Pyrogallol oxidation

FIGURE 1. Examples of reactions catalyzed by molybdenum containing enzymes. From top to bottom, hydroxylation of xanthine, hydroxylation of acetaldehyde, dehydrogenation of carbon monoxide, transhydroxylation of pyrogallol, oxidation of sulfite, reduction of nitrate, reduction of dimethylsulfoxide, oxidation of formate, reduction of polysulfide and formation of formylmethanofuran. 

Figure 15.26 Reaction profiles (monitored at 420 nm) for HRP-catalyzed pyrogallol oxidation at 35 °C.

Pyrogallol monomethyl ether has been prepared by the methylation of pyrogallol with dimethyl sulfate or methyl iodide by the decarboxylation of 2,3-dihj droxy-4-methoxy-benzoic acid and by the methylation of pyrogallol carbonate with diazomethane and subsequent hydrolysis. The method described is taken from the improved procedure of Baker and Savage for the preparation of pyrogallol monomethyl ether from o-vanillin by oxidation with hydrogen peroxide. 

Nitrous oxide [10024-97-2] M 44.0, h -88.5°. Washed with cone alkaline pyrogallol solution, to remove O2, CO2, and NO2, then dried by passage through columns of P2O5 or Drierite, and collected in a dry trap cooled in liquid N2. Further purified by ffeeze-pump-thaw and distn cycles under vacuum [Ryan and Freeman J Phys Chem 81 1455 1977],... 

Two other methods worth discussing are wet air oxidation and regeneration by steam. Wet oxidation may be defined as a process in which a substance in aqueous solution or suspension is oxidized by oxygen transferred from a gas phase in intimate contact with the liquid phase. The substance may be organic or inorganic in nature. In this broad definition, both the well known oxidation of ferrous salts to ferric salts by exposure of a solution to air at room temperature and the adsorption of oxygen by alkaline pyrogallol in the classical Orsat gas analysis would be considered wet oxidations. 

Hydroxyphenylpyruvic acid is rapidly oxidized in alkaline solution. Commercially available compressed nitrogen may be used if the gas is further purified by passage through an alkaline solution of pyrogallol (45 g. of pyrogallol dissolved in 300 ml. of 50% sodium hydroxide solution). 

Synthetic antioxidants are safer, cheaper and purer than natural antioxidants but, nevertheless, the majority of consumers still prefer natural antioxidants. This trend will surely persist in the near future. The mechanisms for the changes of synthetic antioxidants are well known, but the same cannot be stated in the case of natural phenolic antioxidants. They are usually pyrocatechol or pyrogallol derivatives, where the changes during oxidation could be different from those of synthetic antioxidants, which are mostly 1,4-substituted. 

A still more complex reaction pattern underlies the oxidation of purpurogallin 12. The chemiluminescent oxidation of pyrogallol has been known for quite a long time. 

Two different approaches have been used to determine phenols without derivatization. In the first, the corresponding oxalate esters were synthesized in the traditional way (i.e., using oxalyl chloride and triethylamine) [111, 112]. Pen-tachlorophenol, 1-naphthol, bromofenoxim, bromoxynil, and /t-cyanophenol were treated this way, after which the POCL resulting from their reaction was measured in a static system. The second approach exploits the oxidation reaction between imidazole and hydroxyl compounds at an alkaline pH, where hydrogen peroxide is formed [113]. Polyphenols, e.g., pyrogallol, pyrocatechol, and dopa-... 

HTAB has been used, on the one hand, to increase the CL intensity of the reaction of 2,6,7-trihydroxy-9-(4 chlorophenyl)-3-fluorene with hydrogen peroxide in alkaline solution, in the presence of traces of Co(II) as a catalyst [43]. As a consequence, a CL method has been established for determination of ultratraces of Co(II). On the other hand, HTAB micelles sensitize the CL oxidation of pyro-gallol with A-bromosuccimide in an alkaline medium [44], while anionic and nonionic surfactants inhibit the CL intensity of this reaction (Table 3). This sensitized process allows the determination of pyrogallol by flow injection in an interval of 5 X 10 7-3 X 10 5 M. 

