The order of mixing the reagents and the temperature of the ingredients at the time of mixing are the most important factors in the experiment. The temperature at which the reaction mixture is maintained after mixing, provided that it is held below 100'0, is less important from the standpoint of purity.
The reaction mixture is not treated with acetic acid, as usually recommended, for the reason that such a procedure yields a final product contaminated with benzoic acid, unless an alkaline wash is applied subsequently.
The recovered benzyl alcohol can be used for the preparation of a second lot of benzyl benzoate only after it has been boiled with strong sodium hydroxide to remove all traces of benzaldehyde.
3. Other Methods of Preparation
Benzyl benzoate has been identified in certain natural plant products.[1] In the laboratory it has been prepared by the action of (a) benzoyl chloride upon benzyl alcohol,[2] (b) benzyl chloride upon sodium benzoate, and (c) alcoholates upon benzaldehyde.[3] Recently, Gomberg and Buchler[4] have shown that reaction (b) may be conducted even with aqueous solutions of sodium benzoate.
[1] Ann. 152, 131 (1869).
[2] Gmelin's Handbuch der Organ. Chem. 3, 40.
[3] Ber. 20, 649 (1887). Cf. also J. Chem. Soc. 75, 1155 (1899).
[4] J. Am Chem. Soc. 42, 2059 (1920).
The Claisen method (c) furnishes the most convenient and practical procedure for the preparation of this ester. The materials are cheap, the experimental procedure simple, and the product obtained is free from objectionable traces of benzyl chloride. Unfortunately the method has been found to be extremely erratic in regard to yield (10-95 per cent), as well as in regard to purity of the product (87-97 per cent ester).[1] As a result of the present study,[2] causes for variations are fully accounted for and the procedure has been converted into a satisfactory method of preparation.