No abstract

The methyl-radical-induced decomposition of cyclopropane-carboxaldehyde has been studied in the temperature range 100-200°C in order to investigate the use of the aldehyde as a source of cyclopropyl radicals. Decarbonylation of the cyclopropylcarbonyl radical although not complete is extensive and cyclopropyl radicals are produced. Cyclopropyl radicals react by hydrogen atom abstraction from the aldehyde and by Combination with methyl radicals. About 10 % of the cyclopropyl radicals formed react by ring fission to form allyl radicals. These radicals undergo combination reactions with methyl radicals and, to a small extent, abstract hydrogen atoms from the aldehyde. An activation energy of cn. 20 kcal mole-1 has been estimated for the ring fission of the cyclopropyl radical. Arrhenius parameters are reported (based on a value of 1013.34 mole-1 cm3 sec-1 for the rate of combination of methyl radicals) for the following reactions : log A (mole-1 cm3 sec-1) E (kcal mole-1) CH3 + CH3N=N CH3 +CH4+ CH2N=N CH3 11.0 7.9 CH3 + HCO 4 +CH4 + CO 4 12.3 8.7

The reaction of methyl radicals with trideuteromethyl mercaptan has been studied in the temperature range 130-200°C in order to determine the rate at which hydrogen and deuterium atom abstraction occurs. Abstraction of the hydrogen atom is facile, the S-H bond being broken about 120 times faster than is the C-D bond. An unusual feature of the reaction is the abstraction of the mercapto group from the substrate by methyl radicals.Arrhenius parameters (based on a value of 1013.34 mole-1 cm3 sec-1 for the rate of recombination of methyl radicals) have been measured for the reactions :

The thermal decomposition of bicyclopropylformyl peroxide in p-cymene solution has been studied in the temperature range 70-113°C. Values of log A(sec-') = 14.05 and E(kca1 mole-') = 29.8 have been obtained for the Arrhenius parameters for the decomposition reaction : D COO. OCO 0 +2 D COZ. Cyclopropyl radicals are generated by the subsequent decarboxylation of the cyclopropylcarboxyl radicals and dimerize forming bicyclopropyl, and to react by hydrogen atom abstraction with the solvent with an estimated activation energy of 7.3 kcal mole-'.We have studied previously the gas-phase reactions of cyclopropyl radicals, generating them by the methyl-radical-sensitized decomposition of cyclopropane carboxaldehyde and also by the direct photolysis of the aldehyde.2 Our results indicated that cyclopropyl radicals abstracted hydrogen atoms readily from the aldehyde, dimerized to yield bicyclopropyl, isomerized to allyl radicals with an activation energy of ca. 20 kcal mole-l and that cyclopropylcarbonyl radicals were appreciably more stable than other acyl radicals.Bi-acyl peroxides are 3-5 good sources of alkyl radicals, the initial 0-0 bond fission (reaction (1)) being followed by extensive decarboxylation of the acyloxy radical (reaction (2)) thereby generating an alkyl radical :

No abstract