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Org. Synth. 1925, 5, 1
DOI: 10.15227/orgsyn.005.0001
p-ACETAMINOBENZENESULFINIC ACID
[Benzenesulfinic acid, p-acetamido-]
Submitted by S. Smiles and C. M. Bere.
Checked by Henry Gilman and F. Schulze.
1. Procedure
The crude p-acetaminobenzenesulfonyl chloride (p. 8) obtained from 67.5 g. (0.5 mole) of acetanilide is shaken for two hours with a solution of 252 g. (1 mole) of crystallized sodium sulfite (Na2SO3 · 7H2O) in 500 cc. of water. The reaction mixture is kept slightly alkaline by the addition at intervals of small portions of 50 per cent sodium hydroxide solution. The total volume of alkali used varies from 10 to 50 cc. After the alkaline mixture has been shaken for the two-hour period (Note 1) it is filtered, and the filtrate is acidified with 60 per cent sulfuric acid. If the acid is added slowly, the sulfinic acid comes down in fine crystals which, after filtering and drying, melt at 155° with decomposition (Note 2). The yield is 50–55 g.. (43–47 per cent of the theoretical amount based on the acetanilide used).
The product may be purified by crystallization from 400 cc. of hot water, but this is unnecessary when the above procedure is followed carefully.
2. Notes
1. The solution does not clear up when reduction is complete on account of the formation of a gelatinous impurity. Two hours suffice for the completion of reduction.
2. The melting point given in the literature (180°) is incorrect, its publication being due to a typographical error. The observed melting point varies slightly with the rate of heating during the determination of the melting point.
3. Discussion
p-Acetaminobenzenesulfinic acid can be prepared by the reduction of p-acetaminobenzenesulfonyl chloride.1
This preparation is referenced from:

References and Notes
  1. Bere and Smiles, J. Chem. Soc. 125, 2361 (1924).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sulfinic acid

sulfuric acid (7664-93-9)

Acetanilide (103-84-4)

sodium sulfite (7757-83-7)

sodium hydroxide (1310-73-2)

p-Acetaminobenzenesulfonyl chloride (121-60-8)

p-Acetaminobenzenesulfinic acid,
Benzenesulfinic acid, p-acetamido- (710-24-7)