Organozinc Compounds

metallo-organic compounds containing a zinc-carbon bond. There are both complete organozinc compounds, R₂Zn, and mixed organozinc compounds, RZnX, where the R are identical or different hydrocarbon radicals, for example, CH₃, C₂H₅, CH₂=CH, or C₆H₅, and X is an acid residue, most often, Br or I.

Organozinc compounds were first synthesized by E. Frankland in 1849 in the reaction of zinc with alkyl iodides: Zn + RI → RZnI. The mixed organozinc compounds formed are symmetrized upon heating: 2RZnI→ R₂Zn + Znl₂. This method is still important today. Another method for the synthesis of organozinc compounds is the alkylation of zinc chloride by reactive metalloorganic compounds of lithium, magnesium, and aluminum: 2RMgX + ZnCl₂ → R₂Zn + 2MgClX. A third method involves the reaction of zinc with dialkylmercury or arylmercury: Zn + R₂Hg → R₂Zn + Hg.

Organic compounds are either liquids, such as diethylzinc, (C₂H₅)₂Zn, with a boiling point of 116.8°C, or solids, such as diphenylzinc, (C₆H₅)₂Zn, with a melting point of 107°C. They are unstable in the presence of air, so much so that the lower members of the R₂Zn series (up to R = C₅H₁₁) ignite spontaneously. They are vigorously decomposed by water. Thus, their reactions are carried out in an inert atmosphere of nitrogen, argon, or carbon dioxide. The chemical properties of organozinc compounds are similar to those of other metallo-organic compounds of the transition metals, although organozinc compounds are less reactive than organolithium and organomagnesium compounds. Therefore, organozinc compounds are used in the synthesis of ketones, ketoethers, and hydrocarbons with a quarternary carbon atom. Organozinc compounds form donor-acceptor complexes with dioxane, ether, and olefinic oxides, for example, ZnR₂· C₄H₈O₂ and RZnX· O(C₂H₅)₂; with alkyl and hydride compounds of alkali and alkaline-earth metals, they form saltlike complexes, for example, MeZnR₃, Me₂ZnR₄, and MeZnR₂H, where Me is an alkali metal.

The Kazan school of Russian chemists, headed by A. M. Butlerov, made important contributions to the development of the chemistry of organozinc compounds (see, for example, ZAITSEV REACTION). Organozinc compounds are intermediate products in the production of β-hydroxy carboxylic acids (seeREFORMATSKY REACTION) and cyclopropane hydrocarbons. They are used as catalysts for the polymerization of olefinic oxides and carbonyl compounds. However, organozinc compounds are of little industrial significance.