaldehyde dropwise over the course of 5 minutes (at a rate of approximately 1 drop every 3 seconds), making sure that the temperature stays in the range 0-10 °C.
3. Stir the solution for an additional 45 minutes to form a cream paste and then add 40 mL 10% aqueous acetic acid. Be careful not to spill ice into the beaker.
4. Stir the mixture and pour it into a separating funnel. Two phases should appear; if the phases do not separate well, add brine (saturated NaCl solution) to salt out the organic phase. Remove the aqueous (lower) layer, wash the remaining organic layer with 20 mL water, separate the layers and wash the organic layer with 20 mL of brine (saturated NaCl solution), then transfer the (upper) organic layer to a Quickfit conical flask and dry over MgSO4. (Add small portions of MgSO4, with swirling until it remains powdery, rather than clumping together or sticking to the sides of the flask, and the solution is clear.)

Distillation
The demonstrator will collect all the crude products and demonstrate to you as to how a vacuum distillation is carried out.
For the demonstrator to carry out and for students to observe:
To the crude product add boiling chips and distil under vacuum (lit. bp 271°C at 760 mmHg) into a pre-weighed receiver flask. Record the volume of ethyl cinnamate and use this to calculate your yield.

Figure 3. Distillation

Practical Report: follow the format on page ix.

Practical 8 (2 days)___________________________
Isolation of caffeine from Black Tea.
_________________________________________________________________________________
Introduction
The popularity of tea and coffee as beverages stems from their mildly stimulatory activity which is mainly due to the presence of the purine alkaloid caffeine. Caffeine acts as a mild CNS stimulant and relaxes the smooth muscle of the bronchi as well as having diuretic properties.

1. Weigh out 25 g Black tea leaves into a 250 mL Erlenmeyer flask, add 50 mL dichloromethane (CH2Cl2), and then basify the mixture with 2 M NaOH (~ 20 mL; check the pH with red Litmus paper). Swirl the mixture by hand for 10 minutes, and then filter the solution under vacuum.
2. Transfer the filtrate to a 100 mL separating funnel and allow the layers to separate. Run off the (lower) CH2Cl2 layer into a 100 mL round-bottomed flask. Discard the aqueous layer.
3. Rinse the tea-leaf material with 2 x 10 mL portions of CH2Cl2. Filter these washings and combine with the CH2Cl2 extract from step 2 above. Use the separating funnel if necessary to remove any remaining aqueous drops before combining the extracts.
4. Distill (Figure 3) off the CH2Cl2 using a heating mantle, then wash the solid residue with 4 x 1 mL cold hexane:diethyl ether (Et2O) (1:1), using a Pasteur pipette to remove the washings each time.
5. Dissolve the remaining “green” crystals in CH2Cl2 (~3 mL) and filter through a Pasteur pipette fitted with a small cotton wool plug into a pre-weighed 50 mL Erlenmeyer flask. Wash through the cotton wool with a further 3 ml CH2Cl2. Evaporate the solvent and record the crude yield.
6. Recrystallize the crude material from 2-propanol (iso-propanol, PriOH). Filter under vacuum using a Hirsch funnel, washing with 2 x 1 mL cold hexane:Et2O(1:1).
7. Dry the pure crystalline product between two filter papers, then transfer to a pre-weighed, labelled pill vial. If the sample is not completely dry, leave until the following week on paper with your name, then take the mass and determine the melting point.

Practical Report
In no more than half a page, describe the principle of extraction.
Calculate the percentage of caffeine extracted from the tea.

Catchup day ________________________________________
Complete all unfinished work and hand in all your practical reports to your demonstrator to mark.
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Notes: