Photolysis of Dimethyl Peroxide

Abstract

Dimethyl peroxide has been photolyzed in vapor phase by 2537 A‐light under various peroxide pressures at temperatures from 21 to 60°C, and for various light intensities at 30°C. The over‐all rate was measured manometrically. The reaction is self‐inhibiting and is also greatly inhibited by a small amount of formaldehyde. The initial rate is expressed by AI+BI^½[CH₃OOCH₃]^½ (A≪B and I is absorbed light intensity), and it tends to 3I when formaldehyde is added sufficiently. Carbon monoxide, methanol, and formaldehyde were found in the reaction product. The amount of hydrogen was quite small in the normal run and also in the run where much formaldehyde was added. Based on these results the following mechanism has been proposed: $$\begin{array}{c}{\mathrm{CH}}_3\mathrm{OO}{\mathrm{CH}}_3\text{+hν→2(}\mathrm{H}+\mathrm{HCHO}\mathrm{),}\\ \mathrm{H}+{\mathrm{CH}}_3{\mathrm{OOCH}}_3\to {\mathrm{CH}}_3\mathrm{OH}+{\mathrm{CH}}_3\mathrm{O},\\ \{\begin{array}{c}{\mathrm{CH}}_3\mathrm{O}+{\mathrm{CH}}_3{\mathrm{OOCH}}_3\to {\mathrm{CH}}_3\mathrm{OH}+{\mathrm{CH}}_3{\mathrm{OOCH}}_2,\\ {\mathrm{CH}}_3{\mathrm{OOCH}}_2\to {\mathrm{CH}}_3\mathrm{O}+\mathrm{HCHO},\end{array}\\ {\mathrm{CH}}_3{\mathrm{OOCH}}_2+{\mathrm{CH}}_3\mathrm{O}\to {\mathrm{CH}}_3\mathrm{OH}\text{+2}\mathrm{HCHO}.\end{array}$$ From the temperature coefficient of the rate, E_a+E_b—E_c= 5.8 kcal, the difference of activation heats, has been obtained; the numerical value is supposed to be the upper limit of E_b.