Intracluster ion-molecule reactions between V+ and methyl acetate or ethyl acetate clusters

Abstract

Intracluster ion-molecule reactions of V+(CH3COOR)(n) (R = CH3, C2H5, C2D5) complexes produced by the mixing of laser-vaporized plasmas and pulsed supersonic beams were investigated by reflectron time-of-flight mass spectrometry. The mass spectra indicated the presence of a major sequence of cluster ions with the formula V+(CH3COO)(CH3COOR)(n). This sequence is attributed to the insertion of V+ into the C-O bond of CH3COOR within the heteroclusters, followed by alkyl radical (R) elimination. The observation of V+(OR) and V+(CH3)(OR) ions is interpreted as arising from the insertion of V+ into the C(O)-O bond of the ester group, followed by CH3CO and CO elimination, respectively. In addition, the VO+ ion is present throughout the mass spectra, indicating that insertion of V+ into the C=O bond of CH3COOR also occurs. Within the stabilizing environs of a heterocluster, sequential insertions of VO+ ions into a second molecule produced VO+(CH3COO)(CH3COOR)(n) and VO+(CH3)(OR)(CH3COOR)(n) heteroclusters via reaction pathways similar to those of the V+ ion. The results of isotope-labeling experiments suggest that the reaction pathway for formation of V+(CH3COOH)(CH3COOC2H5)(n) involves V+ insertion into the C-O bond of ethyl acetate, followed by beta-H atom transfer from the ethyl group. Density functional theory calculations were carried out to model the structures and binding energies of both the association complexes and the relevant reaction products. The reaction pathways and energetics of each product channel are presented. (C) 2012 Elsevier B.V. All rights reserved.