Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12779/5191
Title: Redox behaviour of pyrazolyl-substituted 1,4-dihydroxyarenes: Formation of the corresponding semiquinones, quinhydrones and quinones
Authors: Lerner, H. W.
Margraf, G.
Kretz, T.
Schiemann, O.
Bats, J. W.
Durner, G.
Fabrizi De Biani, Fabrizia 
Zanello, Piero
Bolte, M.
Wagner, M.
Issue Date: 2006
Project: None 
Journal: ZEITSCHRIFT FÜR NATURFORSCHUNG. B, A JOURNAL OF CHEMICAL SCIENCES
Abstract: 
Pyrazolyl-substituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives have been synthesized by reaction of 1,4-benzoquinone and 1,4-naphthoquinone, respectively, with pyrazole. Cyclovoltammetric measurements have shown that 1,4-benzoquinone possesses the potential to oxidize 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene. The 2,5-bis(pyrazol-1-yl)1,4-dihydroxybenzene reacts with air to give quantitatively black insoluble 2,5-bis(pyrazol-1-yl)- 1,4quinhydrone. Black crystals of 2,5-bis(pyrazol-1-yl)-1,4-quinhydrone suitable for X-ray diffraction were grown from methanol at ambient temperature (monoclinic C2/c). The poor yields of pyrazolyl-substituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives can be explained by the formation of insoluble black quinhydrons in the reaction of benzoquinone and naphthoquinone with pyrazole. The dianions of 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene react with oxygen to give the corresponding semiquinone anions. 2,5-Bis(pyrazol-1-yl)-1,4-benzoquinone shows two reversible one-electron reduction processes in cyclovoltammetric measurements, whereas pyrazolyl-substituted 1,4-dihdroxybenzene and -naphthene derivatives undergo irreversibile electron-transfer processes.
Description: 
40181
URI: http://hdl.handle.net/20.500.12779/5191
ISSN: 0932-0776
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