The reaction mixture of benzoin, prepared by the method described on p. 94, is permitted to stand until the next day, when it is filtered, washed with water but is not dried or purified. In a 30-cm. evaporating dish 500 g. (12.5 moles) of sodium hydroxide and 115 g. (0.76 mole) of sodium bromate (or 125 g. of potassium bromate) are dissolved in 880 cc. of water. The moist benzoin (450–460 g.) is added in portions to this solution and the mixture is stirred, preferably with a mechanical stirrer, while heated on the steam bath (Note 1). As heating continues the mixture thickens and more water is added from time to time. A total of 750–800 cc. is needed. The heating and stirring are continued for about five to six hours or until a test portion is completely or almost completely soluble in water.

The mixture is diluted with about 4 l. of water and is permitted to stand overnight. A small quantity of oily or solid impurity (benzohydrol) is removed by filtration, and dilute sulfuric acid (about 1300 cc. of a solution of 3 parts of water and 1 part of concentrated sulfuric acid, sp. gr. 1.84) is added to a point short of liberation of bromine. The product is filtered, washed with water and dried. Thus 450–484 g. (84–90 per cent of the theoretical amount based on the benzaldehyde) of benzilic acid melting at 149–150° is obtained (Note 2).