SYNTHESIS OF ⳑ-PROLINE (ⳑ-Pyrrolidine-2-carboxylic acid)

Ammonium rhodanilate:

• Heat a mixture of 250g (0.5 mol Cr 3 ®) of hydrated chromium(m) potassium sulphate (chrome alum), 290g (3.0 mol) of potassium thiocyanate and 250 ml of water in a 5-litre flask on a steam bath for 4 hours. 

• Cool, add 235g (230 ml, 2.53 mol) of redistilled aniline and heat in a water bath at 60 °C with stirring for 3 hours. 

• Cool again, add while still stirring 3 litres of water containing 300 ml of glacial acetic acid and leave at 0°C overnight. 

• Filter off the purple precipitate with suction, wash it with water and suck as dry as possible. 

• Extract the filter cake with 750 ml of methanol, filter and run into the filtrate, with stirring, 3 litres of water. 

• Cool at °C for 1 hour and filter off the crystalline purple mass of aniline rhodanilate. 

• Dissolve the damp product in 400 ml of methanol, add 200 ml of concentrated ammonia solution (d 0.88), cool to °C and then run in slowly, with stirring, 2 litres of water. 

• Collect the precipitate by filtration, and again treat it with 250 ml of methanol, 125 ml of ammonia solution and 1250 ml of water in the above manner. 

• Dry the resulting ammonium rhodanilate sesquihydrate in an oven at 50 °C; the yield is 130g (50.5%).

L-Proline:

• Place 150g of good quality sheet gelatin (cut into conveniently sized pieces) in a 1-litre flask and add 450 ml of concentrated hydrochloric acid. 

• Boil gently under reflux for 8 hours (fume cupboard), or boil under reflux for about 3 hours and leave on a steam bath overnight; complete hydrolysis is indicated by a negative biuret reaction (1). 

• Concentrate the hydrolysate to a syrup by distillation under reduced pressure (rotary evaporator), and remove excess hydrochloric acid by dissolving the syrup in water and evaporating twice more. 

• Dissolve the residual syrup finally in 500 ml of water, boil briefly with 3g of decolourising charcoal, filter, cool and dilute with water to 1200 ml. 

• Add this solution slowly with stirring to a filtered solution of 125g of ammonium rhodanilate in 750 ml of methanol and keep at °C for 2 hours to allow the complete separation of proline rhodanilate. 

• Filter off the latter, wash it with water and suck as dry as possible. 

• Dissolve the damp crude product in 400 ml of methanol, filter and add 800 ml of 0.5 m hydrochloric acid slowly with stirring. 

• Cool at °C for 2 hours, filter off the purified proline rhodanilate and wash it with 250 ml of cold water. 

• Dry the product in an oven at 50 °C; the yield is about 100g, m.p. c. 130°C, with preliminary softening and blackening.

• Suspend the purified salt in 850 ml of water in a stoppered bottle, add 25 ml of pure pyridine and shake the mixture for 4-5 hours. 

• Remove the insoluble pyridine rhodanilate by filtration and wash it with 100 ml of cold water (2). 

• Combine the pale pink filtrate and washings, and add glacial acetic acid dropwise until the formation of a small pink precipitate is complete. 

• Filter, evaporate the almost colourless filtrate to dryness (rotary evaporator) and suspend the residue in absolute ethanol and re-evaporate twice. 

• Dry the resulting faintly pink crude proline in a vacuum desiccator over silica gel; the yield is about 18g. 

• Recrystallise from the minimum volume of absolute ethanol to obtain 11g (7.3% based on gelatin) of ⳑ-proline, m.p. 218-219 °C (decomp.), [𝜶]ᴅ¹⁸-85.6° (c3.0 in H₂O). 

• Check the purity of the product by t.l.c. on silica gel using the solvent system butan-1-ol-acetic acid- water, 4:1:1; R𝑓 0.26 (yellow spot with ninhydrin).

Notes to keep in mind:

1. Remove about 0.25 ml of the hydrolysate, cool it and basify it with 5ᴍ sodium hydroxide solution. To a portion add a few drops of very dilute copper(u) sulphate solution, and note the absence of any colour change. As a control, prepare a specimen of biuret (NH₂⋅CO⋅NH⋅CO⋅NH₂) by heating about 10mg of urea just above its melting point for about 2 minutes. Add a little basified hydrolysate warm to dissolve, cool and add a trace of copper(u) sulphate. A deep pink colour superimposed upon the pale brown colour of the hydrolysate should be observed. If the hydrolysate gives a similar colour originally, it contains peptide material and hydrolysis should be continued until the biuret test is negative.

2. About 100g of pyridine rhodanilate is obtained. To convert this into the ammonium salt for re- use, suspend it in 175 ml of methanol and add 90 ml of concentrated ammonia solution. Stir at °C for 30 minutes and then dilute gradually with 900 ml of water. Filter off the precipitated ammonium salt, wash it with water and repeat the methanol-ammonia treatment once more. The final yield of dried ammonium rhodanilate is about 80g.

SYNTHESIS OF ᴅⳑ-PROLINE (ᴅⳑ-Pyrrolidine-2-carboxylic acid)

3-Ethoxycarbonyl-2-piperidone: 

• Dissolve 160g (0.75 mol) of diethyl (2- cyanoethyl)malonate in 600 ml of ethanol and hydrogenate in the presence of about 4-5 g of Raney nickel catalyst at 80 °C and 75 atmospheres pressure of hydrogen in an autoclave; uptake of hydrogen is complete in about 2 hours. 

• Remove the catalyst by filtration and the solvent by distillation under reduced pressure (rotary evaporator) and pour the residue with stirring into 500 ml of light petroleum (b.p. 60-80 °C). 

• Filter off the precipitated piperidone and allow it to dry in the air; yield 115g (90%), m.p. 74 °C. A specimen crystallised from ethanol/light petroleum has m.p. 80 °C.

3-ChIoro-3-ethoxycarbonyI-2-piperidone:

• Assemble in a fume cupboard a 500-ml three-necked flask fitted with a sealed stirrer unit, a dropping funnel and a reflux condenser protected by a calcium chloride guard-tube. 

• Charge the flask with a solution of 111g (0.65 mol) of 3-ethoxycarbonyl-2-piperidone in 175 ml of dry chloroform (CAUTION), and the dropping funnel with 90g (54 ml, 0.67 mol) of redistilled sulphuryl chloride dissolved in 125 ml of dry chloroform; close the neck of the funnel with a calcium chloride guard-tube. 

• Start the stirrer, and slowly run in the solution of sulphuryl chloride so that the reaction mixture refluxes gently. 

