Monomeric dodecylammonium propionate undergoes hydrogen bonded ion-pair formation with 2,4–, 2,5– and 2,6-dinitrophenol and trinitrophenol in dry benzene. The association constants for the formation of these ion pairs parallel those formed between dinitrophenols and triethylamine in the same solvent. Addition of acid to aggregated dodecylammonium proprionate in benzene containing 0.55 mol dm–3 water results in the neutralization of the propionate ion. Determination of the ratio of propionate ion to propionic acid allowed the calculation of the apparent dissociation constants, pKappa values, for 2,4–, 2,5–, 2,6-dinitrophenol, 2,4,6-trinitrophenol, Bromophenol Blue Bromophenol Red, Malachite Green and vitamin B12a in 0.55 mol dm–3 water solubilized by 0.10 mol dm–3 dodecylammonium propionate in benzene. Values of pKappa for these indicators closely resemble the corresponding pKa values in water.