Pyrocatechol, oxidation

Figure 7 Influence of composition (in weight percent) on rate of pyrocatechol oxidation. The enzyme laccase was added to a microemulsion based on AOT-octane-aqueous buffer. The value of kca in bulk water is 28 s . (From Ref. 44.)...

Oxidation. Oxidation of hydroxybenzaldehydes can result in the formation of a variety of compounds, depending on the reagents and conditions used. Replacement of the aldehyde function by a hydroxyl group results when 2- or 4-hydroxybenzaldehydes are treated with hydrogen peroxide in acidic (42) or basic (43) media pyrocatechol or hydroquinone are obtained, respectively. 

Sulfation by sulfamic acid has been used ia the preparation of detergents from dodecyl, oleyl, and other higher alcohols. It is also used ia sulfating phenols and phenol—ethylene oxide condensation products. Secondary alcohols react ia the presence of an amide catalyst, eg, acetamide or urea (24). Pyridine has also been used. Tertiary alcohols do not react. Reactions with phenols yield phenyl ammonium sulfates. These reactions iaclude those of naphthols, cresol, anisole, anethole, pyrocatechol, and hydroquinone. Ammonium aryl sulfates are formed as iatermediates and sulfonates are formed by subsequent rearrangement (25,26). 

On distillation at atmospheric pressure, vanillin undergoes partial decomposition with the formation of pyrocatechol. This reaction was one of the first to be studied and contributed to the elucidation of its stmcture. Exposure to air causes vanillin to oxidize slowly to vanillic acid. When vanillin is exposed to light in an alcohoHc solution, a slow dimerization takes place with the formation of dehydrodivanillin. This compound is also formed in other solvents. When fused with alkaU (eq. 3), vanillin (I) undergoes oxidation and/or demethylation, yielding vanillic acid [121 -34-6] (8) and/or protocatechaic acid (2). 

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. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

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-... 

Thus maleic acid forms from the hydroquinone and oxalic acid forms from pyrocatechol. However, the intermediate compounds are triplets, so the intermediate steps are spin-resistant and may not proceed in the manner indicated. The intermediate maleic acid and oxalic acid are experimentally detected in this low-temperature oxidation process. Although many of the intermediates were detected in low-temperature oxidation studies, Benson [59] determined that the ceiling temperature for bridging peroxide molecules formed from aromatics was of the order of 300°C that is, the reverse of reaction (3.128) was favored at higher temperatures. 

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

Irradiation of an aqueous solution at 296 nm and pH values from 8 to 13 yielded different products. Photolysis at a pH nearly equal to the dissociation constant (undissociated form) yielded pyrocatechol. At an elevated pH, 2-chlorophenol is almost completely ionized photolysis yielded cyclopentadienic acid (Boule et al., 1982). Irradiation of an aqueous solution at 296 nm containing hydrogen peroxide converted 2-chlorophenol to catechol and 2-chlorohydroquinone (Moza et al, 1988). In the dark, nitric oxide (10 vol %) reacted with 2-chlorophenol forming 4-nitro-2-chlorophenol and 6-nitro-2-chlorophenol at yields of 36 and 30%, respectively (Kanno and Nojima, 1979). 

Kennedy and Stock reported the first use of Oxone for many common oxidation reactions such as formation of benzoic acid from toluene and of benzaldehyde, of ben-zophenone from diphenyhnethane, of frawi-cyclohexanediol Ifom cyclohexene, of acetone from 2-propanol, of hydroquinone from phenol, of e-caprolactone from cyclohexanone, of pyrocatechol from salicylaldehyde, of p-dinitrosobenzene from p-phenylenediamine, of phenylacetic acid from 2-phenethylamine, of dodecylsulfonic acid from dodecyl mercaptan, of diphenyl sulfone from diphenyl sulfide, of triphenylphosphine oxide from triphenylphosphine, of iodoxy benzene from iodobenzene, of benzyl chloride from toluene using NaCl and Oxone and bromination of 2-octene using KBr and Oxone . Thus, they... 

