Phenols simultaneous oxidation

Lead tetrafluoride, generated in situ from lead dioxide and hydrogen fluonde, can replace benzylic hydrogen by fluonne [3] Under sirmlar conditions phenol is simultaneously oxidized to 4,4-difluoro-2,5-cyclohexadienone [4 (equations 3 and 4)... 

The NMR spectra of copolymers prepared by simultaneous oxidation of the two phenols and those prepared by sequential oxidation, in either order, are almost identical. The methyl peak is broadened, as is the peak caused by the protons of the pendant phenyl rings centered at 8 7.20 ppm, and all show the same peaks for aromatic backbone protons in about the same intensity ratios. The polymer obtained by oxidizing a mixture of DMP and the separately prepared homopolymer of MPP with a cuprous bromide-tetramethylbutanediamine catalyst, the procedure considered to have the best chance of producing a block copolymer, was completely random. 

Oxidation of Mixtures of Monomers. The method most likely to yield random copolymers of DMP and DPP is the simultaneous oxidation of a mixture of the two phenols, although this procedure may present problems because of the great difference in reactivity of the two phenols. The production of high molecular weight homopolymer from DPP is reported to require both a very active catalyst, such as tetramethylbutane-diamine-cuprous bromide, and high temperature, conditions which favor carbon-carbon coupling and diphenoquinone formation (Reaction 2) from DMP (II). With the less active pyridine-cuprous chloride catalyst at 25 °C the rate of reaction of DMP, as measured by the rate of oxygen... 

In another system, the [Cp Rhm(bpy)(H20)]2+ complex was used for the regeneration of NADH in combination with an isolated flavine-dependent monooxygenase (2-hydroxybiphenyl-3-monooxygenase) from P. azelaica [120]. This enzyme catalyzes the specific ort/m-hydroxylation of several a-substituted phenol derivatives with simultaneous oxidation of NADH (Fig. 25). 

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). 

Thus a reduced catechol substrate would be required for the hydroxyla-tion reaction, and the overall reaction simultaneously hydroxylates a phenol and oxidizes a catechol. It has been shown that DOPA is present in melanoma tissue 117). 

This series of dyestuffs, which were first prepared by Witt and Koechlin, by simultaneous oxidation of paradiamines or para-amido phenols with phenols, exhibit, both as regards constitution and general behaviour, a close relationship to the indamines. Like the latter, they are decomposed by acids with formation of a quinone. In general they possess a weak basic nature, but, unlike the indamines, form colourless salts, and have mostly a blue or violet colour in the free state. 

IP is formed at 0 °C in ether solution by mixing the ingredients. As Saegusa has pointed out, the formation of IP required reduction of the a-keto acid to a-hydroxy add and simultaneous oxidation of the aryloxy phospholane to the penta-coordinated phosphorus compounds. IP polymerizes also by elimination of phenol when reacted with alcohols, amines or water, e.g. ... 

Bennett (1949) observed that the nitrogen content of commmercial lignin was increased substantially by treatment with concentrated ammonium hydroxide, but methylation essentially prevented fixation of the nitrogen. His work seems to support the conclusions of Mattson and Koutler-Andersson that simultaneous oxidation and ammonia fixation take place by way of the phenolic hydroxyl groups. 

Most frequently, SEC with dextran-, pullulan-, or polystyrene calibration standards has been used to characterize the molecular properties of xylans. However, as for viscometric studies [108], a sufficient solvent ionic strength is a prerequisite for useful SEC measurements of charged polysaccharides, including glucuronoxylans [111-113]. An advantage of the SEC technique is that the presence of protein and phenolic components or oxidative changes can be detected by simultaneous ultraviolet (UV) detection. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

The nitrosophenol (10), which may be isolated, is oxidised very rapidly by nitric acid to yield the p-nitrophenol (11) and nitrous acid more nitrous acid is produced thereby and the process is progressively speeded up. No nitrous acid need be present initially in the nitric acid for a little of the latter attacks phenol oxidatively to yield HN02. The rate-determining step is again believed to be the formation of the intermediate (9). Some direct nitration of such reactive aromatic compounds by N02 also takes place simultaneously, the relative amount by the two routes depending on the conditions. 

The first step of the reaction path involves the addition of H2O2 to the Fe " resting state to form an iron-oxo derivative known as Compound I, which is formally two oxidation equivalents above the Fe state (Fig. 2). The well studied Compound I contains a Fe" = 0 structure and a n cation radical. In the second step. Compound I is reduced to Compound II with a Fe =0 structure. The reduction of the n cation radical by a phenol or enol is accompanied by an electron transfer to Compound I and a proton transfer to a distal basic group (B), probably His 42 (Fig. 3, step 1). The native state is regenerated on one-electron reduction of Compound II by a phenol or an enol. In this process, electron and proton transfers occur to the ferryl group with simultaneous reduction of Fe" to Fe (Fig. 3, steps 2-3) and formation of water as the leaving group (Fig. 3, step 4). 

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