An IR spectroscopy method is used to examine the state of nonane and toluene diluted bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR) in the concentration range of 0.025-1.0 M. It was found that in contrast to the ''inert'' solvent nonane, in which marked self-association of the dithiophosphinic acid due to the formation of intermolecular SH…S hydrogen bonds begins at an HR concentration of ,0.1 M, in the aromatic diluent toluene this process begins at HR total >0.4 M. This result is explained by the interaction of the proton of the S-H group of the dithiophosphinic acid with the p-electron system of the toluene aromatic ring and the formation of SH…p hydrogen bonds, preventing the self-association of the organic acid. The presence of the monomeric, dimeric, and tetrameric forms of the extractant in solution was shown to best describe the bis(2,4,4-trimethylpentyl)-dithiophosphinic acid-nonane system. The formation constants of the dimers (K 2 5 0.78 ¡ 0.07) and tetramers (K 4 5 3.42 ¡ 0.26) have been calculated.
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