Enzymatic oxidation of lignin and compounds modeling it. III. Formation of singlet oxygen in the peroxidase oxidation of lignin

The main emitters of radiation in the aerobic oxidation of lignin are the carbonyl groups in an excited state and singlet oxygen. It has been shown that the main source of O₂(¹Δ) may be the radical anion O^?·₂. Singlet oxygen and the radical anion are by-products of the radical oxidation of lignin.     

Enzymatic oxidation of lignin and compounds modeling it. III. Formation of singlet oxygen in the peroxidase oxidation of lignin

The main emitters of radiation in the aerobic oxidation of lignin are the carbonyl groups in an excited state and singlet oxygen. It has been shown that the main source of O₂(¹) may be the radical anion O^–·₂. Singlet oxygen and the radical anion are by-products of the radical oxidation of lignin.Siberian Scientific-Research Institute of Cellulose and Board, Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 510–514, July–August, 1984.     

Formation of volatile organic compounds in the heterogeneous oxidation of condensed-phase organic films by gas-phase OH

The yield of volatile organic compounds (VOCs) from the heterogeneous oxidation of condensed-phase organic and hydrocarbon soot films by gas-phase OH has been studied in a coated-wall flow tube at room temperature. Simultaneously, OH concentrations are measured using a chemical-ionization mass spectrometer (CIMS) operated in negative ion mode and VOCs are measured using a commercial proton-transfer-reaction mass spectrometer (PTR-MS). It is observed that a variety of aldehydes/carbonyls and carboxylic acids are formed. Specifically, detailed experiments were conducted with stearic acid, where products are observed that contain as many as 13 carbon atoms with the average carbon number of the products between 3 and 5. The yield of VOCs, relative to the loss of OH radicals, is strongly dependent on the partial pressure of O2 in the carrier gas, ranging from 0.08 +/- 0.03 in a nominally pure He carrier gas to 0.34 +/- 0.14 in 6 Torr of pure O2. Yields from other organics are somewhat lower than those from stearic acid, ranging in conditions of pure O2 from 0.10 +/- 0.04 for BES (bis(ethylhexyl)sebacate), to 0.03 +/- 0.01 for n-hexane soot, to 0.01 +/- 0.005 for pyrene. Under atmospheric conditions, OH oxidation of select organics may be an efficient source of small VOCs. In particular, formic acid is formed in significant yield from all the surfaces.     

Formation of polyelectrolyte complexes in an organic solvent

The formation of complexes of polyelectrolytes has been investigated with low charged polyelectrolytes soluble in an organic solvent. The degree of complexation has been determined from conductimetric experiments; it is independent of the degree of quaternization of the polycation but decreases as the polymer concentration and the ionic content increase. A change in the conductimetric and in the viscometric curves during addition of polycation to the polyanion (or the reverse) has been found in the range of the ionic stoichiometry. The complex formation corresponds to an electrostatic cross-link the stability of which decreases with the ionic content of the solution.     

Features of the initial stages of the oxidation of lignin by hydrogen peroxide

The kinetics of the initial stages of the oxidation of lignin and of several model compounds have been studied by the stopped-jet method. It has been shown that in the initial stage an intermediate compound is formed with an absorption spectrum close to that of phenoxyl radicals and with a lifetime of 0.013 sec. The high reactivity of the intermediate products leads to a branching of the oxidation process.Siberian Scientific-Research Institute of Pulp and Board, Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 516–518, July–August, 1983.     

Oxidation of 2,3,6-trimethylphenol on titanium dioxide xerogel by hydrogen peroxide in the absence of an organic solvent

Fundamental aspects of the synthesis of 2,3,5-trimethylbenzoquinone by oxidation of 2,3,6-trimethylphenol adsorbed on the surface of a titanium dioxide xerogel and on TiO₂ modified with powdered cellulose with hydrogen peroxide without any organic solvent involved in the process were studied.     

Selective oxidation of aromatic substituents in alicyclic compounds by ozonolysis in an ester solvent

Conclusions A method was proposed for the selective conversion of aryl-substituted alicyclic compounds to cycloaliphatic carboxylic acids by ozonolysis in ethyl acetate, followed by conversion of the ozonolysis peroxide product on Lindlar catalyst in a hydrogen atmosphere.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2146–2148, September, 1979.The authors thank V. A. Smit and B. M. Lerman for supplying the samples for ozonolysis.     

Catalytic oxidation of organic substrates by molecular oxygen and hydrogen peroxide by multistep electron transfer--a biomimetic approach

Oxidation reactions are of fundamental importance in nature, and are key transformations in organic synthesis. The development of new processes that employ transition metals as substrate-selective catalysts and stoichiometric environmentally friendly oxidants, such as molecular oxygen or hydrogen peroxide, is one of the most important goals in oxidation chemistry. Direct oxidation of the catalyst by molecular oxygen or hydrogen peroxide is often kinetically unfavored. The use of coupled catalytic systems with electron-transfer mediators (ETMs) usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions. As a result of the similarities with biological systems, this can be dubbed a biomimetic approach.     

