Hydroxyl phenolic

Key words Activated carbon. Benzene hydroxylation, Phenol, Transition metal 1. INTRODUCTION... 

Keywords Peroxidase, Biocatalysis, Asymmetric synthesis. Kinetic resolution. Hydroperoxide, Epoxidation, Sulfoxidation, Halogenation, Hydroxylation, Phenol coupling. 

Stack and co-workers recently reported a related jx-rf / -peroxodi-copper(II) complex 28 with a bulky bidentate amine ligand capable of hydroxylating phenolates at - 80 °C. At - 120 °C, a bis(yu,-oxo)dicopper(III) phenolate complex 29 with a fully cleaved 0-0 bond was spectroscopically detected (Scheme 13) [190]. These observations imply an alternative mechanism for the catalytic hydroxylation of phenols, as carried out by the tyrosinase metalloenzyme, in which 0-0 bond scission precedes C - 0 bond formation. Hence, the hydroxylation of 2,4-di-tert-butylphenolate would proceed via an electrophilic aromatic substitution reaction. 

In the presence of nitric acids, 4-hydroxylated phenolic acids (and to some extent also hydroxylated indoles from tryptophan) conjugate with l-nitroso-2-naphthol to yield orange/red chromophores [4]. The structure of l-nitroso-2-naphthol is shown in Fig. 1.3.1. 

Oxidations. This peracid has been known since 1910 but a report of its use in oxidation of organic compounds has appeared only recently. It hydroxylates phenol. 

Up to 47 mg/kg of CP-transformation products such as o- and />-hydroxylated phenols (Knuutinen et al., 1990), as well as chloroanisoles such as 2,3,4,6-TeCA and PCA (Palm et al., 1991), have often been found in CP-contaminated soils. An additional route for contamination is the CP-treated utility poles and railway ties that contaminate nearby environments via runoff and leaching (Wan, 1992). 

The pseudo-first order rate constants (resp. coefficients) for the direct reaction of some compounds may almost be in the order of typical hydroxyl rate constants (kR > 10 M s ), due to high concentrations of the pollutants as well as mass transfer enhancement. For example, Sotelo et al. (1991) measured values of 6.35 106 and 2.88 106 M l s"1 for the dissociating hydroxylated phenols, resorchinol (1,3-dihydroxybenzene) and phlorogluci-nol (1,3,5-tn hydroxybenzene) respectively (pH = 8.5 and T= 20 °C). 

External Phenol Hydroxylation. Although the xy ly 1 systems that we have discussed are of great interest, they involve stoichiometric reactions that are more useful in mechanistic investigations than in synthesis. Tyrosinase o-hydroxylates phenols with turnover, and there is considerable industrial interest in catalytic phenol oxygenation. 

Tyrosinase is a copper-containing oxidase (Coche-Guerente et al, 2001 Forzani et al, 2000), which possesses the two different activities illustrated in Figure 57.12. In the first step, referred to as the hydroxylase or cresolase activity, molecular oxygen is used to hydroxylate phenol to form catechol. In the second step, known as the catecholase activity, the enzyme oxidizes catechol to o-quinone, which is simultaneously oxidized by oxygen to its original form, with the production of water. The o-quinone is electro-chemically active and can be reduced back to catechol, as illustrated above in Eq. (57.17). 

Selective activation of carboxylic acids. Carboxylic acids add exclusively to the triple bond of 1 to form an adduct (a) that rearranges to the (Z)-enol ester 2. Hydroxyl, phenolic, amino, and mercapto groups do not react with 1 under the same conditions. The esters (2) react with alkali metal salts of thiols and of selenophenol in THF at 0° to form thiol and selenol esters (3). 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

Another route to hydroxylated phenols is the application of mushroom polyphenol oxidase in chloroform. The primary products of oxidation. 

Vanillyl phenols Syringyl phenols Cinnamyl phenols p-Hydroxyl phenols Sum of phenols ( Lig/g organic carbon) % phenol carbon totd organic carbon ... 

In lakes, the pool of dissolved organic carbon (DOC) is dominated by dissolved humic substances (up to 80% of the DOC). Lake humic substances are similar to soil humic substances in that carboxyl, hydroxyl, phenol, and probably methoxyl groups are of major significance. Fluorescence spectra of DOC may be interpreted in terms of the different geochemical origins of DOC (e.g., allochthonous versus algal derived). One or more moieties of dissolved humic substances are produced autochthonously mechanisms may include polymerization of phenols (promoted by transition metals), Maillard condensations, or oxidation via phenolase systems. Aliphatic structural units in dissolved humic substances provide a flexible conformation to the humic substance molecule. ... 

Reactions with persulfate and pyrosulfate. The persulfate (peroxy-dlsulfate Ion, S2O8 ) reaction, also known as the Elba persulfate oxidation, has been Important In synthesis of hydroxylated phenols. The method has occasionally been used for synthesis of 0-sulfate conjugates. For example, 4-hydroxy-2-nltrophenyl sulfate was obtained when 3-nltrophenolate was stirred with potassium peroxydlsulfate at room temperature for 2 days (91,). The persulfate reaction has been used for the sulfation of various phenols and aromatic amines however the yields are usually low to moderate (77 ). The sulfate group Is preferentially Introduced In the 4-posltlon of phenols and In the 2-posltlon of aromatic amines but If these positions are blocked substitution at the 2- and... 

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