Novel CFCs-substitutes recommended by EPA (hydrofluorocarbon-245fa and hydrofluoroether-7100): Ion chemistry in air plasma and reactions with atmospheric ions

摘要

The ion chemistry of the title compounds, a nonafluorobutyl methyl ether and a hydrofluoropropane, is elucidated by a combination of studies using atmospheric pressure ionization mass spectrometry and triple quadrupole mass spectrometry. In the positive ion mode, the hydrofluoroether readily forms an [M - F](+) ion, attributable to hydronium ion induced dehydrofluorination, the product of which can be further hydrated to give a protonated hydrofluoroester. By contrast, the hydrofluoropropane does not react with the hydronium ion but rather gives hydrofluoroalkenylium cations via H atom and F atom abstraction by the dioxygen radical cation. In the negative ion mode, the fluorobutyl methyl ether undergoes dissociative electron capture with O-2(-.), O-2(-.) (H2O), O-3(-) and NO2- to generate the fluorobutoxy anion, which can dissociate by CF2=O loss to give the perfluorocarbanion when the precursor ions are internally excited. The hydrofluoropropane reacts readily with common atmospheric anions to form molecular complexes with F-, O-2(-.), and O-3(-.) and the strongly H-bonded species, O-2(-.)(HF) and F-(HF). Interestingly, isomeric pentafluoropropanes form in the reaction with O-2(-.), either O-2(-.)(HF) or F-(HF), depending on the specific pattern of the fluoro substitution.