Monoacyl Sulfates as Intermediates for α-Halogenation of Aliphatic Acids

Article abstract of DOI:10.1021/jo00346a007

The mechanism of the α-halogenation of aliphatic carboxylic acids, promoted by ClSO3H or oleum, has been reexamined.Ketenes, which have been postulated as the intermediates in this halogenation, have been found to react with I2 much faster than a mixture of the corresponding acid and ClSO3H.Evidence is presented to support the hypothesis that the halogenation proceeds through the cyclic enol form of the monoacyl sulfate RR'CHCO2SO3H (3) rather than through the ketene.