Reactivities of 2,6-dimethoxyphenyl methyl sulfide, selenide and telluride with their onium salts

Abstract

2,6-Dimethoxyphenyl derivatives of sulfur, selenium and tellurium, such as MeΦE, EtΦE, [Me₂ΦE]X, [MeEtΦE]X {Φ = 2,6-(MeO)₂C₆H₃; E = S, Se, Te; X = MeSO₄, ClO₄, or PF₆} have been prepared, mostly as crystals. The reaction rates and the equilibrium constants for methyl abstraction by MeΦE from [MeRΦE′]ClO₄ {R = Me, Et, Φ; E, E′ = S, Se, Te} were measured by means of ¹H NMR spectra. Some representative results include: (1) RΦE (R = Me, Φ; E = S, Se) react commonly with [MeRΦE]⁺ (R = Me, Et, Φ; E = S, Se) to give the equilibrium mixture, except that MeΦS does not react with [MeEtΦS]⁺; (2) RΦE (R = Me, Φ; E = S, Se) do not react with [MeRΦTe]⁺ (R = Me, Et, Φ); (3) RΦTe (R = Me, Φ) react with [MeRΦE]⁺ (R = Me, Et, Φ; E = S, Se, Te) to complete the methyl abstraction (E = S, Se) or to give the equilibrium mixture (E = Te); (4) the reaction rate of MeΦE with [MeRΦE′]⁺ (R = Me, Et, Φ) increases in the orders E = S < Se < Te and E′ = S ∼ Te < Se; (5) reactions of [Me₂ΦE]⁺ are faster than those of [MeEtΦE]⁺, which react faster than [MeΦ₂E]⁺; (6) Me–E bond strength of [MeΦ₂E]⁺ increases in the order E = S ≤ Se < Te, but those of [Me₂ΦE]⁺ and [MeEtΦE]⁺ increase in the order E = Se ≤ S < Te; (7) Me–E bond strength of [MeRΦE]⁺ (E = S, Se) increases in the order R = Φ < Me < Et or Me < Φ < Et, while Me–Te bond strength of [MeRΦTe]⁺ increases in the order R = Φ < Et < Me.