Preparation of quinones

It is often possible to convert aromatic hydrocarbons directly into quinones. According to a German patent376 / -benzoquinone is obtainable in 50-55% yield by heating benzene with moist lead dioxide in 100% sulfuric acid at 56° for 5 min, then pouring the mass on ice and extracting the quinone with chloroform this quinone can also be prepared by electrolytic oxidation of benzene, in 65% yield.377 

Graebe and Liebermann378 converted anthracene into anthraquinone by oxidation with chromic acid in glacial acetic acid, although it is preferable379 to use sodium chlorate and vanadium pentoxide as catalysts. However, anthraquinone can also be prepared in good yield by use of potassium permanganate  

When melted with oxidizing agents such as nitrates, permanganates, or chlorates, anthracene gives anthraquinone, in some cases in theoretical yield.380 

10-Phenanthraquinone is obtained in 80% yield by treating phenanthrene with chromic-sulfuric acid,381 and 2,3-dimethylnaphthalene gives 2,3-di- 

Teuber and his co-workers have found that monohydric phenols and naph-thols can be converted into quinones by potassium nitrosodisulfonate.384 When the p ra-position is unoccupied, use of 2 moles of N0(S03K)2 per mole usually gives p-quinones phenol gives p-benzoquinone, and 1-naphthol gives 

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Synthesis by oxidation remains the first choice for commercial and laboratory preparation of quinones the starting material (1) provided the generic name quinone. This simple, descriptive nomenclature has been abandoned by Chemicaly hstracts, but remains widely used (2). The systematic name for (2) is 2,5-cyclohexadiene-l,4-dione. Several examples of quinone synonyms are given in Table 1. Common names are used in this article. 1,2-Benzoquinone (3,5-cydohexadiene-l,2-dione) (3) is also prepared by oxidation, often with freshly prepared silver oxide (3). Compounds related to (3) must be prepared using mild conditions because of their great sensitivity to both electrophiles and nucleophiles (4,5). 

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 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. 

DAIB and BTIB oxidations of phenols proceed through aryloxyiodane 129 and/or aryloxenium ion 130 intermediates and are quite useful for the preparation of quinones, quinol ethers, and quinone acetals (e.g., Scheme 39) (88TL677, 92MI2, 93JCS(P1)1891, 01OR327). When phenols bearing nucleophilic side chains are used as substrates, such oxidations provide fertile ground for the assembly of heterocyclic structures. This can be accomplished by oxidative-cyclization reactions of different types. 

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. 

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

Oxidation of 3-phenyl-7-hydroxybenzothiophene with Fremy s salt afforded, in almost equal amounts, 3-phenyl derivatives of 156 and 157 (70MI3). Difficulties were encountered in the preparation of quinones from substituted alkyl benzothienyl-3-acetates. The only successful conversion of ethyl 6-hydroxy-5-methoxybenzothienyl-3-acetate was in a two-phase system with either aqueous periodate or thallate. The quinone was obtained in low yield (79JHC231). Some exteneded analogs could be prepared directly from the hydrocarbons with chromic acid (53CB366 56JCS3435). 

Oxidants especially suitable for the preparation of quinones are salts of trivalent iron. Bromo-m-xyloquinone (2-bromo-3,5-dimethyl-p-benzo-quinone) is obtained in 84% yield by steam distillation of 2-bromo-3,5-dimethylhydroquinone with ferric sulfate and dilute hydrochloric acid [914], The treatment of 2-mercaptohydroquinone with 2 N ferric chloride in ethanol at room temperature gives a quantitative yield of p-benzoqui-none disulfide [907]. Just shaking halogenated hydroquinones with an... 

The quinones are yellow compounds, possessing a characteristic odour they are easily volatile with steam, but with a slight decomposition. They are somewhat volatile even with the vapour of ether, as one observes in the preparation of quinone- On reduction they take up two hydrogen atoms and pass over to hydroquinones. (See the next preparation) e.g. -... 

Since the hydroquinone solution may be extracted with ether with much greater ease than the quinone solution, and since the hydroquinone is smoothly oxidised to quinone, the preparation of quinone may be done as follows The entire quantity of the oxidation product is saturated with sulphur dioxide, and as Just described the hydroquinone may be obtained by repeated extraction with ether. In order to convert it into quinone it is dissolved in the least possible amount of water, to which is added 2 parts of concentrated sulphuric acid to 1 part of hydroquinone the well-... 

Machowska, Z., Mieluch, J., Obloj, J., et al (1987). Process for Preparing Vitamin K3 from 2-methylnaphthalene, Polish Patent PL 140780 Harrison, S., Fiset, G. and Mahdavi, B. (1999). Preparation of Quinones by Oxidation of Aromatic Compounds Using Electrochemically Prepared Ceric Ion, European Patent EP 919533. 

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