Flowing afterglow study of the gas phase nucleophilic reactions of some formyl, acetyl and cyclic esters

Abstract

A variety of nucleophiles have been investigated for their reactions with formyl and acetyl esters in the gas phase in our flowing afterglow. The reactions that are permitted in the gas phase are more varied than those seen in the condensed phase. The rates of reactions of methyl and ethyl esters as well as various lactones have been undertaken with various nucleophiles: H₂N^–, HO^–, CH₃O^–, NCCH₂^–, F^–, CH₃C(O)CH₂^–, CH₃S^– and O₂NCH₂^– . For example, the reaction rate of NCCH₂^– + HCO₂CH₂CH₃ has been found to be (1.3 ± 0.2) × 10^–10 cm³ molecule^–1 s^–1 and the only product is HC(O^–)CHCN which results from nucleophilic acyl substitution (B_AC2) followed by a proton transfer within the ion–molecule complex. Other reaction mechanisms that have been observed include β-elimination (E2), bimolecular nucleophilic substitution at the alkyl group (B_AL2), and the Riveros reaction (elimination of CO). A mechanism for the F^– + HCO₂CH₃ reaction has been determined at the B3LYP/6-31+G(d) level. Most notably, channels were determined computationally (B_AL2 and Riveros), and these channels are also observed experimentally. Furthermore, the B_AC2 pathway which proceeds via nucleophilic attack on the carbonyl group also leads to the Riveros products, F^–(CH₃OH) and CO.