The Kinetics and Mechanism of the Thallium(III) Ion Promoted Hydrolysis of Thiolurethanes in Aqueous Solution. A Metal Ion Promoted Elimination.

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 AAC1-like route (with Tl3+ taking the role of H+) seems to be available to the N-Me derivatives.