Azoxybenzene Research Articles

Shape-controlled preparation of nano gold (Au), Au clusters, and Au single atoms based on layered double hydroxide with closo-dodecaborate and their utilization for selective nitrobenzene reduction

Single-atom (SA) catalysts are superior in terms of catalytic activity, selectivity, and metal utilization. However, the complex preparation methods of SAs hinder their widespread application. Herein, layered double hydroxides (LDHs) with unique charge distributions were ingeniously combined with the dodecahydro-closo-dodecaborate anion [closo-B12H12]2−. We designed two different gold(Au) catalysts based on LDHs with closo-dodecaborate for the selective reduction of nitrobenzenes: composite dual-site Au SA/Au cluster catalysts (B12H12-MgAl-LDH-Au) were prepared using the anion exchangeability and spatial domain–limiting properties of LDH and the reducibility of [closo-B12H12]2−, and other Au nanoparticle catalysts (MgAl-LDH@B12H12@Au) were obtained using the reducibility of [closo-B12H12]2− immobilized on the LDH laminate. Up to 27 different nitrobenzene substrates can be selectively reduced to the corresponding azoxybenzenes (AOBs) with high efficiency at a wavelength of 450-nm radiation catalyzed by B12H12-MgAl-LDH-Au. However, large-size nanoparticles were more efficient in absorbing visible light energy. Therefore, 10 different AOB compounds were prepared using the MgAl-LDH@B12H12@Au system.

Synergic catalysis of W and Ni originating from substitution of trivacant phosphotungstate for the selective oxidation of aniline to azoxybenzene

Partial substitution of polyoxometalate (POM) is an efficient route to modulate the catalytic property of maternal POM. In this work, a new Keggin type POM involving {Ni6} cluster, {[Ni(H2O)2(Dach)2][Ni(Dach)2]2}{[Ni6Cl(μ-OH)3(H2O)(Dach)3(WO4)(PW9O34)][Ni6(μ-OH)3(H2O)2(Dach)3(WO4)(PW9O34)]}Cl·27H2O, (1, Dach = 1,2-diaminocyclohexane) was synthesized. Compounds 1 shows excellent catalytic performance in the selective oxidation of aniline to azoxybenzene (AOB) in water. The apparently different results from that with the matrix {PW9O34} ({PW9}) suggest the successful regulation of the catalytic property of {PW9} by the introduction of the {Ni6} cluster into the skeleton. The experimental results indicate that the highlighted performance of 1 is contributed by the synergy of W and Ni sites, which are respectively responsible for the oxidation and condensation steps in the production of AOB. The good selectivity to AOB is essentially attributed to the effective modulation of the reaction rates of oxidation and condensation steps by W and Ni sites, respectively.

Tuning product selectivity in nitrobenzene reduction over a single Bi2MoO6 photocatalyst in one pot: Mechanisms and roles of reaction compositions

Poor product selectivity of metal oxide photocatalysts is one of crucial issues limiting their application in photocatalytic organic synthesis particularly when multiple parallel reactions as well as several intermediates and products are involved, as in the reduction of nitrobenzene (NB) in this present study. Accordingly, catalyst modification is often needed. Herein, we first demonstrate that without catalyst modification it is feasible to control product selectivity over a single bismuth molybdate photocatalyst to selectively prepare three different valuable compounds including aniline (AN), azobenzene (AZO) and azoxybenzene (AZX) with high efficacy. Two widely used bismuth molybdate photocatalysts, namely Bi2MoO6 and Bi4MoO9, were studied and compared. Bi2MoO6 offers better visible-light-driven photocatalytic performance than Bi4MoO9 partly due to its narrow band gap energy and efficient charge carrier separation and transfer as evidenced from UV–vis DRS, EIS, and transient photocurrent studies. The roles of hydrazine hydrate, alcohol solvent, and KOH additive on the transfer hydrogenation of NB were examined and their concentrations were optimized to solely obtain the three different products with excellent selectivity (>98%). Based on UV–vis DRS and Mott-Schottky analysis, the band energy level of Bi2MoO6 and plausible reactions at solid–liquid interface are proposed. The capability to control product selectivity over a single photocatalyst in one pot demonstrated in this work would make the process more practical especially for continuous flow photochemical systems.

