Chemo-and regioselective aqueous phase, co-acid free nitration of aromatics using traditional and nontraditional activation methods.

Electrophilic aromatic nitrations are used for the preparation of a variety of synthetic products including dyes, agrochemicals, high energy materials, fine chemicals and pharmaceuticals. Traditional nitration methods use highly acidic and corrosive mixed acid systems which present a number of drawbacks. Aside from being hazardous and waste-producing, these methods also often result in poor yields, mostly due to low regioselectivity, and limited functional group tolerance. As a consequence, there is a need for effective and environmentally benign methods for electrophilic aromatic nitrations. In this work, the major aim was to develop reaction protocols that are more environmentally benign while also considering safety issues. The reactions were carried out in dilute aqueous nitric acid, and a broad range of experimental variables, such as acid concentration, temperature, time, and activation method, were investigated. Mesitylene and m-xylene were used as test substrates for the optimization. While the optimized reactions generally occurred at room temperature without any activation under additional solvent-free conditions, slight adjustments in acid concentration, stoichiometric equivalents, and volume were necessary for certain substrates, in addition to the activation. The substrate scope of the process was also investigated using both activated and deactivated aromatics. The concentration of the acid was lowered when possible to improve upon the safety of the process and avoid over-nitration. With some substrates we compared traditional and nontraditional activation methods such as ultrasonic irradiation, microwave and high pressure, respectively, to achieve satisfactory yields and improve upon the greenness of the reaction while maintaining short reaction times.

Ordered mesoporous hairbrush-like nanocarbon assembled microfibers for solid-phase microextraction of benzene series in oilfield sewage.

The development of advanced functional nanomaterials for solid-phase microextraction (SPME) remains an imperative aspect of sample pretreatment. Herein, we introduce a novel SPME fiber consisting of graphene fibers modified with ordered mesoporous carbon nanotubes arrays (CNTAs) tailored for the determination of benzene series in oilfield wastewater, which is synthesized by an ionic liquid-assisted wet spinning process of graphene nanosheets, followed by a precisely controlled growth of metal-organic framework and subsequent pyrolysis treatment. The resulting robust microfiber structure resembles a "hairbrush" configuration, with a crumpled graphene fiber "stem" and high-order mesoporous CNTAs "hairs". This unique architecture significantly enhances the SPME capacity, as validated by gas chromatography-mass spectrometry. The hairbrush-like nanocarbon assembled microfibers possess structural characteristics, a high specific surface area, and numerous binding sites, offering efficient enrichment of benzene series compounds in oilfield wastewater, including benzene, ethylbenzene, m-xylene, p-xylene, and toluene. Our analysis demonstrates that these microfibers exhibit broad linear ranges (0.2-600 µg L-1), low detection limits (0.005-0.03 mg L-1), and excellent repeatability (3.2-5.5% for one fiber, 2.1-6.7% for fiber-to-fiber) for detection. When compared to commercial alternatives, these hairbrush-like nanocarbon-assembled microfibers exhibit significantly enhanced extraction efficiency for benzene series compounds.

Enhanced adsorption of aromatic VOCs on hydrophobic porous biochar produced via microwave rapid pyrolysis.

To customize biochar suitable for efficient adsorption of benzene derivatives, this study presents programmed microwave pyrolysis to produce hydrophobic porous biochar with low-dose ferric chloride. Designated control of the ramping rates in the carbonization stage and the temperatures in the activation stage were conducive to enlarging the specific surface area. Iron species, including amorphous iron minerals, could create small-scale hotspots during microwave pyrolysis to promote microporous structure development. Compared with conventional pyrolysis, programmed microwave pyrolysis could increase the specific surface area from 288.6 m2 g-1 to 455.9 m2 g-1 with a short heating time (15 min vs. 2 h) under 650 °C. Engineered biochar exhibited higher adsorption capacity for benzene and toluene (136.6 and 94.6 mg g-1), and lower adsorption capacity for water vapour (6.2 mg g-1). These findings provide an innovative design of engineered biochar for the adsorption of volatile organic compounds in the environment.

Predictive ability of physiochemical properties of benzene derivatives using Ve-degree of end vertices-based entropy.