Pseudomonas putida 0.1 5 5 30 Nitrophenol, Pyrocatechol, [111,112] Mesityl oxide. Aniline... 

Experimental observations indicate that the oxidation of cobalt (II) to cobalt (III) and the formation of ethylenediamine from N-hydroxyethylethylene-diamine occur simultaneously. This is quite the opposite to what is usually assumed in other instances of transition metal catalysis of organic reactions—for example, the catalytic effect of manganese in the oxidation of oxalic acid (7, 8), of iron in the oxidation of cysteine to cystine (22) and of thioglycolic acid to dithioglycolic acid (5, 23), of copper in the oxidation of pyrocatechol to quinone and in the oxidation of ascorbic acid (29, 30), and of cobalt in the oxidation of aldehydes and unsaturated hydrocarbons (4). In all these reactions the oxidation of the organic molecule occurs by the abstraction of an electron by the oxidized form of the metal ion. 

An appreciable part of the lignin molecule is aromatic in character. Hence it would be expected to take part readily in the reaction of nitration. It has been found, however, that the capacity of lignin to undergo oxidation predominates especially in the presence of dilute nitric acid. This can be explained by the fact that the aromatic part of the lignin molecule derives from pyrocatechol. The reaction of lignin with nitric acid forms the basis of a method of separating cellulose from wood pulp, that consists in treating this mass with dilute nitric acid (3-10%). 

Owing to the reactivity of 1,2-benzoquinone and pyrocatechol towards polymerization and oxidation, the most detailed and reliable investigations concern the chloro, alkyl and aryl... 

The neutral complexes Nil or NiL2B2 (B = py or ibipy) have been conveniently synthesized by reacting the quinone ligand and Ni(CO)4 in apolar solvents (n-pentane, n-hexane, benzene).1 0,1601 The use of anaerobic conditions gives the best results. In one case, that of Ni(C6H402)2, the complex was obtained by the peroxodisulfate oxidation of an aqueous solution of nickel(II) acetate and pyrocatechol. 

Dioxygenases catalyze the incorporation of both atoms of molecular oxygen into the substrate. Microbial pyrocatechol dioxygenases contain non-heme iron as the sole cofactor and catalyze the oxidative cleavage of pyrocatechol to as,cis-muconic acid (intradiol equation 19) or to a-hydroxymuconic s-semialdehyde (extradiol equation 20).63"65 On... 

In the presence of trace amounts of water, the tetrameric p,2-oxo complex (182) in 1,2-dimethoxyethane is transformed into a p, -oxo tetrameric complex (183 equation 254), characterized by an X-ray structure.574 In contrast, (182) 572,575 is inactive towards the oxidation of phenols. The reaction of N,N,N, AT -tetramethyl-l,3-propanediamine (TMP) with CuCl, C02 and dioxygen results in the quantitative formation of the /z-carbonato complex (184 equation 255).s76 This compound acts as an initiator for the oxidative coupling of phenols by 02. 6 Such jz-carbonato complexes, also prepared from the reaction of Cu(BPI)CO with 02 [BPI = 1,3 bis(2-(4-methyl-pyridyl)imino)isoindoline],577 are presumably involved as reactive intermediates in the oxidative carbonylation of methanol to dimethyl carbonate (see below).578 Upon reaction with methanol, the tetrameric complex (182 L = Py X = Cl) produces the bis(/z-methoxo) complex (185 equation 256), which has been characterized by an X-ray structure,579 and is reactive for the oxidatiye cleavage of pyrocatechol to muconic acid derivatives.580,581... 

Tsuji and coworkers reported that copper(I) chloride in the presence of pyridine, methanol and dioxygen promotes the stoichiometric oxidation of pyrocatechol to methyl muconate.606 Labeling lg02 studies have shown that only one atom of the dioxygen molecule is incorporated in the substrate, while the other one is transformed into water as in enzymic monooxygenases (equation 275)607 (and not as in dioxygenases, viz. pyrocatechase). This reaction has been shown by Rogic et al. to proceed via two steps (equation 276).580,58 ... 

