A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1932, 12, 1
DOI: 10.15227/orgsyn.012.0001
Submitted by B. B. Corson and N. A. Saliani.
Checked by Frank C. Whitmore and Marion M. Whitmore.
1. Procedure
To a mixture of 212 g. (1 mole) of benzoin (Note 1), 200 cc. of glacial acetic acid, and 200 cc. (2.1 moles) of acetic anhydride, in a 1-l. beaker provided with a mechanical stirrer, is added slowly, with stirring, 20 cc. of concentrated c.p. sulfuric acid. This requires five minutes, during which the benzoin quickly dissolves and the temperature rises to about 50°. The beaker is placed on the steam bath for twenty minutes (Note 2). The mixture is allowed to cool somewhat, transferred to a large dropping funnel, and added slowly to 2.5 l. of water vigorously stirred in a 4-l. (1-gal.) crock during thirty minutes (Note 3). Stirring is continued for one hour. The mixture is filtered by suction on a 30-cm. Büchner funnel, and the crystals are sucked as dry as possible and spread on filter paper. After about two hours the crystals are transferred to a 1-l. beaker and warmed to about 60° with 400 cc. of 95 per cent ethyl alcohol. The clear solution is cooled with stirring to 5° and filtered by suction. The air-dried benzoin acetate, melting at 80–82°, weighs 220–230 g. (86 to 90 per cent of the theoretical amount). Another crystallization from 400 cc. of alcohol removes the slight yellow tinge and gives a product melting at 81.5–82.5°, with a loss of about 10 g.
2. Notes
1. The benzoin (Org. Syn. Coll. Vol. I, 1941, 94) need not be recrystallized.
2. The mixture should not be heated longer or more vigorously.
3. If the product solidifies in lumps, the lumps must be removed, crushed to a paste in a large mortar, and returned to the mixture for stirring.
3. Discussion
The only method of preparative interest is the acetylation of benzoin, either with acetyl chloride1 or with acetic anhydride.2 The melting point of benzoin acetate was reported by Zinin as "below 100°," by Jena and Limpricht as 75°, but by later investigators as 82–83°.

References and Notes
  1. Zinin, Ann. 104, 120 (1857); Jena and Limpricht, ibid. 155, 92 (1870); Päpcke Ber. 21, 1336 (1888).
  2. Francis and Keane, J. Chem. Soc. 99, 346 (1911).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethyl alcohol,
alcohol (64-17-5)

sulfuric acid (7664-93-9)

acetic acid (64-19-7)

acetic anhydride (108-24-7)

acetyl chloride (75-36-5)

Benzoin (119-53-9)

Benzoin acetate (574-06-1)