Cleavage of active esters by functional thiol compounds: Acceleration and time-dependent effects induced by cationic surfactants

The esterolytic activity of 5(6)-n-alkyl-2-methanethiolbenzimidazoles towards hydrophobic p-nitrophenyl esters has been investigated in the presence of cationic micelles (CTAB). The overall activity of the different pairs (thiol, ester) is characterized by an important variation during the time. The length of time from a very fast process (in comparison with the esterolytic rate constants obtained in a hydro-alcoholic medium) to a slow one depends notably upon the surfactant concentration but also on both thiol and surfactant chain lengths. In the case of a rapid process at pH close to neutrality, the high reactivity of these thiols is essentially due to a cooperative effect involving their neutral form.