OXIDATION CATALYSIS IN RAW COTTON BLEACHING: THE QUEST FOR A SUITABLE MODEL

The dinuclear manganese complexes possessing 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) ligands, first described by Wieghardt et al. in 1988[i] are highly potent activators of H₂O₂towards selective oxidation catalysis and industrial bleaching.[ii] In this presentation, mechanistic studies of the catalysts in high pH aqueous media, of relevance to cotton and wood pulp bleaching, will be reported. Morin (2′,3,4′,5,7-pentahydroxyflavone) is commonly used as a model compound for raw cotton bleaching studies.[iii] Results pertaining to the oxidation of morin in aqueous media using the dimanganese catalyst will be presented.

The photochemical and oxidative behaviour of morin deviates from the behaviour of raw cotton, thus it may not, in fact, be the most suitable model for raw cotton bleaching. Another flavonoid compound will be presented for use as a more relevant model. Oxidation of this new model compound will be presented with particular emphasis on the influence of factors such as pH and buffers and the effect of additives, such as sequestrants.

[i] K. Weighardt, U. Bossek, B. Nuber, J. Weiss, J. Bonvoisin, M. Corbella, S.E. Vitols, J.-J. Girerd,J. Am. Chem. Soc.,1988, 110, 7398.

[ii] (a) R. Hage, A. Lienke,Angew. Chem. Int. Ed.,2006, 45, 206. (b) R. Hage, A. Lienke,J. Mol. Cat. A: Chem.,2006, 251, 150.

[iii] (a) T. Wieprecht, J. Xia, U. Heinz, J. Dannacher, G. Schlingloff,J. Mol. Cat. A: Chem.,2003, 203, 113. (b) T. Topalovic, V.A. Nierstrasz, M.M.C.G. Warmoeskerken,Fibers and Polymers,2010, 11, 72. (c) E. Ember, H.A. Gazzaz, S. Rothbart, R. Puchta, R. van Eldik,Applied Catalysis B: Environmental,2010, 95, 179.