PRODUCTION OF PHOSPHATE ESTERS

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A process for the production of liquid meta-rich triaryl phosphate esters having low triphenyl phosphate content and low viscosity comprises (a) an alkylation stage wherein a phenol is reacted with an olefin having 2 to 12 carbon atoms in the presence of a strong acid catalyst to give a reaction product comprising a mixture of meta and para alkylated phenols; and (b) a transalkylation stage wherein the mixture of alkylated phenols from the alkylation stage is heated in the presence of a strong acid catalyst to increase the meta isomer content of the mixture to at least 25% whilst maintaining a phenol level below 22%; and (c) a phosphorylation stage wherein the mixture of alkylated phenols from the transalkylation stage is reacted with a phosphorylating agent; and wherein the strong acid catalyst used in stages (a) and (b) is a Bronsted acid having an acid strength of less than zero. Preferred catalysts are activated clays such as bentonite, montmorillonite or Fullers Earth clay. The alkylation and transalkylation are conducted at temperatures between 100° C. and 200° C., preferable 150° C. and 180° C.