Novel purification method of commercial o- and m-xylenes by shape selective adsorption on HZSM-5

Liquid-phase competitive adsorption of three xylene isomers on ZSM-5 zeolites was studied. HZSM-5 zeolites exhibited an extremely high para-selectivity, this para-selectivity decreased with increasing adsorption temperatures. The introduction of Na⁺ enhanced the para-selectivity. It is apparent that such a high para-selectivity is caused solely by thermodynamic shape selectivity. The complete removal of impurities with small molecular dimensions, such as p-xylene and benzene, from commercial o- and m- xylenes could be attained by the repetition of the shape-selective adsorption on HZSM-5 zeolites.     

Absolute configuration assignment of ortho,meta, or para isomers by mass spectrometry

A general method based solely on mass spectrometric techniques for the absolute configuration assignment of ortho, meta, or para isomers of acyl nitrobenzenes and derivatives is described. Instead of comparing the mass spectra of the three intact molecules of each positional isomer and investigating each one of the many sets of positional isomers, the method generalizes the effort by performing structural analysis on configurationally diagnostic fragment ions that are common for a given class of compounds. These ions must therefore retain the positional information of the parent molecules and be unequivocally distinguished. Nitrobenzoyl cations are common and stable fragment ions of most acyl nitrobenzenes and derivatives retaining the respective ortho, meta, or para configuration of the precursor molecules. The different NO₂ and CO⁺ ring alignments profoundly influence their collision-induced dissociation and bimolecular reactivity, and the isomeric 2-, 3-, and 4-nitrobenzoyl cations are found to be unequivocally distinguished using both approaches. Absolute ortho, meta, or para positional assignment by tandem MS of every isomeric molecule of the acyl nitrobenzene class and derivatives forming detectable amounts of any of those diagnostic nitrobenzoyl cations is, therefore, possible. The ability to perform absolute (non-comparative) configuration assignment using such diagnostic ions is exemplified for a single test molecule of (2R)-(−)-2-methylglycidyl 4-nitrobenzoate. The general application of this absolute MS-only method for other classes of positional isomers is discussed.     

Synthesis of a Strained Acetylenic Macrocycle Incorporating a para‐Oligo[2]cruciform Bridge Bent over Nanoscopic Dimensions: Structural,Electronic, Spectroscopic,and Ion‐Sensing Properties

An Eglinton–Galbraith diethyne cyclization preferentially yielded a structurally unusual macrocycle, comprising a strained conjugated oligo[2]cruciform wire, forced into a 2.2 nm bow‐shape by a terpyridine rein or tether, and stabilized towards light and heat by four insulating triisopropylsilylacetylene (TIPSA) substituents. Spectroscopic ion‐binding studies revealed the macrocycle to exhibit a particularly high UV/Vis selectivity for Pd^II in dilute solution, and one of its precursors to afford a variety of luminescence quenching and color responses to particular metals, suggestive of promising ion‐sensor applications. Under more concentrated conditions, the new macrocycle is able to bind specific metals (e.g., Au^I) within its cavity despite the steric constraints. Intriguingly, variable‐temperature (VT) UV/Vis/¹H NMR investigations showed the TIPSA substituents to undergo restricted intramolecular motions along with reversible changes in the spectroscopic bandgap of the compound with temperature. In line with the theoretical calculations, the VT UV/Vis observations are consistent with a thermal modulation of the electronic conjugation through the strained oligo[2]cruciform bridge, which is coupled with redistributions within a mixture of conformational isomers of the macrocycle with differing relative twisting between the TIPSA‐substituted phenyl rings. Overall, the generation of a para‐oligo[2]cruciform, bent and flexed over nanoscopic dimensions through conformational tethering within the macrocyclic ring is noteworthy, and suggests a general approach to nanosized, curved, and strained, yet heat‐ and light‐stable, para‐phenyleneethynylene oligomers with unique physicochemical properties and challenging theoretical possibilities.     

