Infrared and UV–vis spectra of phenoxonium cations produced during the oxidation of phenols with structures similar to vitamin E
✍ Scribed by Shanshan Chen; Hong Mei Peng; Richard D. Webster
- Book ID
- 103828303
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 836 KB
- Volume
- 55
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
Several phenols with structures similar to vitamin E were oxidised and the intermediate species produced were characterised by in situ infrared and UV-vis spectroscopies. The Fourier transform infrared (FTIR) measurements were performed by chemically oxidising the phenols with 2 mol equiv. of NO + SbF 6 -in CH 3 CN and recording the spectra between 1900 and 1300 cm -1 with an attenuated total reflectance (ATR) probe utilising a fiber conduit and a diamond composite sensor. The compounds that formed long-lived phenoxonium cations displayed two IR absorbances at 1665 (±15) cm -1 and one at 1600 (±10) cm -1 associated with the carbonyl, symmetric ring stretch and asymmetric ring stretch modes. The paraquinones are one of the long-term products of oxidation of the phenols, and displayed solution phase IR absorbances at 1650 (±10) cm -1 . In situ electrochemical UV-vis experiments performed during the oxidation of the phenols led to the detection of bands due to the phenoxonium cations at 295 (±5) and 440 (±15) nm and due to the para-quinones at 260 (±10) nm. The concentration of the substrate and the water content of the solvent had a major effect on the yields of the intermediates and products that were produced during the oxidation reactions.