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

Abstract

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±0.03M−1a−1 (95% confidence interval) at 60°C with an activation energy of 83kJmol−1. This decreased to 0.17±0.015M−1a−1 in the presence of water, but the addition of sulfuric acid up to 100gL−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.