JSCS Vol 68, No. 3
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Impresum |
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J.Serb.Chem.Soc.
68(3)147–162(2003) |
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Rheokinetic study of crosslinking
of a,w-dihydroxy oligo(alkylene maleate)s with a trisisocyanate
BRANKO DUNJIC,
JASNA DJONLAGIC, SLAVKO VUKASINOVIC, MAURICE SEPULCHRE*, MARIE-ODILE SEPULCHRE*
and NICOLAS SPASSKY*
Faculty of Technology and Metallurgy, Karnegijeva 4, YU-11000
Belgrade, Serbia and Montenegro and
*Laboratoire de Chimie Macromoléculaire, Université Pierre et Marie Curie, 4,
Place Jussieu, 75005 Paris, France
(Received 19 June,
revised 4 December 2002)
The crosslinking reaction of three series of a,w-dihydroxy
oligo(alkylene maleate)s with a trifunctional isocyanate was followed by dynamic
mechanical analysis and FTIR spectroscopy. The evaluation of rheological
parameters, such as storage G’ and loss modulus G", was
recorded. A typical G’ versus time curve has a characteristic “S” shape,
indicating autoacceleration of the crosslinking reaction. The whole curing
process starting from G’ equal G" or the beginning of
gelation is described by a second - order phenomenological rheokinetic equation
which takes into account the autoacceleration effect, the latter being a
consequence of the superposition of both the chemical reaction and phase
segregation. It appears that the crosslinking reaction rate depends on the
concentration of the functional groups, i.e., on the molecular weight of
the polyester prepolymer and on the length of the aliphatic sequence in the
repeating unit or the segmental mobility. The crosslinking rate decreases in
the order: poly(octamethylene maleate) > poly(hexamethylene maleate) >
poly(butylene maleate).
Keywords: hydroxyl terminated polymaleates,
polyurethane, rheokinetic analysis.
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J.Serb.Chem.Soc.
68 (3)163–170(2003) |
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Retention behaviour of some
estradiol derivatives on alumina in normal phase chromatography
MARIJANA
M. ACANSKI
Department of General and Inorganic Chemistry, Faculty of
Technology, University of Novi Sad, Bulevar Cara Lazara 1, YU-21000 Novi Sad,
Serbia and Montenegro (e-mail: marijana@tehnol.ns.ac.yu)
(Received 24 September, revised
8 November 2002)
The retention constants of variously substituted
estradiol derivatives were measured as a function of the composition of various
binary mobile phases in order to study the relationship between chemical
structure and retention behaviour in TLC on alumina. The slopes and intercepts
of the linear relationships between the retention constant RM and the logarithm of the volume fraction of the polar mobile
phase component were calculated and are discussed in relation to the
characteristics of the solute and mobile phase. The RFvalues and relative retention DRM of the compounds depend largely on the retention behaviour of
their substituents. The results obtained in this investigation are compared
with the results of the same derivatives obtained in previous investigations on
silica gel.
Keywords: thin layer chromatography, alumina,
non-aqueous binary mobile phases, estradiol derivatives, Soczewinski equation.
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J.Serb.Chem.Soc.
68(3)171–182(2003) |
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Sulfur retention by ash during coal
combustion. Part II. A model of the process
VASILIJE
MANOVIC, BORISLAV GRUBOR*, MLADEN ILIC* and BRANIMIR JOVANCICEVIC**,***
Mining and Geology Faculty, University of Belgrade, Djusina
7, 11000 Belgrade,
*Institute for Nuclear Sciences - Vinca, P. O. Box 522, 11001
Belgrade (e-mail: grub@rt270.vin.bg.ac.yu),
**Faculty of Chemistry, University of Belgrade, P. O. Box 158,
11001 Belgrade and
***ICTM - Center of Chemistry, P. O. Box 473, 11001 Belgrade,
Serbia and Montenegro
(Received 29 August,
revised 18 November 2002)
An overall model for sulfur self-retention in
ash during coal particle combustion is developed in this paper. It is assumed
that sulfur retention during char combustion occurs due to the reaction between
SO2 and CaO in the form of uniformly distributed
non-porous grains. Parametric analysis shows that the process of sulfur
self-retention is limited by solid difussion through the non-porous product
layer formed on the CaO grains and that the most important coal characteristics
which influence sulfur self-retention are coal rank, content of sulfur forms,
molar Ca/S ratio and particle radius. A comparison with the experimentally
obtained values in a FB reactor showed that the model can adequately predict
the kinetics of the process, the levels of the obtained values of the SSR
efficiencies, as well as the influence of temperature and coal particle size.
