Electrochemical Synthesis of Poly-o-phenylenediamine and Its Spectroelectrochemical Properties

The anodic synthesis of a poly-o-phenylenediamine film at gold, platinum, and ITO electrodes and peculiarities of its doping–undoping are studied by cyclic voltammetry. Absorption spectrum of undoped films is obtained in visible and near-IR light.     

Spectroelectrochemical studies of poly-o-phenylenediamine Part 2. In situ UV—vis subtractive reflectance spectroscopy

In our previous paper, the phenazine-like structure of the poly-o-phenylenediamine (PoPD) and its three steady redox states have been revealed mainly by using in situ resonance Raman spectroscopy. It has also been shown that the semi-oxidized state of PoPD is the most stable state of PoPD, while the totally-oxidized state of PoPD is chemically unstable and can exist only at certain electrode potentials. In the present work, the more detailed reaction mechanism of a PoPD film in strong acid solution has been studied by using in situ UV—vis substractive reflectance spectroscopy. The semi-oxidized state and the totally-oxidized state of PoPD have electronic absorption bands around 300 nm, 430 nm, 500 nm and 300 nm, 450 nm, 530 nm, 735 nm respectively in the in situ steady state UV—vis subtractive reflectance spectra with respect to the reduced state of PoPD, which verifies once again that three redox states of PoPD exist in the redox process of PoPD. Moreover, the relative intensity between two oxidized states of PoPD at the maximum absorption wavelength (λ_max) reveals that only about one third of the semi-oxidized state of PoPD can be oxidized to the totally-oxidized state of PoPD. The in situ resonance Raman spectra and the cyclic voltammograms of PoPD display the same quantitative relationship. New absorption bands were observed in the in situ time-resolved UV—vis subtractive reflectance spectra with appropriate time resolutions, which illustrate the dynamic structure changes of PoPD in its redox process. These intermediate states of PoPD are more unstable than its three redox states.     

Molecular Structure of ortho-Fluoronitrobenzene Studied by Gas Electron Diffraction and Ab Initio MO Calculations

The molecular structure of ortho-fluoronitrobenzene (o-FNB) has been investigated by gas-phase electron diffraction and ab initio MO calculations. The geometrical parameters and force fields of o-FNB were calculated by ab initio and DFT methods. The obtained force fields were used to calculate vibrational amplitudes required as input parameters in an electron diffraction analysis. Within the experimental error limits, the geometrical parameters obtained from the gas-phase electron diffraction analysis are mostly in agreement with the results obtained from the ab initio calculations. The main results are: the molecular geometry of o-FNB is nonplanar with a dihedral angle about C–N of 38(3)°. The r _g (C–F) bond is shortened to 1.307(13) Å in comparison with r _g (C–F) = 1.356(4) Å in C₆H₅F.     

Continuous-flow separation and pre-concentration coupled on-line to solid-surface fluorescence spectroscopy for the simultaneous determination of<Emphasis Type="Italic"> o</Emphasis>-phenylphenol and thiabendazole

A novel and single flow-injection system combined with solid-surface fluorescence detection is proposed in this work for the resolution of a mixture of two widely used pesticides (o-phenylphenol and thiabendazole). The continuous-flow methodology is based on the implementation of on-line pre-concentration and separation of both analytes on the surface of C₁₈ silica gel beads placed just inside the flow cell, implemented with gel-phase fluorimetric multi-wavelength detection (using 305/358 and 250/345 nm as excitation/emission wavelengths for thiabendazole and o-phenylphenol, respectively). The separation of the pesticides was possible owing to the different retention/desorption kinetics of their interactions with the solid support in the zone where the stream impinges on the solid material. No previous separation of the analytes before they reach the flow cell is needed thereby simplifying substantially both the procedure and the manifold. By using a sample volume of 2,600 L, the system was calibrated in the range 0.5–16 and 5–120 ng mL^–1 with detection limits of 0.09 and 0.60 ng mL^–1 for thiabendazole and o-phenylphenol, respectively. The RSD values (n=10) were about 1% for both analytes. The proposed methodology was applied to environmental water samples and also to various commercial pesticide formulations containing both analytes. Recovery percentages were 97–103% and 98–102% for thiabendazole and o-phenylphenol, respectively.     

Destruction ofB-polyfluorosubstitutedo-carboranes into anions ofB-fluorosubstitutednido-7,8-dicarbaundecaborates by the action of ethanolic alkali and amines

The destruction ofB-polyfluorosubstitutedo-carboranes by the action of ethanolic alkali and amines was studied. The destraction of trifluoro-o-carborane was found to occur regioselectively. The nature of the amine was shown to affect the stereochemistry of the destruction of trifluoro-o-carborane. The intermediate of the reaction of tetrafiuoro-o-carborane with diethylamine was detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1141–1145, June, 1995.     

