African
Journals Online
South African Journal of Chemistry
Volume 55, 2002
Abstracts
The Free-Radical Copolymerization of Difurylmethane with
Maleic Anhydride
Ddamba, W.A.A.Ngila, J.C.Mokoena, T.T.Motlhagodi, K.
Abstract: The copolymerization of difurylmethane with
maleic anhydride in the presence of azobisisobutyronitrile as an
initiator has been investigated at 65 ºC, 72 ºC and 85 ºC in
different solvents. Reaction feeds containing 85 mol % and higher
of difurylmethane yielded a soluble alternating copolymer in
which the furan residue entrained in the polymer chain formed 2,5
linkages and had 3,4 unsaturation. The 1:1 difurylmethane- maleic
anhydride adduct was readily prepared, and at the above
temperatures and in the presence of the radical initiator
partially underwent retro-Diels-Alder reaction. Copolymerization
of the difurylmethane and maleic anhydride thus formed yielded
the unsaturated alternating copolymer. Copolymers prepared from
reaction feeds with proportions of difurylmethane lower than 85
mol % had higher cross-link density and exhibited higher
thermodecomposition temperatures.
1-Alkyl-1,4-dihydro-4-iminoquinoline-3-carboxylic Acids:
Synthesis, Structure and Properties
Van Es, T.Staskun, B.
Abstract:
1-Alkyl-1,4-dihydro-4-iminoquinoline-3-carboxylates undergo
neutral hydrolysis (in H2O or H2O-EtOH
mixtures) to yield water-soluble 4-iminoquinoline-3-carboxylic
acids and the corresponding 4-oxo esters. Such 4-imino acids are
also accessed by treating an appropriate
1-alkyl-1,4-dihydro-4-oxoquinoline-3-carboxylic acid successively
with thionyl chloride and an amine-H2O mixture, or
from treatment of a 4-imino ester salt with aqueous amine. In the
latter procedures 7-fluoro substituted substrates gave rise to
7-alkylamino derivatives even at room temperature. The title
compounds are inferred to have an intramolecularly H-bonded
charge transfer structure, and some of their chemical reactions
and spectral (HRMS, 1H NMR) properties are described.
Cross-linking of LDPE/wax Blends in the Presence of Dicumyl
Peroxide
Krupa, I.Luyt, A.S.
Abstract: Thermal properties of cross-linked and
uncross-linked LDPE/wax blends were investigated. The blends were
prepared by thoroughly mixing the powdery ingredients, followed
by pressing at 180 ºC for ten minutes. The extent of
cross-linking was determined by means of gravimetric analysis of
the gel content of the samples. The thermal properties were
determined by differential scanning calorimetry (DSC). The
analyses of cross-link density of the samples indicated that
increased amounts of peroxide gives rise to more efficient
cross-linking, but only the PE phase in the blends is
cross-linked. The DSC results indicated that LDPE and wax are
probably miscible in the crystalline phase at low wax
concentrations, but at higher wax concentrations the wax is only
partially miscible in the crystalline phase.
On-line Determination of Hydrochloric Acid in Process
Effluent Streams by Potentiometric Sequential Injection Acid-Base
Titration
Van Staden, J.F.Mashamba, M.G.Stefan, R.I.
Abstract: An on-line potentiometric sequential
injection acid-base system for the titration of a hydrochloric
acid solution with a standard sodium hydroxide solution in
process effluent streams is proposed. A solution of 0.1 mol/l
sodium chloride is used as carrier. The sample is sandwiched
between two titrants in a holding coil, with the volume of the
first base being twice to that of the second one and channeled by
flow reversal through a reaction coil to the potentiometric
sensor. A linear relationship between peak width and logarithm of
the hydrochloric acid concentration was obtained in the range
0.025 mol/l - 0.05 mol/l of hydrochloric acid when a solution of
0.001 mol/l sodium hydroxide was used for the titration. Samples
from process effluent streams were used to evaluate the
feasibility of the method with that of an automated and manual
titration. The results showed good agreement between the
different methods. The percentage relative standard deviation
(RSD %) was found to be less than 0.22. The sample frequency is
30 samples per hour.
