Derivatization of thiols under flow conditions using two commercially available propiolate esters

In the present study we report new data on the reaction of three representative thiols – captopril (CAP), cysteine (CYS) and N-acetylcysteine (NAC) – with two commercially available propiolate esters – methyl-propiolate (MP) and butyl-propiolate (BP) – under flow conditions. The reactions were investigated on-line using sequential injection analysis (SI) and the formed derivatives were monitored spectrophotometrically at 285 nm. The effect of critical parameters of the reaction such as the pH, the temperature and the amount concentration of the reagents were studied in detail including stopped-flow (SF) experiments. Both reagents were found to be suitable for the automated derivatization of thiols, although MP offered faster kinetics compared to BP. The applicability of the procedures was demonstrated by the development of SI methods for the dissolution studies of CAP tablets with satisfactory results.