GB818048A - Process for producing triorgano-phosphates - Google Patents

Abstract

Triorgano phosphates of the formula (RO)3PO in which RO is either a phenoxy group containing zero to 3 alkyl substituents, each of which contains 1 to 4 carbon atoms or is an alkoxy group corresponding to a primary alcohol ROH in which R is a primary alkyl group containing from 4 to 13 carbon atoms, are obtained by heating a mixture of phosphorus oxychloride and an organic hydroxyl compound ROH in which RO is as defined above, in the presence of titanium tetrachloride as a catalyst. Specified organic hydroxyl compounds ROH are phenol, o-, m- and p-cresols, the isomeric xylenols, o-, m- and p-n-butyl phenols, the isomeric tertiary butyl phenols and o-, m- and p-isopropyl phenols, oxo alcohols, n-butanol, n-hexanol, 2-ethylbutanol, 2-ethyl hexanol, 2-methylpentanol, 3-methylpentanol and 2-propylheptanol. The reactants are suitably heated to a refluxing temperature at a pressure not above atmospheric pressure. The titanium tetrachloride is generally used in an amount of from 0.01 parts by weight to 5 parts by weight per 100 parts by weight of the total reaction mixture, the preferred amount being from 0.1 to 1.0 part by weight per 100 parts of the reaction mixture. In examples: (1) 8 mols. of 2-ethylhexanol are added over a 3-hour period at 20 DEG C. and at a pressure of 400 mm. Hg to 4 mols. of phosphorus oxychloride containing 0.031 mol. of titanium tetrachloride, the reaction being carried out in a glass jacketed kettle equipped with a thermometer well, stirrer, dropping funnel, reflux condenser and a suitable vacuum system protected by a cold trap. After the addition is complete the pressure is reduced to 30 mm. Hg and the temperature raised to 35 DEG C. and 10.8 mols. of 2-ethylhexanol are added over a period of 45 minutes. The reaction temperature is then slowly raised until there is no further reduction in acidity, this requiring a period of 10 hours and a temperature of 99 DEG C. The crude product obtained contains tri-(2-ethylhexyl)phosphate, excess 2-ethylhexanol and minor amounts of by-products; (2) a mixture of alkyl substituted phenols (15.5 mols.), 5 mols. of phosphorus oxychloride and 0.0294 mol. of titanium tetrachloride are mixed thoroughly and part of the mixture is charged to a glass-jacketed kettle equipped with a thermometer well, stirrer, dropping funnel, reflux condenser and a hydrogen chloride trap protected by a cold trap. The material in the kettle is heated to 100-102 DEG C. at atmospheric pressure and the remainder of the mixture then added over a 2-hour period. The hydrogen chloride trap is replaced by a vacuum system and the temperature raised to 157 DEG C. and the pressure reduced to 50 mm. Hg, these conditions being maintained for 11 hours. The crude product obtained contains triaryl phosphates in high yield. The alkyl phenol mixture used is obtained from the phenolic fraction of coal hydrogenation products and comprises a mixture of m-cresol, p-cresol, o-, m- and p-ethyl phenols, 2,3-, 2,4-, 2.5-, 3,4- and 3,5-xylenol, o-propyl phenol, unidentified phenols and some non-phenolic impurities. Comparative examples are given in which 2-ethylhexanol and the above-described mixture of alkylated phenols respectively are reacted with phosphorus oxychloride to form the triphosphate in the presence of aluminium chloride, magnesium chloride, and zinc chloride respectively. Also in the case of the alkyl phenols an example is given in which ferric chloride is used as catalyst. When no catalyst is used appreciable amounts of di-(2-ethylhexyl)chlorophosphate and tetra-(2-ethylhexyl)pyrophosphate are obtained when 2-ethylhexanol is used and when the mixed alkyl phenols are used the product is a mixture of diaryl chlorophosphates and minor amounts of aryldichlorophosphates.