Mechanism of catalytic hydrogenation of nitrobenzene in an aprotic medium in the presence of quinones

Conclusions The hydrogenation of nitrobenzene in an aprotic medium in the presence of quinones is realized by a reduction-protonation mechanism through alternating stages of electron transfer and protonation. The function of proton donor is fulfilled by the corresponding hydroquinones formed from the quinones under the reaction conditions.Translated from IzvÉstiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1500–1505, July, 1981.     

Selective hydrogenation of nitrobenzene top-Aminophenol by the polymer-supported palladium-based mono- and bimetallic catalyst

In acidic reaction medium, polymer-supported monometallic palladium catalyst, PVP-PdCl₂ [(PVP=poly(N-vinyl-pyrrolidone)], is used to catalyze the hydrogenation of nitrobenzene top-aminophenol and aniline. The addition of a second transition metal compound or a very small amount of 2-mercaptopyrimidine gives rise to an increase in the selectivity forp-aminophenol.     

Application of carbonized cellulose-based catalyst in nitrobenzene hydrogenation

Carbonized cellulose catalyst support was prepared and decorated with 5 wt% Pd nanoparticles using an impregnation method. According to the SEM images, the carbonized cellulose catalyst support kept its original fibrous structure with an average diameter of 200 nm, owing to the carbonization of the cellulose fibers. The surface of the formed carbon fibers is richly coated by palladium with even coverage. The particles can be divided into two groups within which the average diameter is either 5 nm, or 20–70 nm. TGA method was used to measure the amount of the remained carbon, which was 31.71 wt%. The FTIR spectrum shows the presence of oxygen containing functional groups on the surface of the support, which are hydroxyl groups. XRD method was used to determine the phases of Pd on the support where elemental Pd was detected which confirms the success of the activation step. The catalyst was tested in nitrobenzene hydrogenation in methanolic solution as a model reaction for nitroarene hydrogenation, meanwhile the temperature dependence of the reaction was also examined. Catalytic tests were carried out at four different temperatures (283–323 K) and constant hydrogen pressure (20 bar). The highest conversion (>99%) has been reached at 303 K and 20 bar. The corresponding activation energy was calculated by non-linear regression based on Arrhenius plot, and it was 24.16 ± 0.8 kJ/mol. All in all, the granulated cellulose beads are ideal starting points for carbon based catalyst supports.     

Polymeric metal complex catalysts in hydrogenation of nitrobenzene

Conclusions The complexes based on polyethylenimine and the chlorides of Co, Ni, Sn, Pd, and Rh are active in the hydrogenation of nitrobenzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 690–691, March, 1982.     

The oxidation-reduction reaction of dicyclopentadienyltitanium complexes in aprotic media

Dicyclopentadienyltitanium(III) tetrahydridoborate, (π-Cp)₂ TiBH₄, is formed in aprotic solvents by the reaction of dicyclopentadienyltitanium(IV) dichloride, (π-Cp)₂TiCl₂, with the tetrahydridoborate anion. The presence of traces of water in the reaction medium causes formation of an intensely blue compound, probably an aquotitanium(III) complex. It is suggested that the oxidation of (π-Cp)₂ TiBH₄ with oxygen and reduction of the resulting titanium(IV) compound with LiBH₄ are reversible processes. The one-electron oxidation of (π-Cp)₂TiBH₄ produces oxygen radicals, which can initiate homogeneous hydrogeneation of olefins.     

Solvent effect on metal oxidation rates in aprotic media

A correlation between the rates of oxidation of metals with organometallic chlorides in aprotic media and the physicochemical properties of the solvents was established. An equation fitting the experimental data for ten reaction series was suggested. The kinetic parameters of oxidation of cadmium with diphenyl-bismuth chloride in aprotic media, calculated with the correlation equations, coincide with the experimental data.     

Effect of support on activity of palladium catalysts in nitrobenzene hydrogenation

The effect of two types of catalysts on the activity of the catalytic hydrogenation of nitrobenzene was studied. Catalysts were prepared by the surface deposition of palladium hydroxide with a simultaneous reduction with formaldehyde in a basic environment and were characterised by X-ray powder diffraction, transmission electron microscopy, adsorption-desorption, and catalytic tests — hydrogenation of nitrobenzene in methanol. The influence of the supports’ (activated carbon and a mixture of activated carbon and multi-walled carbon nanotubes) surface area is discussed. Despite having a size comparable (4–5 nm) to crystallites of metallic palladium, the catalyst prepared on a mixture of activated carbon and nanotubes (Pd/C/CNT) was significantly less active than the catalyst prepared on pure activated carbon (Pd/C); the rate of this reaction was approximately 30 % lower than the initial reaction rate. This feature could be attributed to the lower specific surface area of the Pd/C/CNT (531 m² g^?1) in comparison with the Pd/C (692 m² g^?1).     

