The reaction between polyphosphoric acid (PPA) and bitumen is ill understood. To help define possible reactions, model compounds, isoquinoline and 1-methyl-2-quinolinone, were reacted with PPA. Both compounds formed salts with PPA. An infrared study of the salts revealed that PPA releases a terminal proton, as opposed to an internal one, and that, with isoquinoline, the charges of the ionic pair are localized but stabilized by bound water. With 1-methyl-2-quinolinone, the charges are delocalized and stabilized by resonance. This study demonstrates that ionic pairs need an environment of high dielectric constant to form in bitumen.