Benzoquinone acetic acid reduction

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

Methoxy-6-propyl-l,4-benzoquinone (170, Scheme 43) with hydrogen chloride undergoes dimerization and yields the biquinone 171 and the di-benzofuran 172. 2-Hydroxy-3,6-dimethyl-1,4-benzoquinone (173, Scheme 44), however, on treatment with boron trifluoride etherate in ether, or with concentrated sulfuric acid in acetic acid at room temperature, yields the extended quinone 174, which on reductive acetylation affords the dibenzo-furan 175. 

A hr dm 3. Recently, the electrochemical incineration of p-benzoquinone in acetate buffer has been reported by Houk et al. [54]. The cell was similar to that above cited for 4-chlorophenol oxidation (see Sec. III.B), with a Ti or Pt anode coated with a film of the oxides of Ti, Ru, Sn, and Sb. These anodes are stable but somewhat less efficient than an Fe(III)-doped Pb02 film coated on Ti employed in a previous work [55], The COD of 50 mL of 100 ppm / -benzoquinone decreased from an initial value of 190 to 2 ppm during 64 hr of electrolysis at 1 A. The major intermediate products identified were hydroquinone and aliphatic acids including maleic, succinic, malonic, and acetic acids. The suggested reaction sequence is given in Fig. 13, where succinic acid is obtained from a cathodic reduction of maleic acid, which is formed from the breakdown of the dihydroxylated derivative generated by an attack of adsorbed hydroxyl radicals onto p-benzoquinone. Further mineralization of succinic acid occurs via its consecutive oxidation to malonic and acetic acids. 

The 1,4-benzoquinone-cyclopentadiene Diels-Alder adduct 2 is well known.5 The procedure described here is adapted for large-scale preparation. For the zinc reduction, aqueous acetic acid has also been used.4 The present procedure allows recovery of most of the acetic acid. The entire procedure can be completed in 3-4 days. 

Reduction of the mixture of products (98) and (99), obtained by the action of an acylhydrazide on 2,5-dihydroxy-6-undecyl-l,4-benzoquinone, with zinc and acetic acid furnishes 1-acety 1-3-ary 1-... 

For synthesis decumbenine B, compound 2-14 was condensed with 2-7 in THF with LDA (lithium diisopropylamide) at -70°C followed by deprotonation with dilute hydrochloric acid. The desired intermediate 2-15 was obtained successfully in 49% yield. Lithium aluminum hydride reduction of 2-15 afforded the amine 2-16, which was converted to 2-17 by debenzylation with palladium on charcoal in acetic acid. The final step was dehydrogenation, after comparison with several reagents including palladium on charcoal in acetic acid and DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone)/l,4-dioxane, the best results were obtained by using DDQ/benzene. The yield of decumbenine B was 41% (Scheme 3). 

A powerful piece of methodology has been developed involving nucleophilic attack on both an r and an T]p-complex in an adaptation of the Wacker reaction. Treatment of cyclohexadiene 9.268 with palladium acetate in acetic acid gives an -complex 9.281 (Scheme 9.76). If the reaction is done in the presence of sodium acetate, this salt will act as a nucleophile to give an t -complex 9.283 via an initial t -complex 9.282. Reductive elimination to form a bond between a ring carbon and the acetate ligand from palladium then gives the diacetate product 9.280. As the first acetate attacks trans to Pd, and the second acetate comes from Pd, the product is the trans isomer. The palladium is now in its zero oxidation state, but inclusion of benzoquinone reoxidizes it to palladium (II) and makes the entire process catalytic. There is an occasional... 

In Scheme 1, the reactive species of Cr(VI) and paracetamol readily form chromate ester as the first step in the reduction of Cr(VI) [14]. Chromate ester undergoes oxidative decomposition in the next step (rate determining), leading to the formation of an intermediate and Cr(IV) [15]. The proposed mechanism is further supported by analysis of the products. Ammonia has been detected as ammonium ions in aqueous solution. Benzoquinone and acetic acid were also detected by the spot tests [16]. 

