Extraction of 4-(2-pyridylazo) resorcinol and 4-(2-thiazolylazo) resorcinol with chloroform and tetraphenylarsonium and phosphonium chlorides

The extraction of 4-(2-pyridylazo)resorcinol (PAR) and 4-(2-thiazolylazo)resorcinol (TAR) with chloroform alone and in the presence of tetraphenylarsonium or tetraphenylphosphonium chloride (Ph4XCl) was studied. In the optimum pH range 3.5−5 for PAR and 1.5−5 for TAR, 94–95% of the reagents was extracted into chloroform. In the presence of Ph4XCl in 10–100-fold excess 95–98% of PAR and TAR were extracted within the pH range 3.5–10 and 1.5–10, respectively. The species extracted with chloroform alone were estimated to be H2R molecules. A quantitative interpretation of PAR and TAR distribution between aqueous solution (μ = 0.33) and chloroform was made. Distribution constants for H2R were determined as 14.9 for PAR and 19.2 for TAR. In the presence of Ph4XCl as extradant H2R molecules were predominantly extracted up to pH 4; between pH 4 and pH 8 two species H2R and Ph4X+HR− were transferred to the chloroform phase. Above pH 8 the Ph4X+HR− ion pairs were the only extracted species. They were studied in solution and by characterization of solid compounds isolated from the organic phase and aqueous solution.