SYNTHESIS OF ETHYL 2-BROMOPROPANOATE

• In a 1 -litre two-necked round-bottomed flask, equipped with a dropping funnel and a double surface reflux condenser to which is attached a gas absorption trap, place 220g (135 ml, 1.86 mol) of redistilled thionyl chloride, and heat to boiling. 

• Add 125g (126 ml, 1.69 mol) of pure propanoic acid at such a rate that the mixture refluxes gently (c. 1 hour). 

• Reflux the mixture for a further 30 minutes to expel the dissolved sulphur dioxide, allow to cool and add 0.5 g of purified red phosphorus. 

• Introduce 310 g (100 ml, 1.93 mol) of dry bromine during 5-7 hours to the gently boiling propanoyl chloride, and then reflux the mixture for 7 hours, by which time the evolution of hydrogen bromide almost ceases. 

• Add the crude 2-bromopropanoyl chloride during 2 hours to 250 ml of absolute ethanol contained in a three-necked round-bottomed flask, equipped with a mechanical stirrer and a reflux condenser. 

• Complete the reaction by heating on a water bath for 4 hours, when hydrogen chloride is slowly evolved. 

• Filter the reaction liquid into 500 ml of distilled water, separate the oil and wash it successively with water, sodium hydrogen carbonate solution and water. 

• Dry over calcium sulphate and distil at normal pressure to remove the low b.p. fraction (largely ethyl bromide: 75 g) and then under diminished pressure. 

• Collect the ethyl 2-bromopropanoate as a colourless liquid at 69-70 °C/25mmHg; the yield is 221 g (72%).