REACTIONS OF FREE RADICALS WITH AROMATICS. III. ISOTOPE EFFECTS IN THE ARYLATION OF DEUTERATED BENZENES. THE MECHANISMS OF ARYLATION

Journal Article · Wed Jun 01 04:00:00 EDT 1960 · Journal of the American Chemical Society (U.S.)

DOI:https://doi.org/10.1021/ja01496a064· OSTI ID:4163829

Eliel, E L; Meyerson, S; Welvart, Z; Wilen, S H

Isotope effects were determined for the free-radical arylation and alkylation of benzene-d and of benzene-cases isotope effects calculated from product deuterium content are in excess of unity. The benzene--benzene-d/sub 6/ mixture recovered from a chlorophenylation experiment (product isotope effect 1.3) is, however, unchanged in isotopic composition, indicating that the addition of the chlorophenyl radical to benzene to form an arylcyclohexadienyl radical is not freely reversible under the conditions of arylation. The product isotope effect is, therefore, ascribed to a competition between arylcyclohexadienyl radicals which go on to product biaryl and radicals which are diverted into side products (such as dimers), this competition being subject to isotopic discrimination. DeTar and Long have shown that arylcyclohexadienyl radicals may disproportionate, at least in dilute solution, into arylbenzenes and aryldihydrobenzenes. In accordance with this it has now been shown that the apparent product isotope effect in biphenyl obtained from benzene-d and benzoyl peroxide in dilute solution is higher when the biphenyl is carefully separated from the dihydrobiphenyl than when the dihydrobiphenyl is allowed to be air- oxidized to biphenyl which becomes commingled with the primary biphenyl product. Biphenyl isolated under the latter circumstances contains biphenyl-d/sib 2, as expected. Biphenyl-d/sub 2/ is formed also in the decomposition of benzoyl peroxide in benzene-d in relatively concentrated solutions, indicating that even under these conditions some biphenyl is formed by disproportionation of the phenylcyclohexadienyl intermediate, followed by dehydrogenation, rather than by direct hydrogen loss from the intermediate radical. (auth)

• Research Organization: Univ. of Notre Dame, Ind.
• Sponsoring Organization: USDOE
• NSA Number: NSA-14-016595
• OSTI ID: 4163829
• Journal Information: Journal of the American Chemical Society (U.S.), Journal Name: Journal of the American Chemical Society (U.S.) Vol. Vol: 82; ISSN JACSA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

AIR
ALKENES
AROMATICS
BENZENE
CHEMICAL REACTIONS
CHEMISTRY
CYCLOALKANES
DEUTERIUM COMPOUNDS
FREE RADICALS
HEXANE
HYDROGEN PEROXIDES
ISOTOPE EFFECTS
ORGANIC COMPOUNDS
OXIDATION
PHENYL RADICALS
POLYPHENYLS
REACTION KINETICS