Solvent Extraction Equilibria of Acids. VI. The Extraction of Several Mono- and Dicarboxylic Acids with Trioctylphosphine Oxide in Hexane

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Abstract
The solvent extraction equilibria of acetic, propionic, and butyric acid and mono-, di-, and trichloroacetic acid (HA), as well as those of oxalic, malonic, succinic, glutaric, and adipic acid (H2A), have been determined in liquid–liquid systems of hexane containing none or a certain amount of trioctylphosphine oxide (E) and an aqueous 1 mol dm3 chloride solution at 25°C. The constants, Kd=[HA]org/[HA], Kdim=[(HA)2]org/[HA]org2, Kex1′=[HAE]org/[HA][E]org, Kex2′=[H2AE2]org/[H2A][E]org2, and β1(org)=[HAE]org/[HA]org[E]org2, have then been determined from the data. It was found that, among the three fatty acids, the value of Kex1′ was higher as the chain length increased, but the values of β1(org) were nearly all the same, while among the chloroacetic acids they were higher as the number of chloride atom increased. The extraction of the dicarboxylic acids with E was not very different, although the number of the –CH2– between the two carboxyl groups changed from zero to four.