Monosubstituted Aromatic Compounds Research Articles

A Close‐to‐Aromatize Approach for the Late‐Stage Functionalization through Ring Closing Metathesis

AbstractAn efficient approach for the synthesis of monosubstituted aromatic compounds relying on a ring‐closing metathesis followed by spontaneous 1,2‐elimination is presented. The efficiency for late‐stage functionalization is highlighted in various solvents (up to 920 TON). This approach is compatible with strained cycles and other multiple bonds in the substrate.

Nucleophilic Aromatic Substitution of Polyfluoroarene to Access Highly Functionalized 10-Phenylphenothiazine Derivatives

Nucleophilic aromatic substitution (SNAr) reactions can provide metal-free access to synthesize monosubstituted aromatic compounds. We developed efficient SNAr conditions for p-selective substitution of polyfluoroarenes with phenothiazine in the presence of a mild base to afford the corresponding 10-phenylphenothiazine (PTH) derivatives. The resulting polyfluoroarene-bearing PTH derivatives were subjected to a second SNAr reaction to generate highly functionalized PTH derivatives with potential applicability as photocatalysts for the reduction of carbon–halogen bonds.

The Effect of the Monosubstituted Benzenes Functional Groups on the Inhibition of Methane Gas Biosynthesis

Aromatic compounds are inhibitors of methane biosynthesis in anaerobic treatment of solid wastes and industrial effluents. Anaerobic treatment of solid wastes and industrial effluents may be limited by the methanogenic bacteria inhibition exerted by these types of compounds, the production of biogas is not possible and the organic matter contained in the effluent is not reduced. These effluents poured in the nature can be the basis of the pollution. The objective of this study is to evaluate the effect of monosubstituted aromatic compounds functional groups on the methanogenic inhibition. The toxicity to acetoclastic methanogenic bacteria has performed in serum flasks, utilizing digested pig manure as inoculums, by measuring methane production. The nature of aromatic functional groups was observed to have a profound effect on the toxicity of the monosubstituted aromatics. Among the monosubstituted aromatic, the chlorobenzene was the most toxic with 50% of inhibition occurring at the concentration of 30.08 mg/l. In contrast, benzoic acid is the least inhibitory with IC50 of 2515.20 mg/l. The partition coefficient octanol/water (logPoct), an indicator of hydrophobicity, had a significant correlation with the methanogenic toxicity.

Theoretical Study of Some Benzene Derivatives in Water

Using the HyperChem programme, the influence of water on the properties of some monosubstituted aromatic compounds was studied from the point of view of the intermolecular interactions. There have been estimated some physico-chemical parameters of the benzene, fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, nitrobenzene, phenol and aniline when solved in water, surrounded by one or two solvation spheres. The boundary lengths, total energies, border levels energy, dipole moments, polarizabilities, wavelengths and the probabilities of the electronic transitions have been obtained.

Electrophilic Aromatic Nitration: Understanding Its Mechanism and Substituent Effects

Theoretical calculations and gas-phase mass spectrometric studies were performed for the reaction of the naked (NO2+) and monosolvated (CH3NO2.NO2+) nitronium ion with several monosubstituted aromatic compounds. From these studies, we propose a general model for regioselectivity based on the single-electron transfer (SET) mechanism and an alternative mechanistic scheme for electrophilic aromatic nitration. This scheme considers the SET and the polar (Ingold-Hughes) mechanisms as extremes in a continuum pathway, the occurrence and extents of both mechanisms being governed mainly by the ability, or lack of ability, of the aromatic compound to transfer an electron to NO2+.

