Reactive
Extraction of Saturated Aliphatic Dicarboxylic
Acids with Trioctylamine in 1‑Octanol: Equilibria, Model, and
Correlation of Apparent Reactive Equilibrium Constants
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Abstract
Extraction equilibria for saturated
aliphatic dicarboxylic acids,
namely oxalic, malonic, succinic, and adipic acids, with trioctylamine
(TOA) in 1-octanol were determined at various TOA concentrations.
Using quantitative FT-IR spectra, we determined that the formation
of 1:2 acid–amine complexes depends on the p<i>K</i><sub>a2</sub> value, and wavenumbers of specific peaks for the COO<sup>–</sup> of the acid–amine ion-pair complexes depend
on the p<i>K</i><sub>a1</sub> value. An equilibrium model
is presented that employs the mass action law and is used to determine
model parameters and apparent extraction equilibrium constants (<i>K</i><sub>11</sub>, <i>K</i><sub>12</sub>, and <i>K</i><sub>21</sub>). The extraction abilities for dicarboxylic
acids depend on the p<i>K</i><sub>a1</sub> value. The typical
overloading curves of TOA/1-octanol for dicarboxylic acids are given.
The loadings of TOA calculated using the equilibrium model parameters
and apparent extraction equilibrium constants agree with the experimental
data. The apparent extraction equilibrium constants depend on the
acidity of the dicarboxylic acid and the specific basicity of TOA.
The quantitative correlation of log <i>K</i><sub>11</sub> (or log <i>K</i><sub>12</sub>) is obtained using p<i>K</i><sub>a1</sub> (or p<i>K</i><sub>a2</sub>) and
p<i>K</i><sub>a,B</sub><sup>′</sup>