The Thermal and Mass Spectral Fragmentation of N-Butyl Thiolo-, Thiono-, and Dithio-Chloroformate

Abstract

Thermal decomposition of n-butyl thiolochloroformate at 150°C follows a similar pattern to that reported previously for n-butyl chloroformate, to give butyl chloride which is largely rearranged to the s-butyl isomer. An ion-pair mechanism, involving 1,2- and 1,3-hydride shifts, is proposed. The less stable thiono- and dithio-chloroformates decompose to give lower yields of butyl chlorides (mainly without rearrangement) together with numerous other byproducts, indicating the operation of a more complex combination of reaction pathways. The mass spectra of all three thio compounds exhibit molecular ions; the most prominent fragment ions in their spectra are the n-butyl cation, and the radical cations COS^{+ •} and CS₂ ^{+ •}. Numerous chlorine-containing ions of low intensity are also observed, and their mode of formation is discussed.

GRAPHICAL ABSTRACT

Keywords:

• Carbocation rearrangement
• dithiochloroformate
• mass spectrometry
• protonated cyclopropane intermediate
• thiochloroformate

Acknowledgments

We thank Professor J. Charalambous for helpful discussions.