A facile and fast electrochemical method for the simultaneous determination of <Emphasis Type="Italic">o</Emphasis>-dihydroxybenzene and <Emphasis Type="Italic">p</Emphasis>-dihydroxybenzene using a surfactant

A fast and convenient analytical technique has been suggested to detect dihydroxybenzene (DHB) isomers directly and simultaneously. In 0.1 M HAc-NaAc buffer solution (pH 5.6), the reduction peaks of p -DHB and o -DHB were partly separated by differential pulse voltammetry at the glassy carbon electrode. By adding a surfactant (cetyl pyridinium chloride) to enhance the detection sensitivity and using a semi-derivative technique to improve the separation, p-DHB and o-DHB were detected simultaneously. The linear calibration ranges were 1.2 × 10⁻⁶ to 1.0 × 10⁻⁴ M for p -DHB and 8.2 × 10⁻⁷ to 1.0 × 10⁻⁴ M for o -DHB, with detection limits of 3.6 × 10⁻⁷ and 2.4 × 10⁻⁷ M, respectively. The proposed method has been applied to the direct determination of DHB isomers in water sample, and the results were excellent. The text was submitted by the authors in English.     

Electrochemical preparation of poly(<Emphasis Type="Italic">p</Emphasis>-phenylene) thin films

We report the electrochemical preparation of poly(p-phenylene) (PPP) thin films with a polymerization degree of approximately 20 using biphenyl as starting material. The PPP films are prepared directly on a tin oxide electrode, presenting a positive charge carrier mobility of 5×10⁻⁷ cm² V⁻¹ s⁻¹.     

Standard molar enthalpies of formation and sublimation of <Emphasis Type="Italic">N</Emphasis>-phenylphthalimide

The standard (p ⁰=0.1 MPa) molar enthalpy of formation, Δ_f H ⁰ _m, for crystalline N-phenylphthalimide was derived from its standard molar enthalpy of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as –206.0±3.4 kJ mol^–1. The standard molar enthalpy of sublimation, Δ^g _cr H ⁰ _m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.3±1.0 kJ mol^–1. The derived standard molar enthalpy of formation, in the gaseous state, is analysed in terms of enthalpic increments and interpreted in terms of molecular structure.     

Study on Inclusion Complex Formation of <Emphasis Type="Italic">m</Emphasis>-Aminobenzoic Acid with Native and Substituted <Emphasis Type="Italic">β</Emphasis>-Cyclodextrins

The complex formation of native and substituted β-cyclodextrins with m-aminobenzoic acid in water was characterized by calorimetry, ¹H NMR and UV spectroscopic studies. These studies showed that β-, hydroxypropyl-β- and methyl-β-cyclodextrins form 1:1 inclusion complexes with m-aminobenzoic acid. The thermodynamic properties of complex formation (K,Δ_c G ^o,Δ_c H ^o,Δ_c S ^o) were calculated. It was found that the processes of complexation are mainly favorable entropically. Introduction of hydroxypropyl- and methyl-substituents into the β-CD molecule results in negligible enhancement of stability of the complexes formed. The structure of these substituents has no influence on the stability constant values. The insertion of the carboxylic group of m-aminobenzoic acid into the cyclodextrin cavity was confirmed by ¹H NMR data.     

Low-temperature thermodynamic properties of <Emphasis Type="Italic">L</Emphasis>-cysteine

Heat capacity C _p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C _p; entropy, S _m⁰(T)-S _m⁰(0); difference in the enthalpy, H _m⁰(T)-H _m⁰(0), are equal, respectively, to 144.6±0.3 J K⁻¹ mol⁻¹, 169.0±0.4 J K⁻¹ mol⁻¹ and 24960±50 J mol⁻¹. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.     

Functionalization of sterically hindered <Emphasis Type="Italic">o</Emphasis>-benzoquinones: amino-substituted 3,6-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-<Emphasis Type="Italic">o</Emphasis>-benzoquinones

New sterically hindered functionalized o-quinones were synthesized by the 1,4-nucleophilic addition of secondary cyclic amines to 3,6-di(tert-butyl)-o-benzoquinone. The ability of these o-quinones to form o-semiquinone complexes with transition and main-group metals was studied by ESR spectroscopy in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1786–1793, September, 2007.     

Photolysis of <Emphasis Type="Italic">p</Emphasis>-benzoquinone and <Emphasis Type="Italic">p</Emphasis>-chloranil in aqueous sodium sulfite solution

Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10⁻⁴ l mol⁻¹ s⁻¹. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate constant of 0.005 s⁻¹.     

