Decomposition of Methanol Induced by Methoxy Radicals

Abstract

Kinetical studies were made at 167°C on the decomposition of methanol induced by methoxy radicals, by pyrolyzing a small amount of dimethyl peroxide in methanol. A considerable amount of ethylene glycol was found. The following mechanism was proposed, and the kinetical equations derived therefrom could express the most part of the reaction quantitatively: $$\begin{array}{c}{\mathrm{CH}}_3{\mathrm{OOCH}}_3\text{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}→2}{\mathrm{CH}}_3\mathrm{O},\\ {\mathrm{CH}}_3\mathrm{O}+{\mathrm{CH}}_3\mathrm{OH}\to {\mathrm{CH}}_3\mathrm{OH}+{\mathrm{CH}}_2\mathrm{OH}\mathrm{,\hspace{0.17em}\hspace{0.17em}(}\mathrm{a})\\ {\mathrm{CH}}_3\mathrm{O}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\to }{\mathrm{CH}}_2\mathrm{OH},\\ {\mathrm{CH}}_3\mathrm{O}+{\mathrm{CH}}_2\mathrm{OH}\to {\mathrm{CH}}_3\mathrm{OH}+\mathrm{HCHO},\\ 2{\mathrm{CH}}_3\mathrm{O}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\to }{\mathrm{CH}}_3\mathrm{OH}+\mathrm{HCHO},\\ {\mathrm{CH}}_3\mathrm{O}+\mathrm{HCHO}\mathrm{\hspace{0.17em}\hspace{0.17em}\to }{\mathrm{CH}}_3\mathrm{OH}+\mathrm{CHO}\mathrm{,\hspace{0.17em}\hspace{0.17em}(}\mathrm{b})\\ {\mathrm{CH}}_3\mathrm{O}+\mathrm{CHO}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\to }{\mathrm{CH}}_3\mathrm{OH}+\mathrm{CO}\mathrm{\hspace{0.17em}\hspace{0.17em}}\mathrm{or}\text{\hspace{0.17em}\hspace{0.17em}2}\mathrm{CHO}\to \mathrm{HCHO}+\mathrm{CO},\\ 2{\mathrm{CH}}_2\mathrm{OH}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\to }{\mathrm{CH}}_2\mathrm{OH}-{\mathrm{CH}}_2\mathrm{OH}.\end{array}$$ The dissociation rate constant of dimethyl peroxide is represented by 4.1×10¹⁵ exp (—36.9 kcal/RT) sec^—1, and the activation heat of (a) is 3.0∼4.3 kcal higher than that of (b).