• When the addition is complete, warm on a steam bath until hydrogen chloride .evolution ceases. 

• Remove the solvent under reduced pressure using a rotary evaporator, and cool the residue, scratching the sides of the flask to induce crystallisation.

•  Dissolve the solid in 70 ml of hot ethyl acetate, add hot light petroleum (b.p. 80-100 °C) until the solution is slightly turbid, and cool while scratching the side of the vessel vigorously until the product crystallises (it helps to add a few crystals of the crude solid as a seed). 

• Add 30 ml more of light petroleum, cool further and filter. The chloropiperidone is obtained as a somewhat sticky white solid, m.p. 64-68 °C; yield is 100g (82%).

ᴅⳑ-Proline hydrochloride:

• Boil 103g (0.5 mol) of the above chloropiperidone under reflux with 200 ml of concentrated hydrochloric acid (fume cupboard) for 5 hours during which time decarboxylation ensues. 

• Boil the solution with about 2g of decolourising charcoal (acid-washed grade), filter and evaporate under reduced pressure using a rotary evaporator; dissolve the residue in water and re-evaporate to assist the removal of most of the excess hydrochloric acid. 

• Dissolve the resulting pale golden syrup in 80 ml of water, add a solution of 60g of sodium hydroxide in 120 ml of water and leave at room temperature for 2 days. 

• Acidify the solution to Congo red paper with concentrated hydrochloric acid (about 130 ml are needed) and evaporate to dryness under reduced pressure (rotary evaporator). 

• Dry the resulting solid completely by leaving it overnight in a vacuum desiccator over phosphorus pentoxide and potassium hydroxide pellets, and then extract it with 200 ml of boiling absolute ethanol. 

• Filter off the sodium chloride and re-extract it with 150 ml more of boiling ethanol. 

• Evaporate the ethanol from the combined filtrates and boil the residue under reflux for 1 hour with 1.25 litres of 2ᴍ hydrochloric acid to hydrolyse any proline ester formed in the extraction process. 

• Evaporate to dryness, redissolve the residue in water and re-evaporate, and dry the resulting crude ᴅⳑ-proline hydrochloride in a vacuum desiccator over phosphorus pentoxide and potassium hydroxide; the yield is 70g. 

• Recrystallise the product from 175 ml of hot propan-2-ol, cool in ice, filter and wash the crystals with 20 ml of ice-cold propan-2-ol. The yield of the purified product, m.p. 148-150 °C, is 50g (66%).

Conversion to ᴅⳑ-proline:

• Suspend 15g (0.1 mol) of dry proline hydrochloride in 70 ml of dry chloroform, stir vigorously and run in dropwise 15g (0. 15 mol) of dried, redistilled triethylamine. 

• Continue stirring for 1 hour, filter off the product and wash it with a little cold chloroform. The yield of ᴅⳑ-proline is 10g (87%); a sample crystallised from absolute ethanol has m.p. 206-207 °C (with preliminary sintering).

SYNTHESIS OF ᴅⳑ-TRYPTOPHAN [2-Amino-3-(3-indolyl)propanoic acid]

Phenylhydrazone of 4-acetamido-4,4-diethoxycarbonylbutanal

CAUTION: Carry out all operations in an efficient fume cupboard. 

• Place 43.5g (0.2 mol) of diethyl acetamidomalonate and 70 ml of benzene (CAUTION) in a 250-ml three-necked flask fitted with a stirrer and dropping funnel and surrounded by a bath of water at room temperature. 

• Stir mechanically, add about 0.5 ml of a concentrated solution of sodium ethoxide in ethanol and then add slowly from the dropping funnel a solution of 12g (14ml, 0.215 mol) of acrylaldehyde [acrolein - CAUTION: highly toxic and irritant vapour (1)] in 14 ml of benzene; adjust the rate of addition so that the temperature of the reaction mixture does not exceed 35 °C. 

• When the addition is complete, stir for 2 hours more and filter off any traces of insoluble material. 

• Add 5 ml of glacial acetic acid and 24g (22 ml, 0.22 mol) of redistilled phenylhydrazine [CAUTION: (2)], warm to 50 °C and leave the resulting orange solution at room temperature for 2 days. 

• Collect the crystalline phenylhydrazone by filtration and wash it thoroughly by trituration with two 40 ml portions of benzene. 

• The yield of off-white crystals, m.p. 141 °C, is 50 g (69%). If the yield is low, warm the filtrate to 50 °C and set it aside for a further 2 days, when a further crop of the product may be obtained.

Diethyl (3-indolylmethyi)acetamidomalonate:

• Add 47g (0.13 mol) of the phenylhydrazone to 300 ml of water containing 14 ml of concentrated sulphuric acid in a 500-ml two-necked flask fitted with a sealed stirrer unit and a reflux condenser. 

• Boil the mixture under reflux with vigorous stirring for 4.5 hours; the suspended solid liquefies and then solidifies during this time. 

• Cool, filter off the resulting product (in the form of hard nodules) and wash it thoroughly by grinding it with water and re-filtering. 

• Recrystallise the product from 1:1 aqueous ethanol to obtain the purified malonate derivative; yield 32g (71%). The product melts at 143 °C, re-solidifies and then melts at 159 °C.

DL-Tryptophan:

• Boil 31g (0.09 mol) of the above product under reflux for 4 hours with a solution of 18g (0.45 mol) of sodium hydroxide in 180 ml of water. 

• Add a little decolourising charcoal, filter and cool the filtrate in an ice-salt bath. 

• Acidify the filtrate by adding about 55 ml of concentrated hydrochloric acid slowly and with shaking, keeping the temperature below 20 °C. 

• Cool the resulting suspension at 0°C for 4 hours and then collect the crude (indolylmethyl)malonic acid, a pale buff solid, by filtration. 

• Boil the crude product under reflux with 1 30 ml of water for 3 hours; decarboxylation ensues and some N-acetyltryptophan separates. 

• Add a solution of 16g (0.4 mol) of sodium hydroxide in 30 ml of water, continue to boil under reflux for 20 hours and then add about 1g of decolourising charcoal and filter. 

• Cool, acidify the filtrate by adding 24g (23 ml, 0.4 mol) of glacial acetic acid and cool the mixture at °C for 5 hours. 

• Collect the crude tryptophan by filtration, dissolve it in a solution of 5g of sodium hydroxide in 200 ml of water and warm to 70 °C. 

• Dilute the solution with 100 ml of ethanol at 70 °C and decant it from a little gummy precipitate which separates. 

• Acidify the hot solution with 7.5 ml of glacial acetic acid and allow to cool slowly. 

