- Photobromination of C2H5Cl in the Presence of C2H6. The Heat of Formation of the CH3CHCl Radical and the D0 (CH3CHCl-H) Bond Dissociation Energy
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The gas-phase photobromination of C2H5Cl in the presence of ethane as competitor has been studied between 32 and 95 deg C at total reactant pressures of ca. 32 Torr and sevenfold hydrocarbon excess over bromine.Under these conditions hydrogen abstraction by bromine atoms from C2H5Cl occurs almost exclusively from the CH2Cl group.Over the temperature range stated, the relative rate constants conform to an Arrhenius rate law, which combined with the known rate parameters for ethane, log (A/cm3 mol-1 s-1) = 14.135 +/- 0.056, E = 13.66 +/- 0.14 kcal mol-1, yield for the abstraction of secondary hydrogen in CH3CH2Cl k1/cm3 mol-1 s-1 = 1E12.182+/-0.091 exp-1)/RT>.From an analysis of kinetic and thermochemical data on these and related compounds in the literature the following radical heats of formation and C-H bond dissociation energies are deduced: ΔHf0(CH3CHCl) = 16.75 +/- 1.0; D0(CH3CHCl) = 1.0; ΔHf0(CH3CHF) = -17.7 +/- 1.1; and D0(CH3CHF-H) = 97.3 +/- 1.1 kcal mol-1.
- Tschuikow-Roux, E.,Salomon, D. R.
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- Preparation des α-monohalogenoalkyllithiums non fonctionnels
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The preparation of very unstable α-monohaloalkyllithiums (carbenoids), potential electro- and nucleophiles, from easily accessible gem-halogenated alkanes, by halogen-lithium exchange at low temperatures is described.R-CHXLi type carbenoids (R aryl, H or CH3 ; X = Cl, Br) are obtained by bromine-lithium exchange in a THF-ether-pentane mixture at temperatures below -115 deg C.The α-silylated organolithiums Me3SiCXLiR (R = H, alkyl; X = Cl, Br) despite their greater stability, must be prepared at the same temperature; secondary reactions are limited by the use of an inverse addition of secondary butyllithium.CH2XLi an RCXLiMe carbenoids (R = H, CH3 ; X = Cl, Br) have to be prepared in the presence of one equivalent of lithium bromide in order to reduce the halogen-lithium carbenoid interaction which is responsible for their instability.
- Villieras, Jean,Tarhouni, Radhouane,Kirschleger, Bernard,Rambaud, Monique
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p. 825 - 830
(2007/10/02)
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