Ion-molecule reactions in thiols and alkyl sulfides. Photoionization of methyl, ethyl, propyl and tert-butyl mercaptan, and methyl and ethyl sulfide

Abstract

Photoinduced ion-molecule reactions of the primary ions occurring in a number of thiols and alkyl sulfides have been investigated over the pressure range 1-20 mTorr using a Kr resonance lamp (10.03 and 10.6 eV) as the excitation source. Rate coefficients at 298 K have been determined for the reaction R2_"+SHn + R2_nSH" -* R,_"+SHn+1 + R2-"SHri (-H) (ki), n = 0,1. For the mercaptans values of kx were found to be 14.1,12.5,11.3, and 5.7 X 10"10 cm3 s"1 for R = CH3, C,H5, C3H7, and (CH3)3C. These values agree with the general trend established for the analogous reactions in amines. In the case of (CH3)2S and (C2H5)2S, no hydrogen transfer was observed. Photoionization of C2H5SH in CH3OH could indicate that mercaptans behave as hydrogen atom acceptors rather than as proton donors. However, for fert-butyl mercaptan, the proton transfer reaction (CH3)3C+ + (CH3)3CSH -»• (CH3)2CCH2 + (CH3)3CS+H2 (k2) was also observed.