Triphenyl phosphate

Chemical properties

Triphenyl phosphate (TPP) is a colorless crystalline powder with a faint, phenol-like odor. Triphenyl phosphate is practically insoluble in water at 1.9 × 10 7 mg/l at 24 °C (Yalkowsky et al., 2010). It is very soluble in carbon tetrachloride (Haynes, 2010) and is soluble in most lacquers, solvents, thinners, and oils, as well as in alcohol, benzene, ether, chloroform, and acetone (Lewis, 1996). It begins to decompose at about 600 °C in inert gas, and in a large excess of air, complete combustion to carbon dioxide occurs in the range 800–900 °C (Lhomme et al., 1984). Hydrolysis of TPP occurs very slowly in acidic or neutral solutions, but occurs rapidly in alkaline solutions (Barnard et al., 1966).

The Uses of Triphenyl phosphate

Triphenyl phosphate is known as a product with manifold fields of applications regarding its qualities in particular as a flame retardant. One primary use is as a flame retardant in phenolic- and phenylene oxide-based resins for the manufacture of electrical and automobile components, for auto upholstery, and as a nonflammable plasticizer in cellulose acetate for photographic films. It has also been used to impregnate roofing paper. Triphenyl phosphate occurs as a plasticizer in various lacquers and varnishes (O'Neil, 2006), and as a component of lubricating oil and hydraulic fluids (ACGIH, 2012).

Definition

ChEBI: Triphenyl phosphate is an aryl phosphate resulting from the formal condensation of phosphoric acid with 3 mol eq. of phenol. It has a role as a flame retardant and a plasticiser. It is functionally related to a phenol.

What are the applications of Application

Triphenyl Phosphate is used in the insecticidal composition. It is also use in hydraulic liquids, and adhesives, inks, coatings, as a plasticizer in lacquers and varnishes, and as a substitute for camphor in celluloid materials to make the latter stable and fireproof.

Preparation

Triphenyl phosphate is prepared by reacting phosphorus pentoxide and phenol (Budavari, 2001), or by reacting phosphorus oxychloride and phenol (Snyder, 1990). On a larger scale phosphorus oxychloride and phenol are reacted in an esterification tank with heating. The HCL formed is trapped and condensed, while the crude triphenyl phosphate runs into a large tank where it is purified.

Reactivity Profile

Organophosphates, such as Triphenyl phosphate, are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.

Hazard

Toxic by inhalation. Cholinesterase inhibitor. Questionable carcinogen.

Health effects

Non-industrial:
An allergic reaction in a 67-year old woman to spectacle frames containing triphenyl phosphate was reported. Patch tests with analytical grade triphenyl phosphate in that individual indicated a reaction at concentrations as low as 0.05%. This observation was confirmed in another male patient (Carlsen et al 1986).
Industrial:
Occupational exposure of men engaged in manufacturing triphenyl phosphate produced a statistically significant reduction in erythrocyte acetylcholinesterase activity and plasma cholinesterase activity. There was no evidence of adverse clinical effects in men exposed to triphenyl phosphate for as long as 10 years. Exposure was to triphenyl phosphate mist, vapor, and dust at a weighted average air concentration of 3.5 mg/m3 (Sutton et al 1960).

Fire Hazard

Noncombustible solid. Incompatibility— none.

Safety Profile

Poison by subcutaneous route. Moderately toxic by ingestion. Absorbed slowly, particularly by skin contact. Not a potent cholinesterase inhibitor. Combustible when exposed to heat or flame. To fight fire, use CO2, dry chemical. When heated to decomposition it emits toxic fumes of POx. See also TRITOLYL PHOSPHATE.

Potential Exposure

Triphenyl phosphate is used to impregnate roofing paper and as a fire-resistant plasticizer in plastics; for cellulose esters in lacquers and varnishes. Used in making adhesives, gasoline additives; flotation agents; insecticides, surfactants, antioxidants, and stabilizers. A substitute for camphor.

Source

Triphenyl phosphate was identified as a component in outer covers of brand-new computer video display units. Concentrations were estimated to be 8 to 10 and 0.3 to 0.5 wt % in 4 and 6 video display units, respectively. The concentrations of triphenyl phosphate in the remaining 8 video display units were <0.02 wt % (Carlsson et al., 2000).

Environmental Fate

Chemical/Physical. When an aqueous solution containing triphenyl phosphate (0.1 mg/L) and chlorine (3 to 1,000 mg/L) was stirred in the dark at 20 °C for 24 h, the benzene ring was substituted with one to three chlorine atoms (Ishikawa and Baba, 1988). The reported hydrolysis half-lives at pH values of 8.2 and 9.5 were 7.5 and 1.3 d, respectively (Howard and Doe, 1979).
Decomposes at temperatures greater than 410 °C (Dobry and Keller, 1957)

Metabolism

Rat liver microsomal enzymes degraded triphenyl phosphate in the presence of NADPH, but also in the absence of NADPH. The product of incubation was diphenyl phosphate. It was clear that the reaction was cytochrome P-450-linked since the reaction was inhibited by carbon monoxide (Sasaki et al 1984). Goldfish liver microsomes metabolized only about 10% of triphenyl phosphate (Sasaki et al 1985). Houseflies treated with triphenyl phosphate were analyzed after 24 h and the presence of diphenyl p-hydroxyphenyl phosphate was confirmed (Eto et al 1975).

Shipping

UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous hazardous material, Technical Name Required.

Purification Methods

Crystallise the phosphate from EtOH or pet ether (b 60-80o)/EtOH. [Cox & Westheimer J Am Chem Soc 80 5441 1958, Krishnakumar & Sharma Synthesis 558 1983, Cherbuliez in Organo Phosphorus Compounds (Kosolapoff & Maier eds) Wiley Vol 6 pp 211-577 1973, Beilstein 6 III 658, 6 IV 720.]

Toxicity evaluation

Triphenyl phosphate(TPP) is neurotoxic, causing paralysis at high dosages. Like tri-o-cresyl phosphate (TOCP), it is a cholinesterase inhibitor. The acute oral toxicity is low. The acute toxicity via subcutaneous administration is low to moderate. The toxic symptoms from high dosages in test animals were tremor, diarrhea, muscle weakness, and paralysis.
LD50 value, oral (mice): 1320 mg/kg
LD50 value, subcutaneous (cats): 100 mg/kg
Cleveland et al. (1986) investigated the acute and chronic toxicity to various species of freshwater fish of phosphate ester compounds containing TPP. The adverse toxic effects occurred at exposure concentrations of 0.38–1.0 mg/L.

Incompatibilities

Incompatible with strong oxidizers; strong acids; nitrates may cause fire or explosions. Phosphates are incompatible with antimony pentachloride, magnesium, silver nitrate, zinc acetate.

Waste Disposal

Incinerate in furnace equipped with alkaline scrubber.