Question

12. (S)-2-butanol is first reacted with methanesulfonyl chloride and this is followed by reacting it with methane thiolate in methane thiol. Show the detailed mechanisms for these transformations.

Answer 1

Reaction of (S)-2-butanol with methyl sulphonyl chloride is used to convert OH into a good leaving group because OH itself is a very bad leaving group.

Reaction initiates by an acidic proton abstraction from methyl if methyl sulphonyl chloride using NEt3 i.e. triethylammonia as a base. Resultant carbanion undergoes rearrangement to remove Cl- and to fotm sulphene. Then 'O' of 2-butanol act as a nucleoohile and attack on the electrophillic 'S' of sulphene. The resulting molecule undergoes some rearrangements to form methyl sulphonyl substituted product which undergoes nucleophilic substitution reaction with CH3S- acting as a nucleophile to give product with inversion of configuration.