Topological indices relate chemical structure to chemical reactivity, physical properties, and biological activity. Quantitative structure-activity relationships (QSPR) are mathematical models proposed for the correlation of various types of chemical reactivity, biological activity, and physical properties with topological indices/entropies. In this article, we have proposed the QSPR between the ve-degree of end vertices of edge based entropies and the physiochemical properties of benzene derivatives. We have designed a Maple-based algorithm for the computation of entropies. The relationship was analyzed using SPSS. We have shown that the physiochemical properties such as critical pressure, Henry's law, critical temperature, Gibb's energy, logP, critical volume, and molar refractivity can be predicted by entropies. All the results were highly positive and significant. The Randic, Balaban, and redefined third Zagreb entropies showed the best relations with physiochemical properties.Communicated by Ramaswamy H. Sarma.

Adsorption Mechanism of Benzene Derivatives by Pagoda[n]arenes.

Despite the widespread use in industrial production, benzene derivatives are harmful to both human beings and the environment. The control of these substances has become an important subject of scientific research. This study introduces a new approach for adsorption and separation of benzene derivatives utilizing pagoda[n]arene based supramolecular materials. Density functional theory calculations were employed to investigate the molecular recognition mechanism of benzene derivatives by pagoda[4]arenes and pagoda[5]arenes (Pa[4]As and Pa[5]As). Results indicate that Pa[4]As and Pa[5]As can effectively accommodate benzene derivatives through non-covalent interactions, leading to the formation of stable host-guest complexes. Additionally, molecular dynamics simulations revealed that both crystalline and non-crystalline supramolecular aggregates of Pa[4]As and Pa[5]As possess the ability to adsorb benzene derivatives and maintain the stability of the adsorption. Moreover, increasing the temperature causes benzene derivatives to desorb from the adsorbing aggregates, and thus the material can be reutilized.

Development of reliable quantitative structure-toxicity relationship models for toxicity prediction of benzene derivatives using semiempirical descriptors.

The Health and environmental hazards of benzene and nitrobenzene (NB) derivatives have remained a topic of interest of researchers. In silico methods for prediction of toxicity of chemicals have proved their worth in accurate forecast of environmental as well as health toxicity and are strongly recommended by regulatory authorities. Two quantitative structure-toxicity relationship (QSTR) models explaining Scenedesmus obliquus toxicity trends among 39 benzene derivatives and Tetrahymena pyriformis toxicity of 103 NB and 392 benzene derivatives are developed using semiempirical quantum chemical parameters. The best constructed QSTR models have good fitting ability (R2 = 0.8053, 0.7591, and 0.8283) and robustness (Q2LOO = 0.7507, 0.7227, and 0.8194; Q2LMO = 0.7338, 0.7153, and 0.8172). The external predictivity of all the models are quite good (R2EXT = 0.8256, 0.9349, and 0.8698). Electronegativity, Cosmo volume, total energy, and molecular weight are responsible for the increase and decrease of toxicity of benzene derivatives against S. obliquus while electronegativity, electrophilicity index, the heat of formation, total energy, hydrophobicity, and cosmo volume are responsible for modulation of toxicity of NB and benzene derivatives toward T. pyriformis. These models fulfill the requirements of all the five OECD principles.

Recent Advances in Gold(I)-Catalyzed Approaches to Three-Type Small-Molecule Scaffolds via Arylalkyne Activation.

Gold catalysts possess the advantages of water and oxygen resistance, with the possibility of catalyzing many novel chemical transformations, especially in the syntheses of small-molecule skeletons, in addition to achieving the rapid construction of multiple chemical bonds and ring systems in one step. In this feature paper, we summarize recent advances in the construction of small-molecule scaffolds, such as benzene, cyclopentene, furan, and pyran, based on gold-catalyzed cyclization of arylalkyne derivatives within the last decade. We hope that this review will serve as a useful reference for chemists to apply gold-catalyzed strategies to the syntheses of related natural products and active molecules, hopefully providing useful guidance for the exploration of additional novel gold-catalyzed approaches.

