Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part 2. Log k--pH profile for sulfadimidine autoxidation.

The overall first order rate constants for the reaction of degradation of sulfadimidine (kobs. = kOX+kh) in the presence of the air oxygen were determined from the measurements of absorbance in 0-1 M HCl at 243 nm, using "the feathering technique". The apparent first order rate constants for autoxidation of sulfadimidine at 403, 411 and 418 K, in the pH range 2-0--9-2 were calculated from the equation kOX = kobs. -- kh, where kh are the rate constants for hydrolysis carried out under nitrogen. The rate of sulfadimidine autoxidation is a function of concentration of the undissociated form (kOX = kOX-fHA). The thermodynamic parameters of the reaction: Ha, deltaHNo., deltaSNo. and logA were determined for the specific rate constant of autoxdiation (kOX).