Theoretical correction on the existing understanding for hydroper-oxymethyl formate dissociation in DME low temperature oxidation

Abstract

Hydroperoxymethyl formate (HPMF), a carbonyl-hydroperoxide-like species, plays a vital role in the low temperature oxidation of DME because HPMF is formed with ȮH as a co-product, and it can also decompose to generate ȮH radicals. Unfortunately there is neither theoretical nor experimental evidence nor an established explanation of HPMF kinetics in the literature. A theoretical understanding of the potential energy surface of HPMF dissociation kinetics is evaluated at the CCSD(T)/CBS//M06-2X/6-311++G(d,p) level of theory. Microcanonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus/Master Equation calculations were performed to obtain temperature- and pressure-dependent rate coefficients. Two main reaction pathways, (1) the widely recognized channel involving O–O bond fission to produce ȮH + ȮCH2OCHO radicals, and (2) a novel channel producing HOCHO + CH2OO, were considered to be the most competitive reaction channels. Calculation results reveal that there are significant differences between the current calculations and literature values, and the pressure-dependent behavior of HPMF decomposition cannot be ignored, particularly at low temperatures (T < 600 K). The orders of magnitude difference between the model recommendations and theoretical calculations make it reasonable to doubt the previous kinetic description of HPMF O–O bond fission, with its mechanism remaining unreliable. Generally, this study serves as theoretical evidence to provide new insights into HPMF kinetics but also questions our current understanding of the low temperature DME oxidation mechanism.