Aerobic oxidation of organic compounds catalyzed by vanadium compounds

Aerobic oxidation of α-hydroxy ketones catalyzed by dichloroethoxyoxovanadium in ethanol causes a carbon–carbon bond cleavage that produces diesters or diketones. This reaction is highly chemoselective, and disecondary glycols do not react at all. However, ditertiary glycols effectively react with dichloroethoxyoxovanadium or trichlorooxovanadium to provide the corresponding ketones. Aerobic oxidation of α-hydroxy ketones catalyzed by dichloroethoxyoxovanadium or trichlorooxovanadium in aprotic solvents almost quantitatively affords the corresponding α-diketones. The reaction of tertiary cyclopropanol compounds with vanadyl acetylacetonate under an oxygen atmosphere causes fragmentation of the cyclopropane moiety to produce β-hydroxy ketones and β-diketones. For the 6-substituted bicyclo[4.1.0]heptanol derivatives, the endoperoxides are also obtained together with β-hydroxy ketones. Conversely, 2-ethoxycarbonylcyclopropyl silyl ethers produce γ-oxocarboxylate derivatives given the same reaction conditions. Monothioacetals are easily deprotected into carbonyls using a catalytic amount of trichlorooxovanadium in 2,2,2-trifluoroethanol under an oxygen atmosphere. Thiols are converted into the corresponding disulfides by the aerobic oxidation catalyzed by trichlorooxovanadium in the presence of molecular sieves 3A. Polymer-supported vanadium compounds are synthesized by the reaction of vanadium oxytrichloride with polymers bearing hydroxyl moieties. The catalyst prepared from TentaGel S OH was highly active and reusable for the aerobic oxidations.     

Kinetics of the catalytic oxidation of model compounds of lignin with hydrogen peroxide in the presence of peroxidase from horse-radish

A kinetic scheme was suggested for the oxidation of guaiacol, ferulic acid, acetovanilon, and vanillyl alcohol with hydrogen peroxide. A number of kinetic parameters were determined.     

Enzymatic oxidation of lignin and compounds modeling it. I. Investigation of the peroxidase oxidation of lignin by the chemiluminescence method

In the enzymatic oxidation of lignin, superweak fluorescence is detected which confirms the radical mechanism of peroxidase-catalyzed oxidation. The rate constants of the recombination and disproportionation of the radicals have been calculated. Both the degradation and the partial polymerization of the initial substance have been established by the gel filtration of the lignin oxidation products.     

Role of the solvent in the oxidation of furfural with hydrogen peroxide

The effect of the nature of the solvent on the direction and rate of oxidation of furfural by hydrogen peroxide was studied. The use of alcohol and dioxane as the solvents substantially increases the selectivity of the process and leads to the primary formation of furfural hydroxyperoxides (the -hydroxyhydroperoxide in dioxane, and the , -dihydroxyperoxide in alcohol). The polarity of the medium and specific solvation have a substantial effect on the rate of formation of the peroxides. The effect of specific solvation predominates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 603–607, May, 1977.     

Catalytic oxidation of organic compounds with oxygen in the presence of Mo-V-phosphoric heteropoly acid solutions

The studies carried out at the Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, on the selective catalytic oxidation of organic compounds with oxygen in the presence of aqueous solutions of Mo-V-phosphoric heteropoly acids (HPAs) are reviewed. Alkylphenols are oxidized into 1,4-quinones with a selectivity of 85–99%, and C₂-C₄ olefins in the presence of Pd complexes are oxidized into carbonyl compounds with a selectivity of 98–99%. The bifunctional (acidic and oxidizing) properties of HPA solutions were used for the first time to synthesize anthraquinones and vitamin K₃.     

The oxidation of organic compounds

In a study of the behavior of tris(hydroxymethyl)-4-picoline (I) under the conditions of vapor-phase oxidation on a vanadium-tin oxide catalyst, it was found that with the addition of 150–250 mole of water and 125–200 mole of O₂ per mole of I and a contact time of 0.35–0.45 sec, the main reaction product was isonicotinic acid (II), the yield of which amounted to 60–65% of theoretical, calculated on the I passed.For part XLVIII, see [1].     

Enzymatic oxidation of lignin and compounds modeling it. II. A study of the peroxidase oxidation of model compounds of the structural unit of lignin by the chemiluminescence method

An investigation of the radical mechanism of the peroxidase oxidation of monomeric phenols (vanillin, vanillyl alcohol, isoeugenol, and α-quaiacylpropanone) has been made by the chemiluminescence method. It has been established that chemiluminescence is observed in those compounds that contain hydroxy or carbonyl groups on a carbon atom in the α position or have a C=C bond in the β position conjugated with the aromatic ring. The hypothesis has been put forward that peroxide compounds are inhibitors of autocatalytic processes in the oxidation of lignin in the presence of peroxidase.     

Influence of unsaturated aliphatic and aromatic volatile organic compounds on the oxidation of aqueous sulfur dioxide by oxygen in aqueous medium

The trace atmospheric volatile organic compounds(VOCs) are reported to influence the oxidation of dissolved sulfur dioxide, S(IV), by oxygen, which is an important reaction in atmospheric acid formation. In this work, the influence of 15 VOCs on uncatalyzed oxidation of S(IV) by oxygen has been investigated by following the disappearance of [O₂]. The inhibition of oxidation reaction by toluene, aniline, benzene, cinnamic acid, hydroquinone, acrylamide, acrylonitrile and allyl alcohol was defined by the rate law(A):k_VOC = k₀/(1+B [Inh]) (A)where, k_VOC, and k₀ are the first order rate constants in the presence and the absence of VOCs respectively. B is the inhibition parameter and [Inh] is the concentration of inhibitor.On the other hand, fumaric, maleic and crotonic acids, which have conjugated CC bonds, catalyze the reaction defined by the rate law(B):k_VOC = k₀ + k_cat [VOC] (B)where k_cat is catalytic constant and [VOC] is the concentration of catalytic VOC.Interestingly, presence of 1-hexene, cyclohexene, methacrylic acid, methyl acrylate was without any significant effect on the rate of reaction.