Pyridinols, hl73, hl74, hl75 3-Pyridinol A-oxide, hi 77 2(l//)-Pyridone, hl73 2-(2-Pyridyl)pyridine, d705 Pyrocatechol, d377... 

Pospisil, J. and Ettel, V., Oxidation of pyrocatechol to muconic acid, Chem. Prumysl (Czechoslovakia), 7, 244, 1957. 

Of special interest for petrochemical and organic synthesis is the implementation of thermodynamically hindered reactions, among which incomplete benzene hydrogenation or incomplete cyclohexene and cyclohexadiene dehydrogenation should be mentioned. Cost-effective methods of cyclohexene production would stimulate the creation of new processes of phenol, cyclohexanol, cyclohexene oxide, pyrocatechol synthesis, cyclohexadiene application in synthetic rubber production, and a possibility for designing caprolactam synthesis from cyclohexene and cyclohexadiene via combined epoxidation. At present, the most... 

T o stabilize polypropylene against oxidation by atmospheric oxygen, phenolic mononuclear and polynuclear antioxidants containing one hydroxyl group on the aromatic nucleus are used successfully. Thus far the behavior of antioxidants having the structure of polyhydric phenols has not been studied extensively for stabilizing polyolefins. We have systematically observed the properties of dihydric mononuclear phenols with the structure of pyrocatechol and hydroquinone in isotactic poly-... 

The relationship of structure to activity is discussed on the basis of measurements performed in the presence of 0.05 mole of antioxidant per kg. of polypropylene. The results obtained at lower concentrations (0.01 and 0.025 mole/kg.) showed some differences in details. On the other hand, almost identical relationships were found (45) in stabilizing polypropylene at higher antioxidant concentrations (0.1 mole/kg.). Analysis of those concentration relationships supports our assumption that the activity of pyrocatechol derivatives is influenced above all by reactions between the peroxidic bodies and antioxidants in the oxidation chain-breaking mechanism. 

Contrary to our results, other workers (4, 9, 20, 36) state that in the stabilization of carotene, paraffin wax, and lard the activity of pyrocatechol is favorably affected by substitution at position 4, not only by normal but by tertiary alkyl groups as well. Disparate influences of substitution are not surprising when comparing the activity in different substrates owing to the possibility of directive influences in the process of inhibited oxidation. The participation of phenolic antioxidants in the inhibition of autoxidation can be demonstrated (1, 2, 3) simply as a reaction between the molecule of antioxidant AH and the alkylperoxy radical ROO formed duririg the autoxidation of the substrate RH. During this process, an aryloxy radical (A ) is first generated. 

Chloro- and 4-Nitropyrocatechol. In comparing the influences of the nature of substitution in position 4 we also studied polypropylene oxidation in the presence of la substances, where R2 = Cl or N02. The activity of both compounds at a concentration of 0.05 mole/kg. polypropylene is practically equal to pyrocatechol (Ar being within the range 0.96-1.03). At twice these concentrations where side reactions may be more extensive (45), the relative activity of 4-nitropyrocatechol decreased (Ar = 0.70) on the other hand the 4-chloro derivative was slightly more... 

The direct oxidation, shown by Reaction 2, is regarded by some authors (40, 41, 42) as an important process which initiates new chains in the autoxidation. Within the observed range of concentrations, the reaction ratio causing the deactivation of antioxidant and/or initiation was not large enough with any of the three antioxidants to cause inversion of activity. The results of this study confirm that by a suitable substitution of the pyrocatechol nucleus it is possible to influence the rate of Reaction 1 and to suppress the side reactions of the inhibitor as well. 

Stabilizing Activity of Pyrocatechols in Thermal Oxidation and in y-Irradiation of Polypropylene. It is interesting to compare the relationships found on stabilizing isotactic polypropylene oxidized over the melting temperature with the results of our previous study (22, 23) of the stabilizing properties of some derivatives of pyrocatechol in y-irradiated polypropylene. 

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