Unique para‐effect in electron ionization mass spectra of bis(perfluoroacyl) derivatives of bifunctional aminobenzenes

A new kind of ‘para‐effect’ under electron ionization (EI) conditions has been discovered for a series of bis(perfluoroacyl) derivatives of o‐, m‐ and p‐phenylenediamines, ‐hydroxybenzeneamines and ‐mercaptobenzeneamines of a common structure RCOX–C₆H₄–NHCOR (X = NH, S, O; R = CF₃, C₂F₅, C₃F₇). Only the para‐isomers showed successive loss of a radical RCO^? and a molecule RCN, leading to very intense peaks in the EI spectra. The composition and the origin of the [M–COR–NCR]⁺ ions were confirmed by exact mass measurements and linked scan experiments. The proposed mechanism of their formation takes into account likely para‐quinoid structures of the precursor ions. A similar rearrangement has not been observed for para‐isomers in the series of bis(perfluoroacyl) derivatives of benzenediols, mercaptophenols and dimercaptobenzenes. Published in 2010 by John Wiley & Sons, Ltd.     

Theoretical and experimental interpretations of phenol oxidation by the hydroxyl radical

Phenol oxidation by OH radicals produced by the Fenton reaction was studied and the oxidation process was monitored by the UV–visible, ¹³C NMR and LC techniques. The results show that benzoquinone is formed. In the NMR and LC experiments, since the peaks corresponding to isomers ortho and para- benzoquinones are unresolved, DFT was used to determine the branching ratios of the isomers formation that coincides with their ΔG values (ortho > para > meta): 72% for ortho, 23% for para and 5.0% for meta. Furthermore, the energy profile of the OH attack at ortho is quite similar to that at the para position while the meta position attack is less favored by 2.0 kcal/mol.     

Effect of Industrial Detonation Nanodiamonds on the Ratio of Mononitrotoluene Isomers in Nitration of Toluene with a Sulfuric-Nitric Acid Mixture

A qualitative and quantitative influence exerted by addition of detonation nanodiamonds on the formation selectivity of mononitrotoluene isomers in the heterophase nitration of toluene with a sulfuric-nitric acid mixture having low nitration activity was found. It is shown that the isomer ratio of the ortho-/paramononitrotoluenes can be varied within the range 1.00–2.7 at a temperature of 50°C by changing the stirring intensity within the range 300–5000 rpm. It was found that the strongest influence on the ortho-/para-ratio of the mononitrotoluene isomers is exerted by nanodiamonds having surface chemically modified via oxidation with a mixture of concentrated nitric and sulfuric acids.     

Synthesis of 6-Substituted 1-Deazapurine 2′-Deoxyribonucleosides

The synthesis of 6-substituted 1-deazapurine 2′-deoxyribonucleosides is described. Glycosylation of the 1-deazapurine (imidazo[4,5-b]pyridine) anions with the α-D -halogenose 5 gives stereoselectively N⁷- and N⁹- regioisomers. ¹H-NMR NOE and ¹³C-NMR spectroscopy are used for unambiguous assignment of isomers, and ¹⁵N-NMR chemical shifts are correlated with σ_para Hammett constants and point charges.     

The Relevance of Size Matching in Self-assembly: Impact on Regio- and Chemoselective Cocrystallizations

Decamethonium diiodide is reported to perform the chemo- and regioselective encapsulation of para-dihalobenzenes through the competitive formation of halogen-bonded cocrystals starting from solutions that also contain ortho and meta isomers. Selective caging in the solid occurs even when an excess ortho or meta isomers, or even a mixture of them, is present in the solution. A prime matching between the size and shape of the dication and the formed dianions plays a key role in enabling the selective self-assembly, as proven by successful encapsulation of halogen-bond donors as weak as 1,4-dichlorobenzene and by the results of cocrystallization trials involving mismatching tectons. Encapsulated para-dihalobenzenes guest molecules can be removed quantitatively by heating the cocrystals under reduced pressure and be recovered as pure materials. The residual decamethonium diiodide can be recycled with no reduction in selectivity.     

Alkali metal cation complexation by 1,3-alternate,mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs⁺ efficiency and selectivity. Single-species extraction pH profiles of Cs⁺ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs⁺ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs⁺ complexes.     

Beyond p-Hexaphenylenes: Synthesis of Unsubstituted p-Nonaphenylene by a Precursor Protocol

The synthesis of unsubstituted oligo-para-phenylenes ( OPP ) exceeding para-hexaphenylene—in the literature often referred to as p-sexiphenyl—has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para-nonaphenylenes ( 9PP s) by extending our precursor route to poly-para-phenylenes ( PPP ) to a discrete oligomer. Two geometric isomers of methoxylated syn- and anti-cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical, infrared and solid-state ¹³C NMR spectroscopy as well as atomic force microscopy and mass spectrometry, and compared to polymeric analogues. Due to the lack of substitution, para-nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular excitonic coupling leads to formation of H-type aggregates, red-shifting emission of the films to greenish. 9PP allows to study the structure–property relationship of para-phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor.     

