Oxidants 2,6-dimethyl- 1,4-benzoquinone

Several products were also detected in base-degraded D-fructose solution acetoin (3-hydroxy-2-butanone 62), l-hydroxy-2-butanone, and 4-hydroxy-2-butanone. Three benzoquinones were found in the product mixture after sucrose had been heated at 110° in 5% NaOH these were 2-methylbenzoquinone, 2,3,5-trimethylbenzoquinone, and 2,5-dimethyl-benzoquinone (2,5-dimethyl-2,5-cyclohexadiene-l,4-dione 61). Compound 62 is of considerable interest, as 62 and butanedione (biacetyl 60) are involved in the formation of 61 and 2,5-dimethyl-l,4-benzenediol (63) by a reduction-oxidation pathway. This mechanism, shown in Scheme 10, will be discussed in a following section, as it has been proposed from results obtained from cellulose. 

Treatment of 5,6-dichloro-2,3-dimethyl- -benzoquinone with sodium sulfide followed by oxidation with nitric acid yields the thianthrene derivative (60). Sulfur extrusion from 60 with peracetic acid leads to 2,3,7,8-tetramethyl-l,4,6,9-dibenzothiophene tetrone (61) (overall yield 57%). ... 

Dimethyl-1,4-benzoquinone (328) and ethylenediamine (329) gave 7,8-dimethyl-6(4//)-quinoxalinone (330) (EtOH-CH2Cl2, 20°C, light exclusion 35% the required oxidation was probably provided by an excess of the quinone). ... 

Similarly, 1-vinylcyclohexane can be trapped with dimethyl acetylenedicarboxylate in refluxing xylene to afford 195 in 78% yield (equation 126) . Benzo[ ]anthracene can be obtained by the reaction of 196 and 1,2-dihydronaphthalene (equation 127) and oxidation of 197 with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone . 

Dimethyl 2-(17/-indol-2-yl)but-2-enedioate, easily available by reaction of 4,7-dihydroindole with dimethyl acet-ylenedicarboxylate followed by oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), treated with PTAD provided compound 703, which was thermaly isomerized to 704 (Scheme 111) <2006JOC7793>. 

Tetraphenylporphin (H2TPP) was prepared from pyrrole and benzaldehyde (25). The tetraphenylchlorin contamination was oxidized by use of 2,3-dichloro-5,6-dicyano-p-benzoquinone (26). Octaethylporphin (H2-OEP)was prepared by the method of Paine et al.(27) from 3,4-diethyl-2-ethoxy-carbony1-5-methyl-pyrrole (28). Zinc(II)-tetraphenylporphin (ZnTPP) was prepared by refluxing H2TPP and zinc acetate in dimethyl-formamide (29). ZnTPP was dissolved at a concentration of 10 -10 ... 

The synthesis of acrylic acid or its ester (228) from ethylene has been investigated in AcOH from the standpoint of its practical production 12]. The carbonylation of styrene is a promising commercial process for cinnamate (229) production[207,213,214]. Asymmetric carbonylation of styrene with Pd(acac)2 and benzoquinone in the presence of TsOH using 2,2 -dimethoxy-6, 6 -bis(diphenylphosphino)biphenyl (231) as a chiral ligand gave dimethyl phenylsuccinate 230 in 93% ee, although the yield was not satisfactory, showing that phosphine coordination influences the stereochemical course of the oxidative carbonylation with Pd(II) salt[215]. 

The classical and the most useful laboratory method for the preparation of quinones is the oxidation of monohydric phenols with the radical reagent, potassium nitrosodisulphonate [(K03S)2NO] (Fremy s salt) (the Teuber reaction).5 Details for the conversion of 3,4-dimethylphenol into 3,4-dimethyl-1,2-benzoquinone may be regarded as typical55 the probable mechanistic pathway is formulated below. 

Thus two successive oxidations of 429 (Scheme 59) involving the Jones reagent and dichlorodicyano-p-benzoquinone respectively led to the enone 430. A similar reductive cleavage as above of the derived dimethyl acetal 431 with diisobutylaluminium hydride occurred from the less hindered a-side to furnish the P-methoxyether 432 as the major isomer. Selective O-debenzylation of432, achieved with iodotrimethylsilane led to ( )-coccinine (413). 