Thermodynamic and spectroscopic characterization of a weakly polar liquid crystalline compound dispersed with polyvinyl pyrrolidone capped gold nanoparticles

In the present study a deliberate attempt has been made to examine the consequences of dispersion of gold nanoparticles in an azoxybenzene-based nematic liquid crystal, namely 4,4′- di pentyl azoxy benzene. Investigations were made on gold nanoparticles doped nematic liquid crystals analysing differential scanning calorimetry, polarized light microscopy, ultraviolet–visible absorption spectroscopy, photoluminescence and Fourier-transform infrared spectroscopy (FTIR). Gold nanoparticles of different concentrations 0.25, 0.5, and 1.0 wt% were dispersed in pure 4,4′- di pentyl azoxy benzene, and it was observed in the experiment that no significant change occurs in the crystal to nematic phase (Cr-Ne) transition temperature with the increase in gold nanoparticles concentration. However, the nematic to isotropic (Ne-Iso) transition temperature decreases significantly with the increase in gold nanoparticles concentration. This study reports around 76% increase in ultraviolet–visible absorbance and 46% enhancement of photoluminescence intensity with the suitable amount of gold nanoparticles dispersion in 4,4′- di pentyl azoxy benzene. The surface plasmonic resonance (SPR) and re-excitation of 4,4′- di pentyl azoxy benzene molecule due to collision with gold nanoparticles has been accredited to the escalation in photoluminescence intensities.

Deciphering Intermediates and Additives Effect on the Reduction of Nitrobenzene by SmI2

AbstractProduct distribution in the reaction of nitrobenzene (NB) with SmI2 shows a strong dependence on the number of equivalents of SmI2 used. Phenylhydroxylamine (PHA), azoxybenzene (AZOB) and azobenzene (AZB) are the main products when the number of equivalents of SmI2 is up to 4 equivalents. When 6 equivalents are used, aniline (AN) yield is higher and with 8 equivalents, the yield of aniline is 95 %. Using various techniques including chemical labelling, it was shown that none of the above compounds is an intermediate on the path of nitrobenzene to aniline. The suggested mechanism involves the formation of nitrosobenzene which is converted to an intermediate that could generate phenylhydroxylamine. Yet, in the presence of a large amount of SmI2 it is converted directly to aniline, circumventing the production of phenylhydroxylamine. The ratio of aniline production to the condensed products (AZOB and AZB) was shown to be inversely proportional to the ability of the additives used to coordinate to SmI2. The observed order was: MeOH>Water>ethylene glycol>HMPA. Trapping of proposed intermediate with benzaldehyde gives synthetically useful products such as nitrone and Imine.

Ir(iii)-Catalyzed site-selective amidation of azoxybenzenes and late-stage transformation

An efficient site-selective C–H amidation of azoxybenzenes with 1,4,2-dioxazol-5-ones by Ir catalysis has been established for the diversification of azoxybenzenes.

Liquid phase hydrogenation of nitrobenzene

Hydrogenation of nitrobenzene (NB) was carried out in methanol solutions (initial concentration 0.8moll−1) over a Pd/C catalyst (3wt.% of Pd; reaction mixture contained 2.2mgPdl−1) over the pressure range of 2–4MPa and temperature 30–70°C in a laboratory scale batch reactor. Zero order kinetics was observed at hydrogen pressures above 2MPa Under applied experimental conditions the apparent activation energy was 35±1kJmol−1. A detailed analysis of the reaction mixture inspired the hypothesis that a C6H5–NO(H) moiety is formed on the catalyst surface and it undergoes further condensation to azoxybenzene (AOB) releasing water. However, very low concentrations of azobenzene (AB) and hydrazobenzene (HAB) in the reaction mixture indicate that the reaction route to the formation of aniline by hydrogenation of AOB to AB, hydrazobenzene (HAB) and subsequent hydrogenolysis to AN is of low probability. Hydrogenolysis of AOB to C6H5–NO(H) and C6H5–N(H), where the latter is hydrogenated to AN, is more likely. Based on the experimental observations a new reaction scheme for the heterogeneous catalytic hydrogenation of NB was proposed.

A highly efficient iron doped BaTiO3nanocatalyst for the catalytic reduction of nitrobenzene to azoxybenzene

A heterogeneous Fe doped BaTiO3efficient nanocatalyst for the catalytic reduction of nitrobenzene (NB) to synthesize azoxybenzene (AOB) in the presence of 2-propanol and molecular H2has been investigated. This method offers 100% NB conversion with 93–95% AOB yield.

