Formation, equilibrium properties and decomposition in aqueous solution of monoorganothallium(III) ions containing RC(O)CH 2 groups. Preparation of monoaceteonylthallium(III) compounds

Abstract

The reactions of thallium(III) with some ketones in the presence and absence of Cl −, Br −, CN −, CH 3COO − and CF 3COO − ions in acidic aqueous solution, and the stabilities of the resulting monoorganothallium(III) species in solution have been examined. the rate-determining step in the formation of these compounds is the acid-catalyzed enolisation of the ketones. The formation reactions are reversible: the ketonyl groups can be exchanged by Cl −, Br −, CN − and by other ketones. The equilibrium constant at 25°C for the reaction: H + + CH 3C(O0CH 2TlCl + + Cl − ⇌ TlCl 2 + + CH 3C(O)CH 3 in about 1 molar HClO 4 was found to be 780 (±160) M −1. This unusual behaviour of the Tl III-ketone systems can be accounted for by assuming that enolate complexes are present in low concentration, in equilibrium with the monoorganothallium(III) species. Two routes for decomposition of these species have been established. One of them takes place through RCH 2C(O)CH 2Tl 2+ ions and the other (when an excess of Cl − is present) through RCH 2C(O)CH 2TlCl + ions. The latter results in formation of α-monochlorinated product with the composition RCHClC(O)CH 3 (where R  R, alkyl, aryl), probably via a five-ring enolate intermdiate. Formation of diorganothallium(III) species of the type [RC(O)CH 2] 2Tl + has also been demonstrated. Some new solid monoorganothallium(III) compounds with the composition ArC(O)CH 2TlCl 2 (Ar  C 6H 5, 4′-ClC 6H 4, 4′-CH 3C 6H 4, 2′-C 10H 7, RC(O)CH 2-TlCl(NO 3) (R  CH 3, (CH 3) 3C) and (CH 3) 3CC(O)CH 2Tl( 2CNEt 2) 2 have been prepared. 205Tl NMR parameters for some mono- and di-organothallium(III) species are given.