Reactions Of Aromatic Compounds Research Articles

On non‐hydrogen‐atom products of thermal decomposition of benzyl radical: A theoretical investigation by the transition state theory/multi‐well master equation approach

AbstractBenzyl radical (C7H7), one of the resonantly stabilized hydrocarbon radicals, is one of the significant precursors of polycyclic aromatic hydrocarbons in interstellar media and combustion engines. The unimolecular decomposition of benzyl radical is still incompletely understood despite of its importance and relatively small molecular size. The decomposition reactions of benzyl radical were investigated in the present study by using the ab initio transition state theory (TST) and the multi‐well master equation theory. Specifically, all reaction pathways on the potential energy surface of C7H7 was calculated at the level of QCISD(T)/CBS. For the reactions with multireference characters, the CASPT2(9e,7o)/aug‐cc‐pVTZ method was used to calculate the vibrational frequencies and energies of structures along the one‐dimensional reaction coordinate of the breaking bond. The high‐pressure limits of rate constants for all the reactions were obtained by using the TST except those for C7H6 + H and C6H4 + CH3 by the variational TST. The pressure‐dependent rate constants were obtained by using the multi‐well master equation simulations. The calculated rate constants agree well with available experimental and theoretical data in the literature. Moreover, the present results identify the composition of the non‐hydrogen‐atom production observed in previous experiments, which provide new insights into the reactions of aromatic compounds.

Rose Bengal-photocatalyzed perfluorohexylation reactions of organic substrates in water. Applications to late-stage syntheses.

The Rose Bengal-photocatalyzed perfluorohexylation of olefins, alkynes, and electron-rich aromatic compounds in water was achieved employing perfluorohexyl iodide as fluoroalkyl source and TMEDA as sacrificial donor under green LED irradiation. Alkenes and alkynes rendered products derived from the atom transfer radical addition (ATRA) pathway, and in the case of alkynes, exclusively as E-stereoisomers. These are the first examples of photocatalyzed ATRA reactions carried out excursively in water alone. The reactions of aromatic compounds under the current protocol in water present the advantage of employing a perfluoroalkyl iodide (C6F13-I) as source of perfluorohexyl radicals. Examples of photocatalytic late-stage incorporations of fluoroalkyl moieties into two commercial drugs of widespread use are reported.

Enrichment of aromatic compounds during the high-pressure reactive distillation of bio-oil

The bio-oil produced from the renewable biomass is a sustainable source of aromatic compounds. The aromatic compounds in bio-oil would generally contribute to the coke formation during its further processing, which is a bottleneck problem for its further application due to the complex composition of bio-oil. In this study, the distribution and reaction of aromatic compounds during the high-pressure reactive distillation of bio-oil are investigated to achieve the enrichment of aromatic compounds to the distillate fraction. It is found that pressure could help transfer aromatic compounds into the distillate fraction. In addition, the increase of pressure could contribute to the reduction of polymerisation and the production of aromatic monomers due to the hydrothermal environment. Besides the process parameters, methanol could also be used to inhibit the polymerisation of aromatic compounds. Furthermore, the transfer of aromatic compounds could also be intensified using Ca(OH)2 based on the acidity of phenolic compounds.

The Influence of Copper on Halogenation/Dehalogenation Reactions of Aromatic Compounds and Its Role in the Destruction of Polyhalogenated Aromatic Contaminants

The effect of copper and its compounds on halogenation and dehalogenation of aromatic compounds will be discussed in the proposed article. Cu oxidized to appropriate halides is an effective halogenation catalyst not only for the synthesis of halogenated benzenes or their derivatives as desired organic fine chemicals, but is also an effective catalyst for the undesirable formation of thermodynamically stable and very toxic polychlorinated and polybrominated aromatic compounds such as polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans accompanied incineration of waste contaminated with halogenated compounds or even inorganic halides. With appropriate change in reaction conditions, copper and its alloys or oxides are also able to effectively catalyze dehalogenation reactions, as will be presented in this review.

