Aggregation Phenomena in the Organic Phase

The extractant, which consists of an equimolar solution of trioctylamine and 2-ethylhexanoic acid in toluene, to some extent undergoes acid-base interaction, forming trioctylammonium octanoate. 

Ammonium octanoate tends to aggregate in solvents of low polarity, as was first found by Fendler [7], who used proton nuclear magnetic resonance (H-NMR) measurements. Fendler was the first to state that long- 

In the present work H-NMR spectroscopy of trioctylammonium octa-noate also proved to be an important tool in tracking the onset of aggregation. The low-field section of a 0.5 M water-saturated 2-ethylhexanoic acid solution dissolved in benzene shows a broad resonance line at 10.98 ppm, as shown in Fig. 9. 

When trioctylamine is added to the 2-ethylhexanoic acid solution, there is an upfield shift of this resonance line, indicating a proton shift to R3N, R3NH being formed. In Fig. 10 a correlation between the chemical shift and the increase in the concentration of water-saturated extractant is shown. 

A gradual linear proton shift from the carboxylic acid to the amine as a function of extractant concentration is observed. The interesting feature of Fig. 10 is the discontinuity of the straight line, which was also observed by Fendler [7 and signifies the onset of aggregation. 

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