Calculations of thermodynamic stability of CpCoC<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript> cobaltacarborane isomers

Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC₂B₉H₁₁ (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative stabilities of the 1,2,3-(17.57 kcal mol⁻¹), 1,2,4-(3.72 kcal mol⁻¹), and 1,2,9-isomers of 1 (0 kcal mol⁻¹) are similar to the corresponding values for the ortho (17.61 kcal mol⁻¹), meta (3.21 kcal mol⁻¹), and para isomers (0 kcal mol⁻¹) of carborane C₂B₁₀H₁₂. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005.     

Deviations from the normal ortho/para ratio for water (3 : 1) in the vapor phase in dynamic sorption

Deviations of the ortho/para ratio from its normal value (3: 1) were observed by spectral selective detection of ortho and para water molecules when water vapor passed through a column with a nanoporous polymeric adsorbent. The effect was suggested to be related to the nonstationary dynamics of sorption, that is, nonequilibrium character of chromatography. In terms of this model, the factor of spin ortho/para selectivity is slow and unequal diffusion of the spin isomers of water molecules inside the adsorbent, a process spurious for ideal equilibrium chromatography. Original Russian Text ? P.O. Kapralov, V.G. Artemov, A.M. Makurenkov, V.I. Tikhonov, A.A. Volkov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 4, pp. 769–775.     

Influence of isomerism of the ligand on the enthalpies of formation of copper tetrapyridylporphine

The enthalpy of dissolution of the tetrapyridylporphine isomers in water and in aqueous solutions of magnesium and copper acetates at a constant salt concentration (∼7 mmol/l) were observed for the first time by the calorimetric method with spectrophotometric monitoring. A substantial influence of the electronic effects of the tetrapyridyl fragment with different (para, meta, and ortho) positions of the heteroatom on the enthalpies of coordination of the ligands by the Cu²⁺ ions was revealed.     

Natural abundance 17O NMR study of 2- and 4-substituted benzoyl chlorides

Natural abundance ¹⁷O NMR chemical shift data for 17 ortho and para benzoyl chlorides recorded in acetonitrile at 75°C are reported. ¹⁷O NMR data for the para substituted benzoyl chlorides are correlated with ¹⁷O NMR data for similarly substituted acetophenones and methyl benzoates. The ¹⁷O NMR signals for ortho isomers are downfield (ca 30 ppm) from their para isomers; the downfield shifts are consistent with torsion angle change. The ¹⁷O NMR data for the para isomers gave good correlations with σ⁺ constants and with dual substituent parameters (DSP).     

Mass Spectral Fragmentation Patterns of 11-(o- and p-R-Anilino)-5H-dibenzo[b,e][1,4]diazepines. IV

The mass spectral fragmentation patterns of eleven 11-(o- and p-R-anilino)-5H-dibenzo[b,e][1,4]diazepines obtained by electron impact have been studied. All the spectra analyzed contain molecular ions, which are base peak for para isomers and the principal fragmentation routes takes place either from the molecular ion, or from (M⁺ - 1) ion. There are, however, some deviations from the general fragmentation pattern in the case of 1,4-dibenzodiazepines with o-amino and p-methoxy substituents caused by direct interaction of these groups with the dibenzodiazepine ring.     

Relative Stabilities and Molecular Structures of Isomeric Dihalobenzenes. A DFT Study

The molecular structures, total energies, and other computational data of benzene, and its monoand dihalogenated derivatives (halogen = F, Cl, Br) have been studied by DFT calculations. The main aim of the study was to estimate the relative stabilities (energies) of the ortho, meta, and para isomers of the six series of dihalobenzenes investigated. The computational data show that the ortho isomers always have the highest, and the meta isomers usually, but not always, the lowest total energies. Thus, 1,2-difluorobenzene is ca. 16.6 kJ mol^–1, and 1,4-difluorobenzene 2.5 kJ mol^–1 less stable than 1,3-difluorobenzene. Among the other isomeric dihalobenzenes, the differences in stability are less pronounced. For the dibromo-, dichloro-, and bromochlorobenzenes, the para compounds are calculated to be slightly (0.2–0.4 kJ mol^–1) more stable than their meta isomers. In addition to the thermochemical aspect of the study, the computational molecular structures of the halobenzenes are compared with available experimental data and discussed in terms of the substituent-induced deformation of the ideal geometry of the benzene ring. The computational electric dipole moments, especially for the fluorine-containing compounds, compare favorably with the respective experimental (gas-phase) values.     