• When crystallisation is complete, filter off the purified DL-tryptophan and wash it successively with ice-cold water (2 x 40 ml), ethanol (2 x 40 ml) and ether (2 x 40 ml). The yield of colourless plates is 15g (82%), m.p. 283-284 °C (decomp.).

Notes to keep in mind:

1. Acrolein is usually supplied in sealed amber-coloured ampoules stabilised by the addition of a little hydroquinone. The ampoule should be cooled thoroughly before being opened with great care. It has been recorded that opened samples of acrolein stored in screw-capped bottles may explode violently, presumably as the result of rapid exothermic polymerisation.

2. Phenylhydrazine is highly poisonous and produces unpleasant burns in contact with the skin. Always wear disposable gloves. If any liquid does come in contact with the skin wash off immediately with 2 per cent acetic acid, then with soap and water.

SYNTHESIS OF ᴅⳑ-SERINE (2-Amino-3-hydroxypropanoic acid)

• Prepare a suspension of 43.5g (0.2 mol) of diethyl acetamidomalonate in 25 ml of water and add in one portion 17g of neutral (1) 37-41 per cent w/v aqueous formaldehyde (0.21-0.23 mol). 

• Add 0.5 ml of 1 m sodium hydroxide solution as the catalyst, shake vigorously and leave at room temperature for 2 hours. 

• (Most of the solid goes into solution within 30 minutes; the mixture may require gentle warming on a steam bath to complete the dissolution of the solid.) Then add a solution of 18g (0.45 mol) of sodium hydroxide in 350 ml of water and leave at room temperature overnight. 

• Acidify the solution by adding 40g (38 ml, 0.67 mol) of glacial acetic acid and heat almost to boiling, when brisk decarboxylation sets in. 

• Continue to heat on a boiling water bath under reflux for 1 hour to complete the decarboxylation and then evaporate the solution to a syrup under reduced pressure on a rotary evaporator. 

• Dissolve the syrup in 120 ml of concentrated hydrochloric acid, boil under reflux (fume cupboard) for 1 hour and evaporate to dryness under reduced pressure. 

• Extract the dry residue with 200 ml of boiling absolute ethanol, filter off the sodium chloride and extract the latter with a further 100-ml portion of hot ethanol. 

• Evaporate the ethanol extracts on the rotary evaporator and boil the residue under reflux with 100 ml of concentrated hydrochloric acid for 1 hour (fume cupboard). 

• Evaporate again to a syrup, and dissolve the latter in water and re-evaporate twice more to remove most of the excess hydrochloric acid. 

• Finally dissolve the residual gum in about 200 ml of distilled water and pass the solution through a 50 x 2.75 cm column of a weakly basic anion exchange resin (e.g. Amberite IR 45, ᶿOH form, about 300 ml of moist granules). 

• Continue to elute the column with distilled water (about 1.5 litres) until the eluate gives no purple coloration when a portion is tested by boiling with a few mg of ninhydrin (2). 

• Combine all the ninhydrin-positive eluates, which should be free from chloride ion, and evaporate to dryness under reduced pressure (rotary evaporator). 

• Dissolve the straw-coloured residue in 150 ml of hot water, boil with a little decolourising charcoal, filter and add to the filtrate 750 ml of hot ethanol. 

• Cool in ice, filter off the purified ᴅⳑ-serine which crystallises, wash it with a little cold ethanol and dry in an oven at 50 °C. 

• The yield is 12g(57%), m.p.c. 235 °C (decomp.). The product thus obtained is homogeneous (R𝑓 0.57) on t.l.c. (silica gel, 15 cm run; butan-1-ol-formic acid-water, 6:3:1) (3).

Notes to keep in mind:

1. If necessary, the formaldehyde solution should be neutralised (narrow range pH paper) by the careful dropwise addition of 1 m sodium hydroxide solution.

2. After use, regenerate the resin in the following way. Firstly exhaust the column by passing 0.25 m hydrochloric acid through it until the pH of the eluate is about 2. Wash the column with 2 or 3 bed-volumes if distilled water, and then regenerate the resin by passing through it 0.25 m sodium hydroxide solution until the eluate is strongly alkaline. Finally wash the column thoroughly with much distilled water until the pH of the eluate is within the range 5.5-6.5 (narrow range indicator paper).

3. Using this solvent system, serine is not completely separable from glycine (R𝑓 0.58) which is a possible contaminant. The latter may be distinguished, however, by the characteristic brownish-pink spot which it gives on spraying with ninhydrin; that of serine is purple.

SYNTHESIS OF ᴅⳑ-PHENYLALANINE (2-Amino-3-phenylpropanoic acid)

• In a 1-litre three-necked flask, fitted with a reflux condenser, a sealed stirrer unit and dropping funnel, place 25g (0.1 mol) of 4-benzylidene-2-phenyloxazol-5-one 20g (0.65 mol) of purified red phosphorus and 135g (125 ml, 1.32 mol) of acetic anhydride. 

• Add with stirring over a period of 1 hour 125 ml of hydriodic acid (d 1.56; 50%). 

• Reflux the mixture for 3 hours, cool and filter with suction; wash the unreacted phosphorus on the filter with two 5 ml portions of glacial acetic acid. 

• Evaporate the filtrate and washings on a water bath (rotary evaporator) and collect the distillate (which may be used for another reduction) in a flask cooled in ice. 

• Add 100 ml of water to the dry residue and repeat the evaporation to dryness. 

• Shake the residue in the flask with 150 ml of water and 150 ml of ether until solution is complete; separate the acqueous layer and extract it with three 75 ml portions of ether. 

• Discard the ether extracts. 

• Introduce 2-3 g of decolourising carbon and a trace of sodium sulphite into the aqueous phase, heat on a water bath until the dissolved ether has been removed, filter, heat the filtrate to boiling and neutralise to Congo red with ammonia solution (d 0.88; about 25 ml are required). 

• When cold, filter the colourless dl-phenylalanine at the pump and wash with two 30-ml portions of cold water and finally with a little cold ethanol. The yield is 11g (67%), m.p. 284-288 °C (decomp., rapid heating).

SYNTHESIS OF AMINOACETONITRILE AND GLYCINE (Aminoacetic acid)

N-Methyleneaminoacetonitrile

• Place 160g (3 mol) of ammonium chloride in a 2-litre flange or three-necked flask surrounded by a large bath containing a cooling mixture of ice and salt (fume cupboard). 

• Add 450 ml (6 mol) of filtered 40 per cent w/v formaldehyde solution and stir the mixture with an efficient mechanical stirrer. 

• When the temperature has reached °C, begin the dropwise addition of a solution of 150g (3 mol) of sodium cyanide (98% pure) (CAUTION) in 250 ml of water; the addition should take about 5 hours and the temperature throughout should be kept between and 5 °C. 

