Molecular structure and decomposition mechanism of peracetic acid esters AcOOR (R = Me, But)

Abstract

The molecular structure and conformational mobility of methyl and tert-butyl esters of peracetic acid AcOOR (R = Me (1), But (2)) were studied by the ab initio MP4(SDQ)//MP2(FC)/6-31G(d,p) method and density functional B3LYP/6-31G(d,p) approach. The B3LYP calculated equilibrium conformations of the molecules are characterized by the C-O-O-C torsion angles of 93.6° (1) and 117.0° (2). Structural features of the molecules under study and a distortion of tetrahedral bond configuration at the Cα atom were explained using the natural bonding orbital approach. The standard enthalpies of formation of AcOOMe (−328.5 kJ mol−1) and AcOOBut (−440.4 kJ mol−1) were determined using the G2 and G2(MP2) computational schemes and the isodesmic reaction approach. The transition state of AcOOMe decomposition into AcOOH and formaldehyde was calculated (Ea = 122.8 kJ mol−1). The thermal effects of homolytic decomposition of the peroxy esters following a concerted mechanism (Me· + CO2 + ·OR) and simple homolysis of the peroxide bond (AcO· + ·OR) were found to be 97.5±0.3 and 155.1±0.3 kJ mol−1, respectively. At temperatures below 400 K, the most probable decomposition mechanism of peroxy esters 1 and 2 involves simple homolysis of the O-O bond.