Organic Syntheses | Page 6

ester. A yield of 410-420 g. is obtained, which corresponds to 90-93 per cent of the theoretical amount. This benzyl benzoate supercools readily, but after solidifying melts within one degree of the highest recorded value (19.4'0) and therefore need not be refractionated, unless material of exceptional grade is required.
2. Notes
In the presence of sodium benzylate two molecules of benzaldehyde react with the alcoholate to form an addition product. When the reaction mixture is overheated an important side reaction may occur, as follows:
/ OCH2C6H5 C6H5C -- OCH2C6H5 --> C6H5CO2Na + C6H5CH2OCH2C6H5 \ ONa
Dibenzyl ether no doubt forms the chief impurity in benzyl benzoate. Since the boiling-point of the former lies near that of the ester, it is not removed during the process of purification by distillation.
The causes of variations in yield by the use of the older methods can now be explained. When benzaldehyde is added TO THE ALCOHOLATE, and especially when the latter is still warm, local overheating results; in fact, the temperature may rise far above 100'0 with the result that benzyl ether is formed. Simultaneously, the sodium benzylate is converted into sodium benzoate, which is of no value for inducing the desired reaction, and consequently very little benzyl benzoate is obtained. The same side reactions explain the failure of this experiment when the benzyl alcohol used in preparing the catalyst (sodium benzylate) is contaminated with benzaldehyde.
The benzyl alcohol used in this preparation must be free from impurities, especially aldehyde. One cc. dissolved in 50 cc. of water and treated with a freshly prepared clear solution of phenylhydrazine acetate should give no appreciable precipitate. If it is not pure, it must first be treated with alkali as described below.
The benzaldehyde should be titrated in order to determine its acidity. If it is found to contain sufficient benzoic acid to react with a considerable proportion of the sodium alcoholate, a poor yield of ester will be obtained. Less than 1 per cent of benzoic acid will not interfere seriously with the yields obtained, but the presence of larger quantities of acid will be found to be detrimental and must be removed by washing the benzaldehyde with a sodium carbonate solution and redistilling with the precautions necessary to prevent too free an access of air to the distillate.
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.
[1] C. A. 14, 3500 (1920).
[2] J. Am. Pharm. Assoc. 11, 599 (1922).

III
BENZYL CYANIDE
C6H5CH2Cl + NaCN--> C6H5CH2CN + NaCl
Prepared by ROGER ADAMS and A. F. THAL Checked by O. KAMM and A. O. MATTHEWS.
1. Procedure
IN a 5-l. round-bottom flask, fitted with a stopper holding a reflux condenser and separatory funnel, are placed 500 g. of powdered sodium cyanide (96-98 per cent pure) and 450 cc. of water. The mixture is warmed on a water bath in order to dissolve most of the sodium cyanide, and then 1 kg. of benzyl chloride (b. p. 170-180'0) mixed with 1 kg. of alcohol is run in through the separatory funnel in the course of one-half to three-quarters of an hour. The mixture is then heated with a reflux condenser