1961 Volume 34 Issue 3 Pages 328-334
Dimethyl ether has been decomposed thermally in the presence and absence of hydrogen sulfide over the temperature range 360∼440°C. The rate of decomposition is enhanced by the presence of hydrogen sulfide, but the rate law is unchanged, i. e., the rate is proportional to the 3/2 power of the ether concentration, irrespective of the presence of hydrogen sulfide.
The catalytic action of hydrogen sulfide is satisfactorily explained by the steps, CH3+ H2S→CH4+HS (6), HS+CH3OCH3→H2S+ CH3OCH2 (7) and CH3OCH2→CH2O+CH3(4). Overall rate constants in the absence and presence of hydrogen sulfide are represented by 1015.16exp(−54,500⁄RT) and 1015.26exp(−51,800⁄RT) mol.−1⁄2cc−1⁄2sec−1⁄2 respectively. The combination of these gives k3⁄k7=0.8exp(−2,700⁄RT), where k3 refers to the reaction CH3+CH3OCH3→CH4+CH3OCH2 (3). If, therefore, the activation energy of reaction 3 is 9.5 kcal./mol. as reported by Trotman-Dickenson and Steacie, that for reaction 7 is 6.8 kcal./mol. The results obtained indicate that the decomposition of the formaldehyde formed intremediately is also catalyzed by hydrogen sulfide.
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