Open Access Published by De Gruyter Open Access

Volume 1 Issue 4

December 2003

Issue of Open Chemistry

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Journal Overview

Open Access December 1, 2003

Combined polymerization catalysis of nickel complex and zirconocene for branched polyethylene

Yong Cui, Changxing Shao, Wen-Hua Sun

Page range: 325-338

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Abstract

The polymerization behavior of 2-(2′-pyridyl) quinoxaline nickel dibromide/Cp2ZrCl2/MAO system was investigated in three ways: the Ni catalyst was added first, followed by addition of Zr catalyst (method I); the Ni and Zr catalysts were added simultaneously (method II); and the Zr catalyst was added first, followed by addition of Ni catalyst (method III). Results of GC-MS, GPC,13C NMR and DSC investigations indicated that the properties of resulting polyethylene were greatly varied by changing feeding orders of the two catalysts. Decreasing Ni/Zr molar ratio or increasing polymerization temperature gave corresponding polyethylenes with less branches and higher melting point. Compared to the procedure using Cp2ZrCl2 catalyst only, the activity of Zr catalyst in those combined system decreased because of the competition of ethylene between the [Ni−C] and [Zr−C] active centers. In addition, other zirconocenes were also employed as copolymerization catalysts in the combined system with nickel complex. compared to Cp2ZrCl2 case, the ethyl-bridged Zr catalyst performed better for polymerization of ethylene while the Si-bridged Zr catalyst showed better copolymerization ability.

Open Access December 1, 2003

Sonolysis of chlorobenzene in the presence of transition metal salts

Carmen Stavarache, Rokura Nishimura, Yasuaki Maeda, Mircea Vinatoru

Page range: 339-355

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Abstract

Sonolysis of aqueous solution of chlorobenzene at 200 kHz frequency in the presence of transition metals chlorides was investigated. Through analyzing the nature and distribution of the products detected in the reaction mixture, a new mechanism of sonodegradation is advanced. Depending on the metals used and their behavior during sonolysis, we were able to discriminate between inside and outside cavitation bubble mechanisms. Iron and cobalt chlorides, which could undergo redox reactions in the presence of HO radicals generated ultrasonically, give higher amounts of phenolic compounds compared with palladium chloride that undergoes a reduction to metal. Palladium reduction takes place in bulk solution and therefore all organic reactions that compete for hydrogen must occur also in bulk solution. Accordingly, palladium can be a useful tool in determining the reaction site and the decomposition mechanism of organic compounds under ultrasonic irradiation.

Open Access December 1, 2003

IR-spectral study of photoinduced tautomerization in 1,3-diphenyl-pyrazol-5-one

Bojidarka Ivanova, Atanas Tchapkanov, Michail Arnaudov, Ivan Petkov

Page range: 356-365

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Abstract

The UV-photoinduced prototropic isomerization of 1,3-diphenyl pyrazol-5-one (DPhP) embedded in polyvinyl chloride (PVC) film is studied by means of difference in IR spectral analysis. The initially existing CH-form in non-irradiated compound is transformed to NH-form, and a hydrochloride salt is stabilized because of the photodegradation of the PVC. An additional comparative IR spectral study of DPhP in different solutions as well as of its hydrochloride salts in solid state is also carried out.

Open Access December 1, 2003

Composition of extraction products from alkylated high-sulphur coals

Mieczysław Kozłowski, Helena Wachowska, Jan Yperman

Page range: 366-386

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Abstract

Products of reductive and non-reductive methylation of two high-sulphur coals (Mequinenza and Illinois No. 6) have been extracted by dichloromethane. It has been established that the efficiency of the transformation of coal to the products soluble in CH2Cl2 is higher for coals subjected to non-reductive methylation by the Liotta method than for those after reduction in the potassium/liquid ammonia system. The extracts and the extraction residues were subjected to elemental analysis, IR spectroscopy, and AP-TPR (Atmospheric Pressure-Temperature Programmed Reduction) measurements. It has been shown that the main species undergoing extraction by CH2Cl2 are aliphatic compounds or aromatic structures of low degree of condensation. The effect of the extraction on the sulphur groups in coal has been discussed.

