Free radical intermediates in the dissociative adsorption of halogenated hydrocarbons on copper surfaces
Conference
·
OSTI ID:141421
- Columbia Univ., New York, NY (United States)
Because metal-halogen bonds are of comparable strength to carbon-halogen bonds, it is thermodynamically and kinetically feasible to produce organic free radicals during the dissociative adsorption of halogenated hydrocarbons on metal surfaces. The authors have studied this progress for alkyl and aryl halides on atomically-clean, single-crystal copper surfaces under ultra-high vacuum conditions. In the case of CH{sub 3}I on Cu(111), it is found that methyl radicals are ejected from the surface during C-I bond dissociation at 140 K. The majority of the methyl groups, however, are trapped on the surface where they are thermally stable to temperatures above 400 K. For alkyl chlorides and bromides as well as longer chain alkyl iodides, radical evolution into the gas phase is not observed, but intramolecular cyclization reactions by 1,3-dihalopropanes suggest that free radicals are intermediates in these reactions as well. The competition between radical bonding to the copper surface and reaction with other adsorbed species will be illustrated with results for the Ullmann coupling reaction in which iodobenzene is coupled to form biphenyl on a Cu(111) surface.
- OSTI ID:
- 141421
- Report Number(s):
- CONF-930304--
- Country of Publication:
- United States
- Language:
- English
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