Selective reduction of aromatic nitro compounds with stannous chloride in non acidic and non aqueous medium

Aromatic nitro compounds are readily reduced by SnCl₂, 2 H₂O in alcohol or ethyl acetate or by anhydrous SnCl₂ in alcohol where other reducible or acid sensitive groups such as aldehyde, ketone, ester, cyano, halogen and O-benzyl remain unaffected.     

Polymerization of aqueous formaldehyde induced by ionizing radiation

In this work we examined the formation of polymeric material from the radiation-induced reactions of aqueous formaldehyde. The polymers obtained by this procedure are very different from those formed by thermal or UV polymerization. Two polymeric materials precipitated between 0.8 and 1.3 MGy. Although these polymers have the same chemical composition (C₂H₃O), infrared spectrum, and NMR spectrum, they differ in density, color and melting point. The interconversion of the polymeric materials increase when the dose is raised.     

Thiosulphate in the Wollak procedure-analysis and kinetics in acidic formaldehyde medium

The Wollak procedure for the determination of the sum of dithionite and thiosulphate has been investigated. Analytical data and a kinetic study confirm that thiosulphate reacts with formaldehyde under acidic conditions. Both pH and CH(2)O concentration affect the results and satisfactory analysis can be performed only if the pH of the initial sample-formaldehyde mixture remains high enough.     

Studies on interaction of ferrofluid with ascorbic acid in aqueous acidic medium

The solution chemistry of the interaction of ferrofluid with ascorbic acid in dilute solutions has been investigated in the temperature range of 15–45°C. Kinetic, mechanistic and thermodynamic aspects of the reactions were studied by spectrophotometric and potentiometric techniques.     

The ozonization of model lignin compounds in aqueous solutions catalyzed by Mn(II) ions

The influence of Mn(II) ions on the rate of the reaction between ozone and model lignin compounds, guaiacol and veratrole, was studied. The catalyst did not influence the rate of the destruction of the aromatic ring and intermediate ozonolysis products, compounds with conjugated double bonds, in acid media but substantially increased the rate of oxidation of saturated carboxylic acids, ketoacids, and aldehydes. Ozone consumption then increased from 2 to 5 moles per mole of the transformed substrate. A mechanism of the catalytic action of Mn(II) in reactions between ozone and the compounds studied was suggested.     

Catalytic degradation of lignin model compounds in acidic imidazolium based ionic liquids: Hammett acidity and anion effects

Ionic liquids based on the 1-methylimidazolium cation with chloride, bromide, hydrogen sulfate, and tetrafluoroborate counterions along with 1-butyl-3-methylimidazolium hydrogen sulfate were employed to degrade two lignin model compounds, guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether. The acidity of each ionic liquid was approximated using 3-nitroaniline as an indicator to measure the Hammett acidity (H₀). While all of the tested ionic liquids were strongly acidic (H₀ between 1.48 and 2.08), the relative acidity did not correlate with the ability of the ionic liquid to catalyze β-O-4 ether bond hydrolysis. The reactivity of the model compounds in the ionic liquids is dependent not only on the acidity, but also on the nature of the ions and their interaction with the model compounds.     

Thermal analysis of some lignin model compounds

Compounds acting as model biphenyl and phenylcoumarane structural units in the lignin molecule (dehydrodivanillin and dehydrodiisoeugenol) were investigated by thermal analysis. The results were compared with previously obtained data on the thermal degradation of model phenylpropane monomer units of lignin. It was found that the mechanism of thermal degradation of these models and the thermal stabilities of the bonds depend on the structure. The thermal stability of the models increases in the absence of reactive functional groups in the side chain.

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Zusammenfassung Modellverbindungen mit Biphenyl und Phenylcumaran Bindungen im Lignin wie Dehydrodivanillin und Dehydrodiisoeugenol wurden einer thermoanalytischen Prüfung unterworfen und die Ergebnisse mit jenen der thermischen Zersetzung von Phenylpropan-monomeren Modellen des Lignins verglichen. Es wurde festgestellt, daß der Mechanismus der thermischen Zersetzung und die thermische Stabilität der Bindungen strukturabhängig sind. Die thermische Stabilität der Modelle nahm mit Abwesenheit reaktionsfähiger funktioneller Gruppen an der Seitenkette ab. Die Bindung vom Typ des Phenylcumarans ist thermisch am stabilsten. Das Zerreissen der Bindungen scheint durch einen Mechanismus durch freie Radikale zu erfolgen.

