Of triaryl phosphates

Blends of triaryl phosphates and pentabromodiphenyl oxide are leading flame-retardant additives for flexible urethane foams. A principal advantage is their freedom from scorch. 

Johannsen and colleagues (1977) report dermal LD50 values for rabbits at levels of >3,700 mg/kg for a group of triaryl phosphates, >5,000 mg/kg for dibutyl phenyl phosphate, 5,000 mg/kg for both asymmetrical and symmetrical triaryls, and >3,100 mg/kg for tributyl phosphate. This study looked at structural activity relationships for the organophosphate esters. 

FMC. 1978b. Part of unidentified submission (exhibit G) Environmental fate of triaryl phosphate [microfiche 0519259], FMC Corporation, Philadelphia, PA. 

Muir DCG, Grift NP, Solomon J. 1981. Extraction and cleanup of fish, sediment, and water for determination of triaryl phosphates by gas-liquid chromatography. J Assoc Off Anal Chem 64 79-84. 

Pickard MA, Whelihan JA, Westlake WS. 1975. Utilization of triaryl phosphates by a mixed bacterial population. Can J Microbiol 24 140-145. 

Evaluation of kinetic parameters from the synthesis of triaryl phosphates using reaction calorimetry. Organic Process Research af Development, 6,... 

Synthesis of Phosphoric Acids and their Derivatives. - Among various approaches to phosphate esters the phosphorylation of phenols with dialkyl cyanophosphonate and the synthesis of triaryl phosphates under phase-transfer conditions are worthy of mention. Mixed trialkyl phosphates are also reported to be formed by brief cathodic electrolysis of the reaction of dialkyl phosphonates with aromatic aldehydes and ketones, presumably by rearrangement of the initial a-hydroxy compounds. Further reports have appeared of the generation of metaphosphates by various methods. The synthesis of analogues 1 of famesyl pyrophosphate which incorporate photoactive esters has been reported both compounds are competitive inhibitors of farnesyl transferase. 

The thermal stability of triaryl phosphates is considerably superior to that of the trialkyl esters, which degrade thermally by a mechanism analogous to that of the carboxylic esters, Reaction (2.13) ... 

Hammett (and related sigma) relationships have been applied to aquatic reactions of several classes of aromatic contaminants. For example, alkaline hydrolysis of triaryl phosphate esters fits a Hammett relationship (Table 3) is t he sum of the substituent constants for the aromatic groups and k0 is the hydrolysis rate constant for triphenyl phosphate (0.27 M 1 s-1 t1/2 = 30 days at pH 8). Triaryl esters thus hydrolyze much more rapidly than trialkyl or dialkyl-monoaryl esters under alkaline conditions. Rates of photooxidation of deprotonated substituted phenols by singlet oxygen have been found to be correlated with Hammett a constants (Scully and Hoigne, 1987). The electronic cllects of substituents on pKa values of substituted 2-nitrophenols also fit a I lammett relationship this, of course, is not a kinetic LFER. Two compounds (4-phenyl-2-NP and 3-methyl-2-NP) did not fit the relationship and were not included in the regression. Steric effects may account for the discrepancy for the latter compound. Nitrophenols are used as intermediates in synthesis of dyes and pesticides and also used directly as herbicides and insecticides. 

Alkylation of heterofunctionalities. Etherification of alcohols can be conducted in the absence of solvent using a polyether." The O-alkylation of 1-perfluoro-alkyl-2-fluoroethanols is accompanied by dehydrofluorination thus the products are enol ethers. Selective (9-alkylation of o-aminophenols is observed, and an efficient method for the synthesis of triaryl phosphates from sodium phenolates and... 

Study of the photolytic behaviour of triaryl phosphates has been further extended new model substrates examined include tri-l-naphthalenyl, tri-9-anthracenyl, and tri-8-quinolinyl phosphates, together with some of their methoxy derivatives and analogous dialkyl aryl and alkyl diaryl esters. Noted reactions include aryl migrations with the formation of, for example, l-[2-(l-naphthalenyl)-naphthalenyl] phosphate, in substantial amounts, together with appropriate biaryls. A preliminary report describes the photolysis of methyl alkenyl aryl phosphates (58) which undergo transformation along more than one pathway. The isolated products from (58) (R = OMe, = Me) were (60),... 

Triaiyl phosphates are prepared by phosphorylation of alkyl phenols without phosphorylation catalyst. This simplifies purification of the plasticizer by eliminating the need to withdraw the pirrified product as a distillate. Mixed alkyl diaiyl esters are produced in the presence of a catalytic amoimt of an alkali metal phenoxide. The plasticizer needs to be separated by distillation. Figure 2.39 shows the distillation process of pmifi-cation of triaryl phosphates. A crude triaryl phosphate ester reaction mixtrrre is passed... 

Figure 2.39. Purification process of triaryl phosphate esters. [Adapted from Aal R A, Chen N H C, Chapman J K, US Patent 3,945,891, 1976.]...

Zinc enhances the flame retardancy of triaryl phosphate in m-PPO, leading to the highest LOI values. Zinc powder, however, is coated with zinc oxide. Woik has shown that zinc oxide enhances the decomposition of m-PPO. Thus a zinc coating (zinc arc spray) is perfiaps more representative of the effect of zinc with triaryl phosphate than zinc powder, with the latter having a greater zinc oxide surface. 

In m-PPO the FR triaryl phosphate has a particular role in smoke formation. Zinc borate is an effective smoke and flame retardant with or without the presence of triaryl phosphate. With zine borate, low heat release and smoke release m-PPO materials are possible. It is interesting that in the latter case, LOI values are low and the zinc borate deactivates triaryl phosphate in those materials that contain it. Since LOI only measures ease of extinction, it will not necessarily correlate with other flammability properties. 

Rigid PVC produces its own HCl on burning, even without a flame retardant, but plasticised grades may be flammable unless the plasticiser is itself flame retardant. This explains the popularity of triaryl phosphate plasticisers. 

Alkyl Diphenyl Phosphates. These are products originally developed to provide improved low temperature flexibility, a fault of triaryl phosphate plasticizers in PVC (103). These phosphates generally provide slightly less flame-retardant efficacy but are generally superior to the triaryl phosphates in regard to smoke when the vinyl formulation is burned. Two commercial products of this family are 2-ethylhexyl diphenyl phosphate [1241-94-7], C20H27O4P, Ferro s SANTICIZER 141 or Akzo Nobel s PHOSFLEX 362, and isodecyl diphenyl phosphate [29761-21-5], C22H31O4P, Ferro s SANTICIZER 148 or Akzo Nobel s PHOSFLEX 390. A... 

Brandstrem, A., Synthesis of triaryl phosphate. Pure Appl. Chem., 54, 1769, 1982. 

TAP is used as a plasticizer in flame-retardant rubber compounds because the other plasticizers provide a fuel source that feeds a fire in the case of combustion. That is why many times this phosphate plasticizer is selected instead of other plasticizers. Recently, the use of triaryl phosphates has attracted attention again because of... 

Many times rubber compounds require a piasticizer. However, most plasticizers or processing oils hurt flame retardancy because they provide a fuel source to a potential fire if there is combustion. If a plasticizer must be used, the correct type of triaryl phosphate should function as both a plasticizer and a flame retardant in both the gas and condensed phases. 

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