Open Access December 1, 2003

Thermal and kinetic characteristics in non-isothermal conditions of some aromatic copolyethers containing an octomethylenic spacer

Mihaela Prajinaru, Natalia Hurduc, Silvia Alazaroaie, Otilia Catanescu, Nicolae Hurduc

Page range: 387-401

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Abstract

The paper presents a study of the thermal properties of some aromatic polyethers obtained by phase trasfer catalysis technique. The polymes were synthesized starting from 1,8-dichloro-octane and various bisphenols: 4,4′-dihydroxyazobenzene, 4,4′-dihydroxydiphenyl, bisphenol A and 2,7-dihydroxynaphthalene. Molecular simulations were performed in order to obtain supplementary information concerning the chain conformation and inter-chain interactions. The presence of azobenzenic moieties induces high phase transition values, situated near the thermal stability limit. Therefore, the thermogravimetrical study of these polymers is very important for establishing the temperature limits for DSC and optical microscopy studies. All the polymers present a good thermal stability situated above the isotropization values. In these circumstances no special precautions are necessary for the characterization methods of the liquid crystalline behavior. The kinetic characteristics suggest a similar degradation mechanism by successive reactions. The inter-chain interactions do not influence the thermostability of the samples if the polar surface of the polymer is situated below a certain value.

Open Access December 1, 2003

Methods for the calculation of occupied volumes in glassy polymers: The lattice integration and the monte carlo methods

E. Rozhkov, B. Schukin, I. Ronova

Page range: 402-426

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Abstract

A new model for characterizing the free volume of a glassy polymer—gas systems is proposed. An improved method for the calculation of occupied volume per monomer unit was developed within the limits of this model. The model assumptions, error estimates and algorithm efficiencies are described. Using the example of polyvinyltrimethylsilane, it is shown that linear dependences of logarithms of the diffusion and the permeability coefficients on specific accessible volume for inert gases exist.

Open Access December 1, 2003

Thermally induced oxidative trimerization of benzimidazole by copper(II) chloride in the solid state

Rahul Bhattacharya, Sibdas Ray, Jayanta Ray, Ashutosh Ghosh

Page range: 427-440

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Abstract

Benzimidazolium trichlorocuprate(II) undergoes a redox reaction in the solid state at elevated temperature (∼240°C) to produce the cyclic trimer of benzimidazole and cuprous chloride. The trimer has been characterized by IR, NMR, and Mass spectroscopy. It has also been synthesized in lower yield by heating the mixtures of CuCl2 and benzimidazole in different ratios or heating other compounds of CuCl2 and benzimidazole. The absorption, emission, and excitation spectra of the trimer in two different solvents (TFA and DMSO) and a comparison of these results with those of benzimidazole are presented here.

Open Access December 1, 2003

New thallium(III) chloride complexes with pyridine carboxylic acids: from molecular compounds to supramolecular associations

Monica Toma, Agustín Sánchez, José Casas, José Sordo, María García-Tasende, Eduardo Castellano, Javier Ellena, Ioan Berdan

Page range: 441-464

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Abstract

Reactions of TlCl3 with picolinic acid (Hpic), nicotinic acid (Hnic), isonicotinic acid (Hinic) and 3-hydroxy-picolinic acid (H3hpic) afford the isolation of new chlorothallium(III) complexes. The compounds are characterized by IR, Raman and multinuclear NMR (1H,13C,205Tl). The molecular structures of [TlCl2(pic)(Hpic)]·0.5H2O (1), [TlCl2(nic)(Hnic)] (2), [TlCl(inic)2]·0.6C2H5OH (3) and [TlCl(3hpic)2(h3hpic)] (4) are determined by single-crystal X-ray diffraction. A distorted octahedral TlCl2N2O2 core containing the O,N-chelating ligands is achieved in the monomeric complex 1. The coordination polyhedron in compounds 2–4 is pentagonal bipyramidal, i.e. TlCl2NO4 in 2, and TlClN2O4 in 3 and 4, respectively. O,O′,N-Bridging ligands result in a polymer chain for 2 and a three-dimensional polymeric association in 3, while compound 4 is monomeric (O, N-and O,O-chelating ligands).

