Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part 1. Log k--pH profile for sulfadimidine solvolysis.

The degradation of sulfadimidine (SDMP) in the pH range 5-83--10-0, at 403, 411 and 418 K, was investigated by UV spectrophotometry. Semilogarythmic plots (A242--A') vs. time in 0-1 M HCl for the degradation of SDMP in the above pH range were linear. The log k--pH profile constructed from the experimental results served for estimation of specific rate constants and pKa values. These, in turn, were used to calculate the theoretical log k--pH profile, acc. to the equation for the rate of reaction proportional to the concentration of the dissociated form of SDMP, in the pH range 5-8--10. Thermodynamic parameters of the reaction--energy, entropy and enthalpy of activation and the frequency factor for the specific rate constants were determined.