Tri-n-butyl phosphate (TBP) is used as the extraction agent for the extraction of o-aminophenol (OAP) in active solvents and inactive solvents. The effects of aqueous solution pH, solvents, concentration of TBP, and the initial OAP concentration on distribution coefficient (D) are investigated. Results show that the neutral OAP molecule is hydrogen-bonded to TBP effectively into the organic phase, and D was maximum when the equilibrium pH was between pKa1 and pKa2. The extraction efficiency is TBP–1-octanol > TBP–kerosene > TBP–carbon tetrachloride > TBP–chloroform, when the concentration of TBP is between (0.3632 and 0.7264) mol·L–1, while the result is TBP–kerosene > TBP–1-octanol > TBP–carbon-tetrachloride > TBP–chloroform when the concentration increases [(1.0896 to 1.8159) mol·dm–3]. Fourier transform infrared spectroscopic analysis shows that the extractive behavior is controlled by hydrogen bonding. An expression for equilibrium D is proposed, and the parameters of the apparent extraction equilibrium constants (K) and the complex ratio (n) (TBP vs OAP) were calculated by fitting the experimental data. It was found that the K and n are 5.97, 5.37, 5.47, and 2.99 and 1.56, 1.51, 1.47, and 1.76 in TBP/kerosene, 1-octanol, carbon tetrachloride, and chloroform, respectively.
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