Synthesis of 3-isocyano-nido-7,8-dicarbaundecaborate salts and their use as new isonitrile ligands in transition-metal complexes

The treatment of 3-isocyano-o-carboranes with an alkali solution in alcohol results in the regioselective splitting out of a boron atom from position 6 of theo-carborane nucleus to give 3-isocyano-nido-7,8-dicarbaundecaborate salts, in which the isonitrile group is attached to the boron atom of thenido-polyhedron anion. 3-Isocyano-nido-7,8-dicarbaundecaborate salts are new isonitrile ligands in transition-metal complexes. Complexes with chromium, molybdenum, tungsten, and iron compounds have been obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1458–1460, August, 1993.     

Microscopic observation of the crystalline form of poly(<Emphasis Type="Italic">o</Emphasis>-methoxyaniline) on a membrane electrode

We describe electrochemical and microscopic (SEM) studies on the electrochemical polymerization of poly(o-methoxyaniline). The crystalline form of the polymer was obtained. The poly(o-methoxyaniline) crystals are formed on a membrane electrode from an acidic solution of the monomer. It is suggested that the pores of the membrane work as nuclear crystallization points.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Partial Molar Volumes of Tetraalkylammonium Ions in N, N-Dimethylformamide

The densities of tetraalkylammonium bromide, R₄NBr (R = Et, Pr, Bu, Hex, Hep, Oct), solutions in dimethylformamide have been measured for the composition range (0.05–0.4) mol-kg⁻¹ at 25 ^∘C. Apparent molar V_φ and limiting partial molar volumes ⫫₂^o of the electrolytes have been evaluated. Using the extrapolation values, the limiting partial molar volumes of the tetraalkymammonium ions (⫫_i^o) have been calculated. Analysis of different contributions to the ionic ⫫_i^o indicated partial penetration of solvent molecules into the van der Waal’s volume of tetraalkylammonium (TAA) ions.     

Electrochemical surface plasmon resonance studies on the deposition of the charge-transfer complex from electrooxidation of o-tolidine and effects of dermatan sulfate

The electrochemical surface plasmon resonance (ESPR) technique was used to investigate the electrodeposition of the charge-transfer complex (CTC) generated during electrooxidation of o-tolidine (o-TD) in pH 4.5 Britton–Robinson buffers and the effects of coexisting dermatan sulfate (DS). The peak-type surface plasmon resonance (SPR) responses (versus time) observed in the cyclic voltammetric experiments indicated the precipitation and dissolution of a poorly soluble CTC, an oxidation intermediate, formed during the redox switching of o-TD in a weakly acidic medium. The effects of potential scan rate and solution pH were examined. The height of the peak-type SPR response to the redox switching of the o-TD/CTC “couple” was notably enhanced by the introduction of DS, due to the formation of a mass-enhanced CTC-DS adduct, as also supported by UV–vis spectroelectrochemistry. The SPR signal responded linearly to the DS concentration up to 14 μmol L⁻¹, with a limit of detection (LOD) down to 8 nmol L⁻¹ (S/N = 3). The analytical performance of the ESPR technique was found to be better than that of the quartz crystal microbalance technique with an LOD value of 70 nmol L⁻¹. The CTC-based ESPR assay is recommended as a new, highly sensitive and dynamically surface-regenerated biosensing technology for other species.     

Selective hydrogenation of o-chloronitrobenzene (o-CNB) over supported Pt and Pd catalysts obtained by laser vaporization deposition of bulk metals

Carbon nanotubes (CNTs), γ-alumina (γ-Al₂O₃) and silica (SiO₂) supported Pt and Pd catalysts were produced by laser vaporization deposition of respective bulk metals. The catalysts were characterized by inductive coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic properties of the catalysts were investigated in the liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) under 333 K and 1.0 MPa hydrogen pressure. The results show that the catalytic properties are greatly affected by the supports. Pt/CNTs catalyst exhibits the best catalytic performance among the Pt-based catalysts, producing o-CAN with 99.6% selectivity at complete conversion. Pd/CNTs catalyst exhibits the best catalytic performance among the Pd-based catalysts, giving o-CAN with 95.2% selectivity at complete conversion. For Pt-based catalysts, geometric effect and the textures and properties of the supports play important roles on catalytic properties. On the other hand, geometric effect, electronic effect and the textures and properties of the supports simultaneously influence the catalytic properties of the Pd-based catalysts. In addition, hydrogenolysis of the C–Cl bond can be well inhibited over all catalysts prepared by laser vaporization deposition.     

