Organic Syntheses | Page 6

it is then warmed on the water bath for about one or two hours, with
occasional shaking.
The cooled reaction product is treated with 200 cc. of water, the layer
of oil separated, washed once with a second portion of water, and
subjected to distillation in vacuo. The first fraction of the distillate
contains benzyl alcohol together with unchanged aldehyde, as well as a
small quantity of water. The temperature then rises rapidly to the
boiling-point of benzyl benzoate, when the receivers are changed. The
product boils at 184-185'0/15 mm., and analysis by saponification
shows it to consist of 99 per cent 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.