SYNTHESIS OF ETHYL 6-BROMOHEXANOATE

• Place a mixture of 140 ml of concentrated hydrobromic acid and 34 ml of concentrated sulphuric acid in a 500-ml, three-necked round-bottomed flask fitted with a sealed stirrer unit, a reflux condenser and a dropping funnel. 

• Cool the flask contents in an ice-salt bath and add with stirring 28.5g (0.25 mol) of 6-hexanolide. 

• Allow the reaction mixture to reach room temperature and then to stand for 2 hours; heat on a water bath for a further 4-hour period. 

• Cool the mixture and pour on to 300g of crushed ice and separate the organic layer; saturate the aqueous layer with ammonium sulphate and extract the solution with four 50 ml portions of ether. 

• Wash the combined organic phases with three 25 ml portions of a saturated aqueous solution of ammonium sulphate, dry (anhydrous sodium sulphate) and evaporate the ether on a rotary evaporator. 

• Boil the residual bromo acid under reflux for 8 hours with 85 ml of absolute ethanol containing 2 ml of concentrated sulphuric acid and then remove the ethanol on a rotary evaporator. 

• Dissolve the residue in 100 ml of ether and wash the ethereal solution first with water and then with 5 per cent aqueous sodium carbonate to remove mineral acid. 

• Dry the ethereal solution over anhydrous sodium sulphate, remove the ether (rotary evaporator) and distil the residue under reduced pressure. 

• Collect the ethyl 6-bromohexanoate having b.p. 120-124 °C/ 14mmHg; the yield is 28g (50%).