Reactions in Fluorinated Acetic Acid Esters Triggered by Slow Electrons:Bond Cleavages,Hydrogen Transfer Reactions and toss of Halocarbons

摘要

Low energy electron induced reactions in the four fluorinated acetic acid esters CF3COOCH3,CF3COOC2H5,CF3COOCH2CF3 and CH3COOCH2CF3 are studied by means of a crossed electron-molecular beam experiment and mass spectrometric detection of the anions.All target molecules exhibit a prominent resonance located near 1 eV which is subjected to a variety of unimolecular reactions.The observation of the carboxylate anion CF3COO~-/CH3COO~-indicates rupture of the O-R ester bond,which in turn demonstrates that the prominent cleavage of the O-H bond recently observed in trifluoroacetic acid and acetic acid is not blocked when O-H is replaced by O-R(R=-CH3,-C2H5,-CH2CF3).In CF3COOCH3 and CF3COOC2H5 an ion of the form CF2COO~-is generated which is identified to arise from a complex reaction involving multiple bond cleavages and substantial rearrangement in the transitory negative ion ultimately generating CH3F and C2H5F,respectively,as neutral counterpart.A fragment ion of the type(M-H)~-(M:target molecule),i.e.loss of a neutral hydrogen atom,is only observed in CH3COOCH2CF3 which directly demonstrates that dehydrogenation selectively occurs at the CH3 site.