Cu/CuxO and Pt nanoparticles supported on multi-walled carbon nanotubes as electrocatalysts for the reduction of nitrobenzene

Cu/CuxO and Pt nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) were studied as electrocatalysts for the reduction of nitrobenzene in a half-cell set-up. This reaction not only produces valuable chemicals, but has the potential to generate electricity if applied in a fuel cell device. MWCNTs with and without functional groups were investigated as supports for the nanoparticles, employing either ethylene glycol (EG) or H2 gas as reductant. Cu/CuxO nanoparticles supported on pristine multi-walled carbon nanotubes prepared using H2 as reductant (Cu/MWCNT-H2) were identified as the best electrocatalyst for the reduction of nitrobenzene on the basis of its onset potential and of the number of electrons transferred per nitrobenzene molecule. This material consists of well-dispersed Cu/CuxO nanoparticles with an average size of 8nm. The stability of Cu/MWCNT-H2 was tested by cyclic voltammetry (CV) for 1000 cycles, showing that the activity of this electrocatalyst does not deteriorate over time. The electrochemical reduction of nitrobenzene over Cu/MWCNT-H2 in acidic ethanolic medium at −0.62V vs. Fc/Fc+ led to 44% conversion with an overall selectivity toward azoxybenzene (AOB) of 82%.

Twisted Grain Boundary Phase in Binary Mixture of Liquid Crystals

In the present work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds, namely, cholesteryl chloride and 4,4′-hexyloxy azoxy benzene, which exhibits a very interesting liquid crystalline twisted grain boundary (TGB) phase and induced smectic phases like SmA, SmC*, SmE, and SmB phases. The chiral liquid crystalline TGB phases have been observed at different concentrations and at different temperatures. The mixture with concentration from 26% to 37% of shows I-Ch-TGB-SmA-SmC*-SmE-SmB phases sequentially when the specimen cooled from isotropic phase. The existence of TGB phase is confirmed by DSC and optical microscopic studies. The temperature variation of optical anisotropy is also discussed. X-ray studies have been carried out to understand the intermolecular interactions in the mixture. With the help of phase diagram, the phase behavior has also been discussed.

ChemInform Abstract: Reduction of Nitroarenes to Azoxybenzenes by NaOH—PEG 400.

AbstractOn refluxing nitroarenes with NaOH and PEG 400 in benzene varying yields of the corresponding azoxybenzenes are obtained.

Density Measurements and Thermodynamic Parameters of 4,4′-Dibutoxyazoxybenzene

Thermodynamic functions using the coefficient of volume expansion (α) of a system, a number of thermoacoustic and anharmonic parameters such as the isochoric temperature coefficient of internal pressure (X), isochoric temperature coefficient of volume expansivity (X′), reduced compressibility (β∼), reduced volume (V ∼), isothermal microscopic Gruneisen parameter (Γ), fractional free volume (f), and Sharma parameter (So) can be investigated. The temperature dependence of these parameters gives a basic understanding about the intermolecular interactions in general. These studies also can applied to a solute in dilute solutions. In the present study these different parameters have been determined using volumetric measurements in the case of a liquid crystal, namely, 4,4′-dibutoxy azoxy benzene (HPOAB), which is a typical liquid crystal with a nearly linear structure, in dilute solutions at different temperatures. Variations in various parameters with respect to temperature are discussed in the light of the results obtained. The variation of the properties is analyzed and discussed in this article.

Thermodynamic and acoustical parameters of some nematic liquid crystals

Ultrasonic and density measurements on solutes in dilute solutions are used to obtain thermodynamic and acoustical parameters and their excess values. The physical parameters that can be obtained such as molar sound velocity or Rao's number ( R), molar compressility or Wada's constant ( B), characteristic acoustic impedance ( Z), intermolecular or free length ( L f), free volume ( V f), available volume ( V a) and adiabatic compressibility ( β) play an important role in the phenomenon of sound transmission. For example, the parameter Z determined by the product of density ( d) and ultrasonic velocity ( c) has a greater significance as a characteristic property than density or velocity. In the case of sound transmission the parameter of more concern is the molar sound volume ( V m) rather than molar sound velocity or Rao's number. Such studies on pure liquid crystals around phase transition temperature yield important information. In view of the above facts, the ultrasonic velocity and density measurements on pure samples of nematics, namely, 4,4′-azoxy anisole and 4,4′-dibutoxy azoxy benzene in dilute solutions were taken up. The results of this work is presented in this paper and discussed.

