The Formation of Protonated Dimethyl Ether from the Metastable Molecular Ions of 1-Methoxy-2-Propanol, CH3OCH2CH(OH)CH3

Abstract

The unimolecular metastable decomposition of 1-methoxy-2-propanol, CH3OCH2CH(OH)CH3 (mol. wt. 90) induced by electron ionization, has been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling in conjunction with thermochemical data. In the metastable time window, the molecular ions decompose almost exclusively into ions at m/z 47 [i.e. protonated dimethyl ether, CH3O+(H)CH3] by the loss of a C2H3O radical species following a double hydrogen atom transfer (DHT). Until now, only one DHT mechanism has been proposed, involving and accounting for the loss of an acetyl radical, C2H3O. In the present study it is shown that more DHT mechanisms are operative, leading to the losses of isomeric C2H3O radicals. The results obtained are best explained by the formation of the key intermediate ion–molecule complexes [CH3OCH3+•, CH3CHO] and [CH3OCH3, CH2=C(H)OH+•] following unimolecular metastable dissociation of the molecular ion. Subsequent hydrogen atom abstraction channels by CH3OCH3+• in the former complex and proton abstraction channels by CH3OCH3 in the latter complex lead eventually to the formation of protonated dimethyl ether with m/z 47.