Methyl butanoate is a widely-study surrogate for biodiesel fuel.  Here we report a detailed analysis of the thermodynamics and kinetics of low-temperature oxidative decomposition of methyl butanoate. We employ composite (CBS-QB3) and density functional (M05-2X) calculations to construct the potential energy profiles of radicals derived from methyl butanoate, with an emphasis on peroxy radicals (ROO�) and hydroperoxyalkyl radicals (�QOOH) that are critical for autoignition of diesel fuel. Of great interest for the ROO� is the competition between various H-migration reactions and  HO2 elimination. For the �QOOH, the focus is on the competition between cyclic ether formation reactions and �-scission reactions. We evaluate the significance of reaction pathways by comparing rate coefficients in high-pressure limit. Unexpectedly, we find a low activation barrier for 1,8 H-migration of peroxy radicals (see Figure). This low barrier is accompanied by a relatively low Arrhenius pre-exponential factor, which means that other H-migration reactions will compete with it at temperatures relevant to autoignition. 

Quantum chemical study of the oxidative decomposition of methyl butanoate

248th National Meeting (2014)

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