
%0 Journal Article
%A Tajima, Susumu 
%A Mamada, Masashi 
%A Nakajima, Satoshi 
%A Takahashi, Yutaka 
%A Nibbering, Nico M. M. 
%T Unimolecular Gas-Phase Reactions of Diethyl Phthalate, Isophthalate, and Terephthalate upon Electron Ionization
%J Australian Journal of Chemistry
%D 2003/05/23
%V 56
%N 5
%P 473-479
%K 
%R https://doi.org/10.1071/CH03077
%U https://www.publish.csiro.au/paper/CH03077 
%X Unimolecular gas-phase reactions of diethyl phthalate (1), isophthalate (2), and terephthalate (3), upon electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and deuterium labelling. The metastable molecular ions (1)+ decompose to give exclusively the ions m/z 176 ([M &#8211; CH3CH2OH]+) and not the ions by the loss of CH3CH2O as proposed earlier in the literature. The metastable molecular ions (2)+ and (3)+ fragment differently from (1)+ and lead not only to the formation of the major fragment ions m/z 194 ([M &minus; CH2CH2]+) via a McLafferty rearrangement but also to minor fragment ions m/z 193 ([M &#8211; CH2CH3]+).Yet, molecular ions decomposing in the ion source all show as primary fragmentation channel the loss of CH3CH2O to give the ions at m/z 177, which further dissociate to give the ions at m/z 149 through the loss of C2H4 or CO, indicating the resulting ions are +COC6H4COOH and +C6H4COOCH2CH3. The +COC6H4COOH ions decompose into the m/z 121, 93, and 65 ions by the consecutive losses of three carbon monoxide molecules, respectively. Prior to the second CO loss, a migration of the OH group to the benzene ring occurs. During the metastable fragmentation of the +C6H4COOCH2CH3 ions no ethoxy migration occurs, in contrast to the methoxy migration taking place in the metastable decomposition of the lower homologue +C6H4COOCH3 ions. 
