Chemical Reactions of Omeprazole and Omeprazole Analogues. II. Kinetics of the Reaction of Omeprazole in the Presence of 2-Mercaptoethanol.

Abstract
The rate at which 5-methoxy-2-(4-methoxy-3,5-dimethyl-2-pyridinylmethylsulfinyl)-1H-benzimidazole, omeprazole, reacts with 2-mercaptoethanol is equal to the rate at which it is converted into a sulfenamide. This reaction proceeds via two intermediates, a spiro compound and a sulfenic acid. A kinetic study of the reaction at different pH values has revealed that the conversion into the spiro compound is the slowest step. It can be an uncatalyzed reaction, but can also be acid catalyzed. Even the conversion of the spiro compound into the sulfenic acid can occur by an uncatalyzed reaction as well as by an acid-catalyzed one. The conversion of the sulfenic acid to the sulfenamide is very rapid. The rate constants for the different steps can usually be predicted.