Browsing by Author "Hosoya, Takashi"

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  • Cyclic peroxides as key intermediates in the degradation of cellulosic key chromophores by alkaline hydrogen peroxide
    (2018-06-01) Bacher, Markus; Hosoya, Takashi; Zwirchmayr, Nele Sophie; Nomura, Satoshi; Gille, Lars; Dietz, Thomas; Erata, Tomoki; Potthast, Antje; Vuorinen, Tapani; Rosenau, Thomas
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Abstract: 2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) and 5,8-dihydroxy-[1,4]-naphthoquinone (DHNQ) are two key chromophores which are almost ubiquitous in cellulosic materials. Their fate under conditions of alkaline peroxide bleaching (P stage) has been established previously, but the intermediacy of cyclic peroxides, which so far had only been postulated, remained an open issue. By means of 17O NMR spectroscopy, additionally supported by other NMR techniques, it was demonstrated that both DHBQ and DHNQ form cyclic peroxides as primary intermediates in the reaction with hydrogen peroxide under alkaline conditions. These intermediates are subsequently further degraded to products already known. The experimental confirmation of the cyclic peroxides is an important step in the understanding of reaction mechanisms in pulp bleaching chemistry. Graphical Abstract: [Figure not available: see fulltext.].
  • A note on the chemical fate of the DABCO catalyst in amine-catalyzed hypochlorite bleaching of cellulosic pulps
    (2024-05) Lehrhofer, Anna F.; Isaza Ferro, Estefania; Hosoya, Takashi; Hettegger, Hubert; Vuorinen, Tapani; Rosenau, Thomas
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Hypochlorous acid bleaching under amine catalysis (Hcat bleaching stage) is an optimized bleaching stage variant that is characterized by working at weakly acidic, near-neutral pH, having high bleaching efficiency, and discharging only very small amounts of chloro-organics. This study addressed the chemical fate of the used 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyst. While literature proposed either homolytic or heterolytic breakage of one ethylene bridge and subsequent release of the resulting fragments as two molecules of formaldehyde, we demonstrated the degradation to proceed by ionic elimination of one ethylene bridge starting from mono-N-chlorinated DABCO. The resulting N-vinyl (enamine) derivative adds water under the release of acetaldehyde and formation of piperazine. The generation of acetaldehyde was experimentally confirmed by 2,4-dinitrophenylhydrazine trapping, directly from the processing liquid. The experimental findings agreed superbly with computations which showed the “acetaldehyde mechanism” to be much favored over the previously proposed pathways under C–C bond cleavage and release of formaldehyde. The results of this study add to a better understanding of the novel Hcat bleaching system. Graphical abstract: (Figure presented.).