- Zinc dithiophosphate
Zinc dithiophosphates are a family of
coordination compound s 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 andsynthetic oil s used aslubricant s. They come underCAS number CASREF|CAS=68649-42-3. In aftermarket oil additives, the percentage of ZDDP ranges approximately between 2-15% . [Allyson M. Barnes, Keith D. Bartle and Vincent R. A. Thibo “A review of zinc dialkyldithiophosphates (ZDDPS): characterisation and role in the lubricating oil” Tribology International 2001, Pages 389-395. DOI|10.1016/S0301-679X(01)00028-7.]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 CASREF|CAS=84605-29-8. List of other examples with their CAS numbers is [http://apps.kemi.se/flodessok/floden/kemamne_eng/zinkdialkyl_eng.htm here] .
Coordination chemistry
These species are produced in a two steps. First
phosphorus pentasulfide is treated with suitablealcohol s 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 addingzinc oxide ::2 (RO)2PS2H + ZnO → Zn [(S2P(OR)2] 2 + H2OIn Zn [(S2P(OR)2] 2, the zinc is tetrahedral. This monomeric compound also exists in equilibrium with dimers and
oligomer s caused by opening of the four-membered ZnS2P ring. Partial hydrolysis gives the cluster Zn4O [(S2P(OR)2] 6, which adopts the structure seen for basic zinc acetate.Applications
The main use of ZDDP is in anti-wear additives to
lubricant s such as greases, gear oils, andmotor oil s), which contain about 1%. For applications in oils for gasoline engines, zinc and phosphorus emissions could damagecatalytic converter s.The same compounds serve also ascorrosion inhibitor s andantioxidant s.Naming
These compounds are widely used and correspondingly have a numerous names, including ZDDP, ZnDTP, and ZDP.
References
External links
* [http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=1236 Household Product Database]
* [http://www.baileycar.com/oil_additives_html.htm Oil additives]
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