Product channeling in the reactions of CS+(X-2 Sigma(+)) with simple carboxylic acids and esters
. Int J Mass Spectrom 2001
In the present work, a selected ion flow tube was used to study the reactions of CS+(X (2)Sigma (+)) with H-2, CO, and a series of carboxylic acids and esters, RCO2R' (R, R' = H, CH3, C2H5), at 296 +/- 4 K. The CS+ ion is expected to be a reasonable ionic analogue of the neutral pseudohalogen, CN, because of its strong chemical bond and isovalency. The reactions of CS' with the RCO2R' series were all fast at greater than 80% of the theoretical upper-limit ion/dipole capture rate coefficient. Numerous binary ion products were observed, the most prevalent being the acylium ion (RCO+), the radical ion of the neutral reactant, and HCS+; no ternary association products were observed. Despite the abundance of product channels, these reactions were simple mechanistically, proceeding either by the induction of lone pair electrons on the carboxyl 0 atoms, or by H-atom transfer, which was chiefly homolytic rather than heterolytic. Induction of an O-atom lone pair by the C-terminus of CS+ into a molecular orbital of the activated complex is believed to lead to product formation through an oxonium ylide intermediate. The CS+ was converted, with few exceptions, into the small product molecules OCS, CS, and HCS+. Except in one instance, rupture of the strong C-S bond did not occur. The reactions of CS+ with the RCO2R' series are compared with the analogous reactions of S-2(+), SO+, S+, H3O+, NO+, and O-2(+) which have been studied previously. The reactive behavior of CS+ is discussed with regard to the pseudohalogen character of this ion and its potential role in studies of chemical reaction dynamics. Additionally, the rate coefficients and product distributions for the reactions of S+ with NO2 and C3H4 (allene) at 296 +/- 4 K are presented. (C) 2001 Elsevier Science B.V.