Keywords: coal combustion, sulfur retention
by ash, modelling.
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J.Serb.Shem.Soc.
68(3)183–190(2003) |
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SHORT COMMUNICATION
Separation
of Y(dcta)– complexes from Nd(dcta)– and Sm(dcta)– complexes on polyacrylate
anion-exchangers
HALINA HUBICKA*
and DOROTA KOLODYNSKA
Department of Inorganic Chemistry, Faculty of Chemistry, Maria
Curie-Sklodowska University, Maria Curie-Sklodowska Sq. 3, 20-031 Lublin,
Poland
(Received 20 September, revised
4 December 2002)
The formation of anion rare earth element
complexes with aminopolycarboxylic acids gives new possibilities for the
separation of these elements on anion-exchangers. The higher affinity of the
Nd(dcta)- and Sm(dcta)- complexes for the
anion-exchangers compared to Y(dcta)- complexes indicates the
possibility of yttrium purification as a macrocomponent from the former by
frontal analysis. The weakly basic polyacrylate gel anion-exchanger Amberlite
IRA 68 was more effective in the purification of Y(III) from Nd(III) and
Sm(III) complexes with DCTA than the strongly basic anion-exchangers of this
type.
Keywords: rare earth elements, polyacrylate
anion-exchangers, DCTA.
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J.Serb.Chem.Soc.
68(3)191–205(2003) |
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Electrochemical oxidation of carbon
monoxide: from platinum single crystals to low temperature fuel catalysts.
Part II: Electrooxidation of H2, CO and H2/CO
mixtures on well characterized PtMo alloy
BRANIMIR N.
GRGUR, NENAD M. MARKOVIC* and PHILIP N. ROSS JR.*
Faculty of Technology and Metallurgy, University of Belgrade,
Karnegijeva 4, 11001 Belgrade, Serbia and Montenegro and
*Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS
2-100, Berkeley, CA 94720, USA
(Received 5 November
2002)
The oxidation of hydrogen and hydrogen–carbon
monoxide mixture has been investigated on well-characterized metallurgically
prepared platinum–molybdenum (PtMo) alloys. It was concluded that the optimum
surface concentration of molybdenum is near 23 mol.%. Based on experimentally
determined parameters and simulations, the mechanism of the oxidation of CO/H2 mixtures is discussed.
Keywords: fuel cell, anode, platinum,
molybdenum, hydrogen, carbon monoxide.
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J.Serb.Chem.Soc.
68(3)207–218(2003) |
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Kinetics of the zinc anodic
dissolution reaction in near neutral EDTA solutions
SLAVKA
STANKOVIC, BRANIMIR GRGUR, NEDELJKO KRSTAJIC and MILAN VOJNOVIC
Faculty of Technology and Metallurgy, University of Belgrade,
Karnegijeva 4, 11000 Belgrade, Serbia and Montenegro
(Received 8 October,
revised 11 November 2002)
Polarization curves of the anodic dissolution
reaction of zinc were determined in EDTA solutions of different total molar
concentrations (0.05, 0.10, 0.15 and 0.20 mol dm-3), the pH values of which were systematically varied (pH 3.0 –
10.0). The Tafel slopes of the anodic polarization curves are close to 40 mV
dec-1 at lower current densities (10-5 – 5x10-4 A cm-2), while at higher
current densities (5x10-4 – 10-2 A cm-2) the slopes are in the range of 60 – 120 mV dec-1. The order of the anodic reaction determined from the anodic
polarization curves at lower current densities are: z+ (H+) ~ –1/2 for pH < 8 and z+(H+) ~ 1 for pH > 8, while z+(H4Y) ~ 1 for all pH values of the examined EDTA
solutions. On the basis of these results, two mechanisms of the zinc anodic
dissolution reaction are proposed: at pH < 8 and at pH > 8. In both cases
the relevant EDTA species directly participate as reactants in the anodic
reaction. The dependences of the corrosion potential on pH and on total molar
EDTA concentration indicate that the relevant EDTA species take part as
reactants in both the cathodic (hydrogen evolution) and anodic (zinc
dissolution) reactions of the zinc corrosion process.
Keywords: zinc, EDTA, anodic dissolution,
kinetics, mechanisms.
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J.Serb.Chem.Soc.
