Oxidation of Aromatic Hydrocarbons to Quinones

—40% theoretical (5 gms.) (cf. yield in Preparation 171). Yellow plates with sharp odour insoluble in water soluble in hot alcohol volatile in steam M.P. 125°. (J. C. S., 37, 634 A., 167, 357.) 

—Almost theoretical (35 gms.). Orange needles odourless not volatile in steam insoluble in water and in cold alcohol soluble in glacial acetic acid M.P. 198°. (A., 167, 139.) 

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Oxidation of Aromatic Hydrocarbons to Quinones Areno-quinone transformation... 

Reactions for detection and identification of aromatic hydrocarbons can be divided into substitution reactions (nitration, chlorosulfonation, acetylation), addition reactions (7r-complexes), and oxidative reactions (oxidation of aliphatic chains, oxidation of aromatic hydrocarbons to quinones). The... 

Zinc dichromate tiihydrate, ZnCr207<3H20, is obtained as an orange-red solid by adding zinc carbonate to a cold solution of chromium trioxide in dilute sulfuric acid [660]. The applications are oxidations of acetylenes lo a-diketones, of aromatic hydrocarbons to quinones, of alcohols to aldehydes, and of ethers to esters and the oxidative regeneration of carbonyl compounds from their oximes [660]. 

The applications of ruthenium tetroxide range from the common types of oxidations, such as those of alkenes, alcohols, and aldehydes to carboxylic acids [701, 774, 939, 940] of secondary alcohols to ketones [701, 940, 941] of aldehydes to acids (in poor yields) [940] of aromatic hydrocarbons to quinones [942, 943] or acids [701, 774, 941] and of sulfides to sulfoxides and sulfones [942], to specific ones like the oxidation of acetylenes to vicinal dicarbonyl compounds [9JS], of ethers to esters [940], of cyclic imines to lactams [944], and of lactams to imides [940]. 

A mixture of arene oxides and quinones is reported to have been formed by the electrochemical oxidation of aromatic hydrocarbons in an atmosphere of oxygen or oxygen-containing gaseous mixtures. The method is patented and details have not been disclosed.37... 

The synthesis of quinones from arenes is an area which demands further research, despite the number of reagents presently available for this transformation. This is highlighted by the synthesis of the naphthoquinone (3). Direct oxidation of the dibromoarene (1) was unsatisfactory, and therefore Bruce and coworkers had to resort to a multistep sequence involving nitration, reduction, diazotization, displacement by hydroxide and finally oxidation of the phenol (2) with Fremy s salt (Scheme 1). Although there are examples of the oxidation of polynuclear aromatic hydrocarbons to quinones, the direct oxidation of an arene to a quinone is a process not encountered in the synthesis of more complex mt ecules. 

The relationship of quinones to aromatic compounds is revealed by their preparation by the oxidation of aromatic hydrocarbons, phenols or amines (Scheme 3.52). 

Oxidations with chromic oxide encompass hydroxylation of methylene [544] and methine [544, 545, 546] groups conversion of methyl groups into formyl groups [539, 547, 548, 549] or carboxylic groups [550, 55i] and of methylene groups into carbonyls [275, 552, 553, 554, 555] oxidation of aromatic hydrocarbons [556, 557, 555] and phenols [559] to quinones, of primary halides to aldehydes [540], and of secondary halides to ketones [560, 561] epoxidation of alkenes [562, 563,564, and oxidation of alkenes to ketones [565, 566] and to carboxylic acids [567, 565, 569]. 

Manganic sulfate, Mn2(S04)3, is obtained by the oxidation of manganese sulfate (tetrahydrate) in 6 M sulfuric acid by aqueous potassium permanganate at 0-25 °C. This oxidant oxidizes aromatic hydrocarbons to quinones [802]. 

Introduction. The quinones are intermediate products in the oxidation of the aromatic nucleus. They may be prepared in some cases by the direct oxidation of aromatic hydrocarbons. For example, anthracene, naphthalene, and phenanthrene are oxidized to the corresponding quinones by chromic acid mixtures. Quinones are prepared more conveniently by oxidation of primary aromatic amines, particularly the p-substituted amines. p-Benzoquinone is obtained by the oxidation of aniline, p-toluidine, sulfanilic acid, p-aminophenol, and other similar compounds. Similarly the a-naph-thoquinone is obtained by oxidation of 1,4-aminonaphthol, and /9-naphthoquinone by the oxidation of 1,2-aminonaphthol. In the laboratory, although it is possible to prepare p-benzoquinone by the oxidation of aniline with acid-dichromate mixture, the method is tedious and the yield poor. Since hydroquinone is used extensively as a photographic developer and is made industrially, it is more convenient to prepare quinone by its oxidation. 

Oxidation of aromatic compounds. Chambers et aO explored oxidation of aromatic hydrocarbons with anhydrous pertrifluoroacetic acid in methylene chloride and, except in the case of benzene and toluene, obtained mixtures shown to contain small amounts of phenols and quinones, as exemplified by the case of m-xylene ... 

