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).
Uses
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.
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.
