Lead Compound, Organic

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.