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7954884 
Journal Article 
ROLE OF REVERSIBLE HYDROGEN ABSTRACTION IN MECHANISM OF BROMINATION OF CYCLOHEXANE - COMPARISON OF DIFFERENCES BETWEEN LIQUID AND VAPOR-PHASE REACTIONS 
Tanner, DMB; Pace, RH; Marsh, KN 
1975 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
97 
15 
4303-4307 
English 
WOS:A1975AK26900027 
The role of reversible hydrogen abstraction in the bromination of cyclohexane has been investigated by a study of the kinetics of the bromination of perdeuteriocyclohexane in the presence of large amounts of hydrogen bromide and molecular bromine. By a determination of the relative rate constants for transfer of the radical with the two transfer agents, bromine (k2) and hydrogen bromide (k-1), a ratio of rate constants k2/k-1 could be obtained. In solution at 30° k2/k-1 varied depending upon the concentration of molecular bromine and hydrogen bromide, while in the vapor phase, 20-28°, (k2/k-1) = 2.81 ± 0.06 at all concentrations. The change in the ratio of transfer rates in solution and their difference from the vapor phase value is attributed to a complex formation between hydrogen bromide and molecular bromine, the complex acting as a transfer agent at a faster rate (k′-1) than hydrogen bromide itself. The ratio of transfer rates for the solution reaction of bromine relative to HBr3, k2/k′-1, is approximated, (k2/k-1)vP/(k′-1/k -1) = 0.13, and found to be in good agreement with the values obtained at high bromine concentration. Cage return of the radical with hydrogen bromide as a kinetically masked process in the bromination reaction is also discussed.