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

•The mechanism of reaction between DEHPA and TBP is established.•The rate coefficient of the reaction is presented.•The commercial relevance of this reaction is demonstrated.•Organic acid-catalysed hydrolysis of TBP is also observed.

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.