A new class of bleaching and brightness stabilizing agents. Part IV: Probing the bleaching chemistry of THP and BBHPE

To study the bleaching chemistry of recently discovered phosphorus-based bleaching and brightness stabilizing agents, we reacted lignin model chromophores, milled wood lignin (MWL) and pulps with tris(hydroxymethyl)phosphine (THP), 1,2-bis[bis(hydroxymethyl)phosphino]ethane (BBHPE) and sodium hydrosulphite (Y). Ultraviolet-visible spectroscopy and mass spectrometry studies showed that nucleophilic addition was the major reaction between the phosphines and the model chromophores 2-methoxy-p-benzoquinone and coniferaldehyde. THP and BBHPE were equally reactive toward the model chromophores and the o- and p-quinones introduced to a spruce thermomechanical pulp via oxidation of the pulp with Fremy's salt. BBHPE had a higher reactivity than THP or Y toward the etherified coniferaldehyde structures in spruce MWL.