Solubilities of Protocatechuic Aldehyde, Caffeic Acid, d-Galactose, and d-Raffinose Pentahydrate in Ethanol–Water Solutions

Abstract

3,4-Dihydroxybenzaldehyde (protocatechuic aldehyde), (E)-3-(3,4-dihydroxyphenyl)prop-2-enoic acid (caffeic acid), (2S,3R,4S,5R,6R)-6-(hydroxymethyl)oxane-2,3,4,5-tetrol (d-galactose), and (3R,4S,5R,6R)-2-[[(2R,3S,4S,5R)-6-[(2S,3S,4S,5R)-3,4-dihydroxy-2,5-bis(hydroxymethyl)oxolan-2-yl]oxy-3,4,5-trihydroxyoxan-2-yl]methoxy]-6-(hydroxymethyl)oxane-3,4,5-triol (d-raffinose) are substances contained in danshen. In this study, the solubilities of protocatechuic aldehyde, caffeic acid, d-galactose, and d-raffinose pentahydrate in the mixtures of ethanol and water from 273.2 K to 303.2 K were determined. The solubilities of protocatechuic aldehyde and caffeic acid in ethanol–water solutions are significantly higher than those in pure water. The solubilities of d-galactose and d-raffinose pentahydrate decrease as ethanol mass fraction increases. The solubilities of the four compounds increase as equilibrium temperature increases. Prediction values of d-galactose calculated using universal functional activity coeff...