Selective recognition of alkyl pyranosides in protic and aprotic solvents

The design and synthesis of receptors capable of selective, noncovalent recognition of carbohydrates continues to be a signature challenge in bioorganic chemistry. We report a new generation of tripodal receptors incorporating three pyridine (compound 2) or quinoline (compound 3) rings around a central cyclohexane core for use in molecular recognition of monosaccharides in apolar and polar protic solvents. These tripodal receptors were investigated using (1)H NMR, UV, and fluorescence titrations in order to determine their binding abilities toward a set of octyl glycosides. Receptor 2 displayed the highest binding affinity reported to date for noncovalent 1:1 binding of an alpha-glucopyranoside in chloroform (Ka = 212,000 +/- 27,000 M(-1)) and an approximately 8-fold selectivity for the alpha anomer over the beta anomer of the glucopyranoside. Most importantly, 2 retained its micromolar range of affinities toward monosaccharides in a polar and highly competitive solvent (methanol). The quinoline variant 3 also displayed micromolar binding affinities for selected monosaccharides in methanol (as measured by fluorescence) that were generally smaller than those of 2. Compound 3 was found to follow a selectivity pattern similar to that of 2, displaying higher affinities for glucopyranosides than for other monosaccharides. The binding stoichiometry was estimated to be 1:1 for the complexes formed by both 2 and 3 with glucopyranosides, as determined by Job plots. Nuclear Overhauser effect spectroscopy allowed for the derivation of a binding model consistent with the observed selectivities.     

催化加氢还原法制备对氯苯胺的工艺研究

氯代芳烃苯胺一般由氯代芳烃硝基化合物还原制得,主要途径有:铁粉还原法、硫化碱或水合肼还原法、电化学还原法以及催化加氢还原法[1,2].其中,铁粉还原法工艺简单,设备投资小,生产较易控制,但产生大量的含胺废液、废渣,造成严重的环境污染[3];硫化碱或水合肼还原路线存在着流程长、三废多、产品质量差等问题;电解还原工艺路线虽属清洁工艺,但能耗高,设备投资大.而催化加氢还原法具有环境友好、生产能力高,产品质量稳定的特点[1].     

Selective catalytic hydrogenation of acetylenes

The products of the stepwise catalytic hydrogenation of undeca-1,7-diyne (I) have been examined and the sequence of the reduction established. The ethynyl group may be protected during catalytic hydrogenation by conversion into the corresponding 1-bromoacetylene.

Certain palladium catalysts have been shown to produce substantial amounts of trans-ethylene in the catalytic partial reduction of several acetylenic hydrocarbons. Catalytic stereomutation of cis- to trans-ethylene has been observed, the extent of which depends on the relative proportions of catalyst and unsaturated hydrocarbon.     

硝基苯催化加氢制对氨基苯酚的合成工艺研究进展

介绍了硝基苯在酸性介质中一步加氢重排的反应机理及模型。以提高对氨基苯酚产率和纯度为宗旨，在大量文献调研的基础上提出了控制副反应的几种方法，并讨论了改进对氨基苯酚产量和纯度的可能途径。引用文献22篇。     

The hydrogenation of nitrobenzene to aniline: a new mechanism

The Haber mechanism describing the process of hydrogenating nitrobenzene to aniline is shown to be incorrect and a new mechanism is proposed.     

Solvent effects on the polarographic behaviour of halobenzenes in aprotic media

The polarographic behaviour of fluoro, chloro, bromo and iodobenzene in dimethylformamide, dimethylsulfoxide and acetonitrile at 25 °C is reported. The viscosities and densities of these species in the three solvents have been measured and the corresponding viscosityB-coefficients and molar partial volumes at infinite dilution for halobenzenes are reported. The results, which show a clear dependence upon solvent nature, are analysed in terms of solute-solvent interactions and solvent structure.

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Lösungsmitteleffekte des polarographischen Verhaltens von Halogenbenzolen in aprotischen Medien

Zusammenfassung Es wird über das polarographische Verhalten von Fluor-, Chlor-, Brom- und Iodbenzol in Dimethylformamid, Dimethylsulfoxid und Acetonitril bei 25 °C berichtet. Viskositäten und Dichten wurden in diesen drei Lösungsmitteln gemessen und die entsprechenden Viskositäts-B-Koeffizienten und die molaren partiellen Volumina für unendliche Verdünnung der Halogenbenzole bestimmt. Die Ergebnisse, die eine starke Abhängigkeit vom Lösungsmittel zeigen, werden mittels der Wechselwirkung Lösungsmittel —gelöster Stoff und Lösungsmittelstruktur interpretiert.

     

Direct and indirect electrochemical reduction of organic halides in aprotic media

Cyclic voltammetric reduction of 17 different organic halides including alkyl, allyl, and benzyl chlorides, bromides, and iodides in aprotic media (DMF, DMSO, and acetonitrile, AN), containing 0.1 M Bu₄NClO₄, have been reported at glassy carbon (gc) and graphite as working electrodes. A single two-electron irreversible and diffusion-limited reduction of the carbon-halogen bond is observed, the reduction potentials ranging from –1.20 to –2.70 V (versus silver wire quasireference electrode) depending on the halide, the solvent, and the electrode. Indirect reduction of these 17 halides, however, is effected at much lower potentials (–0.79 to –0.92 V versus SCE) depending on the experimental conditions by in situ electrogenerated superoxide ion (O ₂ ^– ) by CPE. The products have been characterized by TLC, GC, CV, or chemical estimation. The diorganic peroxide and the organic hydroperoxide were the major products. In case of tertiary alkyl halides, however, alkenes predominated, due to basic nature of O ₂ ^– in these reactions. These studies indicate sufficient strength of O ₂ ^– as a nucleophile or base depending on the experimental conditions.From Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 350–355.Original English Text Copyright © 2005 by Vasudevan.This article was submitted by the author in English.