Selective membrane transport of dicarboxylic acids in their neutral form by a synthetic receptor containing amidopyridine groups

A synthetic receptor that can discriminate dicarboxylic acids based on host-guest principles has been prepared. This compound incorporates two amidopyridine units as hydrogen-bonding centers that are capable of binding the carboxylic acid functional group. The receptor was dissolved in a kerosene/dodecanol mixture and used as a carrier in supported liquid membranes. Facilitated transport based on the liquid-liquid distribution of dicarboxylic acids between aqueous feed and stripping solutions and an organic phase containing the carrier was accomplished. This transport was driven by a pH gradient that assures the predominance of the protonated neutral form of the carboxylic acids in the feed solution and the corresponding deprotonated form in the stripping solution. Selective transport of dicarboxylic acids was observed allowing for an efficient separation of different carboxylic acids.