Rate constants for the reaction of tert‐butyl radicals with chloroform in solution

Abstract

The decay of photochemically generated tert -butyl radicals in methylcyclopentane solutions containing chloroform is studied by time-resolved ESR spectroscopy. In the pure solvent it perfectly follows the second-order rate law for radical self-termination. Increasing chloroform concentrations cause increasing admixture of a pseudo-first-order decay from which the rate constant of the title reaction is obtained.

Effects of diffusion on the self‐termination kinetics of isopropylol radicals in solution

“…Similar low A factors were found for hydrogen abstraction reactions of the tert-butyl radical [24,35]. Rate constants 2kt of the self-reaction of isopropylol have previously been reported by several groups of authors [16,17,.…”

Photolysis of carbon tetrachloride in the presence of alkanes

“…The absence of termination products involving tertiary butyl radicals precludes a direct estimate of the rate constant for chlorine atom abstrac-tion from C C 4 by t-C4H9 radicals. In solution it appears that the rate constant for chlorine atom abstraction by alkyl radicals increases with increasing a-alkyl substitution of the attacking carbon-centered radical [21]. Thus the rate constant at 25OC for chlorine atom abstraction from C C 4 by the tertiary butyl radical is over three orders of magnitude faster than the corresponding rate constant for the methyl radical [21].…”

“…In solution it appears that the rate constant for chlorine atom abstraction by alkyl radicals increases with increasing a-alkyl substitution of the attacking carbon-centered radical [21]. Thus the rate constant at 25OC for chlorine atom abstraction from C C 4 by the tertiary butyl radical is over three orders of magnitude faster than the corresponding rate constant for the methyl radical [21]. The absence of termination products involving the t-C4Hg radical in the gas phase photolysis of CC4-isobutane mixtures may simply reflect the facile nature of reaction (3).…”

Rate constants for the bimolecular self‐reaction of cyano‐substituted alkyl radicals in solution

“…Dutsch and Fischer [22] have demonstrated the possibility of extracting first-and second-order rate constants from the time profile of the ESR signal intensity. This encouraged us to fit our decay data to the rate law (9) [23], describing the decay reactions (6) and (7):…”

“…In most cases the leastsquares fit to the mixed-decay law is better than to the pure-second-order decay law. Taking into account the relatively broad error limits of some data points, the rate constants are very reasonable for first-and secondorder parallel reactions of this type [22]. The Arrhenius plot of the second-order rate constants yields EA = 11.3 f 2.1 kJ/mol [log A (M-l-s-l) = 11.2 f 0.41 for the dimerization reaction of cyanomethyl, in good agreement with the 12.6 kJ/mol expected from the temperature dependence of the solution viscosity.…”