Kinetics of the Thermal Decomposition of Dimethylmercury. I. Cyclopentane Inhibition

Abstract

The kinetics of the pyrolysis of gaseous dimethylmercury have been studied in the presence and absence of cyclopentane inhibitor from 290–375°C for the inhibited and 265–350°C for the uninhibited reactions. The decomposition in excess cyclopentane is first order, with methane the major product (accounting for >95% of the carbon). Rate constants are dependent upon the ratio of dimethylmercury (DMM) to cyclopentane and upon total pressure. The constant for DMM loss is: kD=1.1×1015 exp(—55 900/RT) sec—1. The rate constant (from combined data on DMM loss and CH4 formation) extrapolated to the fully inhibited, high‐pressure limit is: k1=5.0×1015 exp(—57 900/RT) sec—1.The data for the uninhibited decomposition agree with the literature; a partial mechanism is suggested which predicts the transition from chain to nonchain behavior with increasing temperature.For the inhibited reaction the following mechanism is proposed: (1) Hg(CH3)2→HgCH3+CH3, (2) HgCH3→Hg+CH3, (3) CH3+Hg(CH3)2→CH4+CH3HgCH2, (4) CH3+C5H10→CH4+C5H9, (5) CH3+Hg(CH3)2→C2H6+HgCH3, (6) 2 CH3→C2H6, (7) CH3HgCH2→HgCH3+CH2.Using the present value of E1=57.9±1.4 kcal/mole in conjunction with known thermochemical data, E2=0±3 kcal/mole. From the inhibition data, k3/k4=0.7±0.2 at 300°C, with a very small temperature coefficient. The inert gas pressure effect is evidence for the unimolecular nature of step (1).