• When half of the cyanide solution has been added and all of the ammonium chloride has dissolved begin the simultaneous gradual addition of 100 ml of glacial acetic acid, and adjust the rate so that addition is complete by the end of the remaining 2.5 hours. 

• Stir the mixture for a further period of 1 hour, and then filter off the product and wash it with a little cold water. 

• Transfer the filter-cake to a beaker, stir thoroughly with 500 ml of water to remove soluble salts, filter, wash with a little more water and dry in a vacuum desiccator. The yield of N-methyleneaminoacetonitrile (1) is 120g (59%), m.p. 127-128 °C.

Aminoacetonitrile sulphate:

• Cautiously add 85 ml of concentrated sulphuric acid to 400 ml of rectified spirit in a 1-litre conical flask and adjust the temperature to 50 °C. 

• Add rapidly 102g (1.5 mol) of dried powdered N-methyl-eneaminoacetonitrile, shake vigorously until the solid has dissolved and continue shaking while the product crystallises. 

• Cool in an ice bath for 4 hours, filter and wash the product with a little cold rectified spirit. 

• Dissolve the crude product in a minimum of water, filter off traces of insoluble matter and run the solution with stirring into 400 ml of cold rectified spirit. 

• Cool well, filter off the purified aminonitrile salt and wash it with a little cold rectified spirit. The yield is 105g (67%), m.p. 164 °C (decomp.).

Hydrolysis to glycine

• Boil a suspension of 79g (0.25 mol) of barium hydroxide octahydrate in 175 ml of water in a 500-ml round-bottomed flask and add in portions 21g (0.1 mol) of aminoacetonitrile sulphate. 

• Fit a reflux condenser and continue boiling until no more ammonia is evolved (about 3 hours). 

• Transfer the suspension to a beaker, add 50 per cent v/v aqueous sulphuric acid (about 20 ml) until precipitation of the barium is complete and the solution is slightly acidic, and digest on a steam bath. 

• Filter the suspension through a medium-speed filter paper (e.g. Whatman No. 30) using gentle suction, and adjust the filtrate to neutrality by carefully adding saturated barium hydroxide solution. 

• Digest further and decant the supernatant solution through a similar filter paper (this is best done under gravity), suspend the precipitate in a little hot water and add this to the filter. 

• Concentrate the filtrate under reduced pressure using a rotary evaporator until a thick suspension is obtained, and complete the precipitation of the glycine by adding 100 ml of methanol. 

• Cool well and filter off the crude glycine (about 12g). 

• Dissolve the product in 25 ml of hot water, add gradually 125 ml of methanol, cool, filter and dry the crystals in an oven at 50 °C. The yield of glycine, m.p. c. 250 °C (decomp.), is 11.2g (75%).

Aminoacetonitrile:

• Stir a suspension of 88g (0.4 mol) of the nitrile sulphate in 100 ml of dry methanol in a 500-ml three-necked flask cooled in crushed ice. 

• Add a few crystals of phenolphthalein as an indicator, pass a slow stream of nitrogen through the flask and run in during 1 hour a solution of sodium methoxide in methanol prepared from 17g (0.75 mol) of sodium and 350 ml of dry methanol; the suspension should at no time be allowed to become permanently alkaline to phenolphthalein. 

• Filter, and remove the methanol and distil the residue under reduced pressure under nitrogen. The yield of amino-acetonitrile, b.p. 73.5°C/15mmHg, is 35g (83% based on sodium). Store the product at 0°C under nitrogen.

Notes to keep in mind:

1. The product in fact has a trimeric structure.

Cognate preparation: DL-2-Aminophenylacetic acid (𝛼-phenylglycine)

• Dissolve 10g (0.2 mol) of sodium cyanide in 40 ml of water, add 11g (0.2 mol) of ammonium chloride and shake until dissolved. Add a solution of 21g (0.2 mol) of redistilled benzaldehyde in 40 ml of methanol and shake vigorously. 

• The mixture soon becomes warm; allow it to stand at ambient temperature for 2 hours, shaking occasionally. 

• Then add 100 ml of water and shake well, and extract out the oily aminonitrile which separates using two portions (60 ml and 40 ml) of toluene. 

• Combine the toluene layers, wash twice with water and extract with two 60 ml portions of 5ᴍ hydrochloric acid. 

• Boil the acid extract under reflux for 22 hours (CARE: hydrogen cyanide is evolved). 

• Cool and filter through a small plug of cotton wool to remove a little tarry matter. 

• Basify the solution by adding about 40 ml of concentrated ammonia solution (d 0.88) with stirring and cooling, collect the resulting precipitate by filtration and wash it with 100 ml of cold water and then with 15 ml of warm ethanol. 

• The crude material is almost colourless; the yield is 11.5g after drying in an oven at 50 °C. 

• To purify the phenylglycine, dissolve it in 80 ml of 1ᴍ sodium hydroxide, add 50 ml of ethanol and clarify the solution by adding a little decolourising charcoal, warming and filtering. 

• Heat the filtrate almost to boiling and neutralise by slowly adding with stirring 16 ml of 5ᴍ hydrochloric acid. 

• Filter off the purified DL-phenylglycine, wash it with 10 ml of ethanol followed by 20 ml of water and dry at 50 °C; the yield of colourless glistening plates is 9g (30%). 

• The compound has no m.p.; when placed in a rapidly heated melting point apparatus when the temperature reaches 275 °C, it sublimes between 300 and 310 °C, depending upon the rate of heating.

SYNTHESIS OF DL-ALANINE (2-Aminopropanoic acid)

• Place 2 litres (1760g, 36 mol) of concentrated ammonia solution (d 0.88, 35% w/w) (1) in a large (e.g. Winchester) bottle, cool thoroughly in an ice bath and pour in slowly 77g (0.5 mol) of 2-bromopropanoic acid. 

• Close the bottle with a rubber bung held in place with wire, and leave at room temperature for 4 days. 

• Concentrate the solution to about 250 ml by distillation under reduced pressure using a rotary evaporator; apply the vacuum with caution in the initial stages when most of the excess of ammonia is being removed. 

• Filter, concentrate further to 150 ml, cool in ice and add 750 ml of methanol with swirling. 

• Leave the resulting suspension overnight in a refrigerator, and then filter off the crude alanine with suction and wash it with 200 ml of methanol. 

• Dissolve the product in 150 ml of water, reprecipitate the alanine by adding 750 ml of methanol and filter and wash as before. The yield of almost pure DL-alanine, m.p. 295-296 °C (decomp.), is 30g (67%).

