3d-orbital resonace in divalent sulphides—V activity of α-hydrogen atom of cyclic mercaptals

Abstract

Previously, 1 it was found that the base-catalysed hydrogen exchange reactions of sulphides is effected 3d orbital resonance involving uncharged sulphur groups. This investigation now extended to several syclic mercaptals, reveals that ring size and conformation affect the exchange rates substantially. Unsubstituted cyclic mercaptals are more reactive than the open chain compounds, the relative rates of open chain, five- and six-membered ring compounds bein 39.9, 516 and 214 respectively. Alkyl substituents reduce the rates substantially in both open chain and cyclic mercaptals; the relative rates of ethyl subtituted compounds being 1·00 for acyclic, 19·1 for five-, 1·55 for six- and 5·37 for seven-membered cyclic compounds. This rate reduction is greater by a factor of about 4—5 for six-membered cyclic compounds 214/1·55 = 138) than for the other compounds. These results are interpreted in terms of comformational changes, solvation and the 3d orbital resonance of sulphur atoms.