The gas phase ion/molecule chemistry of the carbon- 13 labeled ketenyl and methyl ketenyl anions with CS₂, COS, and CO₂

A flowing afterglow-selected ion flow tube apparatus was used to study the gas phase ion/molecule chemistry of carbon-13 labeled ketenyl anions (HCCO) with CS₂, COS and CO₂. In all cases, the ketenyl anion adds to the carbonyl carbon of the neutral; the resulting adduct undergoes subsequent cyclization and elimination, forming the thioketenyl anion (HCCS) in the reactions with CS₂ and COS, and a degenerate anion in the reaction with CO₂ in which the CO group of the ketenyl anion and that of CO₂ are exchanged. In the reaction of the ketenyl anion with COS, both sulfur and oxygen participate in cyclization. After addition to carbon, sulfur undergoes cyclization approximately four times faster than oxygen, but all reactions eventually cyclize through oxygen before cleavage to product. An unexpectedly small reaction efficiency was observed in the reaction of the ketenyl anion with CS₂. To explain this finding, we propose that energy randomization in the initially formed adduct is slow, thereby increasing the probability of decomposition. The reactions of carbon-13 labeled methyl ketenyl anions (CH₃CCO) with CS₂, COS, and CO₂ were also studied and produce analogous results.