Pyrocatechol, also

Benzoquinones and hydroxybenzoquinones are formed from tert-butylated hydroquinone and pyrocatechol also in the course of inhibited oxidation of atactic polypropylene200. But these quinoic compounds are formed also in the direct oxidation by oxygen in trichlorobenzene at temperatures above 100 °C200, 201. ... 

Solvent extraction techniques are useful in the quantitative analysis of niobium. The fluoro complexes are amenable to extraction by a wide variety of ketones. Some of the water-insoluble complexes with organic precipitants are extractable by organic solvents and colorimetry is performed on the extract. An example is the extraction of the niobium—oxine complex with chloroform (41). The extraction of the niobium—pyrocatechol violet complex with tridodecylethylammonium bromide and the extraction of niobium—pyrocatechol—sparteine complex with chloroform are examples of extractions of water-soluble complexes. Colorimetry is performed on the extract (42,43). Colorimetry may also be performed directly on the water-soluble complex, eg, using ascorbic acid and 5-nitrosahcyhc acid (44,45). 

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). 

Antimony pentoxide also reacts with a variety of dihydroxy compounds. Thus pyrocatechol yields a crystalline substance ia which three molecules of the diol are associated with one atom of antimony (52). The configuration of this substance has not been estabUshed, but the foUowiag stmcture seems reasonable ... 

Chlorogenic acid loss is also correlated with its incorporation in browning products.3 During roasting, the diphenols, 4-ethylpyrocatechol and pyrocatechol are formed from the caffeic acid moiety and the quinic acid moiety yields phenol and benzoic acid as well as all the di- and trihydroxybenzenes.39... 

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]. 

D-Erythrose has also been exposed to a boiling solution in pH 4.5 buffer. Low yields (<0.2%) of a number of products were obtained, as shown in Scheme 3. These included 5-(hydroxymethyl)-2-furaldehyde (11), 2-acetyl-5-(hydroxymethyl)furan (12), 3,4-dihydroxyacetophenone (13), 3,4-dihydroxy be nzaldehyde (14), 3,4-dihydroxybenzoic acid (15), 2,3-dihydroxytoluene (16), and 1,2-benzenediol (pyrocatechol) (17). Also detected were formic, hydroxyacetic, and 3-hydroxypropanoic acids. Pyrocatechol seems to be a product formed from all carbohydrates boiled in aqueous solutions at pH 4-10 it may constitute a statistical product arising from retro-aldol and re-aldol reactions. It has been shown that the aldol reaction may operate at a pH as low as 4. An aldol reaction... 

The reaction mixture from acidified dihydroxyacetone also included a series of seven di- and tri-hydroxybenzenes (see Scheme 4), namely, 2,3-dihydroxytoluene (16), pyrocatechol (17), 3,4-dihydroxy toluene (19), 3,5-dimethyl-l,2-benzenediol (20), 1,2,3-trihydroxybenzene (pyrogallol) (21), 1,2,4-trihydroxy benzene (22), 3,4,5,6-tetrahydroxy-2-methy 1-acetophe-none, and 2,3-dihydroxy-5,6-dimethyl-p-benzoquinone. Many of these same phenolic compounds are present after hexoses are similarly treated... 

Five- to six-month-old tobacco plants (Nicotiana tabacum var. Samsun) grown in a glasshouse at 20°C were used for this study. Commercial synthetic substrates employed both for histochemical and biochemical assays were guaiacol, p-phenylenediamine-pyrocatechol (PPD-PC), 3-3 di-aminobenzidine (DAB), tetramethylbenzidine (TMB) and syringaldazine. Isopropylamine and monosodium salts of ferulic acid were also used as substrates as well as their / -fluorinated analogues substituted with a fluorine atom on the / -carbon (Fig. 1). Histochemical observations were done on hand-made transverse sections of fresh tobacco stems. Biochemical assays were performed separately on bark (inner cortical parenchyma, phloem and fibres) and xylem fractions. Technical data of incubation, enzyme extraction, spectrophotometric and electrophoretic assays were given elsewhere (5-7). Synthesis of fluorinated compounds was performed as previously described (4). 

