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Iodine catalyzed pyrolysis of dimethyl sulfide. Heats of formation of CH3SCH2I, the CH3SCH2 radical, and the pibond energy in CH2S

✍ Scribed by Lilian G. S. Shum; Sidney W. Benson

Publisher: John Wiley and Sons
Year: 1985
Tongue: English
Weight: 621 KB
Volume: 17
Category: Article
ISSN: 0538-8066
DOI: 10.1002/kin.550170305

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✦ Synopsis

A kinetic study has been made of the gas phase, I,-catalyzed decomposition of (CH&S at 630-650 K. Some I, is consumed initially, reaching a steady-state concentration. The initial major products are CH4 and CH,S together with small amounts of CH3SCHZI, CHSI, HI, and CS2. The initial reaction corresponds to a pseudo-equilibrium: CH,SCH, + I, & CH,SCH,I + HI accompanied by: CH3SCH21 CHJ + SCH, and CHJ + HI -CH, + I, which brings (I2) into steady state and a final complex reaction: 2 SCH, CS2 + CHI From the initial rate of Iz loss it is possible to obtain Arrhenius parameters for the iodination: I + (CH,),S + HI + CHzSCHB CH,SCH~ + I, I + ICH,SCH,

We measure k , (644 K) = 150 L/mol s and from both the Arrhenius plot and independent estimates A , (644 K) = 10" *'03 L/mol s. Thus, El = 26.7 2 1 kcal/mol. From the steady-state I2 concentration, an assumed mechanism and the known rate parameters for the CH,I/HI system. It is possible to deduce K A (644) = 3.8 x lo-' with an uncertainty of a factor of 2. Using an estimated AS: (644) = 4.2 ? 1.0 e.u. we find AHA ( 6 4 4 ) = 7.0 2 1.1 kcal. With ( A C p A ) 6 4 4 = 1.2 this becomes: A H A , 2 9 R , = 6.6 ? 1.1 kcal/mol. Then (CH,SCH,I) = 6.3 I 1 kcal/mol. Making the assumption that E -] = 1.0 2 0.5 kcal/mol we find AH: (644) = 25.7 2 0.7 kcal/mol and with

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