Palladium-Catalysed Dimerisation of Furfural
Taljaard, B.Burger, G.J.
Abstract: 5,5'-Diformyl-2,2'-difuran has been
synthesized in 60% yield by the palladium acetate-catalysed aryl
coupling of furfural in acetonitrile in the presence of dioxygen
under pressure. Various reaction conditions have been exploited,
and mechanistic aspects of the reaction are discussed.
Analytical Characterization of Volatile Active Principles
from the Leaves of the Alboroseum Backer Plant
Balaban, D.P.Andriamboavonjy, H.Magearu, V.
Abstract: The study presents for the first time the
data concerning the qualitative and quantitative determination of
the volatile active principles from the leaves of the Alboroseum
Backer plant (Crassulaceae). After the extraction of volatile
active principles in water, analytical separation and
quantitative determination using a GC/MS technique was performed.
The compounds detected, are belonging to the following classes:
aldehydes, ketones, aromatic hydrocarbons and alcohols.
Internal Standard Method for the Determination of Au and
some Platinum Group Metals Using Inductively Coupled Plasma
Optical Emission Spectrometry Mokgalaka, N.S.McCrindle,
R.I.Botha, B.M.Marjanovic, L.
Abstract: A method is described for the determination
of Au, Pt, Pd, Ru and Rh in a converter matte sample, using
inductively coupled plasma optical emission spectrometry
(ICP-OES), with Y or Sc as internal standard. The results
obtained by this method are discussed and compared with values
obtained by an independent laboratory. The efficiency of internal
standardization was evaluated by varying the operating conditions
of the ICP-OES. Changes in the amount of energy transferred from
the plasma to analyte, the amount of aerosol reaching the plasma
and analyte residence time, were studied in terms of their effect
on the emission intensity of the analyte and the internal
standard. It was found that changes in the emission signals of
the PGMs due to power variations could be effectively compensated
for, using either Sc, Y or Ar lines as internal standards. For
variations in aerosol gas flow rate, both Sc and Y could only
compensate for Pd and Au between flow rates of 0.60 and 0.80 l
min -1 and for Pt, Ru and Rh at 0.80 l min -1.
The effect of sodium on the determination of Au and the PGMs, and
the use of Sc and Y as internal standards, to compensate for Na
matrix effects on accuracy were also studied. It was found that
emission intensities of the analytes decreased with increasing Na
concentration. Furthermore, Sc as an internal standard could
compensate for Pt, Ru and Rh up to 5 g l-1 Na, while Y
could only compensate for the same elements up to 1 g l -1
Na.
Protection of the Amide Side-Chain of Asparagine with the
1-Tetralinyl Group in the Solid-Phase Peptide Synthesis of
Lysine-Vasopressin
Yusuf, A.O.Bhatt, B.M.Gitu, P.M.
Abstract: Lysine-vasopressin, a nonapeptide, was
synthesised on a benzhydryl-resin using solid-phase peptide
synthesis via the Boc-strategy. The benzyl group was used in the
protection of the side-chains of tyrosine and cysteine, while
1-tetralinyl, benzhydryl and benzyloxycarbonyl groups were used
in the protection of the side-chains of asparagine, glutamine and
lysine, respectively.
Thioanisole-1,2-ethanedithiol-trifluoroacetic
acid-trifluoromethanesulphonic acid (2:1:20:2 v/v) was used to
cleave the peptide-resin under different temperature conditions.
The cleavage at 40 ºC for two hours gave lysine-vasopressin in a
one-pot reaction; the yield after reversed-phase HPLC
purification was 62%.
Isolation and Crystal Structure of
3-Aryl-1-(2-hydroxyphenyl)-3-hydroxy-1- propanones Derived from
Claisen-Schmidt Condensation of 2- Hydroxyacetophenone with Benzaldehyde Derivatives
Mphahlele, M.J.Fernandes, M.A.
