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

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-aminoan-tipyrine, 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.

Automated summary

In this study, the solid-liquid equilibria of three binaries and two ternaries were investigated. Simple eutectic systems were observed for water-antipyrine and water-4-aminoantipyrine, while no eutectic point was found for the other ternaries. The interactions between ethanol and water in the ternary systems were different from those in the ethanol-water binary system.