Alkylsilane-Based Stationary Phases via a Displaceable Surface Template Approach: Synthesis, Characterization, and Chromatographic Performance

A method is presented for the preparation of silica-based alkylsilane stationary phases using octanol as a displaceable surface template to control the rate of alkylsilane condensation with the silica surface, and thereby, the resulting alkylsilane surface coverage. This method improves upon conventional preparation schemes by allowing alkylsilane stationary phases of systematically varying surface coverage to be prepared from a single reaction mixture and a single precursor molecule without rigorous control of water content of the solution or of the silica. Octadecylsilane stationary phases ranging in surface coverage from approximately 3.5 to 6.0 micromol/m(2) were synthesized using one set of experimental conditions with variation of only the octadecylsilane/octanol ratio. The conformational order of the octadecylsilane alkyl chains was assessed using Raman spectroscopy and was found to increase with increasing surface coverage in a manner similar to stationary phases prepared by conventional routes. As chromatographic stationary phases in microbore columns for the reversed-phase separation of monosubstituted aromatic compounds, the performance of these materials is comparable to or better than that of commercially available octadecylsilane stationary phases under identical chromatographic conditions. Furthermore, the high-density stationary phases (>3.5 micromol/m(2)) prepared by this route exhibit geometric shape selectivity comparable to or better than that reported earlier for high-density octadecylsilane stationary phases prepared using conventional methods.

Theoretical and Experimental Studies on the Adsorption of Aromatic Compounds onto Cellulose

The adsorption of several aromatic compounds over microcrystalline cellulose was studied by molecular modeling and experimentally using gas chromatography. Experimental adsorption enthalpies were obtained from an equation based on Clausius-Clapeyron formalism and the temperature dependence of retention volume at infinite dilution. Four different cellulose surfaces (three crystalline (110, 100, and 010) and one amorphous) were modeled. Overall strong agreement was observed between the experimental and theoretical work with 84% of the adsorbate-cellulose systems having differences between measured and predicted values of less than 20%. Based on both calculated and experimental data, a morphology for the microcrystalline cellulose as a weighted combination of the four surfaces was proposed: 39% (110), 28% (100), 10% (010), and 23% amorphous. By adopting this distribution, differences between experimental and weighted average predicted adsorption energies were 10% or less for 14 out of 17 compounds; a maximum of 15% was observed for guaiacol. Experimental results for monosubstituted aromatic compounds revealed that adsorption enthalpies are related to the hydrophilic/hydrophobic character of the substituent groups: 3.5 kJ mol(-1) for a methyl group, 15.7 kJ mol(-1) for a double bond, 21.0 kJ mol(-1) for a methoxyl group, 22.8 kJ mol(-1) for a carbonyl group, and 27.6 kJ mol(-1) for a hydroxyl group. These tendencies were confirmed by modeling, except for the aldehyde carbonyl group, where an overestimation of 10.8 kJ mol(-1) was observed. Analysis of experimental and predicted adsorption enthalpies of multisubstituted aromatic compounds suggests that the efficiency of their interaction with cellulose depends on a compromise between the roughness of the cellulose surface and their conformational adaptability.

Electrochemical radiofluorination. Part 2 . Anodic monofluorination of substituted benzenes using [ 18F]fluoride

Electrochemical fluorination of various monosubstituted aromatic compounds was performed with [ 18F]fluoride using potentiostatic anodic oxidation on platinum electrodes in an undivided cell in acetonitrile with a mixture of Et 3N·3HF/Et 3N·HCl as electrolyte. Maximum radiochemical yields were obtained after a charge of 50 C passed the solution. The results showed a clear dependence of the radiochemical yields on the oxidation potentials E 1/2 of the substrates as a consequence of different substituents namely CH 3CO-, F-, Cl-, Br- and tert.-Butyl. With increasing E 1/2, the fluorination yields decreased from 7.9% ( tert.-butylbenzene) to 1.5% (acetophenone). The ratio between F-for-X substitution and F-for-H substitution correlated with the bond energies of the C–X bond. With higher bond energies, less X-substitution was observed.