Characterization of Some Liquid Crystals through Sound and Thermodynamic Parameters

The structural changes arising from transition between the mesophases of liquid crystalline materials can be better understood by ultrasound in conjunction with specific volume properties. In particular, ultrasonic studies are found to give clear information regarding the nature of the phase transition, pretransitional effects, and molecular ordering. For example, temperature corresponding to the maximum value of acoustic impedance, adiabatic compressibility, and temperature corresponding to the minimum value of ultrasonic velocity, Rao's number, order parameter, and molar compressibility, in thermotropic liquid crystals are very useful in understanding their structural behavior. In view of these facts, it was thought worthwhile to study ultrasonic velocity with data available for density measurements on pure samples of nematics, namely, 4,4′-azoxy anisole and 4,4′-dibutoxy azoxy benzene. The results of this work, are presented in this article and discussed.

Catalytic performance of Preyssler heteropolyacid as a green and recyclable catalyst in oxidation of primary aromatic amines

Many substituted anilines were converted into the corresponding azoxy benzenes as major products, by hydrogen peroxide, using Preyssler catalyst. The ability of various Preyssler catalysts as pure, H 14[NaP 5W 30O 110], mixed addenda, H 14[NaP 5W 29MoO 110], and cetylpyridinium acidic salt, was investigated. In all cases, the highest yield of azoxy compounds was observed, using H 14[NaP 5W 30O 110] as catalyst. The oxidations of anilines with 30% H 2O 2 catalyzed by Preyssler catalysts in various solvents with different molar ratio of amine to oxidant, have been investigated and the results showed that the reaction yields were affected by changing the solvent as well as molar ratio of amine:oxidant.

Twisted Grain Boundary Phase in the Binary Mixture of Neuatic and Ceolesteryl Compounds

The binary mixture of cholesteryl nonanoate(CN) and 4,4′-hexyloxy azoxy benzene (HOB) exhibit a very interesting sesophases like blue phase, twisted grain boundary (TGB) phase, induced smectic A, smectic C and smectic B phases at different temperatures when the mixture is cooled from isotropic phase. The existence of TGB phase is confirmed by DSC and optical microscopic studies. The mixtures with concentration 30 to 45% of CN exhibit TGB phase at higher temperature. The optical anisotropy of cholesteric phase is estimated. Numerous interesting optical textures are also illustrated.

Liquid-Phase Oxidation of Aniline over Various Transition-Metal-Substituted Molecular-Sieves

The oxidation of aniline has been performed in the liquid phase at moderate temperatures over a series of transition-metal-substituted molecular sieves. Experimental data have shown that TS-1 was not the best catalyst for this reaction but that large pore zeolites or mesoporous silicas were preferred. Indeed, these solids could be used with either hydrogen peroxide or tert-butyl hydroperoxide (TBHP) as oxidant. For low oxidant/aniline ratios, azoxybenzene (AZY) was the major product formed over Ti-containing catalysts, but azobenzene (AZO) and nitrosobenzene (NSB) were also detected. The selectivity in AZO was always higher with TBHP than with H 2O 2. In contrast, V-substituted zeolites were only active with TBHP and led to the very selective formation of nitrobenzene.

Chemoselective Deoxygenation of Nitrones and N-Oxides with Tetrathiomolybdate

Reaction of nitrones and N-oxides with benzyltriethylammonium tetrathiomolybdate 1 in acetonitrile (25°C) yielded the corresponding imines and amines in good yields. Sulfoxides and azoxy benzenes are unaffected.

Chemoselective deoxygenation of nitrones and N-oxides with tetrathiomolybdate

Reaction of nitrones and N-oxides with benzyltriethylammonium tetrathiomolybdate 1 in acetonitrile (25°C) yielded the corresponding imines and amines in good yields. Sulfoxides and azoxy benzenes are unaffected.

Shear and rotational viscosity coefficients of two nematic liquid crystals

A new method for the measurement of the shear viscosity coefficients η1, η2, and η3 of nematic liquid crystals is described. A detailed discussion of all sources of errors shows that reliable data can be obtained with this method. Measurements of the shear and rotational viscosity coefficients of a broad range nematic liquid crystal mixture of azoxy benzenes and for octyloxycyanobiphenyl with a transition to a smectic A phase are presented. The results are discussed in the framework of some theories.