Solvent Extraction of Picric Acid from Acid Aqueous Solutions into Cyclohexane with Trioctylphosphine Oxide and Trioctylamine

Abstract

ABSTRACT The solvent extraction of picric acid(Hpic) from acid aqueous chloride solutions into cyclohexane with trioctylphosphine oxide(TOPO) and trioctylamine(TOA) was examined and the UV-visible spectrum of the organic phase was studied. In the organic phase, the acid associates with one or two TOPO molecules but it associates with only one TOA molecule. The absorption peak of the 1:1 associate with TOPO appears only in the UV range and thus it is assumed to be a hydrogen-bonded molecular adduct. The 1:2 associate with TOPO and the 1:1 associate with TOA, on the other hand, has a marked absorption peak in the visible range which is quite similar to that of picrate ions and thus the extracts are assumed to be ion pairs in which an electron transfers from the hydrogen atom to the oxygen atom in the OH-group. For this reason, the spectrum of TOPO extract is dependent on the amount of free extractant but that of TOA extract is not.