Compound properties relevant for assessing the environmental partitioning of nitrophenols

Abstract

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 <I>K</I>_a can be estimated from the Hammett relationship p<I>K</I>_a = 7.23 - 2.59Σσ_<I>i</I>^(-). For these nitrophenols, the aqueous activity coefficient γ_W of the nondissociated species is approximately independent of solute concentration, and a good correlation between octanol/water partition constant <I>K</I>_ow and aqueous solubility of the liquid compound <I>C</I>_w^sat(L) is found: log <I>K</I>_ow = -0.97 log <I>C</I>_W^sat(L) - 0.04 (<I>R</I> = 0.98). In cases in which intramolecular hydrogen bonding is disturbed or impossible (e.g., in 4-nitrophenol), due to solute-solute interactions, <I>C</I>_W^sat(L) does not yield correct information on γ_W 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.