Crystal structures of methyl 3,5-di-methyl-benzoate, 3,5-bis-(bromo-meth-yl)phenyl acetate and 5-hy-droxy-benzene-1,3-dicarbaldehyde.

The crystal structures of the title compounds, methyl 3,5-di-methyl-benzoate (C10H12O2; 1), 3,5-bis-(bromo-meth-yl)phenyl acetate (C10H10Br2O2; 2) and 5-hy-droxy-benzene-1,3-dicarbaldehyde (C8H6O3; 3) were determined by single-crystal X-ray analysis. The crystals of 1 are composed of strands of C-H⋯O=C bonded mol-ecules, which are further arranged into layers. As a result of the presence of two bromo-methyl substituents in compound 2, mol-ecular dimers formed by crystallographically non-equivalent mol-ecules are connected to structurally different two-dimensional aggregates in which the bromine atoms participate in Br⋯Br bonds of type I and type II. In the case of compound 3, which possesses three donor/acceptor substituents, the mol-ecular association in the crystal creates a close three-dimensional network comprising Car-yl-H⋯Ohy-droxy, Cform-yl-H⋯Oform-yl and O-H⋯Oform-yl bonds.

Ex-situ and in-situ rapid and quantitative determination of benzene derivatives in seawater using nanoconfined liquid phase nanoextraction.

Benzene derivatives (BDs) constitute a class of environmental pollutants whose exposure poses a grave risk to human health. These compounds rapidly diffuse from the atmosphere to the marine ecosystem: for this reason, their monitoring in seawater is every day more compelling. In this work, nanoconfined liquid phase nanoextraction (NLPNE), a versatile extraction technique recently described, has been for the first time applied to the gas chromatographic mass spectrometry (GC/MS) analysis of BDs in seawater. Ex-situ and in-situ NLPNE procedures have been developed and optimized in terms of extraction capabilities, analysis time, precision, and accuracy. Compared to the traditional extraction procedures, based on solid-phase microextraction (SPME) and liquid-liquid extraction (LLE), the proposed NLPNE methods allowed a rapid on-site analysis of benzene compounds with low solvent consumption, higher enrichment factors, and improved automation grade. Determination coefficients ranging from 0.9929 to 0.9997 were obtained for all BDs in the range 0.10-500 ng mL-1 and 5.00-500 ng mL-1, for ex-situ and in-situ NLPNE, respectively. Ex-situ and in-situ limits of detection ranged from 0.2 to 7.6 ng mL-1 and 0.04-1.00 ng mL-1. Our results suggest that NLPNE coupled to GC-MS can be considered a powerful technique for high-throughput analyses of trace compounds in environmental, food and biological samples.

Substituent Effect in the Cation Radicals of Monosubstituted Benzenes.

In 30 monosubstituted benzene cation radicals, studied at the ωB97XD/aug-cc-pVTZ level, the phenyl rings usually adopt a compressed form, but a differently compressed form-equivalent to an elongated one-may coexist. The computational and literature ionization potentials are well correlated. The geometrical and magnetic aromaticity, estimated using HOMA and NICS indices, show the systems to be structurally aromatic but magnetically antiaromatic or only weakly aromatic. The partial charge is split between the substituent and ring and varies the most at C(ipso). In the ring, the spin is 70%, concentrated equally at the C(ipso) and C(p) atoms. The sEDA(D) and pEDA(D) descriptors of the substituent effect in cation radicals, respectively, were determined. In cation radicals, the substituent effect on the σ-electron system is like that in the ground state. The effect on the π-electron systems is long-range, and its propagation in the radical quinone-like ring is unlike that in the neutral molecules. The pEDA(D) descriptor correlates well with the partial spin at C(ipso) and C(p) and weakly with the HOMA(D) index. The correlation of the spin at the ring π-electron system and the pEDA(D) descriptor shows that the electron charge supplied to the ring π-electron system and the spin flow oppositely.

Eremophilane Sesquiterpenes and Benzene Derivatives from the Endophyte Microdiplodia sp. WGHS5.