Toxicity and Color Formation During Ozonation of Mono-Substituted Aromatic Compounds

This research investigates the aqueous toxicity occurring during color formation due to ozonation in a semi-batch reactor. The tested mono-substituted aromatic compounds were aniline, phenol (-NH2, -OH, electron-donating group), nitrobenzene and benzoic acid (-NO2, -COOH, electron-withdrawing group). The results revealed that the aqueous toxicity of the Microtox assay from oxidized samples during the early stage of ozonation increased when the color formation was observed, except in the case of nitrobenzene under high pH conditions. Toxicity typically reached a peak at or near the moment of maximum color intensity. Ozonation of these aromatic compounds showed a large increase in toxicity, and the 50% effective concentration (EC50) expressed as chemical oxygen demand (COD) (mg l−1) decreased to 1.4 (aniline), 1.2 (benzoic acid), 0.8 (phenol) and 0.6 (nitrobenzene) orders-of-magnitude. Moreover, the aromatic compounds with an electron-donating group promoted color formation more than did the electron-withdrawing group substituted compounds.

Tetramethylsilane Chemical Ionization Mass Spectrometry of Mono-substituted Aromatic Compounds: Gas-phase Trimethylsilylation

The tetramethylsilane (TMS) chemical ionization (CI) spectra of the mono-substituted aromatics studied contain M+· and adduct [M+(CH3)3Si]+ ions. Abundant M+· ions are observed in compounds with electrondonating groups and are attributed to charge-exchange reactions of reactant ions in the TMS CI plasma. The stability of adduct ions in the halobenzenes was found to increase from fluorobenzene to iodobenzene. A collision-induced dissociation study of the [M+(CH3)3Si]+ ions of these compounds has been carried out to gain an insight into the site of adduction

Acetone chemical ionization studies. VII‐acetylation of some aromatic compounds

AbstractAcetone chemical ionization mass spectra of 14 monosubstituted aromatic compounds were studied. Benzene, toluene and halobenzenes give exclusively charge‐exchange spectra with very little fragmentation. Protonation is characteristic of compounds with higher proton affinities than acetone, with the exception of benzonitrile. Acetylation reactions are observed mainly with benzonitrile, phenol, anisole and aniline. The acetylation of phenol and aniline mostly occurs at the substitutent.

Electrophilic bromination of gaseous aromatic compounds: Mechanism and linear free energy effects on reaction rates

AbstractElectrophilic bromination of monosubstituted aromatic compounds is effected in a pentaquadrupole mass spectrometer using BrCO+ and CH3NH2Br+ as mass‐selected reagent ions. Reaction normally occurs at the ring and the brominated product can be mass selected in turn and caused to dissociate by Br˙ loss upon collision‐induced dissociation. Linear free energy correlations with Brown substituent σ+ constants describe the extent of gas‐phase bromine cation addition under the non‐equilibrium, low‐pressure and solvent‐free conditions which pertain in quadruple collision cells. The electrophilic addition reaction proceeds via a σ‐complex to the ring as suggested by MS3 spectra, except in the case of nitrobenzene, where substituent bromination is suggested by the occurrence of a competitive process in which the nitrosubstituent is displaced by bromine. The reactivity parameters ρ are −0.23 and −0.56 for the gaseous reagents, BrCO+ and CH3NH2Br+, respectively. Both values are much less negative than corresponding values for bromination in solution. The greater reactivity of BrCO+ is evident by the fact that it reacts even with the strongly deactivated substrates and this is consistent with a weak BrCO bond. Competitive protonation occurs in the case of CH3NH2Br+ and, unlike bromination, the rate of this reaction does not correlate with σ+ values. This is suggested to be a consequence of protonation at the ring in some cases and at the substituent in others, including acetophenone and benzonitrile. Evidence for this is that, in contrast to its lack of correlation with substituent constants, the rate of protonation correlates linearly with proton affinity.