Open Access December 1, 2003

Hydrazyl, Nitronyl-, and imino-nitroxides: Synthesis, properties and reaction with nitric oxide and nitrogen dioxide

Titus Constantinescu, Petre Ionita, Ion Chiorescu, Gabriela Ionita

Page range: 465-476

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Abstract

Ten novel and stable free radicals of nitronyl-, imino-nitroxide and hydrazyl type compounds were synthesized and their physico-chemical properties investigated. UV-Vis and ESR spectroscopic data, as well as the lipophilicities and specific hydrophobic areas of the compounds are compiled. The reaction of these radical compounds with nitric oxide and nitrogen dioxide was also investigated. The radicals synthesized, show selectivity in their reaction with these nitric oxides, depending on their structure (nitronyl-nitroxide radicals react with NO, while hydrazyl radicals react with NO2). The processes are easily monitored by UV-Vis or ESR spectroscopy.

Open Access December 1, 2003

Synthesis and crystal structure of 1-ethyl-3-(phenyl)-1,2,3-triazolium percholorate

Beeranahally Doreswamy, Madegowda Mahendra, Sridhar Anandalwar, Javaregowda Prasad, Kempegowda Mantelingu, Basappa, Kanchugarakoppal Rangappa

Page range: 477-490

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Abstract

The isolation of stable carbenes of the Arduengo (1a) and Wanzlick (2a) type has prompted us to look for stable nitrenium ions of the related structural type 1-ethyl-3-(phenyl)-1,2,3-triazolium perchlorate (6+). The title compound C10H14Cl N3O4 was isolated and structure was investigated by X-ray crystallography. It crystallizes in the monoclinic space group P21/c with cell parameters a=6.697(4) Å, b=9.724(9) Å, c=19.844(2) Å and Z=4. The final residual factor is R1=0.0471 for 1545 reflections with I>2σ(I). The structure exhibits intermolecular hydrogen bonds.

Open Access December 1, 2003

Wittig and Wittig-Horner reactions under phase transfer catalysis conditions

Aurelia Pascariu, Gheorghe Ilia, Alina Bora, Alina Bora, Smaranda Iliescu, Adriana Popa, Gheorghe Dehelean, Liliana Pacureanu

Page range: 491-534

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Abstract

Wittig and Wittig-Horner reactions are favorite tools in preparative organic chemistry. These olefination methods enjoy widespread and recognition because of their simplicity, convenience, and effciency. Phase transfer catalysis (PTC) is a very important method in synthetic organic chemistry having many advantages over conventional, homogenous reaction procedures. In this paper, we attempt to summarize the aspects concerning Wittig and Wittig-Horner reactions that take place under phase transfer catalysis conditions.

About this journal

Open Chemistry is a peer-reviewed open access journal that publishes original research, reviews, and communications in the fields of chemistry in an ongoing way. Our central goal is to provide a hub for researchers working across all subjects to present their discoveries, and to be a forum for the discussion of the important issues in the field.

Aims and Scope

Open Chemistry aims to publish high quality research in the following areas:

Biological Chemistry/Biochemistry including bioanalytical chemistry, biochemistry and biological chemistry, biophysics and chemical physics in biology

Analytical Chemistry including electrochemistry, environmental chemistry, spectroscopy
Physical Chemistry including catalysis, chemical kinetics and reactivity, chemical physics, computational chemistry, chemometrics and QSAR, hydrogen technologies, hydrogen storage, nanochemistry, photochemistry, physical chemistry and physical organic chemistry, radiochemistry and nuclear chemistry, supramolecular chemistry, surface chemistry and colloids, theoretical chemistry, thermodynamics
Inorganic Chemistry including coordination chemistry, crystallography, materials and solid- state chemistry
Organic Chemistry including macromolecules and polymers, natural product chemistry, organic chemistry, organometallic chemistry, phytochemistry
Interference with other sciences including clinical chemistry, marine chemistry, medicinal chemistry, pharmaceutical chemistry

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