The kinetics and mechanism of the thallium(III) ion-promoted hydrolysis of thiolurethanes in aqueous solution. A metal ion-promoted elimination

Abstract

The hydrolysis of thiolurethanes R¹C₆H₄NHCOSC₆H₄R²(1), in dilute aqueous perchloric acid, under conditions where the spontaneous hydrolysis is negligible, is promoted by Tl³⁺ ions. The organic products are the corresponding anilinium ion and the thallium salt of the thiophenol. The effects of substituent changes (R¹,R²) of changes in [H₃O⁺], temperature, ionic strength, and of replacement of the NH proton by Me, are all compatible with hydrolysis occurring by elimination–addition mechanisms via the isocyanate as a reactive intermediate; thallium ion-promoted E1 cb and E2 routes are implicated. In effect the elimination–addition type of mechanism which is important for these esters at higher pH has been made available at low pH by complexation with Tl³⁺ ions. With the thiolurethanes RC₆H₄NHCOSEt, (2) which are less susceptible to the sponataneous and base-catalysed elimination–addition mechanisms of hydrolysis than are thiolurethanes (1), the presence of Tl³⁺ ions can also lead to promoted hydrolysis via elimination, but an A_AC1-like route (with Tl³⁺ taking the role of H⁺) seems to be available to the N-Me derivatives.