Determination of Esters

Boil a convenient quantity of ethanol (95 percent) thoroughly to expel carbon dioxide and neutralize it to phenolphthalein solution. Unless otherwise stated in the individual monograph, weigh accurately about 2 g or other suitable quantity of the substance under examination so that the volume of 0.5 M ethanolic potassium hydroxide added is at least twice that theoretically required, dissolve it in 5 ml of the neutralised ethanol contained in a hard-glass flask and neutralise the free acid in the solution with 0.1 M ethanolic potassium hydroxide using 0.2 ml of phenolphthalein solution as indicator. Add 25.0 ml of 0.5 M ethanolic potassium hydroxide and boil under a reflux condenser on a water-bath for 1 hour. Add 20 ml of water and titrate the excess of alkali with 0.5 M hydrochloric acid using a further 0.2 ml of phenolphthalein solution as indicator. Repeat the operation without the substance under examination. The difference between the titrations represents the alkali required to saponify the esters.