Quantitative aspects of Lewis acidity. Part 17. Equilibria between covalent metal halides and thiobenzamide in diethyl ether solution

Abstract

Covalent halides form 1 : 1 adducts with thiobenzamide in diethyl ether solution. The site of co-ordination is probably-the sulphur atom. The equilibrium constants (K) for adduct formation, determined spectroscopically at 25 °C, reveal the sequence of acidities HgBr₂ [graphic omitted] HgCl₂≃ SnCl₄ > ZnCl₂ > GaCl₃ > AlCl₃ > BF₃ AsCl₃, SbCl₃. Comparison of the K values with those found under similar conditions for benzamides (structurally analogous O-bases) shows that whereas the group 3 and group 5 acids are relatively more acidic towards the O-bases than towards the S-base, the zinc and tin acids occupy an intermediate position (co-ordinating about equally well with either class), whilst the mercury acids display an exceptional affinity for the S-base.