Near-Infrared Surface-Enhanced Raman Spectra of 3-Picoline and 3-Chloropyridine on a Copper Electrode

SERS is well suited to detecting and fingerprinting environmental contaminants such as polychlorinated biphenyls. For this reason, we have been investigating SERS for identifying and quantifying the individual components of mixtures of these and related compounds. Initially, very simple monosubstituted aromatic compounds are being studied. One of the simplest of these is 3-chloropyridine (CP). This compound has been found to give very intense NIR-SER spectra on copper colloids and on copper electrodes; these results have been previously reported. In this paper we report the NIR-SER spectrum of 3-picoline on a copper electrode as well as the NIR-SER spectra of a mixture of 3-picoline and 3-chloropyridine on a copper electrode at several different potentials. Electrode potential effects on SER spectra have been mentioned in many reports, but there have been very few studies that have dealt specifically with these effects, and fewer still that have dealt with the SER spectra of mixtures. Most of the qualitative features of SERS are explained by two models, an electromagnetic model and a charge-transfer model. Variation of SER spectra with electrode potential is predicted by the charge-transfer model and is a result of the shift of the energy of the charge-transfer band in the metal with respect to the photon energy from changes in the applied voltage. Therefore, for near-infrared excitation, the optimal electrode potential might be different from that for visible-wavelength excitation. Variation of electrode potential might also have analytical uses. We are investigating the use of electrode potential for obtaining additional information about the SER spectra of mixtures. Eventually, we hope to make these measurements in contaminated aquifers using optical fibers. Near-infrared excitation is being used for these studies because of its high transmission in optical fibers and because it minimizes fiber background fluorescence.

Retention prediction of analytes in reversed-phase high-performance liquid chromatography based on molecular structure : I. Monosubstituted aromatic compounds

A system has been developed to predict retentions in reversed-phase high-performance liquid chromatography based on the molecular structure of the analyte. The retentions are calculated as retention indices, on the alkyl aryl ketone scale, by the summation of a value for a parent compound, increments for the individual substituents and contributions for interactions between the substituents. In this paper the coefficients of the quadratic equations are reported, which define the increments for a range of 17 substituents on an aromatic ring over the cluent ranges 40–80% methanol in buffer and 30–80% acetonitrile in buffer.

Mineralization of monosubstituted aromatic compounds in unsaturated and saturated subsurface soils

The mineralization of benzoic acid, phenol, and benzylamine was determined as a function of depth in two 20-m sandy soil profiles, one of which was adjacent to a leach field receiving wastewater from a laundromat. Soil samples were collected aseptically, adjusted to 20–25% water content and amended with a trace level (50 ng/g soil) of the 14C-ring-labeled compounds. Evolution of CO2 was followed with time. First-order rate constants and the extents of mineralization were estimated from the resulting data by nonlinear regression. All three compounds were mineralized in every sample examined without a lag period. In general, phenol was mineralized more rapidly than benzoic acid, which was more rapidly mineralized than benzylamine. Benzylamine had the highest sorption coefficient; phenol had the lowest. Average half-life was 0.56 days for phenol, 0.84 days for benzoic acid, and 1.31 days for benzylamine. Mineralization rates did not correlate with bacterial number, fluorescein diacetate hydrolysis rate, or any soil characteristic. The ultimate percentage of all three compounds mineralized was lowest in the upper 3 m of both soil profiles. The total amounts of phenol and benzoic acid mineralized negatively correlated with cation-exchange capacity and silt content. Statistical analysis (2-level nested ANOVA) revealed that only the rate of phenol mineralization varied significantly as a function of soil profile, but rates for all three compounds varied significantly as a function of depth within a profile.

Doubly Charged Ion Mass Spectra of Monosubstituted Aromatic Compounds

Abstract The 2E doubly charged ion mass spectra of twelve simple monosubstituted aromatic compounds were recorded. The spectral pattern of these compounds can be classified into three types. When the substituent is strongly electron-donating such as the amino or dimethylamino group, a very intense molecular ion peak appears, no fragment ion peak being observed. Phenol, anisole, toluene, and chlorobenzene show both molecular and fragment ion peaks in varying intensities. The parent benzene itself behaves similarly. Only fragment ion peaks were observed for nitrobenzene and aromatic carbonyl compounds such as benzaldehyde, acetophenone, methyl benzoate, or benzoic acid. The major fragmentation reactions are discussed.