Notes to keep in mind:

1. Alternatively use 225g of 'ammonium carbonate', 175 ml of water and 250 ml (4.5 mol) of concentrated ammonia solution. 'Ammonium carbonate' is a mixture of roughly equimolar amounts of ammonium hydrogen carbonate and ammonium carbamate (NH₄HCO₃⋅NH₂CO₂NH₄).

Cognate preparations:Glycine (aminoacetic acid)

• Use 47g (0.5 mol) of chloroacetic acid (CAUTION: the compound causes blistering if it is allowed to come into contact with the skin) and 2 litres of concentrated ammonia solution. 

• Allow the reaction to proceed for 2 days, concentrate to 60 ml and precipitate the crude glycine by adding 360 ml of methanol. 

• This material contains ammonium chloride as the chief impurity; remove most of this by stirring the crystals with 150 ml of methanol and refiltering. 

• Finally purify the glycine by dissolving it in 50 ml of hot water and adding 250 ml of methanol; the yield is 25g (67%), m.p. c. 252-254 °C (decomp.).

DL-Valine (2-amino-3-methylbutanoic acid):

• Use 60g (0.33 mol) of 2-bromo- 3-methylbutanoic and 400 ml (7.25 mol) of concentrated ammonia solution. 

• Allow reaction to proceed at room temperature for 7 days. 

• Concentrate the solution to 50 ml and filter the resulting thin paste. 

• Dissolve the solid in 1 50 ml of hot water, decolourise with 1g of charcoal, filter hot and dilute the filtrate with 150 ml of ethanol. 

• Cool at 0°C overnight, filter off the purified DL-valine and wash with 10 ml of cold ethanol. 

• The yield is 12.5g (32%); m.p. 280-282 °C (decomp.). A further 2g may be isolated by concentrating the mother-liquor to about 25 ml and adding an equal volume of ethanol.

DL-Norvaline (2-aminopentanoic acid):

• Prepare as for valine, using 2-bromo-pentanoic acid; m.p. c. 300 °C (decomp.).

DL-Norleucine (2-aminohexanoic acid):

• Use 65g (0.33 mol) of 2-bromo-hexanoic acid and 400 ml of concentrated ammonia. 

• Ensure that the bung is securely wired to the reaction bottle and allow the latter to stand in a warm place (50-55 °C) for 30 hours. 

• Filter the amino acid at the pump and keep the filtrate (A) separately. 

• Wash the amino acid well with methanol to remove the ammonium bromide present. Concentrate the filtrate (A) almost to dryness and add 150 ml of methanol. 

• A second crop of amino acid contaminated with ammonium bromide is thus obtained; wash it with methanol and recrystallise from hot water, thus affording a further 6g of pure dl- norleucine. The total yield is 28g -(65%); the decomposition point is about 325 °C.

DL-holeucine (2-amino-3-methylpentanoic acid):

• Allow 65g (0.33 mol) of 2-bromo-3-methylpentanoic acid to react with 400 ml of concentrated ammonia solution as for valine. 

• Concentrate the resulting solution to about 130 ml, filter off a first crop of crude product and wash with 20 ml of ethanol. 

• Further concentrate the aqueous filtrate to about 60 ml to obtain a second crop of crude product, and wash it with 10 ml of water followed by 10 ml of ethanol. 

• Dissolve the combined product (28g) in 400 ml of hot water, decolourise with charcoal and add 200 ml of rectified spirit. 

• Cool well in ice, and filter off the pure DL-isoleucine; yield 16.5g (38%), m.p. 278-280 °C (decomp.). 

• A further 5g may be recovered by concentrating the recrystallisation mother-liquor to 40 ml and diluting with an equal volume of ethanol.

SYNTHESIS OF 4-OXODECANOIC ACID

3-Carboxydec-3-enoic acid. (Heptylidenesuccinic acid.) Potassium t-butoxide. 

• Prepare a solution of potassium t-butoxide in t-butyl alcohol using the following procedure. 

• Equip a two-necked, round-bottomed 1-litre flask with a reflux condenser and a pressure-equalising dropping funnel. 

• Attach to the top of the condenser a nitrogen inlet system with nitrogen escape valve and place the flask in a magnetic stirrer-heating mantle unit. 

• Flush the flask with a stream of dry nitrogen, charge the flask with 375 ml of dry t-butanol and add 19.6g (0.5 mol) of potassium. 

• Heat the mixture under reflux until the potassium completely dissolves (c. 4 hours). 

• To the cooled solution add a mixture of 122g (0.7 mol) of diethyl succinate and 63g (0.5 mol) of heptanal over half an hour; the reaction is exothermic. 

• Finally heat the mixture under reflux for 1 hour. 

• Rearrange the condenser for distillation and remove the t-butyl alcohol by vacuum distillation using a water pump. 

• Acidify the residue with dilute hydrochloric acid and extract with three 200 ml portions of ether. 

• Extract the acidic compounds from the ethereal solution by shaking with 50 ml portions of saturated sodium hydrogen carbonate solution until no more carbon dioxide is evolved. 

• Acidify the combined aqueous solutions by the careful addition of concentrated hydrochloric acid. 

• Extract the 3-ethoxycarbonyldec-3-enoic acid which separates as an oil with ether, dry the ethereal extract over magnesium sulphate and evaporate the ether solution on a rotary evaporator. 

• Saponify the crude half ester by heating it under reflux for 1 hour with 400 ml of 10 per cent sodium hydroxide solution. 

• Cool the solution, acidify with concentrated hydrochloric acid and filter the precipitated acid with suction. 

• Dissolve the crude acid in the minimum volume of ether (about 200 ml are required) and add the solution to an equal volume of light petroleum (b.p. 60-80 °C). 

• Filter the precipitate with suction and recrystallise from benzene. 

• The yield of 3-carboxydec-3-enoic acid, m.p. 128-130 °C, 37.3 g (31.6%). The infrared spectrum shows absorptions at 3500-2300 cm⁻¹ (O — H stretch of carboxylic acid), 1700 cm⁻¹ (C=O) and 1640 cm⁻¹ (C=C).

3-Carboxy-3,4-dibromodecanoic acid:

• This reaction should be carried out in a fume cupboard. 

• Place 5.3g (0.025 mol) of 3-carboxydec-3-enoic acid, 6.0g (0.038 mol) of bromine and 60 ml of carbon tetrachloride in a 100 ml round-bottomed flask equipped with a magnetic stirrer and reflux condenser. 

• Irradiate the stirred mixture with a 100- watt lamp for 6 hours; the dibromide forms and precipitates out during this period. 

• Filter the product with suction and wash thoroughly with hexane. 

