Kinetic comparison of 13 homogeneous thiol-X reactions

An extensive kinetic comparison of 13 thiol X reactions is presented using online FT-IR. Besides the effect of catalysts (tertiary phosphine or tertiary amine), a significant catalytic effect of dipolar solvents on many thiol X reactions is observed. Thus, different overall reactivity orders of the studied substrates toward the thiol group are shown in polar aprotic and nonpolar solvents and compared with previous results in analogous heterogeneous reactions. The reactivities of some substrates toward n-octylamine are also investigated and their reactions with the amine and the thiol are compared. This study can serve as a useful guide for the choice and application of many thioclick reactions as efficient chemical conjugation tools.