Chemical reactivity between bis(2-ethylhexyl)phosphoric acid (DEHPA) and tributyl phosphate

Bis(2-ethylhexyl)phosphoric acid (DEHPA) reacts with tributyl phosphate (TBP) to form the corresponding butyl ester species butyl-bis(2-ethylhexyl)phosphate (DEHPA-OBu) and dibutyl phosphate (DBP) under aqueous-free and hydrous operating conditions. Generation of DEHPA-OBu and DBP was found to occur via a bimolecular nucleophilic substitution (SN2) reaction between TBP and DEHPA. The reaction rate constant under aqueous-free conditions was found to be 0.22 ± 0.03 M− 1 a− 1 (95% confidence interval) at 60 °C with an activation energy of 83 kJ mol− 1. This decreased to 0.17 ± 0.015 M− 1 a− 1 in the presence of water, but the addition of sulfuric acid up to 100 g L− 1 had no further effect. The relevance of this reaction to a commercial operation is demonstrated. Evidence for a second, concurrent organic acid-catalysed hydrolysis reaction resulting in DBP but not DEHPA-OBu formation is also presented and discussed.