Synthesis of isomeric 2-oxazolidinones from (1<Emphasis Type="Italic">R</Emphasis>,2<Emphasis Type="Italic">R</Emphasis>)-and (1<Emphasis Type="Italic">S</Emphasis>,2<Emphasis Type="Italic">S</Emphasis>)-2-amino-1-(4-nitrophenyl)-1,3-propanediols

A synthesis is reported for (4R,5R)-and (4S,5S)-4-hydroxymethyl-5-(4-nitrophenyl)oxazolidin-2-ones and (1′R,4R)-and (1′S,4S)-4-[hydroxy(4-nitrophenyl)methyl]oxazolidin-2-ones from (1R,2R)-and (1S,2S)-2-amino-1-(4-nitrophenyl)-1,3-propanediols. The effect of the experimental conditions on the formation of these compounds was studied. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1562–1570, October, 2007.     

Reaction of frangula-emodin with <Emphasis Type="Italic">α</Emphasis>-bromoalkylmethylketones

The alkylation of 1,6,8-trihydroxy-3-methylanthraquinone (frangula-emodin) by α-bromoalkylmethylketones was investigated. Hydroxyls in the 1-and 8-positions of the β-derivatives were O-acylated. The compositions and structures of the prepared compounds were confirmed by elemental analysis and UV, IR, PMR, and ¹³C NMR spectroscopy. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 324–326, July–August, 2007.     

<Emphasis Type="Italic">Ab initio</Emphasis> Study of Structural and Conformational Properties of Five- to Nine-Membered Cyclic 1,2,3-Trienes

Summary.  The structures and relative energies of fundamental conformations of cyclopenta-1,2,3-triene, cyclohexa-1,2,3-triene, cylohepta-1,2,3-triene, cycloocta-1,2,3-triene, and cyclonona-1,2,3-triene were calculated by the HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods. Only a C _2v symmetric planar conformation is available to cyclopenta-1,2,3-triene and cyclohexa-1,2,3-triene. The calculated energy barrier for ring inversion of the C _S symmetric puckerd conformation of cyclohepta-1,2,3-triene via the planar geometry is 62.2 kJ·mol⁻¹. The C ₂ symmetric twist conformation of cycloocta-1,2,3-triene was calculated to be the most stable one. Conformational racemization of the twist form takes place via the C _S symmetric half-chair geometry, which is by 60.8 kJ·mol⁻¹ less stable than the twist conformer. The C _S symmetric chair and unsymmetrical twist-boat conformations of cyclonona-1,2,3-triene were calculated to have similar energies; their interconversion takes place via an unsymmetrical low-energy (18.4 kJ·mol⁻¹) transition state. The twist (C ₂) and boat (C _S) geometries of cyclonona-1,2,3-triene are higher in energy by 13.2 and 33.9 kJ·mol⁻¹, respectively. Ring inversion in chair and twist-boat conformations takes place via a twist form as intermediate and requires 33.6 kJ·mol⁻¹. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 4, 2002     

Enthalpies of mixing of <Emphasis Type="Italic">o</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-isomers at 298.15 K

Excess enthalpies (H ^E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H ^E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.     

Biosorptive behavior of mango (<Emphasis Type="Italic">Mangifera indica</Emphasis>) and neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) barks for <Superscript>134</Superscript>Cs from aqueous solutions: A radiotracer study

The role of dead biomasses viz., mango (Mangifera indica) and neem (Azadirachta indica) bark samples are assessed in the removal behavior of, one of important fission fragments, Cs(I) from aqueous solutions employing a radiotracer technique. The batch type studies were carried out to obtain various physico-chemical data. It is to be noted that the increase in sorptive concentration (from 1.0·10⁻⁸ to 1.0·10⁻² mol·dm⁻³), temperature (from 298 to 328 K) and pH (2.6 to 10.3) apparently favor the uptake of Cs(I) by these two bark samples. The concentration dependence data obeyed Freundlich adsorption isotherm and the uptake follows first order rate law. Thermodynamic data evaluation and desorption experiments reveal the adsorption to be irreversible and endothermic in nature proceeding through ion-exchange and surface complexation for both dead biomasses. Both bark samples showed a fairly good radiation stability in respect of adsorption uptake of Cs(I) when irradiated with a 300 mCi (Ra-Be) neutron source having an integral neutron flux of ∼3.85·10⁶ n·cm⁻²·s⁻¹ and associated with a nominal γ-dose of ∼1.72 Gy·h⁻¹.     

Energy Storage by Poly(<Emphasis Type="Italic">o</Emphasis>-anisidine) Matrix During Oxidative Hydrolysis