Reactivity of aromatic contaminants towards nitrate radical in tropospheric gas and aqueous phase

Aromatic compounds (ACs) give a substantial contribution to the anthropogenic emissions of volatile organic compounds. Nitrate radicals (NO3) are significant oxidants in the lower troposphere during nighttime, with concentrations of (2-20) × 108 molecules cm−3. In this study, the tropospheric gas and liquid phase reactions of ACs with nitrate radical are investigated using theoretical computational methods, which can give a deep insight into the reaction mechanisms and kinetics. Results show that the reactivity of ACs with nitrate radicals decreases as the electron donating characteristics of the functional group on the ACs decrease, as ΔG≠ of the reaction with NO3 increasing from -1.17 to 17.84 kcal mol-1. The reaction of NO3 towards ACs in the aqueous phase is more preferable, with the atmospheric lifetime 0.07–1281 min. An assessment of the aquatic toxicity of ACs and their degradation products indicated that the risk of their degradation products remains and should be given more attention.

Au@SnO2 and SnO2@Au Hollow Spheres for Gas Sensors with Different Methylbenzene Selectivity

Introduction Hollow or yolk-shell microspheres decorated with catalytic materials have been suggested as the platforms to design high performance gas sensors. For instance, SnO2 and Co3O4 yolk-shell spheres uniformly loaded with Pd catalysts exhibited high selectivity toward methylbenzene [1,2], whereas Pd-loaded SnO2 and Co3O4 nanoparticles in the literature generally did not. This intriguing results can be understood in relation to the micro-reactor role of catalyst-loaded yolk-shell spheres to promote the reforming of less reactive methylbenzene into more reactive species. In order to elucidate the sensing mechanism underlying the improvement of gas selectivity, the effect of catalyst location as well as catalyst material on the gas sensing characteristics of micro-reactor-shaped sensing materials should be investigated. For this, in this contribution, we prepared two different model sensing materials: 1) SnO2 hollow spheres whose inner parts of shells are decorated with 0.3 at% Au (denoted as ‘Au-in-SnO2’) and 2) SnO2 hollow spheres whose outer parts of shells are decorated with 0.3 at% Au (denoted as ‘Au-out-SnO2’) and their gas sensing characteristics were compared and discussed. The Au-in-SnO2 and Au-out-SnO2 sensors showed significantly different gas selectivity and response, suggesting that the location of Au catalysts in micro-reactor-shaped sensing materials is a key factor to determine gas sensing characteristics. Method 0.15 g of sulfonated polystyrene (SPS) beads (diameter: ~ 200 nm) were dispersed in 30 mL ethanol, and 0.075 g of poly-vinylpyrrolidone (PVP, MW = 40,000) was dissolved in 30 mL distilled water. The former slurry and the latter solution were mixed and homogenized by stirring. Then 30 mL of SnSO4 aqueous solution (0.07 M) were added drop by drop to the mixed slurry solution. The slurry solution was stirred at room temperature for 12 h, and subsequently washed and centrifuged five times with distilled water and then ethanol. The precursor powders (SPS@Sn) were converted into SnO2 hollow spheres via a heat treatment at 550 °C for 2 h in air. 0.0021 g of HAuCl4∙3H2O (99.999%) was dissolved in slurry solution containing 30 mL of ethanol and 0.15 g of SPS. After stirring at room temperature for 2 h, 10 mL of NaBH4 (99.99%) aqueous solution (0.0026 M) was added drop by drop to Au containing SPS suspension and stirred at 60 °C for 2 h. After washing and centrifuging five times with distilled water and ethanol, the suspensions were dried at 70 °C for 6 h to obtain SPS@Au. To confine the Au nanoparticles inside SnO2 hollow shell, SPS@Au@Sn was formed by coating SPS@Au with Sn precursor according to the same procedure to prepare SPS@Sn. To load the Au nanoparticles outside the SnO2 hollow shell, SPS@Sn@Au was prepared by loading Au on SPS@Sn using the previous procedure to prepare SPS@Au. The Au-in-SnO2 and Au-out-SnO2 hollow spheres were prepared by thermal annealing of SPS@Au@Sn and SPS@Sn@Au at 550 °C for 2 h in air. The [Au]/[Sn] ratios in both samples were fixed to 0.3 at%. Results and Conclusions The sensor using pure SnO2 hollow spheres exhibited the highest response to ethanol and the responses to other gases (HCHO, p-xylene, toluene, benzene, and CO) were low at all sensing temperatures (300 – 375 oC). Both Au-out-SnO2 and Au-in-SnO2 sensors showed significantly enhanced responses to all the analyte gases. However, they showed completely different gas selectivity depending on the location of Au catalysts. The Au-out-SnO2 sensor showed the highest gas response to 5 ppm ethanol over the entire range of sensing temperatures and the overall sensing characteristics are similar to those of pure SnO2 sensor although the maximum gas responses are different from each other. In contrast, the Au-in-SnO2 sensor showed the highest response to p-xylene at 300 - 350 oC. Moreover, the responses to toluene and benzene were higher than those of ethanol at 350 and 375 oC. High selectivity to xylene and relatively high responses to less reactive benzene as well as toluene can be attributed to the reforming of less reactive aromatic compounds into more reactive species for gas sensing. The catalyst-loaded micro reactor is a good model system to understand the gas sensing mechanism and provide a promising platform to detect the aromatic indoor air pollutants in a highly selective and sensitive manner.

