The solubility at 25°C of p-nitroaniline in aqueous alcohols at concentrations of up to 40 % v/v is reported and activity coefficients are calculated. The rate of increase of the indicator solubility with alcohol concentration diminishes in the order cyclohexanol > n-propanol > isopropanol > ethanol >methanol, and this effect of the alcohol is sufficient to account for the behaviour of the indicator in dilute acid solutions without the assumption of the protonation of the alcohols themselves. Attention is drawn to some weaknesses in the protonation argument.Since changes in the activity coefficient of the base form of an indicator may be as important as proton hydration changes in the interpretation of salt effects,l it seemed that the determination of the solubility of p-nitroaniline in aqueous solutions might throw a different light upon the conclusion, drawn from studies with this indicator, that alcohols and other oxygen-containing molecules are protonated in dilute acid solutions. EXPERIMENTALSamples of p-nitroaniline (twice recrystallized from water) were shaken in 6Oml flasks with 20 ml of 5,10,20, 30, or 40 % vlv alcoholic solutions for at least 3 days in a thermostat at 25"C, after which 5 rnl samples were removed for spectrophotornetric determination of their p-nitroaniline concentrations. With cyclohexanol only 1, 2, and 3 % v/v solutions were used because of its limited miscibility with water. The other alcohols were methanol, ethanol, nand iso-propanol, all of analytical reagent quality. RESULTS AND DISCUSSIONSolubilities axe expressed in table 1 in terms of molarity (column 4) or number of moles of p-nitroaniline per mole of solution (column 5) and the corresponding values of the logarithm of the activity coefficient, -logyB and -logf,, are recorded in columns 6 and 7 respectively : Y , and fB are calculated directly from the ratio of the solubility in pure water (4.02 x to that in the alcohol solution. Column 1 records the alcohol concentration in vol. % and columns 2 and ' H. J. Campbell and J. T. Edward, Can.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.