GORDANA S. USCUMLIC and VERA
V. KRSTIC
(Received 11 December 1995, revised
10 April 1996)
The kinetic data for
the reactions of 2-(4-phenylsubstituted)-cyclohex-1-enylcarboxylic acids with diazodiphenylmethane in ten alcohols were correlated using
the extended Hammett equation. The aim of this work was to detect the presence
or absence of steric effects as well as the
composition of the electronic effect. The solvent effect was interpreted in
terms of the reaction parameters a and Pr. The results obtined
for 2-(4-phenylsubstituted)-cyclohex-1-enylcarboxylic acids were compared with
the results for cis-4-substituted cinnamic
acids under the same experimental conditions.
Key words:a-unsaturated
carboxylic acids, diazodiphenylmethane, double bond,
transmission of the substituent effects, solvent
effects.
STANIMIR KONSTANTINOVIC a,
SVETLANA SIMOVA b, ZORAN RATKOVIC a, JASMINA PREDOJEVICa,
ANA RUFINSKA c, and SLOBODAN MILOSAVLJEVIC d
(Received
10 January, revised 5 March 1996)
(1-Hydroxyalkyl)- and
(1-hydroxy-1-methylalkyl) ferrocenes (a-ferrocenyl carbinols) have been
synthesized and their high resolution 1H-NMR spectra studied as a
function of the stereochemistry of the substitutent
connected to the cyclopentadienyl ring. It was found
that when a-ferrocenyl carbinol
contains a chiral center in the substituent,
the 2,5- and 3,4-positions in the cyclopentadienyl
ring become pairwise diastereotopic
and magnetically unequivalent.
Key words: (1-hydroxyalyl)- and
(1-hydroxy-1-methylalkyl)-ferocenes (synthesis), 1H-NMR
spectra
NEBOJSA CVETKOVIC, MIROSLAVA NESIC and DESANKA
NJEGOVAN
(Received
31 July 1995, revised 15 March 1996)
This paper presents the
results of a swelling study of an anionic polymer i.e. crosslinked
polyacrylic acid in water and media simulating
biological fluids such as artificial gastric juice (AGJ) and artificial
intestinal juice (AIJ). It was shown that the kinetics of swelling could be
presented, not only by the kinetic equation for the normalized degree of
swelling (q) but also by the degree of swelling (a). The mechanism of polyacrylic acid swelling in water is Fickian
diffusion, while in artificial media simulating biological fluids it is non-Fickian diffusion.
Key words: crosslinked polyacrylic acid, swelling, artificial biological fluids,
degree of swelling, normalized degree of swelling, kinetics of swelling,
mechanism of swelling, Fickian diffusion, non-Fickian diffusion.
GUSTAVO PONTICELLI a,
ZORAN D. MATOVIC b, VESNA D. MILETIC b, INESSA A.
EFIMENKO c,
ANNA P. KURBAKOVA c and DUSAN J. RADANOVIC b
(Received
29 March 1995, revised 15 March 1996)
The interactions
between PtCl4 with purine or pyrimidine and imidazole
derivatives (guanine, 2-aminopyrimidine, 4(6)-hydroxypyrimidine,
N-alkylimidazole) were investigated. These
interactions produced complexes of the general formula [PtCl3L1L2]2where
L1 = guanine, 2-aminopyrimidine, 4(6)-hydroxypyrimidine;
L2 = N-methylimidazole, N-ethylimidazole and N-propylimidazole.
The compounds were characterised by IR, Raman and
X-ray Photoelectron (XPS) spectroscopy. On the basis of the XPS spectroscopy it
was shown that the complexes hold equal amounts of PtIIand PtIVmetal.
Studying the IR and Raman spectra some [PtCl3L1L2]2
complexes could be assigned as the mixture of [PtIICl2L1L2]and [PtIVCl4L1L2]
species. On the other hand, the vibrational spectra
of the remaining compounds are indicative for mixed-valence binuclear [PtIIL1L2Cl2PtIVL1L2Cl2]Cl2complexes. Purine
and pyrimidine and imidazole
bases act as monodentate ligands
coordinated via atom N(7) of purine
and N(3) of pyrimidine and imidazole.
Key words: platinum(IV)
complexes, purine derivatives, pyrimidine
derivatives, imidazole derivatives, complex structures
ISMET M. HODZIC and SVETOZAR
R. NIKETIC
(Received 7 August 1995)
Tris(2,4-pentanedionato)cobalt(III) was
resolved into enantiomers by column chromatography
on a chiral stationary phase (CSP) consisting of (+)589-cis[Co(S-Arg)2 (NO2)2] NO3.H2O.
The elution order, determined from the ORD spectra, was found to be consistent
with the one predicted from the calculated energies of the transient complexes
CSP... [M(acac)3]
based on chiral discrimination. Racemization
in benzene-acetone was followed, and the rate constant and activation
parameters were discussed in comparison to the literature values for chlorobenzene and chloroform solutions.
