Iodoethane, reaction with zinc

Gomberg was the first to characterize a free radical when, in 1900, he generated triphenylmethyl radical 5 by reacting chlorotriphenylmethane (4) with zinc metal.l Triphenylmethyl radical 5 is unusual in that it is quite stable and its formation is probably the first experimental verification of a free radical. Frankland, however, may have been the first to generate transient methyl and ethyl radicals in the reaction of iodomethane and iodoethane with zinc, in 1849.2 In the last 30 years, attention has been focused on radicals, their reactivity, and their applications to organic synthesis. Excellent monographs by Davies and Parrott, Lazar et al., Hay, ... 

Pebal 1861. A further six years passed before Pebal [5] discovered the general method for the preparation of organozinc compounds. Instead of sealed tubes and by using diethyl ether as the solvent alkylzinc reagents could be synthesized in ordinary laboratory glassware. He demonstrated this for the reaction of iodoethane with zinc which had first been activated by reaction with sulfuric acid. 

Among the earliest reports of such specialist s tricks to promote a smooth procedure in which an organo halide and a metal were involved, was Pebal s publication on the preparation of diethylzinc in 1861 [1] (see Sect. 1.2.2, p. 3). For the reaction of iodoethane with zinc in diethyl ether he used zinc that had first been etched ( angeatz") with sulfuric acid, washed and carefully dried. 

Alloys with Metals. In the beginning of this chapter reference was made to Pebal s [1] advice, in 1861, to activate zinc by etching with sulfuric acid, for its reaction with iodoethane. 

Rieth and Beilstein 1862. One year later, Rieth and Beilstein [6] reported a facile and productive synthesis of diethylzinc by reaction of iodoethane with a 4 1 zinc/sodium alloy without solvent under an atmosphere of carbon dioxide. 

Meanwhile Frankland had been pursuing his own attempts to isolate free radicals. His method was to react together a metal with an organic cyanide or halide in the hope that combination would occur between the metal and the halide or cyanide, leaving the organic radical in the free state. The most important experiments involved zinc and ethyl iodide (iodoethane). The reactions occurring in terms of modem equations are ... 

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