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Nucleophile and Base Differentiation of Pyridine in Reaction with Tetrahalocatechols and the Formation of Manganese(III)-Catecholate and Pyridinium-Catecholate Complexes for the in situ Generation of Hydrogen Peroxide from Dioxygen

Abstract

Crystal structures of two novel pyridinium catecholate compounds (1,2-dihydroxy-3,5,6-trichlorobenzene-4-pyridinium chloride and 1,2-dihydroxy-3,5,6-tribromobenzene-4-pyridinium bromide) were obtained by the reaction of pyridine with tetrachloro-o-benzoquinone (in the presence of hydroxylamine) and tetrabromocatechol respectively. A similar reaction with tetrachlorocatechol as a starting substrate showed pyridine to act as a base rather than a nucleophile, with a crystal structure of the pyridinium-catecholate salt obtained. The role of a number of manganese-catecholate complexes as catalysts in the reduction of dioxygen to hydrogen peroxide was also investigated. Diaquabis(3,5,6-tribromobenzene-4-pyridinium catecholate)manganese(III) bromide·MeOH, [pyH][MnIII(Br4Cat)2(H2O)(py)] and [4-MepyH][MnIII(Br4Cat)2(H2O)(4-Mepy)] (where CatH2 = catechol) were synthesised and characterised by melting point, FTIR, CHN (and Mn) analysis, mass spectrometry and UV-vis spectroscopy. All showed catalytic behaviour in dioxygen reduction at 20.0±1 °C and pH 8.00 in the presence of hydroxylamine as reducing substrate, with initial rates of hydrogen peroxide generation and turnover frequencies of up to 11.2 × 10–5 mol dm–3 s–1 and 8060 hr–1 respectively in the presence of a 30-fold molar excess of ligand.

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Publication details

The article was received on 25 Jul 2017, accepted on 13 Nov 2017 and first published on 14 Nov 2017


Article type: Paper
DOI: 10.1039/C7NJ02725G
Citation: New J. Chem., 2017, Accepted Manuscript
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    Nucleophile and Base Differentiation of Pyridine in Reaction with Tetrahalocatechols and the Formation of Manganese(III)-Catecholate and Pyridinium-Catecholate Complexes for the in situ Generation of Hydrogen Peroxide from Dioxygen

    N. O. Bakewell, R. Thavarajah, M. Motevalli and T. S. Sheriff, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ02725G

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