Zinc dithiophosphate
Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s that feature zinc bound to the anion of dithiophosphoric acid. These uncharged compounds are not salts. They are soluble in nonpolar solvents, and the longer chain derivatives easily dissolve in mineral and synthetic oils used as lubricants. They come under CAS number
The alkyl groups can be branched and linear alkanes between 1-14 carbons length, 2-butyl, pentyl, hexyl, 1,3-dimethylbutyl, heptyl, octyl, isooctyl (2-ethylhexyl), 6-methylheptyl, 1-methylpropyl, dodecylphenyl, and others. A mix of zinc dialkyl(C3-C6)dithiophosphates come under CAS number
These species are produced in two steps. First phosphorus pentasulfide is treated with suitable alcohols to give the dithiophosphoric acid. A wide variety of alcohols can be employed, which allows the lipophilicity of the final zinc product to be fine-tuned. The resulting dithiophosphate is then neutralized by adding zinc oxide:
In Zn[(S2P(OR)2]2, the zinc is tetrahedral. This monomeric compound also exists in equilibrium with dimers and oligomers caused by opening of the four-membered ZnS2P ring. Reaction with additional zinc oxide gives rise to the oxygen-centered cluster, Zn4O[(S2P(OR)2]6, which adopts the structure seen for basic zinc acetate.
These compounds are also able to form coordination polymers. For example, zinc diethyldithiophosphate, Zn[(S2P(OEt)2]2, crystallizes as a polymeric solid consisting of linear chains.
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