SYNTHESIS OF BUTYL ACETATE

• Mix together 37g (46 ml, 0.5 mol) of butan-1-ol and 60g (60 ml, 1 mol) of glacial acetic acid in a 250 or 500-ml round-bottomed flask, and add cautiously 1 ml of concentrated sulphuric acid (use a small measuring cylinder or a calibrated dropper pipette). 

• Attach a reflux condenser and reflux the mixture for 3-6 hours (1). 

• Pour the mixture into about 250 ml of water in a separatory funnel, remove the upper layer of crude ester and wash it again with about 100 ml of water, followed by about 25 ml of saturated sodium hydrogen carbonate solution and 50 ml of water. 

• Dry the crude ester with 5-6g of anhydrous sodium sulphate. 

• Filter through a small funnel containing a fluted filter paper and distil on a wire gauze or from an air bath. 

• Collect the pure butyl acetate at 124-125 °C. The yield is 40 g (69%). The p.m.r spectrum (CCl₄ , TMS) show absorptions at 𝜹 0.93 (distorted t, 3H, Me⦁CH₂), 1.09-1.72 (m, 4H, ⦁CH₂⦁ CH₂), 1.95 (s, 3H, Me⦁CO) and 3.99 (t, 2H, CH₂⦁O).

Notes to keep in mind:

1.  A slightly better yield of ester can be obtained by increasing the quantity of acetic acid to 90-120g and refluxing for 12-18 hours.

Cognate preparations: sulphuric acid catalyst. Ethyl butanoate

• Use a mixture of 88g (92 ml, 1 mol) of butanoic acid, 23g (29 ml, 0.5 mol) of ethanol and 9g (5 ml) of concentrated sulphuric acid. 

• Reflux for 14 hours. 

• Pour into excess of water, wash several times with water, followed by saturated sodium hydrogen carbonate solution until all the acid is removed, and finally with water. 

• Dry with anhydrous sodium sulphate, and distil. 

• The ethyl butanoate passes over at 119.5-120.5 °C. Yield: 40g (69%). An improved yield can be obtained by distilling the reaction mixture through an efficient fractionating column until the temperature rises to 125 °C, and purifying the crude ester as detailed above under methyl acetate.

Diethyl sebacate

• Reflux a mixture of 101g (0.5 mol) of sebacic acid, 196g (248 ml, 4.25 mol) of absolute ethanol and 20 ml of concentrated sulphuric acid for 12 hours. 

• Distil off about half of the alcohol on a water bath, dilute the residue with 500-750 ml of water, remove the upper layer of crude ester and extract the aqueous layer with ether. 

• Wash the combined ethereal extract and crude ester with water, then with saturated sodium hydrogen carbonate solution until effervescence ceases, and finally with water. 

• Dry with magnesium sulphate or anhydrous sodium sulphate, remove the ether on a water bath and distil the residue under reduced pressure (b.p. 155-157 °C/6 mmHg). Yield: 110g (85%).

Methyl crotonate

• Use 43g (0.5 mol) redistilled crotonic acid (b.p. 180-182°C, m.p. 72-73 °C), 75g (95ml, 2.33mol) of absolute methanol, 3ml of concentrated sulphuric acid and reflux for 12 hours. 

• Isolate as for butyl acetate; the yield is 34g (68%), b.p. 118-120 °C. Record the p.m.r. spectrum and by careful measurement of J values assign the absorptions.

Benzyl acetate

• Mix 31g (29.5 ml, 0.287 mol) of benzyl alcohol and 45g (43 ml, 0.75 mol) of glacial acetic acid in a 500-ml round-bottomed flask; introduce 1 ml of concentrated sulphuric acid and a few fragments of 'porous pot'. 

• Attach a reflux condenser to the flask and boil the mixture gently for 9 hours. 

• Pour the reaction mixture into about 200 ml of water contained in a separatory funnel, add 10 ml of carbon tetrachloride (to eliminate emulsion formation owing to the slight difference in density of the ester and water, compare methyl benzoate) and shake. 

• Separate the lower layer (solution of benzyl acetate in carbon tetrachloride) and discard the upper aqueous layer. 

• Return the lower layer to the funnel, and wash it successively with water, concentrated sodium hydrogen carbonate solution (until effervescence ceases) and water. 

• Dry over 5g of magnesium sulphate, and distil from an air bath. 

• Collect the benzyl acetate (a colourless liquid) at 213-215 °C. The yield is 16g (37%).

Cognate preparations: hydrochloric acid catalyst. Cyclohexyl acetate

• Pass dry hydrogen chloride into 75g (0.75 mol) of pure cyclohexanol until 1.5g are absorbed, mix with 135g (2.25 mol) of glacial acetic acid in a 500-ml round-bottomed flask, attach a reflux condenser and reflux for 14 hours. 

• Pour into excess of water, wash the upper layer successively with water, saturated sodium hydrogen carbonate solution until effer-vescence ceases, and water. 

• Dry with anhydrous calcium chloride. 

• Distil through a well-lagged fractionating column (e.g. an all-glass Dufton column). 

• A small fraction of low boiling point (containing cyclohexene) passes over first, followed by cyclohexyl acetate (57g, 54%) at 168-170 °C. Upon redistillation, the boiling point is 170-172 °C, mainly 171-172 °C.

Cyclohexyl formate

• Use 103g (84.5 ml, 2.24 mol) of formic acid (98/100%) and 75g (0.75 mol) of cyclohexanol in which 1.5 g of dry hydrogen chloride gas are dissolved. 

• Reflux for 14 hours. Work up as above and distil through a well-lagged column; 5.5g of cyclohexene and 57 g (59%) of cyclohexyl formate, b.p. 156-158.5 °C (mainly 157-158.5 °C), are obtained. 

• On redistillation the sample boils at 158-160°C (mainly 159-160°C).

s-Butyl acetate

• Pass dry hydrogen chloride gas into 37g (46 ml, 0.5 mol) of butan-2-ol until 1.5g is absorbed. 

• Mix the solution with 60g (1 mol) of glacial acetic acid, and reflux for 10 hours. Isolate the ester as for butyl acetate (b.p. 110-112°C). Yield: 35g (60%).

Ethyl p-aminobenzoate

• Saturate 80 ml (63.2 g, 1.37 mol) of absolute ethanol with dry hydrogen chloride, add 12g (0.088 mol) of p-aminobenzoic acid and heat the mixture under reflux for 2 hours. 

• Upon cooling, the reaction mixture sets to a solid mass of the hydrochloride of ethyl p-aminobenzoate. It is better, however, to pour the hot solution into excess of water (no hydro-chloride separates) and add sodium carbonate to the clear solution until it is neutral to litmus. 

• Filter off the precipitated ester at the pump and dry in the air. The yield of ethyl p-aminobenzoate, m.p. 91 °C, is 10g (69%). Recrystallisation from rectified spirit does not affect the m.p.