Org. Synth. 1921, 1, 29
DOI: 10.15227/orgsyn.001.0029
BENZILIC ACID
Submitted by Donald A. Ballard and William M. Dehn.
Checked by C. S. Marvel and Tse-Tsing Chu.
1. Procedure
The reaction mixture of
benzoin, prepared by the method described on
p. 94, is permitted to stand until the next day, when it is filtered, washed with water but is not dried or purified. In a
30-cm. evaporating dish 500 g. (12.5 moles) of sodium hydroxide and
115 g. (0.76 mole) of sodium bromate (or
125 g. of potassium bromate) are dissolved in 880 cc. of water. The moist
benzoin (450–460 g.) is added in portions to this solution and the mixture is stirred, preferably with a
mechanical stirrer, while heated on the
steam bath (Note 1). As heating continues the mixture thickens and more water is added from time to time. A total of 750–800 cc. is needed. The heating and stirring are continued for about five to six hours or until a test portion is completely or almost completely soluble in water.
The mixture is diluted with about 4 l. of water and is permitted to stand overnight. A small quantity of oily or solid impurity (benzohydrol) is removed by filtration, and dilute sulfuric acid (about 1300 cc. of a solution of 3 parts of water and 1 part of concentrated sulfuric acid, sp. gr. 1.84) is added to a point short of liberation of bromine. The product is filtered, washed with water and dried. Thus 450–484 g. (84–90 per cent of the theoretical amount based on the benzaldehyde) of benzilic acid melting at 149–150° is obtained (Note 2).
2. Notes
1.
If the reaction mixture is heated to boiling, large quantities of
benzohydrol are obtained. The temperature reached by heating on the steam bath is about 85–90°.
2.
The high purity of the product obtained by this procedure really makes recrystallization unnecessary. Should further purification be desired it is best effected by crystallization from
benzene. It may also be accomplished by crystallizing from hot water with the use of animal charcoal or by dissolving in alkali and reprecipitating by means of
hydrochloric acid.
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In some articles in Organic Syntheses, chemical-specific hazards are highlighted in red "Caution Notes" within a procedure. It is important to recognize that the absence of a caution note does not imply that no significant hazards are associated with the chemicals involved in that procedure. Prior to performing a reaction, a thorough risk assessment should be carried out that includes a review of the potential hazards associated with each chemical and experimental operation on the scale that is planned for the procedure. Guidelines for carrying out a risk assessment and for analyzing the hazards associated with chemicals can be found in Chapter 4 of Prudent Practices.
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The paragraphs above were added in September, 2014. The statements above do not supersede any specific hazard caution notes and safety instructions included in the procedure.
3. Discussion
Benzilic acid can be prepared by the action of
potassium hydroxide on
benzil, in concentrated aqueous solution,
1 in alcoholic solution
2 or in
ether;
3 and by heating
benzil in
toluene with
sodamide and then treating with water.
4 The procedure described has been published.
5
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Benzohydrol
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
ether (60-29-7)
sodium hydroxide (1310-73-2)
bromine (7726-95-6)
benzaldehyde (100-52-7)
Benzil (134-81-6)
Benzoin (119-53-9)
Benzilic acid (76-93-7)
sodium bromate (7789-38-0)
potassium bromate (7758-01-2)
potassium hydroxide (1310-58-3)
toluene (108-88-3)
sodamide (7782-92-5)
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