Determination of the kinetic constants of the reversible opening of a triazolo-1,4-thienodiazepine in water at different pH values: A striking example of the determination of intimately intricate kinetic and equilibrium constants

Abstract

Apparent kinetic constants of the reversible opening of a triazolo-1,4-thienodiazepine were determined by UV-spectrophotometry and by polarography in water at several pH values assuming as a hypothesis a stationary state for the carbinolamine intermediate. Both the apparent kinetic constants, k f and k r , exhibited a maximum for the values H 0 ϭ Ϫ0.25 and pH ϭ 6.07. A possible determination of the elementary kinetic constants of the several acidobasic species which may be involved in the opening and closing process according to the pH and pKa values was studied and is discussed. The results are consistent with the hypothesis that both the opening of the diazepine cycle and the closing of the opened form proceed through a mechanism suggesting that the protonated form of the carbinolamine function of the intermediate is involved.

Reactions of Aldehydes and Ketones and Their Derivatives

“…61 The results have been analysed in terms of several protonated forms of the reactant (30a) and product (30b), and similar forms of potential carbinolamine intermediates.…”