Key words: recemization,
solvent effect, acetylacetonato complexes, cobalt(III) complexes, kinetics
ZIVADIN D. BUGARCIC 1, BILJANA M. MOJSILOVIC 1 and
VUKADIN M. LEOVAC 2
(Received 18 July 1995, revised 12
January 1996)
The reaction between
potassium trichloro(dimethyl sulphoxide)platinate(II) and dimethyl sulphoxide was studied in D2O by 1H
NMR spectroscopy. The second-order rate constant at 22oC for the
substitution of the chloro ligand
which is in trans-position to the already coordinated Me2SO
in [PtCl3(Me2SO)]-,
by Me2SO-d6 is 5.16?0.24 M-1s-1.
The first product of the reacton is trans-[PtCl2(Me2SO)2], which is
thermodynamically unstable and transforms to the thermodynamically more stable cis-[PtCl2(Me2SO)2]
isomer.
Key words: dimethyl sulphoxide, trichloro(dimethyl sulphoxide)platinate(II), reaction kinetics
(Received 10 November 1995, revised 5
April 1996)
The densities of three
binary liquid mixtures were measured at 20, 25, 30, and 35oC. The
mixtures investigated in this study include 2-propanol+2-butanol;
chloroform+2-butanol, and chloroform+2-propanol. The new experimental data for
the density have been correlated by empirical relations given in the
literature.
Key words: density, liquid mixture, correlation, alcohol.
MIHAJLO B. TOSIC and NIKOLA
S. BLAGOJEVIC*
(Received
12 July 1995, revised 17 April 1996)
The level of internal
stresses significantly affects the values of the diffusion coefficients of
glass. Therefore, it is necessary that the heating and cooling rates must be
relatively small in experiments with diffusion pairs. Consequently, the heating
times from room temperature to experiment temperature and, especially, the
cooling times from experiment to room temprature are
relatively long. As diffusion also occurs during this time, it is shown that
due to these reasons, the effective time of diffusion should be used when
calculating the diffusion coefficient according to the model of effective
coefficients. It is also shown that the choice of assumed energy activation of
in the range of 100-200 kJ/mol for the diffusion of K+ ions in
potassium borosilicate glass pairs, in the calculation of effective time,
introduces an error of up to 4.5% in the effective diffusion coefficients. In
order to decrease the influence of heating and cooling time, experiments should
be organized with the longest possible time at the experiment temperature.
Key words: glass, diffusion coeficients,
time effects.
R. CURCIC, V. JOKANOVIC and
P. ZIVANOVIC*
(Received
13 Septembar 1995, revised 1 March 1996)
The synthsis
of nanocomposite copper-molybdenum (7 wt %) powder by
mechanical allloying of the elemental powders was
performed in a conventional horizontal ball mill for a milling time up to 100
h. A steady state, characterized by the formation of equiaxial
particles of uniform size and constant hardness, was achieved after 32 h of
milling. By scanning electron miscrocopy (SEM) and
energy dispersive X-ray spectrometry (EDS), a uniform dispersion of both
components was detected after 100 h milling, while X-ray diffraction revealed
the presence of a very fine nanocrystal
microstructure of copper in the composite particles. As a result of the fine
distribution of molybdenum in the copper, the alloy hardness was 4.5 times
higher than that of the initial copper.
Key words: conventional horizontal ball mill, mechanical
alloying, nanocomposite powder, dispersion hardening
alloys
R. P. MIHAJLOVIC,* Lj. N. JAKSIC** and R. M. DZUDOVIC*
(Received
28 December 1995, revised 12 April 1996)
The application of the
electrode couples (H2/Pd)
Key words: propylene carbonate, hydrogen-palladium
electrode, deuterium-palladium electrode, potentiometric
titration.
ZORAN JANJUSEVIC1,
ZVONKO GULISIJA1, SLOBODAN RADOSAVLJEVIC1, KATA KOVACEVIC2
and ZORAN KARASTOJKOVIC3
(Received
26 May 1995, revised 3 April 1996)
The testings
involved in this paper were part of a comprehensive research project conducted
to find out what complex processes were taking place at metal mould contact
surface. These investigations are of particular importance for metal castings
from relatively high melting temperature, as that of steel (approx. 1600oC).
Steel castings, in regard to their high manufactured temperature and other
specifications in pouring, need a mould mixture of good quality. The used mould
mixture, for casting steel class DIN 50Mn7, was based on the silica sand, and
with water-glass as a binder and AlK(SO4)2
as an active component. This active component is, at pouring temperature of
liquid steel, decomposed in the mould by thermal influence during pouring,
crystallization and cooling the casting. In decomposition process of active
component the gaseous products appear and the water-steam is generated from a chemically bonded water. These processes are influencing
the molten metal oxidation. The penetrated molten metal into the mould surface
is oxidized, too. At the high melting temperature and in the presence of
gaseous products, the silicates were formed in the contact zone between metal
and sand mould mixture. The objective of these tests was to find out to what
extent the composition of the moulding mixture
affects the formation process, shape, type and composition of the silicates.
Key words: steel, casting,
moulds.