Solid-liquid equilibria for ethanol – water – antipyrine and ethanol – water - 4-aminoantipyrine, and their cosolvencies in ethanol – water mixture

Abstract

Antipyrine and 4-aminantipyrine are pyrazolone derivatives, and they are used as raw materials for medical drugs, catalysts and chromophores. In this study, to design the extraction and purification process, the solid-liquid equilibria (SLE) of three binaries, water - antipyrine, ethanol - 4-aminoantipyrine and water - 4-aminoantipyrine, and the two ternaries, ethanol - water - antipyrine and water - ethanol - 4-aminoantipyrine, were investigated by directly measuring the solution temperature at 256.95–338.48 K. Then, an equimolar solvent mixture of ethanol and water was used for the SLE measurements of the two ternaries. Simple eutectic systems were verified for water - antipyrine and water - 4-aminoantipyrine. The eutectic point was not observed for ethanol – 4-aminoantipyrine, ethanol - water - antipyrine and ethanol - water - 4-aminoantipyrine in the experimental temperature range. The ternary SLE were also compared with the three binaries measured in this study, and the other two constituent binaries, ethanol – antipyrine and ethanol –water. The cosolvencies were identified in the two ternary SLE, because antipyrine and 4-aminoantipyrine had larger solubilities in ethanol –water than those in pure water or ethanol at given temperature. NRTL equation provided good reproducibilities for the SLE of the five binaries, ethanol – antipyrine, water – antipyrine, ethanol - 4-aminoantipyrine, water-4-aminoantipyrine and ethanol -water. Especially for ethanol – water, sigmoid functions with the temperature were proposed for the two parameters, g12-g22 and g21-g11, in the NRTL equation. However, the cosolvencies in the ternaries were not evaluated just by the parameters. The ternary data were well correlated with the binary parameters for ethanol - water, which were determined from the ternary SLE. Conversely, the parameters could not provide reproducibility for the SLE of ethanol- water. The results suggested that the interactions between ethanol and water in the ternary systems were different from those in the ethanol –water binary system.