Benzoic Acid → Phenylglyoxylic Acid

Participants

Reaction Steps

A solution of sodium nitrite (35g; 0.5 mole) in water (100 ml.) was added steadily over 95 minutes to a stirred mixture of acetophenone (24.0g; 0.2 mole) in 6N-hydrochloric acid (200 ml.) at 65°. 1.3M Trisodium phosphate (165 ml.) was then added over ca. 3 minutes to raise the pH of the mixture to 1.8. Simultaneously, addition of a second solution of sodium nitrite (28g; 0.4 mole) in water (70 ml.) was commenced, which took 75 minutes to complete. The pH of the mixture was kept below pH 3.5 during the nitrite addition by addition of hydrochloric acid as required, then was lowered to pH 2. Urea (2g) in water (10 ml.) was then added to decompose any excess of nitrite. The mixture was cooled to 20°, and extracted at pH 4.2 with chloroform (2 × 100 ml.) to give a mixture of unreacted acetophenone and benzoic acid (3.8 g; 16%). The aqueous layer was further acidified with 10N hydrochloric acid (50 ml.) and extracted with ethyl acetate (5 × 100 ml.). The combined water-washed extracts were evaporated to dryness and the residual oil (30g.) was crystallised from carbon tetrachloride (25 ml.) to give phenylglyoxylic acid as almost colourless prisms (9.2g; 31%) m.p. 63.5°-65.5°. Dilution of the mother liquors with increasing quantities of light petroleum (b.p. 40°-60°) gave further crops of phenylglyoxylic acid [8.7g (29%) m.p. 60°-64°, and 1.6g (5%)].

Provenance & Evidence