2913-43-1Relevant academic research and scientific papers
Selective oxidation of pseudocumene and 2-methylnaphthalene with aqueous hydrogen peroxide catalyzed by γ-Keggin divanadium-substituted polyoxotungstate
Zalomaeva, Olga V.,Evtushok, Vasiliy Yu.,Maksimov, Gennadii M.,Kholdeeva, Oxana A.
, p. 210 - 216 (2015/09/01)
The catalytic performance of a γ-Keggin divanadium-substituted phosphotungstate, (Bu4N)4[γ-PW10O38V2(μ-O)(μ-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.
Highly selective oxidation of alkylphenols to p-benzoquinones with aqueous hydrogen peroxide catalyzed by divanadium-substituted polyoxotungstates
Ivanchikova, Irina D.,Maksimchuk, Nataliya V.,Maksimovskaya, Raisa I.,Maksimov, Gennadii M.,Kholdeeva, Oxana A.
, p. 2706 - 2713 (2014/08/18)
The catalytic performance of divanadium- and dititanium-substituted γ-Keggin polyoxotungstates, TBA4H[γ-PW10V 2O40] (I, TBA = tetra-n-butylammonium), TBA 4H2[γ-SiW10V2O40] (II), and TBA8[{γ-SiW10Ti2O 36(OH)2}2(μ-O)2] (III) has been assessed in the selective oxidation of industrially important alkylphenols/naphthols with the green oxidant 35% aqueous H2O 2. Phosphotungstate I revealed a superior catalytic performance in terms of activity and selectivity and produced alkylsubstituted p-benzo- and naphthoquinones with good to excellent yields. By applying the optimized reaction conditions, 2,3,5-trimethyl-p-benzoquinone (TMBQ, vitamin E key intermediate) was obtained in a nearly quantitative yield via oxidation of 2,3,6-trimethylphenol (TMP). The efficiency of H2O2 utilization reached 90%. The catalyst retained its structure under turnover conditions and could be recycled and reused. An active peroxo vanadium complex responsible for the oxidation of TMP to TMBQ has been identified using 51V and 31P NMR spectroscopy.
Effect of combination sequence of precursors on the structural and catalytic properties of Ti-SBA-15
Kuo, Feng-Ting,Chen, Shih-Yuan,Lin, Tsung-Han,Lee, Jyh-Fu,Cheng, Soofin
, p. 12604 - 12610 (2013/08/23)
The combination sequence of Ti and Si precursors (TTIP and TEOS) in the synthesis solution of Ti-incorporated SBA-15 mesoporous silica (shortly termed Ti-SBA-15) was found for the first time to be critical for the distribution of tetrahedrally (Td) coordinated Ti(iv) sites in the resultant Ti-SBA-15. It was found that TTIP pre-assembled with P123 in the synthesis solution for 3 h before the addition of TEOS gave Td-coordinated Ti(iv) sites predominately incorporated near the superficial regions of the framework and were highly accessible to the reactants in catalytic reactions. The Royal Society of Chemistry 2013.
Photoprocesses of p-Benzoquinones in Aqueous Solution
Goerner, Helmut
, p. 11587 - 11595 (2007/10/03)
The photochemistry of 1,4-benzoquinone (BQ) and several derivatives, for example, duroquinone, trimethyl-2,5- or 2,6-dimethyl-, and methyl-BQ in aqueous solution or mixtures with polar media, for example, acetonitrile or 2,2,2-trifluoroethanol, was studied by time-resolved UV-vis spectroscopy after pulses at 248 and 308 nm. The triplet state and the semiquinone radical (?QH/Q?-) of BQs are spectroscopically and kinetically separated intermediates. The radical yield in the absence of H-atom donors is low and significantly increased in the presence of alcohols. Efficient photoinduced charge formation, because of Q?- and H+ after H-atom transfer from 2-propanol to the triplet state, and small effects in the absence of a donor were observed by transient conductivity. The quantum yield of photodecomposition, λirr = 254 nm, is substantial for BQ, MeBQ, and Me2BQs in aqueous solution, but small for Me 4BQ. To account for the efficient photoconversion of BQs into hydrobenzoquinones and 2-hydroxy-1,4-benzoquinones, a novel water-mediated reaction not involving free radicals is proposed as major step. This mechanism is consistent with the prediction that the observed triplet state is monomeric and the yield of Q?-, detected by both transient absorption and conductivity, is low for sub-millimolar BQ, MeBQ, and Me2BQs at pH 5-6. In addition, H-atom abstraction from a polar organic solvent or by self-quenching plays a role in mixtures with water or at enhanced quinone concentration, respectively.
A CONVENIENT SYNTHESIS OF ALKYL-SUBSTITUTED p-BENZOQUINONES FROM PHENOLS BY A H2O2/HETEROPOLYACID SYSTEM
Shimizu, Masao,Orita, Hideo,Hayakawa, Takashi,Takehira, Katsuomi
, p. 471 - 474 (2007/10/02)
Alkyl-substituted p-benzoquinones were easily synthesized in good yields by the oxidation of the corresponding phenols with a hydrogen peroxide/heteropolyacid couple in acetic acid
