Quinone hydroquinones from

Selected examples of quinones from hydroquinones and catechols... 

In the presence of pyridine, nicotinium dichromate is also a sufficiently strong oxidant for the preparation of quinones from hydroquinones,... 

Derivatives of phenol or aniline can be oxidized to quinones, the yield and ease of oxidation depending on the substituents. If an amino or hydroxyl group is in the para position, the reaction proceeds readily, as illustrated by the synthesis of quinone from hydroquinone by oxidation with a sodium chlorate-vanadium pentoxide mixture (5>6%) or with chromic-sulfuric acid mixture (92%). A para halogen atom usually has a favorable effect. Any group in the para position is eliminated or oxidized. o-Quinones are usually prepared from the corresponding catechols. A survey of procedures for the synthesis of benzoquinones by oxidation has been made. ... 

In small-scale syntheses, a wide variety of oxidants have been employed in the preparation of quinones from phenols. Of these reagents, chromic acid, ferric ion, and silver oxide show outstanding usefulness in the oxidation of hydroquinones. Thallium (ITT) triduoroacetate converts 4-halo- or 4-/ f2 -butylphenols to l,4-ben2oquinones in high yield (110). For example, 2-bromo-3-methyl-5-/-butyl-l,4-ben2oquinone [25441-20-3] (107) has been made by this route. 

The BASF route started from hydroquinone, which was converted to 2,5-dihydroterephthalic acid by a Kolbe-Schmitt reaction. One mole of this acid was treated with two moles of an arylamine, both components being in the form of a suspension in aqueous methanol. This was added to a small amount of a solution of vanadium(III) chloride and sodium chlorate. Gentle heating gave a 95% yield of 2,5-bis(arylamino)benzo-l,4-quinone-3,6-dicarboxylic acid. Ring closure to the trans-quinacridonequinone took place in the presence of concentrated sulphuric acid at 60-80 °C. This was then reduced to the required crude pigment by zinc or aluminium powder in caustic soda under pressure,in an aluminium chloride/urea melt or by the use of a sulphuric acid/polyphosphoric acid mixture. 

Quinone/Hydroquinone Formation. In studies on biodegradation of lignin models with ligninolytic cultures of P. chrysosporium (and other fungi), a number of quinones and hydroquinones were isolated. In other studies their formation has been implied from the isolation of their structural counterparts (29,30), where rapid fungal degradation of the quinones prevented their isolation. Various routes to these metabolic intermediates exist, which have been extensively reviewed (26,27). 

Very useful building blocks have been generated by silylation of succinic anhydrides to afford 2,5-bis(trimethylsiloxy)furans (80TL3423). These compounds react with various dienophiles to give p-quinones and hydroquinones. The bis(silyloxy)furan thus functions as an equivalent of the inaccessible diketene (38). With an unsymmetrical dienophile, the regioisomer derived from para orientation predominates (Scheme 8). 

Urban S, Capon RJ (1996) Deoxyspongiaquinones New Sesquiterpene Quinones and Hydroquinones from a Southern Australian Marine Sponge Euryspongia sp. Aust J Chem 49 611... 

This deprotection-oxidation can also be applied to the preparation of quinones from trialkylsilyl-pro-tected hydroquinones. This method has wider applicability than that reported employing PCC, since substrates with electron-releasing and those with electron-withdrawing groups are oxidized. Use of the reagent prepared in situ appears to be preferable to the preformed reagoit. 

Phenols are rather easily oxidized despite the absence of a hydrogen atom on the hydroxylbearing carbon. Among the coloured products from the oxidation of phenol by chromic acid is the dicarbonyl compound p-benzoquinone (also known as 1,4-benzoquinone or simply quinone). Dihydroxybenzenes, hydroquinone (7.30) and catechol (7.32) are oxidized to p-benzoquinone (7.31) and o-benzoquinone (7.33), respectively, by milder oxidants such as Jones reagent. Fremy s radical (7.34) is an excellent and very specific oxidizing agent for the oxidation of phenols to o- or p-benzoquinones. (m-Quinones do not exist.)... 

Reaction of Aniline with Organic Functional Groups. In the absence of catalysis by enzymes or metals, aniline undergoes nucleophilic addition reactions to quinone and other carbonyl groups in humic substances to form both heterocyclic and nonheterocyclic condensation products (9). In aqueous solution, aniline undergoes 1,4-addition (Michael addition) to both 1,2- and 1,4-quinones (10-14). The reaction of aniline with 1,4-benzoquinone, from the oxidation of hydroquinone, and with 4-methyl-1,2-quinone, from the oxidation of 4-methylcatechol, are illustrated here. 

Other carbohydrate-derived dienes in the open-chain form have also been investigated. Dienes 5, upon addition to the quinone 6, generated in situ from hydroquinone, reportedly give single adducts 7, which are epimerized on basic alumina to compounds 82. 

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