Formation of the Neurotoxin TMPP from TMPE-Phosphate Formulations

Abstract

Gas phase formation potential of the deadly neurotoxin trimethylolpropane phosphate (TMPP) from reaction in lubricant formulations containing trimethylolpropane ester (TMPE) basestock and tricresyl phosphate (TCP) additive is investigated and found to occur at temperatures of 250°-750°C. The initial formation in the gas phase is found to occur 100°C lower than previously reported. A potential substitute for TCP, T-butylphenyl phosphate (t-BPP), is also found to participate in the formation reaction at nearly the same rate as TCP, producing similar amounts of TMPP. A maximum 15 % theoretical yield of TMPP in air is observed at 550°C, while a maximum 42% yield is observed at 650°C in helium, with two-second exposures of 2 wt% phosphate additive formulations. The reaction is found to be weakly dependent on temperature, with Arrhenius activation energy estimated to be in the 20–40 kj/mol range. Minimization or replacement of TMPE or inhibition of the TMPP formation reaction, rather than restriction of phosphate additives, in synthetic ester lubricant formulations is recommended to reduce or eliminate potential TMPP formation.