The conversion of 2-(methylthio)ethanol into 1-chloro-2-(methylthio)-ethane: a 13C-labelling study with the aid of 13C nuclear magnetic resonance spectroscopy

Abstract

The synthesis of 2-(methylthio)[1-¹³C]ethanol from [1-¹³C]acetic acid is described. This labelled alcohol and ¹³C n.m.r. spectroscopy were used to evaluate the propensity for rearrangement of four methods for effecting the conversion ROH → RCl[R₃P(R = Ph, Prⁱ or n-C₈H₁₇)–CCl₄; CCl₃CN–HCl; MsCl–collidine–LiCl; TsCl–py,-Cl^–]. In every case the product observed at all stages of the reaction was a 1:1 mixture of 1-chloro-2-(methylthio)[1-¹³C]ethane and 1-chloro-2-(methylthio)[2-¹³C]ethane. It is proposed that activation of the hydroxy-group of 2-(methylthio)[1-¹³C]ethanol is followed by internal displacement by the methylthio-group giving the 1-methylthiiranium ion, which is captured by chloride.