• The yield of 3-carboxy-3,4-dibromodecanoic acid is 7.9g (85%). The acid can be recrystallised from toluene, m.p. 142-143 °C. The infrared spectrum shows absorptions at 3400-2400 cm⁻¹ (O — H stretch of CO₂H) and 1730 cm⁻¹ (C=O).

4-Oxodecanoic acid:

• Dissolve 4.0g of 3-carboxy-3,4-dibromodecanoic acid in 60 ml of 2M sodium hydroxide solution and heat the solution at 80-90 °C for 2 hours. 

• Cool to room temperature and acidify with dilute sulphuric acid; carbon dioxide is evolved and a white precipitate is formed. 

• Filter the precipitated keto acid from the cold solution and recrystallise from light petroleum (b.p. 40-60 °C). 

• 4-Oxodecanoic acid, m.p. 68-69 °C, is obtained; the yield is 1.6g (80%). The infrared spectrum shows absorptions at 3400-2400 cm⁻¹ (OH stretch of CO₂H) and 1700 cm⁻¹ (C=0).

• If the dibromo acid is treated with alkali under milder conditions, for example with 1 m sodium hydroxide solution at 20-25 °C for 0.5 hour, the intermediate y-hexylaconic acid (m.p. 123-125 °C) can be isolated after acidification. 

• The infrared spectrum shows absorptions at 3110 cm⁻¹ (C — H stretch, alkene), 1715 and 1745 cm⁻¹ (C=O stretch of carboxylic acid and lactone) and 1630 cm (C=C stretch).

Notes to keep in mind:

1. Great care must be taken in the handling of potassium.

SYNTHESIS OF 4-OXOPENTANOIC ACID

CAUTION: All procedures should be conducted behind a safety screen; particular care should be taken in the handling of acrolein, for the measures to be taken in the handling of 30 per cent hydrogen peroxide.

4-Nitropentanal:

• A 100-ml two-necked flask equipped with a mechanical stirrer is charged with nitroethane (3.75g, 0.05 mol) and cooled with an ice-water bath. Acrolein (2.8g, 0.05 mol) is added and the mixture stirred for 5 minutes. 

• Chromatographic alumina (activity I on the Brockmann scale; 10g) is added and stirring is continued for 6 hours. 

• The reaction is monitored by t.l.c. (ethyl acetate-hexane, 2:8 as eluent). At the end of the reaction, the alumina is washed with ether (4 x 50 ml) and the filtered extract evaporated under reduced pressure. 

• The product is purified by distillation to give 4-nitro-pentanal (50%), b.p. 71 °C/0.4mmHg; i.r. 1720 (C=0) and 1545cm⁻¹ (NO₂).

 

4-Oxopentanoic acid

• Aqueous hydrogen peroxide (30 ml, 30%) is added to a cooled (0°C) and stirred solution of the foregoing 4-nitroalkanal (1.96g, 0.015 mol) in methanol (70 ml). 

• To the resultant solution, potassium carbonate (12g) is added, and stirring is continued for 15 hours at room temperature. 

• The solution is then acidified with 2 m hydrochloric acid and extracted with dichloromethane (3 x 40 ml). 

• The organic layer is washed with water (40 ml), and dried with magnesium sulphate. 

• The solvent is removed under vacuum to leave the crude product which can be used without further purification. 

• The pure 4-oxopentanoic acid (60%) is obtained by distillation and has b.p. 120°C/10mmHg.

 

SYNTHESIS OF ETHYL 3-OXOPENTANOATE (Ethyl propionylacetate)

• Prepare the ethoxy magnesium diethyl malonate derivative from 13g (0.53 mol) of magnesium and 80g (0.5 mol) of diethyl malonate. 

• Then add with vigorous stirring a solution of 49g (46 ml, 0.53 mol) of propanoyl chloride in 50 ml of anhydrous ether. 

• Reflux the reaction mixture for 30 minutes and then cool and acidify with 60 ml of dilute sulphuric acid. 

• Separate the ether layer, extract the residual aqueous solution with two 50 ml portions of ether. 

• Wash the combined organic phases with water, dry over anhydrous sodium sulphate and remove the ether on a rotary evaporator. 

• Add to the residue 8g of naphthalene-2-sulphonic acid monohydrate and heat the mixture slowly to 200 °C in an oil bath. 

• A vigorous evolution of gas sets in at about 120°C; when gas evolution has subsided, cool the reaction mixture and dissolve it in about 150 ml of ether. 

• Wash the ethereal extract with four 25 ml portions of 10 per cent sodium carbonate solution and then with water; back extract the combined aqueous solutions with three 25 ml portions of ether. 

• Dry the combined ether extracts with anhydrous sodium sulphate, remove the ether on a rotary evaporator and distil the residue under reduced pressure. 

• Collect the ethyl 3-oxopentanoate as a fraction of b.p. 100-105 °C/22 mmHg; the yield is 34g (47%).

Cognate preparation: General procedure for the acylation of the dianion of ethyl hydrogen malonate (1)

• To 250 ml of tetrahydrofuran (distilled from sodium/benzophenone under nitrogen prior to use) under nitrogen with stirring is added 13.47g (0.1 mol) of monoethyl malonate (2) and several milligrams of 2,2'-bipyridyl as an indicator. 

• After cooling to — 70 °C, butyllithium (hexane) is added slowly while allowing the temperature to rise to c. - 5 °C near the end of the addition (~ 130 ml of 1.6 m solution, 0.2 mol). 

• After the pink indicator persists at — 5°C the heterogeneous solution is recooled to — 65 °C and the acid chloride (0.057 mol) is added dropwise over 5 minutes.

• After the appropriate reaction time (3), the reaction solution is poured into 400 ml of ether and 200 ml of 1 M hydrochloric acid. 

• After mixing and separating the aqueous phase, the organic phase is washed with 2 x 100 ml of saturated sodium hydrogen carbonate solution and 100 ml of water, dried over anhydrous sodium sulphate and concentrated to yield the 𝛃-keto ester.

Notes to keep in mind:

1. Ethyl hydrogen malonate may be prepared from diethyl malonate by controlled hydrolysis with potassium hydroxide.

2. The following acid chlorides have been used and the reaction times are given in parentheses: Pr·COCl (5 minutes); Me₂CH·CH₂COCl (5 minutes); Bu·COCl (5 minutes); Ph·CH₂COCl (5 minutes); and Ph·COCl (30 minutes).

