THE KINETICS OF THE SOFT METAL-ION PROMOTED HYDROLYSIS OF PHENYL ISOTHIOCYANATES IN AQUEOUS-SOLUTION - THE EFFECTS OF THALLIUM(III) IONS AND OF SUBSTITUENTS

In the Hg2+ ion-promoted hydrolysis of RC6H4NCS a large increase in electron-release by R produces only a small increase in reaction rate. These substituent effects support the mechanism previously proposed. Tl3+ions are surprisingly much (ca. 10(3)-fold) less effective in promoting the hydrolyses than are Hg2+ ions, but show the same kinetic form and similar substituent effects. A similar mechanism is suggested. The low reactivity of Tl3+ ions, the different pattern of their activation parameters, and the greater dependence of the Tl3+ ion-promotion on ionic strength, all suggest that these ions form adducts with isothiocyanates with special difficulty; the comparable reactivity normally found for Hg2+ and Tl3+ ions when promoting the decomposition of organosulphur compounds may require chelating substrates.