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Phosphate esters are chemical compounds formed by esterifying phosphoric acid with one or more alcohol groups. They include mono-, di-, and triesters, with triesters such as trialkyl phosphates being especially common. The defining feature is a phosphorus center bound to one or more alkoxy or aryl-oxy groups and a phosphoryl group (P=O). The general triester motif is (RO)3P=O, though many derivatives exist with mixed alkyl and aryl substituents or with phosphate derivatives in which oxygen atoms carry additional substituents.

Production and handling typically involve reacting phosphoric acid or phosphorus oxychlorides with alcohols. Industrial routes include the alcoholysis of POCl3 or direct esterification of phosphoric acid, often followed by purification steps to remove inorganic byproducts and residual chlorides. Phosphate esters vary in polarity, volatility, and thermal stability, and their properties depend on the nature of the alcohol components.

These compounds are widely used because of their chemical versatility. They serve as plasticizers for polymers such as PVC, flame retardants in electronics and textiles, lubricants, and solvents or extractants in various chemical processes. Some phosphate esters are also used as intermediates in the synthesis of more complex phosphorus-containing compounds. A subset of phosphate esters falls under organophosphate pesticides, and various derivatives have faced regulatory scrutiny due to toxicity concerns.

Safety and environmental considerations vary by structure. Certain organophosphate esters can inhibit cholinesterase enzymes and pose acute or chronic health risks, leading to regulatory controls and exposure guidelines. Environmental fate depends on the compound’s stability and degradation pathways, with some esters slowly biodegrading while others partition into soils or sediments.