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Résumé Étude thermique de composés modèles pour les liaisons structurales de type diphényle et phénylcoumaranne dans la molécule de lignine (déhydrodivanilline et déhydrodiisoeugénol). Comparaison des résultats avec ceux obtenus précédemment dans le cas de la dégradation thermique de composés servant de modèles pour les unités monomères de phénylpropane dans la lignine. Détermination du mécanisme de la dégradation thermique de ces modèles et de la stabilité thermique des liaisons suivant la structure. La stabilité thermique augmente en l'absence de groupes fonctionnels réactifs dans la chaîne latérale. La liaison de type phénylcoumaranne est thermiquement la plus stable. On suppose un mécanisme avec radical libre pour la rupture des liaisons structurales.

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Flash vacuum pyrolysis of methoxy-substituted lignin model compounds

The flash vacuum pyrolysis (FVP) of methoxy-substituted beta-O-4 lignin model compounds has been studied at 500 degrees C to provide mechanistic insight into the primary reaction pathways that occur under conditions of fast pyrolysis. FVP of PhCH(2)CH(2)OPh (PPE), a model of the dominant beta-O-4 linkage in lignin, proceeds by C-O and C-C cleavage, in a 37:1 ratio, to produce styrene plus phenol as the dominant products and minor amounts of toluene, bibenzyl, and benzaldehyde. From the deuterium isotope effect in the FVP of PhCD(2)CH(2)OPh, it was shown that C-O cleavage occurs by homolysis and by 1,2-elimination in a ratio of 1.4:1, respectively. Methoxy substituents enhance the homolysis of the beta-O-4 linkage, relative to PPE, in o-CH(3)O-C(6)H(4)OCH(2)CH(2)Ph (o-CH(3)O-PPE) and (o-CH(3)O)(2)-C(6)H(3)OCH(2)CH(2)Ph ((o-CH(3)O)(2)-PPE) by a factor of 7.4 and 21, respectively. The methoxy-substituted phenoxy radicals undergo a complex series of reactions, which are dominated by 1,5-, 1,6-, and 1,4-intramolecular hydrogen abstraction, rearrangement, and beta-scission reactions. In the FVP of o-CH(3)O-PPE, the dominant product, salicylaldehyde, forms from the methoxyphenoxy radical by a 1,5-hydrogen shift to form 2-hydroxyphenoxymethyl radical, 1,2-phenyl shift, and beta-scission of a hydrogen atom. The 2-hydroxyphenoxymethyl radical can also cleave to form formaldehyde and phenol in which the ratio of 1, 2-phenyl shift to beta-scission is ca. 4:1. In the FVP of o-CH(3)O-PPE and (o-CH(3)O)(2)-PPE, products (ca. 20 mol %) are also formed by C-O homolysis of the methoxy group. The resulting phenoxy radicals undergo 1,5- and 1,6-hydrogen shifts in a ratio of ca. 2:1 to the aliphatic or benzylic carbon, respectively, of the phenethyl chain. In the FVP of (o-CH(3)O)(2)-PPE, o-cresol was the dominant product. It was formed by decomposition of 2-hydroxy-3-hydroxymethylbenzaldehyde and 2-hydroxybenzyl alcohol, which are formed from a complex series of reactions from the 2, 6-dimethoxyphenoxy radical. The key step in this reaction sequence was the rapid 1,5-hydrogen shift from 2-hydroxy-3-methoxybenzyloxy radical to 2-hydroxymethyl-6-methoxyphenoxy radical before beta-scission of a hydrogen atom to give the substituted benzaldehyde. The 2-hydroxybenzyl alcohols rapidly decompose under the reaction conditions to o-benzoquinone methide and pick up hydrogen from the reactor walls to form o-cresol.     

Initiation of electropolymerization of acrylamide and formaldehyde by metallic zinc in aqueous medium

The effect of postpolymerization (polymerization after current interruption) is observed and studied for electropolymerization composition based on acrylamide, N,N′-methylene bisacrylamide, formaldehyde, and zinc chloride. The possible causes of this phenomenon are considered. It is found that the main cause of postpolymerization is the catalytic effect of metallic zinc formed in the course of polymerization and initiation of further polymerization by metallic zinc after current interruption in an electrochemical cell. Kinetics and the mechanism of polymerization initiation by zinc are studied. It is shown that polymerization initiators may be other metals with the electrochemical potential in the studied solution sufficient for discharge of a zinc-acrylamide complex.     