Abstract: 2-Hydroxyacetophenone reacted with
benzaldehyde derivatives under alkalinic conditions followed by
addition of dilute hydrochloric acid solution to afford mixtures
of the known 2-hydroxychalcone derivatives and the corresponding
previously undescribed
3-aryl-1-(2-hydroxyphenyl)-3-hydroxy-1-propanones. The isolation
of the b-hydroxyketone derivatives depends on the work-up
conditions. Their structures were established using a combination
of NMR, IR and mass spectroscopic techniques. The conformation of
the b-hydroxyketones was probed using 1 H NMR
spectroscopy and X-ray crystallography.
Formation and Structural Analysis of Novel Dibornyl Ethers
Kaye, P.T.Duggan, A.R.Matjila, J.M.Molema,
W.E.Ravindran, S.S.
Abstract: One- and two-dimensional NMR spectroscopy has
been used to establish the regio- and stereochemistry of novel
dibornyl ethers, obtained by acid-catalysed condensation of
camphor-derived a-hydroxybornanones.
The Efficient Synthesis of 2-Arylamino-2-imidazolines,
2-Heteroaryl-Substituted Benzimidazoles, and Their
Morpholin-4-ylmethyl Derivatives
Servi, S.
Abstract: 2-Heteroaryl-substituted 1H-benzimidazoles
were synthesized in good yields by heating the HSO3
adducts of heteroaromatic aldehydes with o-phenylenediamine
in DMF under reflux. This procedure is more general and shorter
than earlier methods. 2-Arylamino-2-imidazolines were prepared by
heating dimethyl aryldithioimidocarbonates and ethylenediamine
under reflux. The imine-enamine tautomerization of
2-arylamino-2-imidazolines was investigated by means of 1H-NMR
spectroscopy. Morpholin-4-ylmethyl derivatives of the
benzimidazole and imidazoline products were synthesized
regioselectively by treatment with morpholine and formaldehyde.
Mechanistic and Kinetic Aspects of the Direct
Electrochemical Oxidation of 4-t-Butyltoluene
Loyson, P.Gouws, S.Zeelie, B.
Abstract: The direct electrochemical oxidation of 4-t-butyltoluene
at graphite electrodes in methanol, using NaClO4 as
electrolyte, as been investigated in order to obtain an insight
into the mechanism and kinetics of the anodic reactions taking
place. It is shown that an increase in current density affects
the product distribution, leading to a better yield of the target
product 4-t-butylbenzaldehyde dimethyl acetal and a lower
percentage of unknowns at the expense of an increase in
electrical charge. It is suggested that oxidation takes place by
two mechanisms : a direct one involving oxidation of the
substrate at the electrode, and an indirect one where a pool of
solvent radicals assists in the oxidation process. Further
evidence is provided for reaction mechanisms in studies where the
substrate loading is varied, and also where the ratio of
substrate to solvent is varied ; when the concentration of the
substrate is high, there is evidence of the formation of dimers
and other unknowns. Under certain conditions, these anodic
reactions can be regarded as parallel consecutive second order
reactions. The role played by the solvent is confirmed by kinetic
data.
Novel Synthesis of 1,6,7,9-Tetrasubstituted
8-Oxo-1-azaspiro[4.4]nonanes
Gravestock, D.McKenzie, J.M.
Abstract: The synthesis and isolation of one
diastereomer of
1-benzyl-7,9-dimethyl-8-oxo-1-azaspiro[4.4]nonane-6-carbonitrile
11 was accomplished by the diiron nonacarbonyl-assisted
spirocyclization reaction of
2-(1-benzyl-2-pyrrolidinylidene)acetonitrile 10 and
2,4-dibromo-3-pentanone 12.NOESY NMR spectroscopy experiments of
11 showed it to be the (5R*, 6S*,
7S*, 9S*)-diastereomer.
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