SYNTHESIS OF ETHYL 2,2,4-TRIMETHYL-3-OXOPENTANOATE (Ethyl isobutyrylbutyrate)

Triphenylmethyl sodium

Prepare a 1.5 per cent sodium amalgam from 15 g (0.65 mol) of sodium and 985 g of mercury (Section 4.2.70, p. 464). Place a mixture of 1000 g of the amalgam and 74 g (0.265 mol) of triphenylchloro-methane (Section 4.2.79, p. 466) in a 2-litre Pyrex glass-stoppered bottle and add 1 500 ml of sodium-dried ether. Grease the glass stopper with a little Silicone grease, insert it firmly, clamp the bottle in a mechanical shaker and shake. CAUTION: the reaction is strongly exothermic; cool the bottle with wet rags and stop the shaking from time to time, if necessary. A characteristic red colour appears after about 10 minutes' shaking. After shaking for 4 to 6 hours, cool the bottle to room temperature, remove it from the shaker, wire the stopper down and allow the mixture to stand undisturbed; sodium chloride and particles of mercury settle to the bottom.

Separate the ether solution of triphenylmethyl sodium as follows. Remove the glass stopper and replace it immediately by a tightly fitting two-holed bung carrying a short glass tube that protrudes about 1 cm into the bottle, and a long glass tube bent into an inverted U -shape. Connect the bottle

through a drying train to a cylinder of nitrogen. Lead the other arm of the U-tube into a 2-litre, two-necked round-bottomed flask (which has been previously filled with nitrogen) via a suitable screw-capped adapter and fit a dropping funnel into the other neck. Open the stopcock of the dropping

funnel slightly and force the ether solution of triphenylmethyl sodium slowly and steadily into the nitrogen-filled flask by means of a small pressure of nitrogen from the cylinder. By carefully adjusting the depth of the siphon tube in the bottle, all but 50-75 ml of the clear ether solution may be removed. If pure triphenylchloromethane and freshly prepared sodium amalgam are used, the yield of triphenylmethyl sodium should be almost quantitative and the concentration is usually 0.15 mol per litre (1). The reagent should be used as soon as possible after its preparation.

Ethyl 2,2,4-trimethyl-3-oxopentanoate. Add 24 g (28 ml, 0.21 mol) of ethyl 2-methylpropanoate b.p. 1 10-1 1 1 °C, to the solution of c. 0.21 mol of triphenyl-methyl sodium in approximately 1 400 ml of ether contained in the 2-litre two-necked flask. Stopper the flask, shake well to effect complete mixing and keep at room temperature for 60 hours. Acidify the reaction mixture by adding,

with shaking, 15 ml of glacial acetic acid, and then extract with 100 ml of water. Wash the ethereal solution with 50 ml portions of 10 per cent sodium carbonate solution until free from excess acid, dry over anhydrous sodium sulphate; remove the ether under reduced pressure with a rotary evaporator. Distil the residue under reduced pressure through a short fractionating column. Collect the ethyl 2,2,4-trimethyl-3-oxopentanoate at 95-96 °C/ 18mmHg; the yield is 14.5 g (74%). The b.p. at atmospheric pressure is 201-202 °C.

Note. (1) The solution may be analysed approximately as follows. Remove 25 ml of ether solution, run it into 25 ml of water contained in a small separatory funnel and shake. Run off the aqueous layer into a 250-ml conical flask and extract the ether layer with two 25 ml portions of water. Titrate the combined aqueous extracts with 0.95 m-sulphuric acid, using methyl red as indicator.

Ketonic hydrolysis to di-isopropyl ketone. Mix 1 4 g (0.75 mol) of the ester with 30 ml of glacial acetic acid, 10 ml of water and 10 ml of concentrated sulphuric acid, and boil under reflux until evolution of carbon dioxide ceases. Dilute the cooled solution with 180 ml of water, add 100 ml of ether and render alkaline to phenolphthalein with 20 per cent sodium hydroxide solution. Separate the ether layer, extract the aqueous layer with two 50 ml portions of ether, dry the combined ether layer and extracts with anhydrous sodium sulphate, distil off the ether and fractionate the residue. The yield of di-isopropyl ketone (2,4-dimethylpentan-3-one), b.p. 123-1 24 °C, is 6.5 g (76%).

SYNTHESIS OF PHENYLPYRUVIC ACID

•  Place 10.3g (0.05 mol) of a-acetamidocinnamic acid and 200 ml of 1 m hydrochloric acid in a 500-ml round-bottomed flask and boil the mixture steadily under reflux for 3 hours. 

• Remove a small quantity of green oil by rapidly filtering the hot reaction mixture through a small plug of cotton wool loosely inserted into the stem of a preheated glass filter funnel, cool the filtrate  to room temperature and leave it at °C for 48 hours. 

• Collect the crystalline product by filtration, wash it with a small quantity of ice-cold water and dry it in a vacuum desiccator over anhydrous calcium chloride and potassium hydroxide pellets. 

• The yield of phenylpyruvic acid, which is sufficiently pure for most purposes, is 4.4 g, m.p. 157 °C (decomp.). 

• A further 1.7g of product of comparable purity (total yield 74%) separates from the aqueous acidic filtrate when this is set aside at °C for about one week.

SYNTHESIS OF ETHYL BENZOYLFORMATE

Ethyl 𝜶-oxo-1H-imidazole-1-acetate

• Ethyl oxalyl chloride (20.0 ml, 0.1 79 mol) (Aldrich) (1) in tetrahydrofuran (80 ml) (2) is added to a stirred solution of imidazole (24.3g, 0.35 mol) in tetrahydrofuran (500 ml) at 0°C under nitrogen over a 1-hour period. 

• After an additional 1 hour of being stirred at °C, the mixture is filtered and the precipitate washed with anhydrous tetrahydrofuran (100 ml). 

• The tetrahydrofuran is removed from the filtrate and washings under vacuum, and the residue is distilled to furnish 27.2g (90%) of product, b.p. 100°C/1 mmHg; i.r. (neat) 1730 (ester) and 1770 (amide) cm⁻¹; p.m.r. (CDCl₃, TMS) 𝜹1 .45 (t, 3H), 4.45 (q, 2H), 7.05 (s, 1H), 7.60 (s, 1H), and 8.40 (s, 1H); m/z 168 (M). 

• This material undergoes slow discoloration at room temperature and is stored at 5 °C.

Ethyl benzoylformate:

• The foregoing imidazolide (3.03g, 24mmol) is dissolved in tetrahydrofuran (75 ml) under nitrogen and cooled to -50 °C in a dry-ice-acetone bath. 

• Phenylmagnesium bromide (1.0 equiv. in 50 ml of tetrahydrofuran) is added by a dropping funnel over 1 hour with stirring. 

• The solution is allowed to come to room temperature over 3 hours and poured into ice-water (200 ml). 

• The solution is extracted with ether (a few drops of acetic acid are added to break up emulsions), and the ether extract is washed with brine and dried over magnesium sulphate. 

