Acid — Base properties of 3,4-dimethyl-2-thiazolone, 4-methyl-2-thiazolone,and 5-acetyl-4-methyl-2-thiazolone

In contrast to 2-methoxy-4-methylthiazole and 2,4-dimethylthiazole, the protonation of 3,4-dimethyl-2-thiazolone does not proceed in media with acidities up to H₀=–3.99. The acidity of N-H increases by 2.4 orders of magnitude on passing from 4-methyl-2-thiazolone to its 5-acetyl derivative. The data obtained from a study of the acid-base properties in conjunction with the results of calculations of the 3,4-dimethyl-2-thiazolone and thiazole molecules by the MO method make it possible to conclude that there is a charge in the 5 position of 2-thiazolones and that this is the reason for the facile acylation of these compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1622–1625, December, 1972.