Zinc dialkyl dithiophosphates

December 09, 2019
We are a key to making your engine run smoothly.
What molecules are we?

Zinc dialkyl dithiophosphates (ZDDPs) are very effective antiwear agents that are used as machine lubricants (e.g., greases, hydraulic oils, and motor oils), including applications in the automotive industry.

According to a 2004 article by Hugh Spikes at Imperial College London, ZDDPs were developed in the 1940s. Today, they are still by far the most prevalent antiwear additive in heavy equipment and off-road vehicle engine oils. They are not used in passenger vehicles because the phosphorus in ZDDPs prematurely disables catalytic converters in exhaust systems.

On paper, ZDDPs look like zinc salts, but their properties much more closely resemble those of organic compounds. As an example, they are soluble in nonpolar organic solvents, including oils, and are insoluble in water.

Zinc dibutyl dithiophosphate, shown in the images and information tables, is a typical ZDDP. But commercial ZDDPs almost always contain a mixtures of alkyl groups, ranging from C4 to C12. The specific mixture used depends on the type of lubricant and metallurgy involved. Shorter-chain alkyl groups, however, are the least thermally stable; they thus make protective films more easily.

Currently, concerns over ZDDPs’ environmental effects are driving efforts to curtail or eliminate their use. But no one has found a substitute that performs quite as well; and how harmful ZDDPs actually are at the level of usage is the topic of some rather heated discussions among lubricant formulators, vintage car enthusiasts, and environmental advocacy groups.

[Many thanks to Nancy McGuire for assistance with this article—ED].

Zinc dialkyl dithiophosphates hazard information

GHS classification*: serious eye damage/eye irritation, category 2A
H319—Causes serious eye irritation Chemical Safety Warning
GHS classification: hazardous to the aquatic environment, long-term hazard, category 2
H411—Toxic to aquatic life with long-lasting effects Chemical Safety Warning

**Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

Zinc dialkyl dithiophosphates fast facts

CAS Reg. No. 6990-43-8
Empirical formula C16H36O4P2S4Zn
Molar mass 548.07 g/mol
Appearance Oily solid or liquid
Melting point 36.8 ºC
Boiling point 303.7 ºC
Water solubility Insoluble
Chemical Abstract Service - a division of ACS

Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

Molecule of the Week needs your suggestions!

If your favorite molecule is not in our archive, please send an email to motw@acs.org. The molecule can be notable for its current or historical importance or for any quirky reason. Thank you!

Stay Ahead of the Chemistry Curve

Learn how ACS can help you stay ahead in the world of chemistry.

Find Out More