The reagent has found some use for the oxidation of aromatic hydrocarbons and phenols to para quinones. Arnold and Lawson " heated a mixture of 10 g. of naphthalene, 25 ml. of 30% hydrogen peroxide, and 50 ml. of acetic acid just above 80° for 45 min., distilled off about half of the solvent, added water to precipitate the product, and by crystallization isolated satisfactory 1,4-naphthoquinone in 20% yield. Durene (5 g.) was heated with HjOa-AcOH for 15 hrs. on the steam bath and duroquinone (2.1 g.) was separated by steam distillation. Crude 2-methyl-1,4-naphthoquinone and 2,3-dimethyl-l, 4-naphlhoquinone were obtained in yields of 30 and 78%. Unchanged hydrocarbon wax present at the end of each oxidation. 

The most important application of CAS is in the oxidation of aromatic rings. CAN oxidizes polycyclic aromatic hydrocarbons only in moderate yields (20-60%), and these reactions are often complicated by the formation of nitrate esters. In contrast, CAS generally oxidizes aromatic hydrocarbons to quinones in good yields. For example, naphthalene is oxidized to 1,4-naphthoquinone in excellent yield by CAS in a dilute mixture of H2SO4 andMeCN(eq 1). ... 

Phenols (e.g., phenol itself [CeHs-OH or Ar-OH], Table 6.10, item 2) and their esters (e.g., the trifluoroacetate ester of phenol [C6H5-O2CCF3 or Ar02CCH3], Table 6.10, item 3) have been oxidized with air and oxygen (O2), in neutral and alkaUne solutions, with and without ionic and/or radical catalysts and/or irradiation and in a variety of solvents. Enzymes (this chapter and Chapter 12) from a wide variety of sources have also been used. Frequently, oxidation of aromatic systems to phenols cannot be stopped before quinones and products of ring fragmentation occur and numerous, sometimes ill-defined, products result. Thus, as shown in Equation 6.80, oxidation of the polynuclear hydrocarbon chrysene with anunonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NH,)4(S04)4] is reported to produce 6H-benzo[d]naphtho[l,2-/>]pyran-6-one (8% yield) and a quinone (23% yield). The remainder of the product(s) (69%) was unidentified. 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

In addition to the oxidation of aliphatic hydroxy compounds, aromatic derivatives that contain hydroxyl groups (phenol derivatives) can also be oxidized. The course of the oxidation differs in that the aromatic ring is disrupted, leading to quinones, important components in a variety of natural products.It is also possible to convert aromatic hydrocarbons to phenols by oxidation. Quinones are obtained by oxidation of phenols and a phenol can be very loosely viewed as an enol. Inclusion of this chemistry immediately after discussing the oxidation of alcohols to ketones, aldehydes, or acids is done with the goal of providing some continuity in studying the oxidation of hydroxyl compounds. 

The V-Mo-O oxides are well-known industrial catalysts for the synthesis of acrylic acid from acrolein and maleic anhydride from benzene more recently, V-P-0 systems are being utilized for maleic anhydride production from -butane. The V20s/Ti02 combination was employed for phthalic acid production from o-xylene. V-Fe-O catalyzes oxidation of polycyclic aromatic hydrocarbons to dicarboxylic acids and quinones. Methyl formate is produced by the oxidation of methanol over V-Ti-0 catalysts [58]. For many of these processes, it has been experimentally proved that the catalytic reaction follows a Mars-van Krevelen mechanism. The surface coverage with active oxygen 0 in the steady state of the redox reaction following Mars-van Krevelen mechanism is given by... 

Hydroxy derivatives or phenolics are frequent target for method development using carbon paste electrodes based either on direct oxidation of hydroxy group on an aromatic ring or on enzyme-based reactions with the final determination of the product of the enzymatic reaction involved. The reason lies both in their usual ease of oxidation and in their relatively frequent occurrence as hydroxy derivatives of aromatic hydrocarbons form the base of various biologically active organic compounds used as disinfectants, pharmaceuticals, herbicides, and pesticides. CPE and CPE modified with humic acids were used for the determination of pentachloro-phenol. With modified electrode lower determination limit was reached due to better accumulatiOTi of the analyte. Formation of a quinone-Uke compound during... 

Photoinduced electron transfer (PET Scheme 6.2) is a mild and versatile method to generate radical ion pairs in solution," exploiting the substantially enhanced oxidizing or reducing power of acceptors or donors upon photoexcitation. The excited state can be quenched by electron transfer (Eq. 7) before (aromatic hydrocarbons) or after intersystem crossing to the triplet state (ketones, quinones). The resulting radical ion pairs have limited lifetimes they readily undergo intersystem ... 

Aromatic hydrocarbons which do not have side chains in general form p-quinones and acid anhydrides. Benzene, naphthalene and anthracene have been dealt with above. In the case of phenanthrene, no p-quinone is formed as the adjacent C—H groups of the central nucleus are the most reactive. Phthalic anhydride is the main partial oxidation product, in addition to minor products such as 9,10-phenanthraquinone. Andreikov and... 

It is also possible to exploit quenching of ECL in the detection of various substances. Recently Richter and coworkers have shown that ECL from [(bpy)3Ru]2+, generated following oxidation in the presence of trialkylamines, is quenched by quinones and other aromatic hydrocarbons in nonaqueous solvents [60],... 

A hydrogen peroxide and acetic acid mixture is also used in the following reactions carbon-carbon bond break [50], aromatic hydrocarbon and phenol oxidation to n-quinones [51], 2,6-dihaloanilines oxidation to nitroso-compounds and synthesis of N-oxides of pyridine... 

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