Methyltriphenoxyphosphonium iodide (MTPI); induced dehydration and dehydrohalogenation in aprotic solvents

Abstract

Methyltriphenoxyphosphonium iodide (MTPI) is an effective dehydration and dehydrohalogenation reagent under mild conditions when 1,3-dimethylimidazolidin-2-one is used as an aprotic solvent in place of the more normally used hexamethylphosphoric triamide (HMPT). Since previously suggested mechanisms had proposed alcohol–HMPT interaction as an important mechanistic step, this result coupled with comparative product geometric isomer distributions and the conjugated: non-conjugated triene product ratios leads to the conclusion that MTPI–alcohol interaction with displacement of phenoxide is the primary step in the reaction. In dimethyl sulphoxide (DMSO) alcohol dehydration is hindered by DMSO–MTPI interaction yielding dimethyl sulphide.