The Thermal Decomposition of Dimethyl Ether in the Presence of Hydrogen Sulfide

Abstract

Abstract 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.