Zinc dialkyl dithio phosphate

Zinc dialkyl dithio phosphate (ZDDP, ZnDTP, or ZDP) is a family of zinc salts of dithio organophosphates. They are soluble in nonpolar solvents, so they easily dissolve in mineral and synthetic oils used as lubricants. They come under CAS number. In aftermarket oil additives, the percentage of ZDDP ranges approximately between 2-15%.

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. List of other examples with their CAS numbers is here.

The main use of ZDDP is in anti-wear additives to lubricants (eg. greases, motor oils). To date it is the dominant anti-wear agent, present in most machine and motor oils in amounts of about 1%. However for gasoline engine oil applications the amount of ZDDP has to be minimized; there is concern that zinc and phosphorus emissions could damage catalytic converters,.

ZDDP also has anticorrosive and antioxidant properties.

ZDDP is usually manufactured with dialkyldithiophosphates as intermediates, by a reaction of phosphorus pentasulfide with suitable alcohols. These intermediates are then neutralized by adding zinc oxide, yielding ZDDP.

ZDDP is a known eye irritant, capable of causing severe harm. Protective goggles are recommended when working with mixtures containing high concentration of ZDDP.

One of the zinc-free alternatives lies in using silver-based additives.