Reactions of Polyphosphoric Acid and Bitumen Model Compounds with Oxygenated Functional Groups: Where Is the Phosphorylation?

Polyphosphoric acid (PPA) is used to modify bitumen, but the chemical reactions responsible for the change in bitumen properties remain, for the most part, undetermined. In an effort to better understand these reactions and phosphorylation in particular, four bitumen model compounds with various oxygenated functional groups were heated with PPA in conditions typical of those used to prepare PPA−modified bitumens, namely, bisphenol A (phenol), butyl phenyl ether (ether), acetophenone (ketone), and benzoic acid (carboxylic acid). The reactions were followed by thin-layer chromatography and infrared spectroscopy. It was found that the extent of the reactions decreased as bisphenol A > acetophenone > benzoic acid > butyl phenyl ether. The detailed analysis of the infrared spectra revealed that the hydroxyl group of bisphenol A was not phosphorylated by PPA. Instead, it facilitated the scission of the bisphenol into fragments of lower molecular weight. The reaction of acetophenone had the reverse effect, becau...