Lead Compound, Organic

any of the compounds whose molecules contain a carbon—lead (C—Pb) bond; organic compounds are characteristic of Pb(IV). The principal types of organic lead compounds are R₄Pb, R₃PbX, R₂PbX₂, RPbX₃, R₂PbO,

and R₃Pb—PbR₃, where R is an organic radical and X is an acid residue. Lower-molecular-weight alkyl derivatives of organic lead compounds of the R₄Pb and R₃Pb—PbR₃ type are liquids; aromatic derivatives and all other types are solids.

There are two principal methods of obtaining organic lead compounds. The first involves the reaction of Pb salts with organic compounds of magnesium, lithium, or mercury:

4RMgX + 2PbX₂ → R₄Pb + Pb + 4MgX₂

R₂Hg + Pb(OCOCH₃)₄ → R₂Pb(OCOCH₃)₂ + Hg(OCOCH₃)₂

The second method involves the treatment of PbNa alloy with alkyl halides; this method is used in the industrial preparation oftetraethyllead:

4PbNa + 4C₂H₅Cl → Pb(C₂H₅)₄ + 4NaCl + 3Pb

Organic lead compounds are readily oxidized and decomposed by the acids and salts of certain metals:

R₄ + HX → R₃PbX + RH

R₄Pb + HgX₂ → R₃PbX + RHgX

Organic lead compounds decompose upon heating to yield metallic Pb and free radicals. This property enables Pb(C₂H₅)₄to be used as an additive to motor fuel to prevent knocking. Organic lead compounds, the aliphatic types in particular, are highly toxic.