Thielemann [115] discussed the determination of hydroquinone and its oxidation product 1,4-benzoquinone, both of which are toxic constituents of coal industry waste water. He reviews methods for the quantitative detection of benzoquinone and describes a semiquantitative method for its determination by thin layer chromatography on Kieselgel G using 2% ethanolic solution of 4-aminoantipyrine (l-phenyl-2,3-dimethyl-4-aminopyrazol-5-one) as spray reagent. 

Whereas hydroquinone (p-HOPhOH) in acetonitrile is oxidized via an irreversible two-electron process at +1.18 V versus SCE (Eq. 12.34 and Table 12.2), its dimethyl ether (p-MeOPhOMe) is significantly more resistant with a reversible one-electron oxidation at +1.30 V versus SCE (Figure 12.5).16 The initial oxidation of the latter is followed by a second irreversible one-electron oxidation ( + 1.81 V vs. SCE) that yields a product that is reduced at +0.59 V versus SCE [consistent with the reduction of benzoquinone in the presence of hydronium ions (Table 12.2)] ... 

In an EC2j process, the initial ET step is followed by a second-order irreversible homogeneous reaction. For example, the feedback mode of SECM was employed to study the reductive hydrodimerization of the dimethyl fumarate (DF) radical anion [22]. The experiments were carried out in solutions containing either 5.15 or 11.5 mM DF and 0.1 M tetrabutylammonium tetrafluoroborate in A,A,-dimethyl form amide (DMF). The increase in the feedback current with increasing concentration of DF indicated that the homogeneous step involved in this process is not a first-order reaction. The analysis of the data based on the EC2 theory yielded the fc2 values of 180M-1 s-1 and 160M-1 s-1 for two different concentrations. Another second order reaction studied by the TG/SC mode was oxidative dimerization of 4-nitrophenolate (ArO-) in acetonitrile [23]. In this experiment, the tip was placed at a fixed distance from the substrate. The d value was determined from the positive feedback current of benzoquinone, which did not interfere with the reaction of interest. The dimerization rate constant of (1.2 0.3) x 108 M x s-1 was obtained for different concentrations of ArO-. 

Fig (25) Catechol (201) on oxidation with silver oxide generates 3-isopropyl-o-benzoquinone (199) which undergoes ultrasound-promoted cycloaddition with 6,6-dimethyl-1 -vinylcyclohexene (200) yielding the synthesis of miltirone (197). 

Abbreviations BSA, bovine serum albumin Chi, chlorophyll DCPIP, 2, 6-dichlorophenol indophenol DMBQ, 2, 6-dimethyl-l, 4-benzoquinone DTT, dithiothreitol Fd, ferredoxin Hepes, N-2-hydroxyethyl-piperazine N -2-ethane sulphonate LDAO, lauryldimethyl amine oxide Mes, 4-morpholine ethane sulphonic acid MV, methyl viologen PAGE, polyacrylamide gel electrophoresis PRuK, phosphoribulokinase PS, photosystem Ru5P, ribulose 5-phosphate SDS, sodium dodecyl sulphate TMPD, N, N, N, N -tetramethyl paraphenylene diamine TRX. thioredoxin... 

AD-mix-P 9-BBN Bn Boc Bz BOM CDI m-CPBA CSA Cy DBU DDQ DEAD DIAD DIBAL-H DIPT DME DMF DMAP DMSO EDC HMPA HOBT KHMDS LDA MEM MOM MoOPH NaHMDS NBS NMM NMO Piv PMB Reagent for Sharpless asymmetric dihydroxylation 9-Borabicyclo[3.3.1 ]nonyl Benzyl t-Butoxy carbonyl Benzoyl B enzyloxy methyl Carbonyldiimidazole m-Chloroperoxybenzoic acid Camphorsulfonic acid Cyclohexyl 1,8 -Diazabicy clo[5.4.0] undec-7-ene 2,3 -Dichloro-5,6-dicyano-p-benzoquinone Diethyl azodicarboxylate Diisopropyl azodicarboxylate Diisobutylaluminum hydride Diisopropyl tartrate Dimethoxyethane A,N-Dimethylformamide 4-Dimethylaminopyridine Dimethyl sulfoxide N-(3-Dimethylaminopropyl)-A -ethylcarbodiimide Hexamethylphosphoramide 1 -Hydroxybenzotriazole Potassium hexamethyldisilazane Lithium diisopropylamide Methoxyethoxymethyl Methoxymethyl Oxidodiperoxymolybdenum(pyridine)(hexamethylphophoramide) Sodium hexamethyldisilazane N - Bromosuccinimide A-Methylmorpholine A-Methylmorpholine A-oxide Pivaloyl /j-Methoxybenzyl... 