Electrocatalytic Hydrogenation of Lignocellulosic Biomass to Hydrocarbon Fuels: Life Cycle Assessment and Technoeconomic Analysis

According to the 2016 Billion Ton Report, the annual harvestable biomass in the U.S. (that can be produced at $60/ton or less) by the year 2030 is not sufficient to meet the annual energy demands of the U.S. transportation sector alone. Therefore, for biomass-derived fuels to be considered a realistic alternative to fossil fuels, processes must be developed to upgrade the energy content of these biofuels to match that of petroleum-based fuels. Such energy upgrading must also overcome the barriers resulting from biomass’ dispersed nature and the high costs of transporting a low bulk density feedstock. Depot-based fast pyrolysis partially overcomes these barriers by densifying biomass into bio-oil, however this mixture is reactively unstable and corrosive. Subsequent electrocatalytic hydrogenation (ECH) potentially stabilizes this bio-oil to a form that can be transported and stored at a centralized refinery. ECH involves using mild temperature, atmospheric pressures and renewable electricity, such as wind or solar, to split water on a catalytic cathode to produce in situ hydrogen and consequently perform the reduction of reactive aromatic compounds present in bio-oil. For the bioenergy system studied, the catalytic cathode was selected to be ruthenium on activated carbon cloth with a platinum anode. Bio-oil was modelled as a mixture of eight compounds, each species representing a key functional group. To investigate the merits of this biofuel production strategy, mass, energy and carbon flow analyses were performed for the proposed system. These were compared to the traditional approach of cellulosic ethanol fermentations as described in a 2011 report by NREL. The comparative study revealed the advantages of the proposed process in terms of mass, carbon, and energy efficiency. More recently, a full scale “cradle-to-grave” life cycle assessment (LCA) was performed to quantify the environmental impacts of the proposed process, such as global warming, eutrophication, and water use. As suspected, the LCA analyses revealed that the electrical power source plays a major role in determining the overall climate change potential of systems that upgrade biomass using electrocatalytic hydrogenation. A full-scale economic analysis was also performed to estimate the minimum fuel selling price (MFSP) and to elucidate the most sensitive parameters affecting the MFSP. The LCA and the techno-economic analysis are integral steps in the commercial application of the proposed bioenergy system.

