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5.3.25.6.3 Variation 3: Electrolysis of Alkyl Halides at a Zinc Cathode and a Lead Anode

DOI: 10.1055/sos-SD-005-00813

Eagle, P. A. C.Science of Synthesis, (20035786.

Tetraalkylplumbanes are formed in very good yield by the electrolysis of alkyl iodides at a zinc cathode and a lead anode in polar aprotic solvents such as dimethylformamide or dimethyl sulfoxide; which in combination with a supporting electrolyte, lower the internal resistance of the cell compared to ethereal solvents and hence reduce the voltage needed.[‌72‌,‌73‌] Alternatively, alkyl bromides may be used with a catalytic quantity of an alkyl iodide, which has a lower ionization potential, to initiate the reaction.[‌74‌] During the electrolysis, the alkyl halide reacts with the zinc cathode to form unstable alkylzinc intermediates, and these in turn abstract lead from the anode. The use of alkyl iodides alone gives superior yields of tetraalkylplumbanes with respect to lead metal, but far more zinc is consumed compared to the quantity of product formed. Using this method, tetraethylplumbane can be prepared on the laboratory scale in 76% yield, based upon the loss of lead from the anode (Scheme 10).[‌74‌] A hazard associated with the process is the use of the powerful oxidizing agent sodium chlorate(VII) as a supporting electrolyte, and the alternative tetrabutylammonium salts are recommended.

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