Studies on the stabilities of thiamine and its modified compounds. X. Stabilities of S-alkoxycarbonylthiamines in acid aqueous solution

Abstract

Anaerobic degradations of S-alkoxycarbonylthiamines (B1-S-CO-O-R ; R=C2H5 (I), C3H7, iso-C3H7, C4H9, CH2-CH=CH2, CH2C6H5, and CH2CH2C6H5) were studied in aqueous solutions at 100° in a pH range from 1 to 5, and the results were compared with each other and with those of S-benzoyl, S-morpholinocarbonyl, and S-piperidinocarbonyl-thiamines under the same conditions. Each of these B1 derivatives was degraded by a pseudo first-order reaction, and their minimum rates were found to be within a range of pH 2.5 to 3.0. Except for the morpholino- and piperidinocarbonyl compounds, all these derivatives gave B1 and O-alkoxycarbonylthiamine as their thiochrome-reaction-positive products. A correlation was found between the logarithm of the overall rate constants for the degradation of S-alkoxycarbonylthiamines and σ* values for their alkyl groups. An analog computer analysis was made on the degradation of I on the basis of the relative amounts of the degradation products including B1, O-ethoxycarbonylthiamine (XIII), 2-methyl-4-amino-5-hydroxymethylpyrimidine, and 2-methyl-4-amino-5-aminomethylpyrimidine. The results showed that the main degradation route was the transformation of I to a cyclic intermediate which was very easily converted into XIII. Comparisons were made of each rate constant for the other routes with each and with the overall degradation rate constant of I.