68(3)219–226(2003) |
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Kinetic determination of ultramicro
amounts of Cu(II) ion in solution
Z. M. GRAHOVAC,
S. S. MITIC and E. T. PECEV
Faculty of Natural Sciences and Mathematics, Department of
Chemistry, University of Nis, Visegradska 33, 18000 Nis, Serbia and Montenegro
(Received 19 September,
revised 26 November 2002)
A new kinetic method is described for the
determination of ultramicro amounts of Cu(II) based on its catalytic effect on
the oxidation of trisodium-2-hydroxy-1-(4-sulphonato-1-naphthylazo)naphthalene-6,8-disulphonato
(red artificial color PONCEAU 4R) by hydrogen peroxide in borate buffer (B.B.)
The detection limit given by Perez-Bendito is 0.8 ng/cm3, but the detection limit that we experimentaly determined is 3.8
ng/cm3. The relative error ranges between 7.77 and
2.09 % for the concentration interval 3.8 to 50.1 ng/cm3. Kinetic equations are proposed for the investigated process. The
effects of certain foreign ions upon the reaction rate were determined for an
assessment of the selectivity of the method. The method was applied for the
determination of Cu(II) ions in samples of alloy.
Keywords: kinetic method, copper(II)
determination, PONCEAU 4R, samples of alloy.
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J.Serb.Chem.Soc.
68(3)227–234(2003) |
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Oil pollutants in alluvial
sediments – influence of the intensity of contact with ground waters on the
effect of microorganisms
T. SOLEVIC, B.
JOVANCICEVIC, M. VRVIC and H. WEHNER*
Faculty of Chemistry, University of Belgrade, P. O. Box 158, 11001
Belgrade and ICTM, Chemistry Centre, P. O. Box 815, 11001 Belgrade, Serbia and
Montenegro and
*Federal Institute for Geosciences and Natural Resources, P. O. Box 510153,
Hannover, Germany
(Received 4 October,
revised 3 November 2002)
The influence of the intensity of interaction
between oil pollutants and ground waters in alluvial sediments on the effect of
microbial activity was investigated in this work. The study was based on a
comparison of detailed analyses of two fractions of an oil pollutant
originating from a Danube alluvial formation near the Pancevo Oil Refinery:
fraction 1, separated from the aqueous layer by decantation, presumed to have
been in less intensive interaction with water, and fraction 2, isolated from
the aqueous emulsion by extraction with chloroform, presumed to have been in
stronger interaction with water. Both fractions were shown to originate from
the same type of oil pollutant. Nevertheless, significant compositional
differences between the two fractions were observed. A significantly pronounced
domination of even carbon number homologues of C18–C24 n-alkanes in fraction 2, atypical for
crude oil pollutants, compared to the corresponding distribution observed in
fraction 1, suggested a more intense activity, i.e., a much better
effect of microorganisms in direct contact with the oil pollutant within the
aqueous environment. The identification of even carbon number C14–C18 n-alcohols and C14–C18 fatty acids, as well as cholesterol, in
fraction 2, suggested that microorganisms of the algal type in
non-photosynthetic conditions were most probably responsible for the mentioned
microbial processes.
Keywords: oil pollutants, alluvial ground
waters, microbial activity, n-alkanes, n-alcohols, cholesterol, fatty acids.
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J.Serb.Chem.Soc.
68(3)235–237(2003) |
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N O T E
A
stilbene from the heartwood of Maclura pomifera
NINA DJAPIC,
ZOLTAN DJARMATI*, SNEZANA FILIP* and RATKO M. JANKOV**
Tehnical Faculty “Mihajlo Pupin”, University of Novi Sad, Djure
Djakovica b. b., 23000 Zrenjanin,
*Bio-Ecological Centre, Petra Drapsina 15, 23000 Zrenjanin and
**Chemical Faculty, University of Belgrade, Studentski trg 16,
11000 Belgrade, Serbia and Montenegro
(Received 1 July,
revised 3 December 2002)
Dried heartwood powder of Maclura pomifera,
Moraceae, was extracted with acetone. Silica gel column chromatography (CC) of
the crude extract yielded 2',3',4',5'-tetrahydroxystilbene (oxyresveratrol).
Keywords: Maclura pomifera, Moraceae,
heartwood, oxyresveratrol.
Copyright & copy; SHD 2002.
March
26, 2003.
For
more information contact: SHD@tmf.bg.ac.yu