Three new eremophilane sesquiterpenes phomadecalins G-I (1-3) and two new benzene derivatives microdiplzenes A and B (12 and 13), together with nine known eremophilane sesquiterpenes (4-11 and 14) were isolated from an endophytic fungus, Microdiplodia sp. WGHS5. Their structures were elucidated by the interpretation of HR-ESI-MS and NMR data; meanwhile, the absolute configurations of new compounds were determined on the base of ECD calculations. All compounds were evaluated for the antimicrobial activities and antiproliferative effect on human gastric cancer cell lines (BGC-823).

Catalytic Pyrolysis of Polystyrene over Steel Slag under CO2 Environment.

As the consumption of plastic materials has been dramatically increased, the abundant presence of their debris has become a significant problem worldwide. Thus, this study proposes a sustainable plastic conversion platform for energy recovery. In detail, polystyrene pyrolysis was examined as a case study under CO2 atmosphere in reference to N2 condition. The major gaseous and liquid products from polystyrene pyrolysis include permanent gases (syngas and C1-2 hydrocarbons) and condensable aromatic compounds. Under CO2 environment, the reduction of polycyclic aromatic hydrocarbons (PAHs) was achieved during polystyrene pyrolysis, in comparison with N2 condition. Since its slow reaction kinetics, conversion of condensable hydrocarbons into permanent gases was not fully activated. Therefore, a cheap industrial waste, steel slag (SS), was employed as a catalyst to increase reaction kinetics. The synergistic effects of SS and CO2 contributed to doubling H2 production, while CO formation increased more than 300 times, in reference to non-catalytic pyrolysis. Because CO2 acted as an oxidant for CO production, control of H2/CO ratio was achieved in different conditions. Thus, the utilization of CO2 would suggest a promising way to reduce the formation of PAHs, adopting the reliable platform to produce syngas from plastic waste.

An electronic properties investigation to interpret the substituent constants of monosubstituted benzene derivatives.

In the present work, the π and π∗-electronic nature of substitution constants (σ) of the twenty-two monosubstituted benzene derivatives (MSBDs) are estimated in terms of the para-delocalization index (PDI) and total non-Lewis structure (TNLS), respectively. Since these compounds are aromatic, the other descriptors of aromaticity such as nuclear independent chemical shifts and aromatic stabilization energy have been examined. Because of no considerable variation for the π and π∗-electron delocalization in the ring systems, a very weak correlation has been demonstrated between all aromaticity indices. Also, none of these descriptors has a linear correlation with the values of σ for both electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) in a simultaneous relationship. We now propose the usage of the dipole moments values of molecules, considering their directions, by multiplying the PDI and TNLS values as probes to interpret σ values for benzene and MSBDs since the dipole moment can affect the π and π∗-electron delocalization. It is interesting to note that there is a remarkable linear correlation between our suggested probes, ±µPDI and ±µTNLS, and σp, σm, and σ+/σ- for EDGs and EWGs in simultaneous linear relationships. Also, these probes have a relative relationship with Kirkwood and Westheimer equation. Additionally, the regression coefficient between ±µPDI and ±µTNLS is 0.989.

Changes in global aroma profiles of Cabernet Sauvignon in response to cluster thinning.

Cluster thinning (CT) is a common practice to prevent overcropping in viticulture. CT affects vine balance between vegetative and productive growth and further modifies grape composition. This study investigated the effects of cluster thinning treatments applied at pea-size stage (CT-AF) and the onset of veraison (CT-V), respectively, on volatile compounds of Cabernet Sauvignon in two seasons (2013-2014). The experimental vineyard was located in the north-west of China with semi-arid and monsoon climate. CT exhibited limited effects on the evolutions of volatile compounds. CT-AF exhibited an inhibition on 6-methyl-5-heptene-2-one accumulation. There were no differences in terpene concentrations between CT-treated and control grapes regardless of CT time. Regarding C6/C9 compounds and their derivatives, CT-AF decreased nonanal concentration whilst CT-V increased (Z)-3-hexen-1-ol concentration. Additionally, there were increases in nonanal, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol and (Z)-3-hexen-1-ol concentrations in grapes with delayed CT. Among benzene derivatives, earlier CT resulted in lower phenol concentrations.

