Gas‐phase reactivity of the OP(OCH 3 ) 2 + phosphonium ion towards α,β‐unsaturated esters in a quadrupole ion trap

Ion–molecule reactions between the OP(OCH 3 ) 2 + phosphonium ions and eight α,β‐unsaturated esters (methyl acrylate, ethyl acrylate, methyl crotonate, ethyl crotonate, methyl 3,3‐dimethylacrylate, ethyl 3,3‐dimethylacrylate, methyl methacrylate and ethyl methacrylate) were performed in a quadrupole ion trap mass spectrometer. The OP(OCH 3 ) 2 + phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with α,β‐unsaturated esters to give an adduct [RR′CCR″COOR″′, OP(OCH 3 ) 2 ] + , which lose spontaneously a molecule of trimethyl phosphate (R″′CH 3 ) or dimethyl ethyl phosphate (R″′C 2 H 5 ). An ion corresponding to a protonated trialkyl phosphate is also observed when substituent R″H. To confirm the experimental results, and to elucidate the mechanism for the formation of the ionic species, a theoretical study using the density functional theory (DFT) approach was carried out. The potential energy surface obtained from B3LYP/6–31G(d,p) calculations for the reaction between OP(OCH 3 ) 2 + and methyl acrylate is described. Copyright © 2005 John Wiley & Sons, Ltd.