The reduction of alkyl halides at a lead cathode in dimethylformamide

✍ Scribed by M. Fleischmann; D. Pletcher; C.J. Vance

• Publisher: Elsevier Science
• Year: 1971
• Weight: 498 KB
• Volume: 29
• Category: Article
• ISSN: 0022-0728
• DOI: 10.1016/s0022-0728(71)80094-3

✦ Synopsis

A wide range of metal alkyls has now been prepared electrochemically 1-3. In general, the synthetic procedures involve the electrochemical generation of radicals, either by the reduction of alkyl halides or the oxidation of carbanionic species, at a sacrificial metal electrode. Much of the effort in this field has been concentrated on the study of possible methods of preparation of lead tetraethyl and lead tetramethyl because of their continued use as anti-knock additives in the petroleum industry. Thus, the reactions

have been studied as routes for the synthesis of lead alkyls 4-8. There have been recent reports on the first reaction in propylene carbonate 4,s and in acetonitrile6; in this paper we present the results of a study of the same reaction in dimethylformamide. It will become apparent that this change in solvent has a marked effect on the mechanism and kinetics of the cathodic reduction of alkyl halides; furthermore, the change also gives improved conditions for the production of lead alkyls.

EXPERIMENTAL

Chemicals

Dimethylformamide was B.D.H. Ltd. reagent grade and was purified by two vacuum distillations. On the first occasion it was distilled from anhydrous sodium carbonate in order to remove acidic impurities.

Tetraethylammonium perchlorate was obtained from Eastman Kodak Ltd. and was dried at 100°C in a vacuum oven. The other perchlorates were prepared by the reaction of their carbonates with AnalaR perchloric acid, crystallised from water and dried in vacuo at 100°C. Sodium bromide and sodium iodide were B.D.H. Ltd., AnalaR grade and were dried at 150°C in a vacuum oven. The alkyl halides were reagent grade and were used without purification. The cathodes were made from lead supplied by Johnson Matthey Ltd. (spectrographically standardised grade).