Phenols by oxidation

Cumox [Cumene oxidation] A process for making acetone and phenol by oxidizing cumene, based on the Hock process. This version was further developed and licensed by UOR Three plants were operating in 1986. UOP now licenses the Allied-UOP Phenol process, which combines the best features of Cumox and a related process developed by the Allied Chemical Corporation. 

Dow-Phenol A process for making phenol by oxidizing molten benzoic acid with atmospheric oxygen. The catalyst is cuprous benzoate. 

By using this mild and versatile methodology, symmetrical diaryl ethers have been synthesized in a one-pot, two-step procedure starting from arylboronic acids and their partial conversion to the corresponding phenols by oxidation with hydrogen peroxide and a subsequent coupling of the formed phenols with the remaining arylboronic acids upon addition of copper(II) acetate, molecular sieves and triethyl amine (Scheme 7) [22],... 

The main industrial routes for cyclohexanone manufacture have as starting points cyclohexane and phenol, by oxidation and hydrogenation, respectively. Another interesting method is based on the hydration of cyclohexene obtained by selective hydrogenation of benzene. The intermediate cyclohexanol is further dehydrogenated or separated if desired. 

Figure 7 Activation of phenolics by oxidative enzymes such as polyphenol oxidases (PPO) and peroxidases (POD) and reaction of activated phenolics with protein.

Sec. 17.10) from phenols by oxidation with Fremy s salt [(KSC NO]... 

The further oxidation of phenol may also result in the formation of catechol, C,iH4(OH) (1 2). The transformation may be effected by fusion with sodinm hydroxide.85 The snbstance may also be obtained by oxidizing benzene with hydrogen peroxide in the presence of ferrous sulfate88 and by reducing o-benzoquinone with aqueous sulfurous acid in the cold.81 Quinol may be prepared from phenol by oxidation with potassium persulfate in alkaline solution.38 It can also be obtained directly from benzene by the electrolytic oxidation of an alcohol solution to which... 

Figure 16.3-7. Chemoenzymatic Diels-Alder reactions. Ortho-quinones (dienes), derived from phenols by oxidation with tyrosinase, spontaneously react with dienophils.

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. 

By present routes, catechol arises as a co-product in the synthesis of hydroqui-none from phenol by oxidation with peracids. Catechol is used as an antioxidant, principally for turpentine oil and perfumes. For the latter application, especially in the USA, 4-tert-butylcatechol, obtained by butylation, is used. 

C—O Bond Formation Trapping of ArLi intermediates can be achieved with trimethyl borate or triisopropyl borate [41]. The intermediate hthium borate complexes, when treated with water, afford oxidizable boronates. With fluorodimethoxyborane, spontaneous elimination of flnoride leads directly to boronates, which are precursors of phenols by oxidation. Chemoselective metal-heteroatom exchange or deprotonation generates carbanions in the presence of dialkyl peroxides, and intramolecular trapping provides an efficient route to dihydrobenzofuranes and dihydrobenzopyrans [42]. 

It is generally considered that polyphenol oxidase, which has at least three isoforms, is the key enzyme in the fermentation processes that produce black teas, but there is evidence also for an important contribution from peroxidases with the essential hydrogen peroxide being generated by polyphenol oxidase (Subramanian et al. 1999). The primary substrates for polyphenol oxidase are the flavan-3-ols which are converted to quinones. These quinones react further, and may be reduced back to phenols by oxidizing other phenols, such as gallic acid, flavonol glycosides and theaflavins, that are not direct substrates for polyphenol oxidase (Opie etal. 1993,1995). 

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