TY  - JOUR
A1  - Lerner, Hans-Wolfram
A1  - Margraf, Günter
A1  - Kretz, Tonia
A1  - Schiemann, Olav
A1  - Bats, Jan W.
A1  - Dürner, Gerd
A1  - Fabrizi de Biani, Fabrizia
A1  - Zanello, Piero
A1  - Bolte, Michael
A1  - Wagner, Matthias
T1  - Redox behaviour of pyrazolyl-substituted 1,4-dihydroxyarenes: formation of the corresponding semiquinones, quinhydrones and quinones
T2  - Zeitschrift für Naturforschung, B
N2  - 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)-1,4- quinhydrone. 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 pyrazolylsubstituted 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 electrontransfer processes.
KW  - Quinhydrone
KW  - Semiquinone
KW  - Hydroquinone
KW  - Redoxactive Ligands
KW  - Crystal Structure
Y1  - 2014
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/80732
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-807323
SN  - 1865-7117
SN  - 0932-0776
VL  - 61.2006
IS  - 3
SP  - 252
EP  - 264
PB  - Verlag der Zeitschrift für Naturforschung
CY  - Tübingen
ER  -