Wang et al. (62) reported the oxidative polymerization of a mixture of phenolic compounds in aqueous solution containing mont-morillonlte, illite, and kaolinite, each of which had been mixed with quartz in a 3 7 ratio, and by quartz alone. The mixture of phenolic compounds contained gallic acid, pyrogallol, protocatechuic acid, caffeic acid, orcinol, ferulic acid, p-coumaric acid, syringic acid, vanillic acid, and p-hydroxybenzoic acid. The oxidative... 

Phenols (p-cresol, guaiacol, pyrogallol, catechol) and aromatic amines (aniline, p-tolidine, o-phenyldiamine, o-dianisidine) are typical substrates for peroxidases [90 -109]. These compounds are oxidized by hydrogen peroxide or hydroperoxides under peroxidase catalysis to generate radicals, which after diffusion from the active center of the enzyme react with further aromatic substrates to form dimeric, oligomeric or polymeric products. 

The degradation products of GOS were 1,3-dimethyl pyrogallol (HI), 2-(2 ,6 dimethoxy phenoxy)-2-propenal (Vni), 2-(2, 6 -dimethoxy phenoxy)-3-hydroxypropanal (XII), and GOS-Dimer. These products show that the reaction includes oxidative polymerization and the cleavage of -0-4 ether linkage following the alkyl-phenyl cleavage. This depolymerization pathway of GOS is also similar to that of SOS (Table I). 

A study on the CL produced by the HRP-catalyzed oxidation of pyrogallol (145) and purpurogallin (146) shows a 14-fold enhancement of signal intensity for 145 in the presence of 4-boronobenzenepropanoic acid (147a) and a 314-fold enhancement for 146 in the presence of 4-biphenylboronic acid (147b) . 

Ignarro, L. J., Byms, R. E., Buga, G. M., Wood, K. S., and Chaudhuri, G. (1988b). Pharmacological evidence that endothelium-derived relaxing factor is nitric oxide Use of pyrogallol and superoxide dismutase to study endothelium-dependent and nitric oxide-elicited vascular smooth muscle relaxation, j. Pharmacol. Exp. Ther. 244, 181-189. 

Pyrogallol and some derivatives are oxidized to 3-hydroxy-o-benzoquinones which dimerize by 1,3-addition. The adducts react to purpurogallin by dehydrogenation and splitting off of CO2 (25, 26). By treating with alkali at 175°C. purpurogallin is transformed into 6,7,8-trihydroxynaphthalene-l-carboxylic acid (13, 22). Decarboxylation would be a further step in increasing aromatic character. 

Swain and Goldstein (6, 7) noted a rather large difference in the molar color yield from different phenols with the Folin-Denis reagent. They attributed this to differences in relative oxidation-reduction potentials of the different phenols, but under their conditions pyrogallol gave about half the color of catechol and more than resorcinol. However, they also reported that the molar absorptivity produced by a flavonoid was approximately equal to the sum of the values for the separate phenolic moieties which it contained. 

Nitrous oxide (crit.temp., 32) Perfluorodimethylcyclohexane Perfluoromethylcyclohexane Pyrogallol (m.p. 134)... 

Stable hydrosols may be obtained similarly by reduction of arsenious oxide, dissolved in aqueous sodium hydroxide containing some other protective colloid such as gelatin or egg-albumin, by means of alkaline pyrogallol.6 Salts of metallic acids, such as sodium antimonate or calcium plumbate,-with or without the addition of protalbic acid, may also be employed as protective colloids.1... 

Purpurogallin (5), a red-brown to black mordant dye, forms from electrolytic and other mild oxidations of pyrogallol (1). The reaction is believed to proceed through 3-hydroxy-o-benzoquinone (2) and 3-hydroxy-6-(3,4,5-ttihydroxyphenyl)-o-benzoquinone (3). The last, in the form of its tautomeric triketonic structure, represents the vinylogue of a p-diketone. Acid hydrolysis leads to the formation of (4), followed by cyclization and loss of formic acid... 

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