New Sample Preparation Method for Honey Volatiles Fingerprinting Based on Dehydration Homogeneous Liquid⁻Liquid Extraction (DHLLE).

Qualitative chemical fingerprinting of the honey volatiles by gas chromatography and mass spectrometry (GC-MS) has been an efficient authentication tool that allowed for the classification of the honey botanical origin (strongly related to its medicinal and market value). However, the usage of current sample preparation methods is limited by selectivity of the volatiles extraction from the honey matrix and requires significant solvent volume. Therefore, a new sample preparation method based on dehydrating homogeneous liquid⁻liquid extraction (DHLLE) involving reduced solvent usage was developed for screening volatiles and semi-volatiles from the honey. The effective extraction was achieved by implementing a miscible liquid extraction system (aqueous honey solution/isopropanol) followed by separation through dehydration with MgSO4 and purification by a solvent polarity change and washing. The method was evaluated by estimating accuracy and precision. The DHLLE method showed satisfactory recoveries (75.2 to 93.5%) for typical honey volatiles: linalool, borneol, terpinen-4-ol, α-terpineol, p-anisaldehyde, eugenol, and vanillin. It also showed superior repeatability with percent relative standard deviation (RSD%) 0.8⁻8.9%. For benzyl alcohol, methyl syringate, and caffeine, the recoveries were 54.3 to 63.9% and 67.3 to 77.7% at lower and higher spiking levels, respectively. Applied to unifloral apple honey, the DHLLE method allowed for the identification of 40 compounds including terpenes, hydrocarbons, phenylpropanoids, and other benzene derivatives, which makes it suitable for fingerprinting and chemical marker screening. The obtained results were comparable or better than those obtained with ultrasonic extraction with dichloromethane.

The Degradation of O-ethyltoluene and 1,3,5-Trimethylbenzene in Lake Naivasha Wetland, Kenya.

The primary degradation of benzene derivatives in aquatic environments occurs via microbial and chemical processes. This study investigated the kinetic degradation of o-ethyltoluene and 1,3,5-trimethylbenzene in the wetland of Lake Naivasha. Sediment samples were collected from 6:00 AM to 6:00 PM at intervals of 3 h during the dry season of December 2017. The sediment samples were air dried, ground into powder, followed by soxhlet extraction in a binary mixture of methanol and hexane in the ratio of 1:1. The extract was analyzed using gas chromatograph with mass selective detector. Variation in the concentrations of o-ethyltoluene and 1,3,5-trimethylbenzene with time was monitored kinetically. Accordingly, the half-lives for the degradation of o-ethyltoluene and 1,3,5-trimethylbenzene were 4.9 and 5.4 h, respectively, and their corresponding decay rate constants were 3.93 × 10-5 and 3.56 × 10-5 S-1. 1,3,5-Trimethylbenzene was the most persistent contaminants in the wetland.

Fabrication of bi-monomer copolymer of pyrrole-indole for highly efficient solid phase microextraction of benzene derivatives.

A procedure for direct electrochemical deposition of poly(pyrrole-indole) on gold nanoparticles coated stainless steel wire was established, and the formation of copolymer was confirmed by infrared spectroscopy. The synthesized coating showed unique microstructure, excellent extraction efficiency (2-10 times of corresponding single-component coating), high thermal stability (up to 280°C) and good durability (could be used for more than 200 times). As a novel and promising extraction coating, it was used for the headspace solid phase microextraction-gas chromatography detection of some benzene derivatives, including chlorobenzene, bromobenzene, p-bromotoluene, m-nitrotoluene and p-nitrotoluene. Under the optimized conditions, their GC peak areas were linear to their concentrations in the ranges of about 0.05-100µgL-1, and the detection limits were 0.012-0.029µgL-1 (S/N = 3). The run-to-run RSDs were lower than 3.9% (n = 4), the fiber-to-fiber RSDs were 4.3-7.8% (n = 4). The proposed method was successfully applied to the determination of benzene derivatives mentioned above in real samples with good recoveries from 88.3% to 103.7%.

Chemical constituents from Piper hainanense and their cytotoxicities.

