Unimolecular gas-phase reactions of methyl and ethyl trifluoroacetoacetates upon electron ionization

Abstract

The unimolecular metastable decompositions of methyl and ethyl trifluoroacetoacetates, CF 3COCH 2COOCH 3 (MW: 170 ( 1)) and CF 3COCH 2COOCH 2CH 3 (MW: 184 ( 2)) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. In the metastable time window, the molecular ions 1 + decompose to give exclusively the ions at m/ z 101 [ M−CF 3] +. However, the metastably decomposing ions 2 + lead not only to the formation of the major fragment ion m/ z 115 [ M−CF 3] +, but also to three minor fragment ions m/ z 164 [ M−HF] +, m/ z 156 [ M−C 2H 4] + and m/ z 87. A large part of the metastably decomposing ions 1 + and 2 + has the enol form. The loss of CO 2 from the ions m/ z 101 and m/ z 115 occurs through migration of the methyl and ethyl groups, respectively. The source-generated m/ z 69 ions from 1 + and 2 + are most abundant and consist of both CF 3 + and OCCHCO +. The latter ion, a protonated carbon suboxide, is generated by at least three and four different fragmentation routes from 1 + and 2 +, respectively. The m/ z 43 ion, C 2H 3O +, from 2 + is formed by at least two different routes.