Selectivity comparisons of monolithic silica capillary columns modified with poly(octadecyl methacrylate) and octadecyl moieties for halogenated compounds in reversed-phase liquid chromatography

Stationary phase selectivities for halogenated compounds in reversed-phase HPLC were compared using C18 monolithic silica capillary columns modified with poly(octadecyl methacrylate) (ODM) and octadecyl moieties (ODS). The preferential retention of halogenated benzenes on ODM was observed in methanol/water and acetonitrile/water mobile phases. In selectivity comparison of selected analytes on ODM and ODS, greater selectivities for halogenated compounds were obtained with respect to alkylbenzenes on an ODM column, while similar selectivities were observed with a homologous series of alkylbenzenes on ODM and ODS columns. These data can be explained by greater dispersive interactions by more densely packed octadecyl groups on the ODM polymer coated column together with the contribution of carbonyl groups in ODM side chains. For the positional isomeric separation of dihalogenated benzenes (ortho-, meta-, para-), the ODM column also provided better separation of these isomers for the adjacently eluted isomers that cannot be completely separated on an ODS column in the same mobile phase. These results imply that the ODM column can be used as a better alternative to the ODS column for the separation of other halogenated compounds.     

Metal-Organic Frameworks for Breakthrough Separation of 2-Butene Isomers with High Dynamic Selectivity and Capacity

Developing porous sorbents represents a potential energy-efficient way for industrial gas separation. However, a bottleneck for reducing the energy penalty is the trade-off between dynamic adsorption capacity and selectivity. Herein, we showed this problem can be overcome by modulating the kinetic and thermodynamic separation behaviours in metal–organic frameworks for sieving 2-butene geometric isomers, which are desired for upgrading the raffinates to higher value-added end products. We found that the iron-triazolate framework can realize the selective shape screening of 2-butene isomers assisted by electrostatic interactions at the pore apertures. Further introducing uncoordinated N binding sites by ligand substitution lowered the gas diffusion barrier and greatly boosted the dynamic separation performance. In breakthrough tests under ambient conditions, trans-2-C₄H₈ can be efficiently separated from cis-2-C₄H₈ with a record capacity of 2.10 mmol g⁻¹ with high dynamic selectivity of 2.39.     

Catalytic debutylation oftert-butylphenols by some natural clays

In the catalytic debutylation oftert-butylphenols by some Jordanian, Bulgarian and Turkish natural clays, Jordanian kaolin and bentonite were found to be the most active catalysts among the clays studied. The activity of these clays to converto-tert-butylphenol to phenol,p-tert-butylphenol and other minor products is in the following order: Jordanian kaolin >Jordanian bentonite>Turkish bentonite> Bulgarian bentonite. While for the conversion ofp-tert-butylphenols, Jordanian clays showed moderate activity, with bentonite being the most active, the other clays were not active. Also, all the clays studied were ineffective towards conversion ofm-tert-butylphenol. As to the debutylation selectivity of theortho isomer, Jordanian bentonite proved to be slightly debutylation selective, whereas Jordanian kaolin showed a relatively high selectivity toardsortho topara isomerization. Thepara isomer produced only debutylation products and none of the other isomers.     

Molecular recognition of a self-assembled monolayer of a polydithiocarbamate derivative of β-cyclodextrin on silver

The synthesis and molecular recognition properties of a new sulfur containing β-cyclodextrin (β-CD) derivative chemisorbed on a silver surface are described. Hepta-6-amino-6-deoxy-β-CD was allowed to react with CS₂ in the presence of ammonia to give a mixture of partially substituted dithiocarbamate derivatives with an average degree of substitution of 4.5. A modified silver electrode with this derivative is capable of discriminating between the three positional isomers of nitrobenzoate ion and nitrophenol, as determined by cyclic voltammetry. Only the meta- and para-isomers give a signal corresponding to the reduction of the nitro group. This is attributed to the different orientations of the nitro group with respect to the silver surface after inclusion in the CD cavity. Experiments in the presence of cyclohexanol showed a decrease in signal intensity of the meta- and para-isomers which is associated with the competitive complexation of this guest, suggesting that the electroactive probe is complexed to the cavity.