Tri-ortho-cresyl phosphate
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| Names | |
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| Other names
tricresylphosphate, tri-o-cresyl phosphate, TOCP, tritolyl phosphate, tolyl phosphate, tri-o-tolyl ester of phosphoric acid
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.014.136 |
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| Properties | |
| C21H21O4P | |
| Molar mass | 368.37 g/mole |
| Appearance | colourless liquid |
| Melting point | −40 °C (−40 °F; 233 K) |
| Boiling point | 255 °C (491 °F; 528 K) (10 mmHg) |
| Hazards | |
| Flash point | > 225 °C (437 °F; 498 K) |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Tricresyl phosphate, abbreviated TCP, is an organophosphate compound that is used as a plasticizer and diverse other applications. It is a toxic substance that causes neuropathy through ingestion, and has been the cause of several mass poisonings in history. It is a colourless, viscous liquid, although commercial samples are typically yellow. It is virtually insoluble in water.
Tricresyl phosphate is manufactured by reaction of cresols with phosphorus oxychloride:
The cresol is a mixture of three isomers (ortho, meta, and para). The fact that tricresyl phosphate is derived from a mixture and itself is a mixture ensures that it remains liquid over a wide span of temperatures.
Tri-o-cresyl Phosphate poisoning is characterized by numbness of the legs and hands accompanied by weakness or paralysis of these regions, though all symptoms usually only occur after a latency period of 2–3 days. If the dose is substantial, gastrointestinal distress may occur immediately, and the latency period may be shortened. 10 to 40 days after the onset of numbness, there is a potential for abrupt flaccid paralysis of the toes, feet, and lower parts of the leg, which may be followed by paralysis of the fingers and hands after 4 to 5 additional days. Fatalities are rare, but there is potential for permanent paralysis, due to death of nerve cells and damage to myelin sheaths.
Of the three tricresyl phosphate isomers, only the ortho isomer demonstrates high toxicity, though this toxicity has been demonstrated to be caused by a metabolite that is made from tri-ortho-cresyl phosphate (TOCP). This metabolite is 2-(ortho-cresyl)-4H-1,3,2-benzodioxaphosphoran-2-one (CBDP) and is an irreversible inhibitor of human butyrylcholinesterase (BChE) and human acetylcholinesterase (AChE). CBDP ultimately binds to the BChE and AChE at a serine residue in the active site after two consecutive dealkyalation reactions (aging). Though CBDP readily inhibits BChE and AChE, BChE has a sensitivity to CBDP that is nearly one order of magnitude greater than that of AChE. The inhibition of cholinesterases causes a build up in cholines that would have been broken down by the esterase. The build up of cholines causes an over-activity of neurons, ultimately causing them to function abnormally, or not at all.
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