Journal
JOURNAL OF ORGANOMETALLIC CHEMISTRY
Volume 793, Issue -, Pages 210-216Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jorganchem.2015.04.020
Keywords
Selective aromatic oxidation; Pseudocumene; 2-Methylnaphthalene; Hydrogen peroxide; Vanadium; Homogeneous catalysis
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Funding
- Russian Foundation for Basic Research (RFBR) [13-03-12042, 14-03-31431]
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The catalytic performance of a gamma-Keggin divanadium-substituted phosphotungstate, (Bu4N)(4)[gamma-PW10O38V2(mu-O)(mu-OH)], has been evaluated in the selective oxidation of 1,2,4-trimethylbenzene (pseudocumene, PC) and 2-methylnaphthalene with the green oxidant, 35% aqueous hydrogen peroxide. Under conditions of H2O2 deficiency ([PC]/[H2O2] = 17-22), PC oxidation proceeded with unusually high chemo-and regioselectivity, producing exclusively 2,4,5-trimethylphenol (2,4,5-TMP) and 2,3,5-TMP in a molar ratio of 7.3/1 and a yield of 73% based on the oxidant. Isomeric 2,3,6-trimethylphenol was found in trace amounts. Under conditions of H2O2 excess ([H2O2]/[PC] = 8), 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, vitamin E key intermediate) formed with 41% selectivity at 41% substrate conversion. Atypical regioselectivity was also found in the oxidation of 2-methylnaphthalene which gave predominantly 6-methyl-1,4-naphthoquinone (6-MNQ) rather than isomeric 2-MNQ. The ratio between the isomers could be altered by varying the catalyst and oxidant amounts. (C) 2015 Elsevier B.V. All rights reserved.
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