Arrhenius parameters for the alkoxy radical decomposition reactions

✍ Scribed by Kwang Yul Choo; Sidney W. Benson

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 558 KB
• Volume: 13
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550130907

✦ Synopsis

Abstract

Arrhenius parameters for the decomposition reactions of various alkoxy radicals are evaluated. The recommended values for tert‐butoxy radical decomposition reaction are log A (s^−1^) = 14.1, E~a~ = 15.3 kcal/mol. magnified image The parameters give reasonably self‐consistent results with related rate constants, product distributions of hydrocarbon oxidation reactions, and the values reported in different laboratories in different environments.

A reworking of data by Batt et al. on RO + NO and RO + NO~2~ leads to a lowering of his A factors for these reactions by a factor of 5. It also leads to a similar lowering of the A factors for RO decompositions. The intrinsic activation energies E for the addition of alkyl radicals R to the carbonyl group are not only found to be a function of the exothermicity of reaction, but they are also dependent on the nucleophilicity of the alkyl radicals. For each radical R (Me, Et, i‐Pr) the data can be fit to an Evans–Polanyi plot E = a + b (δ__H__), where a uniform slope b = 0.58 can be found for all R. The intercepts a are then found to decrease nearly linearly with the decreasing ionization potential of R, namely, a = 2.1 [IP] – 6.2 (kcal/mol), with the ionization potential given in electron volts.