• Removal of solvents under reduced pressure and distillation affords ethyl benzoylformate (72%), b.p. 88°C/0.5mmHg.

Notes to keep in mind:

1. Ethyl oxalyl chloride should be handled with care in a fume cupboard since it is lachrymatory.

2. The tetrahydrofuran should be distilled from sodium benzophenone ketyl immediately prior to use.

SYNTHESIS OF PYRUVIC ACID

• Grind together in a glass mortar 200g (1.33 mol) of powdered tartaric acid and 300g (2.2mol) of freshly fused potassium hydrogen sulphate to form an intimate mixture. 

• Place the mixture in a 1.5-litre round-bottomed flask, and fit the latter with a still-head and a long air condenser. 

• Heat the flask in an oil bath maintained at 210-220 °C until liquid no longer distils over. 

• If foaming is considerable and there is danger of the mixture frothing over, heat the upper part of the flask with a free flame. 

• Fractionate the distillate under reduced pressure and collect the pyruvic acid at 75-80 °C/25mmHg. The yield is 60 g (51%).

SYNTHESIS OF 12-HYDROXYDODECANOIC ACID LACTONE (Dodecanolide)

• Cyclododecanone (2.0g, 1 1 mmol) is added to m-chloroperbenzoic acid (4.2g, 21 mmol) in 25 ml of dry chloroform.

• The reaction mixture is heated at reflux for 48 hours after which time a starch-iodide test for peroxide is negative. 

• After the mixture is cooled in ice-water, the precipitated m-chlorobenzoic acid is removed by filtration and the chloroform is evaporated to dryness. 

• The residue is taken up in 60 ml of ether, washed three times with 20-ml portions of aqueous potassium carbonate, and once with brine. 

• After drying and removal of solvent there remains crude dodecanolide (1.9g, 9.6 mmol, 87%), which is used without further purification.

Conversion into 12-iodododecanoic acid:

• The above dodecanolide (1.9g, 9.6 mmol) is added to a mixture of 67 per cent hydriodic acid (5g, 24 mmol) and glacial acetic acid (3g). 

• The reaction mixture is held for 2 hours at 100 °C and after cooling is poured out into 50 ml of a cold 10 per cent aqueous solution of sodium thiosulphate. 

• The reaction mixture is extracted three times with 25-ml portions of chloroform. 

• The combined extracts are dried over magnesium sulphate, and the solvent is removed to leave crude 12-iodododecanoic acid, which after recrystallisation from ether-light petroleum (b.p. 40- 60 °C) is obtained in 93 per cent yield (2.95g), m.p. 61-62.5 °C.

Cognate preparations: Dodecanolide (use of permaleic acid)

• The precautions that must be adopted when using 30 per cent hydrogen peroxide.Safety screens and extra personal protection measures should also be employed.

• Dichloromethane (1.6 litres) and acetic anhydride (1.25 litres) are stirred in a 5-litre flask fitted with a double surface condenser and an overhead stirrer, a dropping funnel, and cooled externally (ice-water) while 30 per cent hydrogen peroxide (1 litre) is added. 

• After 1 hour maleic anhydride (1 kg) is added, the mixture is cooled and stirred for 1 hour, and then the cooling bath is removed, when the temperature rises during 1.5 hours and the mixture begins to reflux. 

• External cooling is resumed when needed to moderate the reaction. 

• When little more heat is evolved, cyclododecanone (250g) is added; this does not greatly increase the rate of heating, and when spontaneous refluxing ceases, a heating mantle is used to maintain the mixture at its boiling point for 15 hours. 

• The mixture is then cooled and the separated maleic acid is filtered off. 

• The filtrate is washed in turn with water (3 x 600 ml), an aqueous solution containing 10 per cent each of potassium hydroxide and sodium sulphite (2 x 300 ml), and then water (600 ml); tests for peroxide are now negative. 

• After being dried over anhydrous sodium sulphate the filtrate is evaporated to give the lactone (210.4g, 77%); when potassium carbonate, rather than potassium hydroxide, is used for washing, the crude lactone contains a pungent contaminant, possibly peracetic acid.

Conversion into 12-hydroxydodecanoic acid:

• The foregoing lactone is added to a solution of potassium hydroxide (150g) in methanol (800 ml) and the mixture is heated under reflux for 1 hour. 

• Most of the solvent is then removed on a rotary evaporator. Water (2 litres) is added and the solution is extracted with ether (2 x 400 ml). 

• The aqueous layer is acidified (concentrated hydrochloric acid) and the precipitated acid is collected, dried in vacuo, and recrystallised from acetone-light petroleum (b.p. 60-80 °C) to afford the acid (185.8g, 63% from cyclododecanone), m.p. 84 °C.

8-Hydroxynonanoic acid lactone

• The precautions to be adopted in the use of 90% hydrogen peroxide. Safety screens and extra personal protection must be employed.

• To a mixture of 90 per cent hydrogen peroxide (1 ml, 40mmol) and dichloro methane (5 ml) at 0°C is added dropwise trifluoroacetic acid (7 ml, 50mmol). 

• The resulting homogeneous solution could be stored at — 20 °C for several weeks. 

• To a solution of 2-methylcyclooctanone (1.12g, 8 mmol) (1) in dichloromethane (8 ml) and buffered with anhydrous disodium hydrogen phosphate (7.1g, 50 mmol), is added at °C dropwise pertrifluoroacetic acid solution (7 ml, 22 mmol). 

• The resulting mixture is stirred at room temperature for 5 hours, poured into water, washed with aqueous sodium hydrogen carbonate and dried over magnesium sulphate. 

• After removal of the solvents at reduced pressure, the oily residue is flash chromatographed using 4 per cent ethyl acetate in light petroleum to yield 890 mg (72%) of the lactone as a transparent sweet-smelling oil (3% of starting material is recovered); i.r. (thin film) 2940, 1730, 1450cm⁻¹ ; p.m.r. (CCl₄ , TMS) 𝜹1.23 (d, 3H, J = 7Hz), 1.1 - 2.0 (m, 10H), 2.15 (m, 2H), 5.00 (m, 1H); t.l.c (silica gel, 5% ethyl acetate in pentane) R𝑓 0.36.

Notes to keep in mind:

1.  2-Methylcyclooctanone may be prepared by the procedures noted in earlier sections. Thus cyclooctanone may be converted into 1-methylcyclooctanol by reaction with methylmagnesium bromide; dehydration then gives 1-methyl-cyclooct-1-ene; hydroboration gives trans-2-methylcyclooctanol; finally, oxidation with PCC yields 2-methylcyclooctanone.