Thermal Decomposition of Acetaldehyde in the Presence of Hydrogen Sulfide. I. Kinetics of the Reaction

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The hydrogen sulfide-catalyzed thermal decomposition of acetaldehyde has been investigated over the temperature range 340 to 494°C. The initial rates of decomposition approximately fit the rate equation －d[CH3CHO]⁄dt=k[H2S] [CH3CHO] +k′[H2S] [CH3CHO]1⁄2 where k=1012.7±1.0exp(－31400±3100⁄RT) mol－1ml.sec－1 and k′=1012±0.27exp(－41100±1200⁄RT) mol－1⁄2ml1⁄2sec－1 A comparison of the above results with those of the decomposition inhibited by propylene and isobutylene, which will be reported on in the following paper, suggests that the first term of the rate equation probably represents a molecular decomposition catalyzed by hydrogen sulfide, while the second represents a radical-chain decomposition. Combining the chain mechanism generally accepted for the pyrolysis of acetaldehyde alone with the reactions CH3+H2S=CH4+HS and HS+CH3CHO=H2S+CH3CO, both of which have been shown to be important in the photolysis of acetaldehyde with added hydrogen sulfide, a rate equation is derived by which the second term of the experimental rate equation and the temperature depedennce of its rate constant k′ can be explained.
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