Benzoquinones, preparation from phenols hydroquinones

Problem 19.33 From phenol prepare (a) p-benzoquinone, (b) p-benzoquinone dioxime, (c) quinhydrone (a 1 1 complex of p-benzoquinone and hydroquinone). 4... 

In small-scale syntheses, a wide variety of oxidants has been employed in the preparation of quinones from phenols. Of these reagents, chromic acid, feme ion. and silver oxide show outstanding usefulness in the oxidation of hydroquinones. ThaUium(lll) trifluoroacetate converts 4-halo-or 4-fOT-butylphenols to 1,4-benzuquinones in high yield. For example, 2 bromo-3-methyl-5-r-butyl 1,4-benzoquinone (4) has been made by this route. 

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. ... 

When phenolate anions are used as substrates, phenazine dioxides are produced. The same product—2-hydroxyphenazine dioxide (173 R1 = H, R2 = OH)—is formed, whether phenol, resorcinol, hydroquinone, or benzoquinone is used,9,390,392 illustrating the variability of the relationship between the oxidation levels of the substrates and products. Benzofuroxan, a trialkylphosphine, and a quinone produce blue-violet phos-phonium betaine derivatives (e.g., 173 R1 = PR3+, R2 = 0-).393 The ether 173 (R1 = H, R2 = O-alkyl) is produced from a hydroquinone monoether.390 1-Hydroxyphenazine dioxide (173 R1 = OH, R2 = H) can be prepared from benzofuroxan, cyclohexane- 1,2-dione, and a base, followed by oxidation of the mixture of mono- and di-iV-oxide formed.394 /J-Naphthol provides benzo[a] phenazine dioxide (174).9,390... 

This reaction was first reported by Haddadin and Issodorides in 1965. It is the preparation of quinoxaline-1,4-dioxides from the cycloaddition between benzofuroxan (i.e., benzofu-razan A -oxide) and dienes, a.y -unsaturated ketones, enamines, or enolates. Unfortunately, this reaction is not named after the authors who discovered it instead it is known as the Beirut reaction after the city in which the inventors carried out is the initial work. In most cases, ketones," /3-diketones, j8-ketoesters, )8-ketonitrile, LS-dinitrile, and/8-ketoamides all are suitable for this reaction, and the corresponding enolates can be easily prepared in the presence of a weak base such as triethylamine. In addition, even phenolic enolates from phenol, resorcinol, hydroquinone, or benzoquinone undergo a similar dehydrative condensation with benzofuroxan under mild conditions (e.g., Na0H/H20, H2O, MeOH/RNH2, Si02/MeCN at room temperature), to give phenazine iV,iV -dioxide derivatives. ... 

Analogously, in the presence of silica-supported palladium catalysts, benzene is oxidized under ambient conditions to give phenol, benzoquinone, hydroquinone and catechol [37b]. Palladium chloride, used for the catalyst preparation, is believed to be converted into metallic palladium. The synthesis of phenol from benzene and molecular oxygen via direct activation of a C-H bond by the catalytic system Pd(OAc)2-phenanthroline in the presence of carbon monoxide has been described [38]. The proposed mechanism includes the electrophilic attack of benzene by an active palladium-containing species to to produce a a-phenyl complex of palladium(ll). Subsequent activation of dioxygen by the Pd-phen-CO complex to form a Pd-OPh complex and its reaction with acetic acid yields phenol. The oxidation of propenoidic phenols by molecular oxygen is catalyzed by [A,A"-bis(salicylidene)ethane-l,2-diaminato]cobalt(ll)[Co(salen)] [39]. 

---