Friedel-Crafts benzoylation reaction of aromatic compounds using zinc oxide nanoparticles in deep eutectic solvent (choline chloride/urea) under microwave irradiation

Synthesis of zinc oxide nanoparticles (ZnO) which was found to be effective catalyst for Friedel-Crafts benzoylation reaction in the presence of deep eutectic solvent (DES). The method is one of the most important intermediates for preparing fine chemicals in the field of pharmaceuticals, which is a tool for organic syntheses of aromatic ketones. ZnO precursor was prepared from Zn(CH3COO)2.2H2O and H2C2O4.2H2O, ZnO nanoparticles were characterized by using X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM). The benzoylation of aromatic compounds and benzoyl chloride using nanoparticles ZnO/ [CholineCl][Urea]2, under microwave irradiation afforded the desired products in high yields and short reaction times. The catalyst/solvent could be recycled several times without loss of efficient catalytic activity.

Aromatic Halogenation Using N-Halosuccinimide and PhSSiMe3 or PhSSPh.

We developed a mild aromatic halogenation reaction using a combination of N-halosuccinimide and PhSSiMe3 or PhSSPh. Less reactive aromatic compounds, such as methyl 4-methoxybenzoate, were brominated with PhSSiMe3 or PhSSPh and N-bromosuccinimide in high yields. No reaction was observed in the absence of PhSSiMe3 or PhSSPh. This method is also applicable to chlorination reactions using N-chlorosuccinimide and PhSSPh.

TiO2-catalyzed photodegradation of aromatic compounds: relevance of susceptibility to oxidation and electrophilic attack by hydroxyl radical

The application of nanostructured titanium dioxide (TiO2) as catalyst for the photodegradation of drugs and dyes is well established. We aimed to evaluate the importance of the reactivity of aromatic compounds submitted to photodegradation. Specifically, we were interested in the correlation between susceptibility to oxidation and/or to electrophilic attack and the efficiency of degradation. We demonstrated that hydroxyl radical (HO˙) is the most relevant species generated in the photodegradation process. Considering that HO˙ has both oxidizing and electrophilic features, the efficiency of degradation of selected aromatic compounds was performed. The choice was based on their susceptibility to oxidation and/or to electrophilic attack. Benzoic acid (C1), salicylic acid (C2), and protocatechuic acid (C3) were compared regarding their oxidability using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and were ranked as follows: C3 ≫ C2~C1. These compounds were efficiently photodegraded and no significant difference was observed among them. To assess the importance of susceptibility to electrophilic attack, anisole (C4), acetophenone (C5), and nitrobenzene (C6) were selected. Compared to C5 and C6, the higher susceptibility of C4 to electrophilic attack was demonstrated using hypochlorous acid, an electrophilic reagent. The photodegradation showed that C4 was also more susceptible to degradation compared to C5 and C6. In summary, we found that by acting as a powerful oxidant/electrophile agent, HO˙ was able to promote the degradation of aromatic moieties. Considering that the majority of drugs and dyes bear aromatic moieties, our findings explain the great success of photodegradation using metal oxides as catalysts.

Syntheses, structures and catalytic activity for Friedel-Crafts reactions of substituted indenyl rhenium carbonyl complexes

The complexes [(η5-C9H6R)Re(CO)3] [R = nBu (8), tBu (9), CH(CH2)4 (10), Ph (11), Bz (12), 4-methoxyphenyl (13), 4-chlorophenyl (14)] were synthesized by refluxing substituted indenyl ligands [C9H7R] [R = nBu (1), tBu (2), CH(CH2)4 (3), Ph (4), Bz (5), 4-methoxyphenyl (6), 4-chlorophenyl (7)], and Re2(CO)10 in decalin. The molecular structures of 9, 10, 12, and 13 were determined by X-ray diffraction analysis. These four crystals have similar molecular structures of the mononuclear carbonyl complex. In each of these molecules, Re is η5-coordinated to the five-membered ring of the indenyl group. Complexes 8–14 have catalytic activity for Friedel-Crafts reactions of aromatic compounds with a variety of alkylation and acylation reagents. Compared with traditional catalysts, these mononuclear metal carbonyl complexes have obvious advantages such as high activities, mild reaction conditions, high selectivity, and environmentally friendly chemistry.

