Compound properties relevant for assessing the environmental partitioning of nitrophenols

Acidity constants, UV/vis absorption maxima, aqueous solubilities, octanol/water partition constants and ratios, vapor pressures, and estimated Henry's law constants are reported and discussed for 17 mono- and dinitrophenols. For substituted 2-nitrophenols in which intramolecular hydrogen bonding between hydroxyl and nitro group is not affected by proximity effects, the acidity constant Ka can be estimated from the Hammett relationship pKa = 7.23 - 2.59Σσi⁽⁻⁾. For these nitrophenols, the aqueous activity coefficient γW of the nondissociated species is approximately independent of solute concentration, and a good correlation between octanol/water partition constant Kow and aqueous solubility of the liquid compound Cwsat(L) is found: log Kow = -0.97 log CWsat(L) - 0.04 (R = 0.98). In cases in which intramolecular hydrogen bonding is disturbed or impossible (e.g., in 4-nitrophenol), due to solute-solute interactions, CWsat(L) does not yield correct information on γW at low concentrations. The electronic effect of substituents on the octanol/water partitioning behavior of the dissociated 2-nitrophenols can be reasonably quantified by using Hammett substituent constants. Nitrophenols (particularly dinitrophenols) exhibit small Henry's law constants and consequently have large water/air ratios even at low pH values.