Ac, acetyl AIBN, azobis(isobutanonitrile) All, allyl AR, aryl Bn, benzyl f-BOC, ferf-butoxycarbonyl Bu, Butyl Bz, benzoyl CAN, ceric ammonium nitrate Cbz, benzyloxycarbonyl m-CPBA, m-chloroperoxybenzoic acid DAST, diethylaminosulfur trifluoride DBU, l,8-diazabicyclo[5.4.0]undec-7-ene DCC, /V. /V - d i eye I oh e x y I c ar bo -diimide DCM, dichloromethyl DCMME, dichloromethyl methyl ether DDQ, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone DEAD, diethyl azodicarboxylate l-(+)-DET, L-(+)-diethyl tartrate l-DIPT, L-diisopropyl tartrate d-DIPT, D-diisopropyl tartrate DMAP, 4-dimethylaminopyridine DME, 1,2-dimethoxyethane DMF, /V./V-dimethylformamide DMP, 2,2-dimethoxypropane Et, ethyl Im, imidazole KHMDS, potassium hexamethyldisilazane Me, methyl Me2SO, dimethyl sulfoxide MOM, methoxymethyl MOMC1, methoxymethyl chloride Ms, methylsulfonyl MS, molecular sieves NBS, N-bromosuccinimide NIS, /V-iodosuccinimide NMO, /V-methylmorpho-line N-oxide PCC, pyridinium chlorochromate Ph, phenyl PMB, / -methoxvbenzyl PPTs, pyridiniump-toluenesulfonate i-Pr, isopropyl Py, pyridine rt, room temperature TBAF, tetrabutylammonium fluoride TBS, ferf-butyl dimethylsilyl TBDMSC1, f-butylchlorodimethylsilane Tf, trifhioromethylsulfonyl Tf20, trifluoromethylsulfonic anhydride TFA, trifluoroacetic acid THF, tetrahydrofuran TMS, trimethylsilyl TPAP, tetra-n-propylammonium perruthenate / -TsOH. / -toluenesulfonic acid... 

N-Substituted 1,2-diazocine 34, containing a conjugated diene moiety, was reacted with dimethyl acetylenedicar-boxylate (DMAD) to give the cycloaddition adduct 35 in excellent yield. The latter was oxidized with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) to give the benzodiazocine 36 (Scheme 7) <2004TL3757>. 

For example, 3,4-dimethylphenol (7.35) is oxidized to 4,5-dimethyl-o-benzoquinone (7.36) with Fremy s radical (7.34) and sodium dihydrogen phosphate. The oxidation of the phenol 2-[(Z)heptadec-10 -enyl]-6-methoxyphenol (7.37) with Fremy s radical produced irisquinone (7.38) in 87% yield. 

With other quinones, the only olefin yielding stable complexes is 1,5-cyclooctadiene. The quinones employed have been trimethyl-p-benzoquinone, 2,5- and 2,6-dimethyl-p-benzoquinone (531), and vitamin E quinone (530). In general, these complexes show higher water solubility, higher dipole moments, and more marked paramagnetism than do the duroquinone complexes. The paramagnetism suggests that there is some electron transfer from nickel to quinone and that the nickel may indeed have an oxidation state midway between Ni(0) and Ni(II). 

Mukaiyama, T., Shintou, T., Fukumoto, K. A Convenient Method for the Preparation of Inverted tert-Alkyl Carboxylates from Chiral tert-Alcohols by a New Type of Oxidation-Reduction Condensation Using 2,6-Dimethyl-1,4-benzoquinone. J, Am, Chem, Soc, 2003,125, 10538-10539. 

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