Oxidative phenols

Stilbenequiaones such as (5) absorb visible light and cause some discoloration. However, upon oxidation phenolic antioxidants impart much less color than aromatic amine antioxidants and ate considered to be nondiscoloring and nonstaining. 

Some oxidations in slurry reac tors include cumene with metal oxides, cyclohexene with metal oxides, phenol with CuO, and n-propanol with Pt. 

Fig. 36. Structure of magnesium oxide-phenolic resin complex.

Cellulose Esters Epoxy Resins Lignins Polystyrene Poly (2-vinyl pyridine) Polyvinyl Chloride Polymethyl methacrylate Polyphenylene Oxide Phenolics Polycarbonate Polyvinyl Acetate, etc. Polyvinyl butyral SBR rubber, etc., etc. 

In the first of these, the key step in the synthetic sequence involves an oxidative phenol coupling reaction patterned after the biosynthesis of the natural product. Preparation of the moiety that is to become the aromatic ring starts by methyla-tion of phloroglucinol (5) with methanolic hydrogen chloride to give the dimethyl ether (6). Treatment of that intermediate with sulfuryl chloride introduces the chlorine atom needed in the final product (7). 

Organic syntheses based on biosynthetic proposals are often extremely concise and elegant.6 Although the constitution and stereochemical complexity of carpanone may seem formidable, the sequential application of the Diels-Alder and oxidative phenolic coupling transforms7 to the natural product provides an exceedingly efficient solution. Chapman s striking synthesis of carpanone typi-... 

The rearrangement of dimethyl 5-hydroxy-l-bcnzothiepin-3,4-dicarboxylate (9, R = OH), the first example of a thermal rearrangement of a thiepin derivative without loss of sulfur,12 is analogous to the oxepin-benzene oxide-phenol rearrangement (cf. Section D,l. Introduction and Section 1.2.5.1). This process is catalyzed by the acidic hydroxy substituent. In fact, if this functional group is modified by an in situ acetylation (R = OAc), the usual loss of sulfur occurs. 

Chaliha S, Bhattacharyya KG (2008) Using Mn(II) - MCM41 as an environment - friendly catalyst to oxidize phenol, 2-chlorophenol and 2-nitrophenol in aqueous solution. Ind Eng Chem Res 47 1370-1379... 

The effect of jumping of the maximal hydroperoxide concentration after the introduction of hydrogen peroxide is caused by the following processes. The cumyl hydroperoxide formed during the cumene oxidation is hydrolyzed slowly to produce phenol. The concentration of phenol increases in time and phenol retards the oxidation. The concentration of hydroperoxide achieves its maximum when the rate of cumene oxidation inhibited by phenol becomes equal to the rate of hydroperoxide decomposition. The lower the rate of oxidation the higher the phenol concentration. Hydrogen peroxide efficiently oxidizes phenol, which was shown in special experiments [8]. Therefore, the introduction of hydrogen peroxide accelerates cumene oxidation and increases the yield of hydroperoxide. 

Besides this protective mechanism, there is the possibility of the effect of other inhibitors, such as oxidized phenolic compounds,297-300... 

Iron, Fe2+ (d6) Iron, Fe2+ (d6) 4, tetrahedral 6, octahedral N-Thiolate O-Carboxylate, alkoxide, oxide, phenolate Electron transfer, nitrogen fixation in nitrogenases, electron transfer in oxidases... 

Schwartz MA, Holton RA (1970) Intramolecular oxidative phenol coupling. II. Biogenetic-type synthesis of (+-)-maritidine. J Am Chem Soc 92 1090-1092... 

The classic oxidizing systems of human myeloperoxidase and horseradish peroxidase were exploited for their well-known abilities to oxidize phenolic substrates. Under conditions of incubations, the following oxidation pathway was defined (155). Peroxidases are first converted to the oxidized... 

Aliphatic acids (fumaric acid, maleic acid) are rapidly oxidized at the Sn02 anode, whereas they are practically electrochemically inactive at the Pt anode. The process at the Sn02 is able to completely oxidize phenol, which is quite unique for a low temperature process. 

Oxidative phenolic coupling. Biosynthesis of the alkaloid narwedine (3) is known to involve oxidative phenolic coupling of norbelladine derivatives (1), but the usual oxidants for such coupling in vitro convert 1(R = H) into the oxomaritidine skeleton (4) rather than 3. A new biomimetic synthesis of 3 involves the palladacycle 2, formed by reaction of 1(R = CH3) with Li2PdCl4, which is known to form complexes with allylic amines or sulfides (8,176-177). Oxidation of 2 with thallium(III) trifluoroacetate effects the desired coupling to give 3. 

MnP catalyzes hydrogen-peroxide-dependent oxidation of Mn to Mn, which in turn oxidizes phenolic components of lignin [102]. Oxidative demethylation, dechlorination, and decolorization of bleach plant effluent by the MnP of Phanerochaete chrysosporium has been demonstrated [103,104]. 

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