Synthesis and catalytic activity of rhenium carbonyl complexes containing alkyl-substituted tetramethylcyclopentadienyl ligands

A series of six alkyl-substituted tetramethylcyclopentadienyl mononuclear metal carbonyl complexes [(η 5-C5Me4R)Re(CO)3] [R = allyl (1), i-Pr (2), n-butyl (3), t-butyl (4), benzyl (5), CH(CH2)4 (6)] have been synthesized by treating the corresponding ligands (C5Me4R) [R = allyl, i-Pr, n-butyl, t-butyl, benzyl, CH(CH2)4] with Re2(CO)10 in refluxing xylene. The six new complexes were characterized by elemental analysis, IR, 1H NMR and 13C NMR spectroscopy. The crystal structures of all six complexes were determined by X-ray crystal diffraction analysis, showing that they have similar molecular structures, being mononuclear carbonyl complexes. In each of these complexes, the Re atom is η 5 -coordinated to the cyclopentadienyl ring. Complexes 1–5 have significant catalytic activity in Friedel–Crafts reactions of aromatic compounds with alkylation reagents. Compared with traditional catalysts, these mononuclear rhenium carbonyl complexes have obvious advantages such as lower amounts of catalyst, mild reaction conditions and environmentally friendly chemistry.

Reactions of aromatic compounds with xenon difluoride

Reactions of substituted benzenes C6H5R (R = Me, F, Cl, Br, CF3, NO2) with xenon difluoride in the presence of boron trifluoride–diethyl ether complex in weakly acidic (1,1,1,3,3-pentafluorobutane) and weakly basic media (acetonitrile) have been studied. These reactions lead to the formation of fluorobenzene derivatives FC6H4R (isomer mixture) together with isomeric difluorobenzenes and fluorinated and non-fluorinated biphenyls. The results have been compared with previously reported data obtained in other solvents using other catalysts.

Facile and Efficient One-Pot Synthesis of Anthraquinones from Benzene Derivatives Catalyzed by Silica Sulfuric Acid

In connection with our research program directed toward the synthesis of anthraquinones by new catalyst, we achieved a new method for preparation of some anthraquinone derivatives from the reaction of aromatic compounds with phthalic anhydride in the presence of silica sulfuric acid (SSA). The advantages of this method are availability of starting materials, simplicity of the reaction, reusability of catalyst and purity of products. In this reaction, the products were obtained via easy work-up in high yields and short reaction times. The structures of products were assigned by physical data and spectroscopic methods.

Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides, Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions

The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3-substituted imidazo[1,5-a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N-methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield.

Formation and infrared absorption of protonated naphthalenes (1-C10H9+and 2-C10H9+) and their neutral counterparts in solid para-hydrogen

Protonated naphthalene (C(10)H(9)(+)) and its neutral counterparts (hydronaphthyl radicals, C(10)H(9)) are important intermediates in the reactions of aromatic compounds and in understanding the unidentified infrared (IR) emissions from interstellar media. We report the IR spectra of 1-C(10)H(9)(+), 2-C(10)H(9)(+), 1-C(10)H(9), and 2-C(10)H(9) trapped in solid para-hydrogen (p-H(2)); the latter three are new. These species were produced upon electron bombardment of a mixture of naphthalene (C(10)H(8)) and p-H(2) during matrix deposition. The intensities of IR features of 1-C(10)H(9)(+) decreased after the matrix was maintained in darkness for 19 h, whereas those of 1-C(10)H(9) and 2-C(10)H(9) increased. Irradiation of this matrix sample with light at 365 nm diminished lines of 1-C(10)H(9)(+) and 2-C(10)H(9) and enhanced lines of 1-C(10)H(9) and 2-C(10)H(9)(+); the latter species was unstable and converted to 1-C(10)H(9)(+) in less than 30 min and 2-C(10)H(9) was converted to 1-C(10)H(9) at 365 nm. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method. Compared with spectra recorded previously with IR photodissociation of Ar-tagged C(10)H(9)(+) or IR multiphoton dissociation of C(10)H(9)(+), our method has the advantages of producing high-resolution IR spectra with a wide spectral coverage, true IR intensity and excellent ratio of signal to noise; both protonated species and their neutral counterparts are produced with little interference from other fragments. With these advantages, the IR spectra of 1-C(10)H(9)(+), 2-C(10)H(9)(+), 1-C(10)H(9), and 2-C(10)H(9) are here clearly characterized.

