Organolead compounds are compounds with carbon-lead bonds in their molecules. The first synthetic organic lead compound is hexaethyl diphosphate, synthesized in 1858, where the lead is tetravalent and bonded to three carbon atoms. In organic chemistry, the dominance of Pb(IV) in organolead chemistry is remarkable, which is quite special because divalent lead is more often found in inorganic lead compounds. The reason for this is that the electronegativity of lead in inorganic lead compounds is lower than that of nitrogen, oxygen, and halogen, and the partial positive charges on the lead atoms leads to a stronger contraction of the 6s orbital than the 6p orbital, which is known as inert pair effect.
Applications
Organic chemistry: Organolead triacetates have been developed as inexpensive and versatile reagents for electrophilic arylation, alkynylation and vinylation of carbon nucleophiles. Their reaction with phenols and dicarbonyls illustrates their regioselectivity, which shows a significant preference for the generation of quaternary carbon centers. This unique aspect of their reactivity has been used in many natural product syntheses and can lead to the formation of highly hindered structures. For example, reactions occur with vinyllead and alk-1-ynyllead triacetates can yield products with comparable synthetic potential.
Industry: Tetraethyllead is widely used as an additive to gasoline to increase the car's engine efficiency and power. Gasoline-fueled reciprocating engines require fuel with a sufficient octane rating to prevent uncontrolled combustion known as engine knock, and allow the use of higher compression ratios of antiknock agents to increase efficiency and peak power. The greatest advantage of tetraethyllead compared to other antiknock agents or high-octane gasoline blends is that it requires only very low concentrations to increase the octane number of the fuel. The typical addition method is to add a volume of ethyl liquid (containing tetraethyllead) to a volume of 1260 parts of untreated gasoline. Other antiknock agents must be added at higher concentrations. At the same time, alcohol is used as an antiknock agent, but bio-contamination problems can occur with high humidity of the fuel, which can cause bacterial reproduction as some bacteria could multiply on the surface of water and gasoline. Tetraethyllead toxicity helps prevent fuel pollution and bacterial growth
Material chemistry: Polyvinyl chloride (PVC) is general-purpose plastic; however, PVC has poor thermal stability during molding. Thus adding heat stabilizer and lubricant is indispensable in PVC processing. Organolead compounds have been reported as a promising lubricant.
Fig.1. Organolead triacetates in organic synthesis.
Reference
- Pinhey J T. Organolead (IV) triacetates in organic synthesis[J]. Pure and applied chemistry, 1996, 68(4): 819-824.
