Kinetics and mechanism of general acid-catalysed thiolytic cleavage of 9-anilinoacridine Original Research Article

The rates of the reactions of 2-mercaptoethanol (2-ME) with 9-anilinoacridine (9-ANA) have been studied in the buffer solutions of 2-ME, hydroxylamine, phosphate and morpholine. Both ionised and non-ionised forms of 2-ME and free hydroxylamine show nucleophilic reactivity toward protonated 9-ANA. The rate constants for general acid-catalysed thiolytic cleavage of protonated 9-ANA reveal a Brønsted plot of slope (α) of 0.93 which indicates that probably the rate-determining step involves proton transfer in a thermodynamically unfavourable direction. A stepwise mechanism for thiolysis has been suggested. General acid catalysis could be detected for thiolysis of non-protonated 9-ANA only in the buffer solutions of phosphate and morpholine. General acid catalysis seems to be unimportant when the nucleophile is non-ionised 2-ME which is attributed to the probable occurrence of intramolecular general acid catalysis.