ChemInform Abstract: Efficient and Eco‐Friendly Synthesis of Iodinated Aromatic Building Blocks Promoted by Iodine and Hydrogen Peroxide in Water: A Mechanistic Investigation by Mass Spectrometry.

AbstractThe reaction of aromatic compounds with molecular iodine in the presence of aqueous hydrogen peroxide gives mono‐, di‐ and triiodinated arenes and hetarenes under the same conditions.

Towards mechanisms of bimolecular nucleophilic reactions in solution—probing the variation of the activation parameters in the reactions of aromatic compounds

Variation of the activation parameters in the SN2, acyl‐transfer, SNAr, SNV, and AdN reactions offers a uniquely useful probe for the mechanistic features of these reactions in solution. New approach uses the substituent effects on the aromatic ring to the variation of the activation parameters, ΔH≠ and ΔS≠, in the above reactions in the frameworks of the Hammett‐like equations in order to evaluate the resultant δΔH≠ and δΔS≠ reaction constants. Compensation relationships of δΔH≠ versus δΔS≠ allow one to estimate the contribution of changes of the internal enthalpy, δΔH≠int, to the enthalpy reaction constant, δΔH≠, that is inherent to bimolecular nucleophilic reactions and gives a single linear dependence on the Hammett ρ reaction constants for these reactions. The deviations from dependence of δΔH≠int versus ρ serve as useful points of interpretation of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the substrates, nucleophiles, and leaving groups on the mechanistic features in bimolecular nucleophilic reactions are governed by the magnitude of δΔH≠int. Copyright © 2011 John Wiley & Sons, Ltd.

Microwave-assisted acylation of aromatic compounds using carboxylic acids and zeolite catalysts

Acylation of aromatic compounds with carboxylic acids smoothly proceeded at 190–230 °C in the presence of zeolite catalysts under microwave irradiation to give aromatic ketones efficiently. H–Y (SiO 2/Al 2O 3 = 30–80) and H–beta (25) zeolites were active for the acylation reaction, giving the aromatic ketones in good yields. Carboxylic acids such as hexanoic and butyric acid smoothly underwent the acylation, while propionic acid showed somewhat lower reactivity. Anisole gave the para-acylation products nearly selectively. Anisole, 2,3-dihydrobenzofuran, and thiophene were reactive aromatic compounds. 2,3-Dihydrobenzofuran also reacted at the para position to the oxygen atom predominantly to give the corresponding ketones as the major products. The microwave reactions were generally faster than the conventional oil bath reactions and gave higher yields of the acylation products. Activation energies for the reaction of anisole with butyric acid by microwave and by oil bath heating were also estimated on the basis of the Arrhenius plots.

Elaboration of Simplified Vinca Alkaloids and Phomopsin Hybrids

Nine simplified vinca alkaloids and phomospin A hybrids, in which vindoline moiety has been replaced by a simpler scaffold, have been elaborated to evaluate their activity on the inhibition of tubulin polymerization. This article deals with the synthesis of various simplified vinca alkaloids, using a stereoselective coupling of catharantine with reactive aromatic compounds and methanol as well as their subsequent condensation with a large peptide chain mimicking those of phomopsin A. Biological evaluation and molecular modeling studies are also reported.