Investigation of isothermal bulk polymerization ofo-alkyaryl methacrylates by DSC

The kinetics of the AIBN-initiated free radical bulk polymerization of fiveo-alkylphenyl methacrylates was studied by means of DSC in the temperature range 353–373 K, and the enthalpy of polymerization, the overall reaction rate constant and the activation energy were determined. The results were compared with those published recently on correspondingp-alkylaryl methacrylates. All measured reaction rate constants were found to increase with increasing temperature and to decrease with increasingo-alkyl substituent mass and size. It was shown thato-substituents influence the rates of polymerization to a greater extent thanp-substituents. At about 373 K, all differences in rate, most probably resulting from steric hindrance caused by the alkyl groups, disappear in both series, a phenomenon earlier observed for dimethyl phenyl methacrylates.This work was supported by the Ministry of Science of the Republic of Serbia.     

Synthesis of novel dibenzo-2,6,9-triazabicyclo[3.3.1]nonanes from <Emphasis Type="Italic">o</Emphasis>-tosylamino- and <Emphasis Type="Italic">o</Emphasis>-mesylaminobenzaldehydes

Condensation of o-tosylaminobenzaldehyde with γ-aminobutyric, 4-aminophenylthioacetic, and p-aminobenzoic acids and β-alanine gave 6,12-epimino-5,11-ditosyl-5,6,11,12-tetrahydrodibenzo[b, f]-1,5-diazocines with carboxyl-containing substituents at the bridging N atoms. The structures of three products were examined by X-ray diffraction analysis. Condensation of o-mesylaminobenzaldehyde (prepared by the McFadyen-Stevens reaction) with NH₄OAc and primary amines afforded 6,12-epimino-5,11-dimesyl-5,6,11,12-tetrahydrodibenzo[b, f]-1,5-diazocine derivatives.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2165–2171, October, 2004.     

Synthesis and recyclization reactions of 4-(o-R-phenyl)-3-imidazolines

1-Hydroxy-4-phenyl-3-imidazoline reacts with butyllithium to give the product oforthometallation of the phenyl group. Reactions of this compound with electrophiles followed by oxidation afford 4-(o-R-phenyl) derivatives of nitroxyl radicals. When a hydroxyalkyl group is present in theortho-position, an unusual pathway of the decay of stable nitroxyl radicals of the imidazoline series has been observed due to the existence of a spirobicyclic tautomer. The reaction of theo-metallated derivative with CS₂ leads to a profound transformation of the imidazoline ring and to the formation of isoindolethione. Fast recyclization into isoquinolines occurs in the case of the 4-(o-benzoyl)phenyl derivative of 3-imidazoline. The product ofo-metallation reacts with methyl nitrate to yield the 4-(o-hydroxy)phenyl derivative (a potential paramagnetic chelate-forming reagent) and theo-nitro derivative, the starting material for further chemical transformations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 899–903, May, 1994.     

High levelab initio stabilization energies of benzene

Summary G2 theory is shown to be reliable for calculating isodesmic and homodesmotic stabilization energies (ISE and HSE, respectively) of benzene. G2 calculations give HSE and ISE values of 92.5 and 269.1 kJ mol^–1 (298 K), respectively. These agree well with the experimental HSE and ISE values of 90.5±7.2 and 268.7±6.3 kJ mol^–1, respectively. We conclude that basis set superposition error corrections to the enthalpies of the homodesmotic or isodesmic reactions are not necessary in calculations of the stabilization energies of benzene using G2 theory. The calculated values of the enthalpies of formation of such molecules containing multiple bonds such as benzene ands-trans 1,3-butadiene, which are found from the enthalpies of isodesmic and homodesmotic reactions rather than of atomization reactions, demonstrate good performance of G2 theory. Estimates of theH _f ^o value for benzene from the G2 calculated enthalpies of homodesmotic reaction (2) and isodesmic reaction (3) are 80.9 and 82.5 kJ mol^–1 (298 K), respectively. These are very close to the experimentalH _f ^o value of 82.9±0.3 kJ mol^–1. TheH _f ^o value ofs-trans 1,3-butadiene calculated using the G2 enthalpy of isodesmic reaction (4) is 110.5 kJ mol^–1 and is in excellent agreement with the experimentalH _f ^o value of 110.0±1.1 kJ mol^–1.     

Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

New molecular species of potential interest to interstellar chemistry: A theoretical study of MgSiN, MgNSi and related species

An ab initio study has been performed to characterize the probable magnesium containing interstellar species MgSiN, MgNSi and their ionized, hydrogenated and protonated forms. We are able to locate four protonated and four hydrogenated magnesium species with planar geometry at MP2(Full)/cc-pVTZ level of theory. MgNSi is found to be more stable than MgSiN and their connecting transition state is also located. The ionization potential for both MgSiN and MgNSi are small, 7.91 eV and 7.01 eV, respectively. All possible protonation sites are considered for these two species but the preferred protonation sites are found to be silicon for MgNSi and nitrogen for MgSiN. Enthalpies of formation at 0 K (Δ_fH°) and bond dissociation energies (D^o(X–Y)) are computed for all the species at G3 and G3MP2 level of theory. Finally, the reaction enthalpies for ion–molecule processes are calculated and most of the processes are found to be exothermic and hence thermodynamically favorable in interstellar region.     

Synthesis of 9-benzyl-o- and 9-benzyl-m-carboranes containing functional substituents in the benzene ring by electrophilic alkylation ofo- andm-carboranes by the correspondingR-benzyl halides

9-Benzyl-o- andm-carboranes containing NO₂, COOH, COOMe, and COPh groups in thepara-position of the benzene ring were synthesized by the Friedel—Crafts reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1138–1140, June, 1995.This study was financially supported by the International Science Foundation (Grant MSE 000).     

Thermodynamics of tri- and pentabromide anions in aqueous solution

Formation constants for the tribromide and pentabromide anions were measured by a vapor partitioning method from 5 to 80°C. The molal thermodynamic parameters for these respective species at 25°C are: K ₃ –16.73, H ^o =–5.90 kJ-mol ^–1 , Cp ^o =–29 J-K ^–1 -mol ^–1 , and S ^o =3.6 J-K ^–1 -mol ^–1 ; K ₅ =37.7, H ^o =–13.0 kJ-mol ^–1 , S ^o =–13.6 J-K ^–1 -mol ^–1 , with Cp ^o assumed zero. These results are used to reevaluate published emf results for the bromine/bromide couple.     

Thermodecomposition ofo-benzoquinone complexes of transition metals

Thermodecomposition of 3,5- and 3,6-di-tert-butyl-o-benzoquinone complexes of Cu, Fe, Co, Cr, Mo, and W has been investigated in the solid phase by the thermogravimetric method. The relative stability of a series of complexes has been determined from the temperatures at which their decomposition begins. Detachment of a neutral electron-donor ligand takes place in the first stage. Detachment of ano-quinone ligand and decomposition of theo-benzoquinone formed occur in the next stage. Thermodecomposition of Fe, Co, Cr, Mo, and W complexes gives oxides or carbides, while copper complexes decompose to pure metal.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 327–329, February, 1994.     

Chemoselectivity of 6-bromo-2-methyl-3,1-benzoxazin-4-one towards amines,Schiff bases,and azines

Summary 6-Bromo-2-methyl-3,1-benzoxazin-4-one (1) undergoes an unusual cleavage at position 4 when it is allowed to react witho-phenylenediamine or anthranilic acid in dry benzene to give the corresponding compounds2–5, respectively. The reaction of1 withSchiffbases and azines results in the formation of the compounds6a–d and8a,b, respectively. The reaction involves a cleavage of theSchiff base or the azine into its amine and arylidene moieties which are smoothly incorporated into1 via nucleophilic attack of the amine at position 4 and condensation of the aldehyde with a reactive methyl group, at position 2 respectively. No displacement of the arylidene segment was observed.

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Zur Chemoselektivität von 6-Brom-2-methyl-3,1-benzoxazin-4-on gegenüber Aminen,Schiffschen Basen und Azinen

Zusammenfassung 6-Brom-2-methyl-3,1-benzoxazin-4-on reagiert mito-Phenylendiamin oder Anthranilsäure in trockenem Benzol unter einer ungewöhnlichen Bindungstrennung zu den Verbindungen2–5. Die Reaktion von1 mitSchiffschen Basen und Azinen führt zu den Verbindungen6a–d und8a,b. Die Reaktion verläuft über eine Spaltung derSchiffschen Base oder des Azins in ihre Amin- und Arylidenreste, die über einen nucleophilen Angriff des Amins an Position 4 und Kondensation des Aldehyds mit der reaktiven Methylgruppe in Position 2 glatt in1 übergeführt werden. Es wurde kein Arylidenaustausch beobachtet.