Mechanistic Investigations of Zero-Valent Metal Reactions with Organohalides
Abstract
Mechanisms of organohalide reactions with zero-valent metals in aqueous solution were examined in batch reactors. Of particular interest were questions of concertedness of electron transfer; reaction kinetics and pathways (especially the extent to which reductive alpha and beta elimination competed with stepwise hydrogenolysis); and correlations between reactivity and reduction potentials. Results with probe compounds (vicinal dibromide stereoisomers and alkyl monobromide free radical "docks") suggested that reactions might be initiated by transfer of a single electron, but that transfer of a second electron was so fast that free alkyl radical intermediates were unlikely to undergo such characteristic reactions with dissolved species as dimerization and hydrogen atom abstraction. Chlorinated ethylenes react with both zinc and iron to a significant extent via reductive beta-elimination. For zinc rate constants for chloroethylene reduction increase with one- or two-electron reduction potential, while for iron, the reverse situation occurs. Substantial intra- and interspecies competitive effects were observed for iron, requiring the use of a Langmuir-Hinshelwood model. 1,1,1-Trichloroethane also reacts with zinc and iron (and also with two bimetallic reductants, copper/iron and nickel/iron) to a significant extent via reductive alpha-elimination pathways. Evidence suggests in some cases reactions may proceed via organometallic intermediates.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 10, 1999
- Accession Number
- ADA378793
Entities
People
- A. L. Roberts
- J. P. Fennelly
- L. A. Totten
- U. Jans
- W. A. Arnold
Organizations
- Johns Hopkins University