The Woodward synthetic route was initiated with a Diels-Alder reaction between 1,4-benzoquinone (14) and diene 15. The cycloadduct 16 formed in this way underwent Meerwein-Pondorff-Verley reduction to afford tricyclic lactone 17 which was converted to bromoether 18. Treatment of this substance with methoxide gave the methyl ether 19. Conversion of 19 to its halohydrin followed by chromium oxidation provided the a-bromo ketone 20 which upon treatment with zinc in glacial acetic acid afforded the bicyclic enone 21. This substance was transformed to the aldehyde-acid 23 by an osmylation-periodate cleavage sequence. The acid function in 23 was es-terified and the aldehyde moiety was condensed with 6-methoxytryptamine. The Schiff base intermediate obtained in this fashion was reduced to give an amine which provided the lactam 24 upon intramolecular acylation. Bischler-Napieralski cyclization of 24 gave the pentacyclic intermediate 25 in which... 

Thiele acetylation. Quinones, when treated with acetic anhydride in the presence of perchloric acid or of concentrated sulphuric acid, undergo simultaneous reductive acetylation and substitution to yield triacetoxy derivatives, e.g., benzoquinone gives 1 2 4-triacetoxybenzene. 

Benzenetetrol has been prepared by the hydrolysis of 2,4,6-triaminophenol with dilute hydrochloric acid and by heating aqueous solutions of <0.2 M 2,4,6-triaminophenol at >130° C (223—225). The acid hydrolysis is improved by copper (226). 1,2,3,5-Benzenetetrol also has been prepared in 46% overall yield by the nitration of hydroquinone diacetate at low temperature to 2,6-dinitrohydroquinone acetate, followed by reduction to the corresponding diamine hydrochloride with tin and hydrochloric acid. The diamine hydrochloride is hydrolyzed to the tetrol with 1 wt % hydrochloric acid at 155—160°C (224). Hydrogenation of 2,6-dibenzoyloxy benzoquinone over Pd—C gives a 90% yield of 1,2,3,5-tetrahydroxybenzene (227). 

Electrochemical reduction of 1,2-benzoquinone-l,2-dioxime in 2 M sulfuric acid/ethanol (1 1, 0 V) gives a mixture of phenazinc-2,3-diamine (39%), 2-amiiiophenazin-3-ol (6%), and benzene-1,2-diamine (51%). In acetate buffer/ethanol (—0.4 V) only phenazine-2,3-diamine is formed. See also Houben-Weyl, Vol. 4/1 d, p 699. 

The reduction of anthranils is a particularly valuable route to 5-chloro-2-aminobenzophenones, the precursors of benzodiazepinones of the Valium and Librium type. Reductions are successful with ferrous sulfate,209 zinc,190 or iron181 in hydrochloric acid iron in acetic acid1 54,155,175-177 zinc and calcium chloride in boiling ethanol165 and hydrazine hydrate in warm ethanol.154 Phenylhydrazine reduces anthranils of type 134 to diamino-p-benzoquinones, e.g., 133.195... 

In 1985, O Malley et al. published the total syntheses of rac-averufin (103) and rac-nidurufin (104) (65). These are both early precursors of the aflatoxins in their biosynthesis. Nidurufin (104) is the direct successor of averufin (103) and the direct precursor of versiconal hemiacetal acetate (12, see Scheme 2.1). Nidurufin (104) and averufin (103) are accessible by the same synthesis route only the two last steps differ firom each other (see Scheme 2.17). The first reaction was a double Diels-Alder reaction with dichloro-p-benzoquinone (97) and two equivalents of diene 98. Then, three of the four alcohol functions were selectively MOM-protected (—> 99). The remaining alcohol was converted into the allyl ether and then subjected to a reductive Claisen rearrangement, followed by MOM-protection of the redundant alcohol ( 100). By addition/elimination of PhSeCl, 101 was formed. Deprotonation of t-butyl 3-oxobutanoate, followed by reaction with 101 yielded the pivotal intermediate 102. This could be converted into rac-averufin (103) by deprotection of the alcohols and decarboxylation at the side chain. The last step was a p-TsOH-catalyzed cyclization to give 103. By treating 102 with /m-CPBA, the double bond is epoxidized. rac-Nidurufin (104) was then formed by cyclization of this epoxide under acidic conditions. 

Preparation by oxidation of 2-hydroxy-4,5-dimethoxybenzophenone with nitric acid (d = 1.2) for 30 min at 15-20°, followed by reduction of the 2-benzoyl-5-methoxy-l,4-benzoquinone formed (93%) with sulfur dioxide in warm ethanol containing a drop of acetic add for 1 h (79%) [763]. 

Also obtained by reduction of 2-acetyl-3,5,6-trimethoxy-l,4-benzoquinone with zinc dust in acetic anhydride, followed by hydrolysis of the acetic ester formed with dilute sulfuric acid [2443]. 

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