A-Benzoylphenylhydroxylamine (BPHA) reacts with Nb20 in bioling acidic aqueous solutions to yield a monomeric seven-coordinated niobium compound [NbO(BPHA)3]. The hydroxylamine ligand could be displaced by tropolone or 8-quinolinol, and the ratedetermining step was shown to be associative (equation 38).427 Oxoniobium and tantalum(V) 8-quinolinolates have also been reported. The optimal conditions for the formation and extraction of the [Nb0(C6H402)3]3 ion formed in the niobium(V)-pyrocatechol system, have been investigated.428... 

Golden (28) unsuccessfully attempted to prepare polymers by elimination of acetyl chloride and acetic anhydride from p-acetoxy-chlorobenzene and diacetoxybenzene, respectively. He was also unable to dehydrate hydroquinone. In the course of his study on the dehydration of phenols to aromatic ethers over thoria, Briner (8) also attempted, unsuccessfully, to dehydrate the polyphenols pyrocatechol, resorcinol and hydroquinone. 

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... 

In addition to the above method, based on the use of pyrocatechol violet, Tecator also describes a flow injection analysis for determining 0.5-0.5mg/l aluminium in soil extracts based on the measurement of the chromazurol-aluminium complex at 570 nm [4,5]. 

A compound similar to (XIII) has also been prepared from the pyrocatechol compound Ti(02C6H4)Cl2 by reduction with sodium amalgam in THF, and has been formulated to be similar to (XIII) with the two phenoxide groups at each titanium being replaced by the pyrocatecholate dianion. The ESR signal from both these complexes suggests the presence of one unpaired electron per dimer (50). 

Besides the reactions between phenols and peroxidic bodies, other factors can influence the activity of antioxidants—e.g., compatibility with substrate and volatility. The results show that under the conditions used the influence of the antioxidant structure is dramatic. In this connection we note agreement of the general conclusions dealing with the influences of pyrocatechol antioxidant structure on the activity in polypropylene at 180°C. and those influences found in Tetralin (28) at 80 °C. Despite great differences in experimental conditions, the sequences of the activities of pyrocatechol antioxidants I-VI were in agreement. Great similarities were also found within each particular group of antioxidants. 

Under the conditions used these compounds were the most active derivatives of pyrocatechol. High activity was found also with two derivatives having acyl groups (Table I). The decrease in the rate of oxygen absorption in isotactic polypropylene in the presence of 4-caproyl-, 4-lauroyl-, and 4-stearoylpyrocatechol compared with pyrocatechol is shown by Fic (10). The activity of 4-alkyl and 4-acyl derivatives of pyrocatechol found at high temperatures in polypropylene differs from the published data on the activity of 4-dodecyl- and 4-lauroylpyrocatechol in lard (39) compared with pyrocatechol, the relative activity decreased in the presence of the first substance by 15%, and it decreased in the presence of the second by as much as 68%. Tamura and co-workers... 

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... 

T Tnsubstituted hydroquinone reportedly possesses antioxidative prop- erties in various substrates. It is a common chemical and by comparison with pyrocatechol does not stain. However, it is less efficient than pyrocatechol and relatively insoluble, especially in nonpolar media— e.g., the difference in efficiency is evident from the data obtained in the study dealing with the stabilization process of carotene solutions in mineral oil the ratio (2) of activity of phenol, hydroquinone, and pyrocatechol is 1 8 84. A lower efficiency of hydroquinone, compared with pyrocatechol, was also found in the stabilization of fats (5,7) and poly-... 

Among polyhydric phenols, only the nitro derivatives of resorcinol have gained considerable practical importance. The nitro derivatives of phloroglucinol may also be of some value. Both phenols have hydroxyl groups in the meta position to each other, thus enabling the introduction of three nitro groups. Among dinitro derivatives, those of pyrocatechol have found some uses. 

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