Glycosides of N-hydroxy-N-arylamine derivatives. Part 3. Kinetic and mechanistic studies on the degradation reaction of O-glycosides of N-hydroxy-N-arylamines and their acetohydroxamic acids in acidic and alkaline media

Abstract

Good first-order kinetics of the degradation reaction of 1-[(N-acetyl-N-arylamino)oxy]-1-deoxy-β-D-glucopyranoses (1a–d), 1-(N-arylamino)oxy-1-deoxy-β-D-glucopyranose (2a) and sodium 1-[(N-acetyl-N-phenylamino)oxy]-1-deoxy-β-D-glucopyranuronate (3a) in aqueous acidic solutions have been observed. Compounds (1a–d) and (3a) were fairly stable in neutral solution, but in aqueous acidic solutions at 20 °C these compounds decomposed to the corresponding arylamino derivatives (4a–d) and D-gluconic acid (5)[D-glucaric acid in the case of the compound (3a)]. The compound (2a) decomposed ca. 7 400 times faster than compound (1a) to the same products (4a) and (5) in the same conditions. In an alkaline solution, compounds (1a)–(3a) gave the corresponding azoxybenzene. In the acid-catalysed redox degradation reaction, the hydrolysis of the N-acetyl group of compounds (1a–d) and (3a) is considered to be the rate-determining step. The effects of pH and additives on the reaction rate are reported. The mechanism of the acid-catalysed redox fission of the N–O linkage in the above O-glycosides is discussed.