(A) In a 500-cc. Claisen distilling flask with a low side tube connected to a condenser, are placed 105 g. (0.69 mole) of mandelic acid (p. 336) (m.p. 118°) and 151 g. (137 cc., 1.92 moles) of acetyl chloride. A reaction sets in without the application of heat (Note 1). As soon as a clear solution results, the flask is warmed on a water bath and the excess acetyl chloride is distilled. The last trace of acetyl chloride may be removed by prolonged drying in a vacuum. The acetylmandelic acid then crystallizes in large, round, white clusters after one or two days' standing. The yield is 130–133 g. (97–99 per cent of the theoretical amount) (Note 2).

(B) To the crude acetylmandelic acid still containing some acetyl chloride obtained as described above, is added 250 g. (149 cc., 2.1 moles) of thionyl chloride. The reaction starts at once without warming but it is necessary to reflux for four hours to complete the reaction (Note 3). The excess thionyl chloride is then distilled and the residue distilled under reduced pressure (Note 4). The yield is 115–120 g. (79–82 per cent of the theoretical amount) of almost colorless liquid boiling at 125–130°/10 mm. (150–155°/33 mm.).