Structure of a monomeric zinc dialkyldithiophosphate
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 a dialkyldithiophosphoric acid (e.g.
ammonium diethyl dithiophosphate). These uncharged compounds are not salts. They are soluble in
nonpolar solvents, and the longer chain derivatives easily dissolve in
synthetic oils used as
lubricants. They come under
CAS number 68649-42-3. In aftermarket oil additives, the percentage of ZDDP ranges approximately
between 2–15%. Zinc dithiophosphates have many names including ZDDP, ZnDTP, and ZDP..
The main application of ZDDPs are as
anti-wear additives in
hydraulic oils, and
motor oils. ZDDPs also act as
corrosion inhibitors and
antioxidants. They are almost ubiquitous in
lubricants and treatment rates are usually between 600 ppm for modern, energy conserving low viscosity oils to 2000 ppm of this additive in some racing oils.
It has been reported that zinc and phosphorus emissions may damage
catalytic converters and standard formulations of lubricating oils for gasoline engines now have reduced amounts of the additive due to the API limiting the concentration of this additive in new API SM and SN oils, however this only affects 20 and 30 grade
"ILSAC" oils, 40 and higher grades have no regulation regarding the concentration of ZDDP except for diesel oils meeting the API CJ-4 specification which have had the level of zddp reduced slightly, although most diesel Heavy Duty Engine oils still have a
higher concentration of this additive. Crankcase oils with reduced ZDDP have been cited as causing damage to, or failure of, classic/collector
car flat tappet camshafts and lifters which undergo very high boundary layer pressures and/or shear forces at their contact faces, and in other regions such as big-end/main bearings, and piston rings and pins. Roller
camshafts/followers are more commonly used to reduce camshaft lobe friction in modern engines.
There are additives, such as STP(R) Oil Treatment, and some racing oils such as PurOl, Brad Penn and Valvoline VR-1, which are available in the retail market with the necessary amount of ZDDP for engines using increased valve