ORGANO-METALLIC COMPOUNDS are chemical substances containing a metal or metalloid in direct association with one or more hydrocarbon radicals. These compounds never arise by natural processes in the vegetable and animal kingdoms, being produced synthetically by the art of the chemist. They have played an important part in the development of modern chemistry and among them are several substances of great prac tical utility. Lead tetraethyl (see p. 898), a most effective anti detonant in motor gasolene or petrol, and salvarsan, a specific remedy in syphilis, are two outstanding examples of organo metallic compounds of proven worth. Included in this group of carbon compounds are the organic derivatives of magnesium known after their discoverer as Grignard reagents (q.v.). The application of these reagents in chemical synthesis has proved to be one of the most fruitful and far-reaching improvements in practical organic chemistry since the end of the 19th century.
Brief references to organo-metallic compounds have been given under the headings of certain of the metals and metalloids, and the present article affords a general survey of the whole group. The arrangement adopted below follows the natural sequence of the elements according to the periodic law (q.v.).
First Series. Alkali Metals.—Although the production of alkyl derivatives of sodium was claimed by Buckton in 1859, the existence and properties of these substances remained doubtful until comparatively recently (W. Schlenk and 1913-17). Lithium ethyl, is prepared by the action of metallic lithium on mercury diethyl ; it crystallizes from benzene or high boiling petroleum in colourless, six-sided plates melting at 95° C. Lithium methyl, Li.CH3, and lithium phenyl, are crystal line powders obtained by double decomposition between lithium ethyl and mercury dimethyl and diphenyl respectively (Schlenk and Holtz, 1917). Sodium triphenylmethyl, a con venient starting point in the preparation of simpler sodium alkyls, is obtained by the action of 1% sodium amalgam on triphenyl chloromethane, dissolved in dry ether in an at mosphere of oxygen-free nitrogen. The product, a brownish-red
substance, when allowed to react with mercury dimethyl in inert media, furnishes sodium methyl, Na.CH3, as a white powder which burns in air with explosive rapidity. Sodium ethyl, sodium n-propyl, and sodium phenyl, are colourless solids having similar properties.
Currency Metals.—Cuprous phenyl, Cu.C6H5, obtained by the interaction of cuprous iodide and magnesium phenyl bromide in ethereal solution, is a white powder decomposing at 8o° C into copper and diphenyl. Silver phenyl, an even more un stable substance obtained from phenyl magnesium bromide and silver bromide, is a yellow solid, exploding on rubbing, on gentle warming or on treatment with acids.
An ethereal solution of auric bromide and magnesium ethyl bromide yields on evaporation colourless crystalline diethylauric bromide, (C2H5)2AuBr, melting at 58° C and exploding at 7o° C. Bromine in chloroform converts this monobromide into the ruby-red ethylauric dibromide, (W. J. Pope and C. S. Gibson, 1907).