Two new compounds, (Z,R)-1-phenylethylcinnamate (1) and (1R,2R,3R,6S)-pipoxide (2) were isolated from the aerial part of Piper hainanense, along with 12 known compounds, including nine benzene derivatives (4-11), one isobutylamide (12), and two polyoxygenated cyclohexene derivatives (13-14). Their structures were elucidated on the basis of the HRESIMS, 1D and 2D NMR spectroscopic analyses, and ECD in cases of 2 and 3. The absolute configuration of ellipeiopsol B (3) was determined for the first time. All these compounds 1-14 were reported from the titled plant for the first time. Most of the isolates were tested for their cytotoxicities against five human cancer cell lines. Four of which, 2, 3, 9, 14 showed moderate bioactivities. Among them, the new compound 2 showed potential cytotoxicity against SMMC-7721, MCF-7, and SW-480 with IC50 values of 9.7, 15.0, and 13.2 µM, respectively.

Predicting Adsorption Affinities of Small Molecules on Carbon Nanotubes Using Molecular Dynamics Simulation.

Computational techniques have the potential to accelerate the design and optimization of nanomaterials for applications such as drug delivery and contaminant removal; however, the success of such techniques requires reliable models of nanomaterial surfaces as well as accurate descriptions of their interactions with relevant solutes. In the present work, we evaluate the ability of selected models of naked and hydroxylated carbon nanotubes to predict adsorption equilibrium constants for about 30 small aromatic compounds with a variety of functional groups. The equilibrium constants determined using molecular dynamics coupled with free-energy calculation techniques are directly compared to those derived from experimental measurements. The calculations are highly predictive of the relative adsorption affinities of the compounds, with excellent correlation (r ≥ 0.9) between calculated and measured values of the logarithm of the adsorption equilibrium constant. Moreover, the agreement in absolute terms is also reasonable, with average errors of less than one decade. We also explore possible effects of surface loading, although we demonstrate that they are negligible for the experimental conditions considered. Given the degree of reliability demonstrated, we move on to employing the in silico techniques in the design of nanomaterials, using the optimization of adsorption affinity for the herbacide atrazine as an example. Our simulations suggest that, compared to other modifications of graphenic carbon, polyvinylpyrrolidone conjugation gives the highest affinity for atrazine-substantially greater than that of graphenic carbon alone-and may be useful as a nanomaterial for delivery or sequestration of atrazine.

Hexahalogenated and their mixed benzene derivatives as prototypes for the understanding of halogen···halogen intramolecular interactions: New insights from combined DFT, QTAIM-, and RDG-based NCI analyses.

A large number of fully halogenated benzene derivatives containing the fluorine, chlorine, bromine, and iodine atoms have been experimentally synthesized both as single- and co-crystals (e.g., Desiraju et al., Chem. Eur. J. 2006, 12, 2222), yet the natures of the halogen ··· halogen interactions between the vicinal halogens in these compounds within the intramolecular domain are undisclosed. Given a fundamental understanding of these interactions is incredibly important in many areas of chemical, biological, supramolecular, and material sciences, we present here our newly discovered theoretical results that delineate whilst the nature of an F···F interaction in a pair of two adjacent fluorine atoms in either of the hexafluorobenzene and 1,4-dibromotetrafluorobenzene compounds examined is almost unclear, each of the latter three hexahalogenated benzene derivatives (viz., C6 Cl6 , C6 Br6 , and C6 I6 ), and each of the seven of their fully mixed hexahalogenated benzene analogues, are found to be stabilized by means of a number of halogen···halogen interactions, each a form of long-range attraction within the intramolecular domain. The Molecular Electrostatic Surface Potential model was found to be unsurprisingly unsuitable in unraveling any of the aforesaid attractions between the halogen atoms. However, such interactions successfully enunciated by a set of noncovalent interaction descriptors of geometrical, topological, and electrostatic origins. These latter properties were extracted combining the results of the Density Functional Theory electronic structure calculations with those revealed from Atoms in Molecules, and Reduced Density Gradient charge density-based topological calculations, and are expounded in detail to formalize the conclusions. © 2015 Wiley Periodicals, Inc.