The chromaticity of poly(o-anisidine) (POAN) doped with different acids (HA), HA-doped POAN, has been studied by the spectrophotometric technique and the results were substantiated by molecular mechanics (MM+) calculations. The observed absorbance decrease (λ around 720 nm, dark green coloration) with increasing concentration of the inorganic oxidizing agent (KMnO₄) can be attributed to the oxidative hydrolysis mechanism. The oxidative hydrolysis constant (K _h) is highly dependent on the strength of the acid used. The HClO₄-doped POAN matrix has the ability to store about 128.878 kJ⋅g⁻¹ chromogenic energy (CE) at the wavelength 720 nm in a condensed lightweight form. MM+ calculations suggest that the potential energy (PE) in kJ⋅mol⁻¹ of the optimum molecular geometric (OMG) structure of the HClO₄-doped POAN matrix is at least two (2.052) times more stable than the OMG of the base form (POAN-EB) of the POAN matrix. Kinetic parameters of the oxidative hydrolysis reaction of the HA-doped POAN matrix were deduced from absorbance variations with time. The results of computer-oriented kinetic analysis indicate that the rate-controlling step for HA-doped POAN oxidative hydrolysis is governed by the Ginstling-Bronshein equation that represents three-dimensional diffusion (D4). Activation parameters for the oxidative hydrolysis of the HClO₄-doped POAN matrix were computed and discussed.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

Chemiluminescence determination of <Emphasis Type="Italic">o</Emphasis>-chlorobenzylidenemalonic acid dinitrile in extracts

A chemiluminescence method was developed for determining o-chlorobenzylidenemalonic acid dinitrile (o-CBMA DN) in extracts. The method is based on chemiluminescence developed in a strong alkaline solution upon the interaction between 3-aminophthalic hydrazide (luminol) with the superoxide radical formed in the reaction of atmospheric oxygen activated by hemin with the products of the alkaline hydrolysis of o-chlorobenzylidenemalonic acid dinitrile and with the products of their condensation with p-nitrobenzaldehyde. The luminescence intensity of luminol was proportional to the concentration of o-CBMA DN in the range 1 × 10⁻⁶−1 × 10⁻¹ mg/mL. The determination limit for o-CBMA DN was (1 ± 0.3) × 10⁻⁶ mg/mL (p = 95%, n = 5, RSD = 29%) at 293 K.     

Oxidation of α-methylstyrene on an MCM-22 encapsulated (<Emphasis Type="Italic">R,R</Emphasis>)-(−)-<Emphasis Type="Italic">N,N′</Emphasis>-bis(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) catalyst

(R, R)-(−)-N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) was encapsulated into MCM-22 using the zeolite synthesis method. The encapsulated catalyst proved to be active in the oxidation of α-methylstyrene with NaOCl with higher specific activity than the homogeneous catalyst. At the same time, this encapsulated catalyst was completely inactive in the hydrolytic kinetic resolution of racemic styrene oxide. This observation is in a good correlation with the assumption of the cooperative bimetallic mechanism proposed by Annis and Jacobsen.     

<Emphasis Type="Italic">o</Emphasis>-Semiquinone metal complexes as derivatives of sterically hindered di-<Emphasis Type="Italic">o</Emphasis>-quinone

ESR spectroscopy was used to study a series of mono- and binuclear o-semiquinone metal complexes, viz., derivatives of sterically hindered di-o-quinone 1,2-bis(2,5-di-tert-butylcyclohexadiene-1,5-dion-3,4-yl)ethane (1). Hindered rotation was found in the o-semiquinone moiety of the generated complexes. Magnetochemical measurements for polymeric bis(o-semiquinolate)copper(II) based on di-o-quinone 1 showed two antiferromagnetic channels of interaction between the paramagnetic centers. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1580–1584, July, 2005.     

Mechanism of OH radical-induced oxidation of <Emphasis Type="Italic">p</Emphasis>-cresol to <Emphasis Type="Italic">p</Emphasis>-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H₃O⁺ concentration yielding a bimolecular rate coefficient of 1.8 × 10⁸ mol^–1 dm³ s^–1. In the alkaline range a linear dependence was found on the OH^– concentration with rate coefficient of 4.9 × 10¹⁰ mol^–1 dm³ s^–1. These findings were interpreted in terms of acid-base catalysis of the H₂O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH₃C₆H₄OH^+. was not observed as intermediate.     

Conductivity Studies of <Emphasis Type="Italic">n</Emphasis>-Tetrabutylammonium Tetraphenylborate in 3-Pentanone in the Temperature Range from 283.15 to 329.15 K

The molar conductivities (Λ) of solutions of n-tetrabutylammonium tetraphenylborate (NBu₄BPh₄) in 3-pentanone have been measured in the temperature range from 283.15 to 329.15 K. The conductance data have been analyzed using the Lee-Wheaton conductivity equation with the distance parameter (a) set at Bjerrum’s pairing distance, and the limiting molar conductivities (Λ_o) and the association equilibrium constants (K _A) have been derived. The limiting ion conductivities (λ_±^o) have been evaluated according to the method of Krumgalz. The λ₊ ^o values have been compared with λ₊ ^o values calculated from the empirical equation of Gill. The thermodynamic functions, Gibbs energy (Δ G _A ^o), enthalpy (Δ H _A ^o) and entropy (Δ S _A ^o) for the process of ion-pair formation as well as the activation energy of the ionic movement (ΔH ^∗) have been evaluated. The obtained results are discussed in terms of ion-ion and ion-solvent interactions.