Polymerization with organoboron compounds

In the presence of organoboron compounds, free-radical polymerization of vinyl monomers can proceed in spite of the presence of excess of typical radical inhibitors. The concept of free radical–organoboron complex formation is introduced to explain the unique role of organoboron compounds in such a polymerization system.     

Mechanism of disproportionation of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate in acidic aqueous medium

The cation of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate disproportionates in acidic aqueous medium to give piperidinoxyl and/or 1-hydroxypiperidine, nitrone, and acetone. A mechanism of this reaction was proposed and the rate constants for its particular steps were calculated.     

木质素降解模型化合物愈创木酚及苯酚原位加氢制备环己醇

以Raney Ni为催化剂,研究了甲醇水相重整制氢与木质素降解模型化合物愈创木酚／苯酚加氢的耦合反应.考察了反应前冷压、反应温度、反应时间、物料配比等条件对木质素降解模型化合物原位加氢反应性能的影响,并对影响机制进行了讨论.结果表明,在反应温度为220 ℃、反应前冷压0 MPa(表压)、物料比水／甲醇／模型化合物为20∶5∶0.8的条件下,反应7 h后愈创木酚转化率与环己醇选择性分别达99.00％和93.74％,反应12 h后苯酚的转化率与环己醇选择性分别达90.50％和99.29％.采用原位加氢反应,木质素降解的酚类模型化合物转化率和选择性明显优于外部供氢反应的转化率和选择性,同时,避免了外部供氢反应存在的氢气制备、储存、传输及加氢条件苛刻等问题,为木质素解聚产物制备化工品提供了新思路与实验基础.     

Iridium(III) catalyzed oxidation of iodide ions in aqueous acidic medium

Oxidation of iodide ions by K₃Fe(CN)₆, catalyzed by hydrogen ions obtained from hydrochloric acid was found to be further catalyzed by iridium(III) chloride. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated from the rate when iridium(III) and H⁺ions both, catalyze the reaction. Reactions studied separately in the presence as well as in the absence of IrCl₃ under similar conditions were found to follow second order kinetics with respect to [I⁻]. While the rate showed direct proportionality with respect to [K₃Fe(CN)₆] and [IrCl₃]. At low concentrations the reaction shows direct proportionality with respect to [H⁺] which tends to become proportional to the square of hydrogen ions at higher concentrations. Strong retarding affect of externally added hexacyanoferrate(II) ions was observed in the beginning but further addition affects the rate to a little extent. Changes in [Cl⁻] and also ionic strength of the medium have no effect on the rate. With the help of the intercept of catalyst graph, the extent of the reaction, which takes place without adding iridium(III), was calculated and was found to be in accordance with the values obtained from the separately studied reactions in which only H⁺ ions catalyze the reaction. It is proposed that iridium forms a complex, which slowly disproportionates into the rate-determining step. Thermodynamic parameters at four different temperatures were calculated.     

Thermophysical properties of model compounds of the lignin structural unit

Russian Chemical Bulletin - Sixteen lignin related aromatic compounds formed by the thermal degradation of lignin and being potentially valuable products of the processing of renewable raw...     

Kinetics of oxidation of ethyldigol by vanadium(V) in aqueous acidic medium

The kinetics of oxidation of ethyldigol by vanadium(V) in aqueous acidic medium has been carried out. The reaction is first order with respect to vanadium(V) and the substrate and is acid catalysed.Hammett acidity function (H ₀) andBunnett hypothesis have been applied. The formation of free radicals during the course of the reaction has been indicated. A probable reaction mechanism is proposed.

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Die Kinetik der Oxidation von Ethyldigol mit Vanadium(V) in wäßrigem saurem Medium

Zusammenfassung Es wurde die Kinetik der Oxidation von Ethyldigol mittels Vanadium(V) in wäßriger saurer Lösung untersucht. Die Reaktion ist erster Ordnung bezüglich Vanadium(V) und Substrat und ist säurekatalysiert. Es wurden dieHammett-Aciditätsfunktion (H ₀) und dieBunnett-Hypothese angewandt. Die Bildung von freien Radikalen während der Reaktion konnte bestätigt werden. Es wird ein Reaktionsmechanismus vorgeschlagen.