South African Journal of Chemistry - Volume 65, Issue 1, 2012
Volumes & issues
Volume 65, Issue 1, 2012
Source: South African Journal of Chemistry 65, pp 125 –130 (2012)More Less
CdWO4 nanorods with wolframite structure were synthesized in the presence of the surfactant SDBS by a hydrothermal method, and characterized by a variety of techniques. The obtained products are CdWO4 nanorods with length of 0.8-2.5 µm and width of 50-250 nm. The surfactant SDBS plays a key role in the formation of the CdWO4 nanorods. The pH value impacts on crystallinity of the products. The PL properties of the CdWO4 nanorods prepared under different conditions were studied. The intensity of the PL emissions of the samples increases with crystallinity and aspect ratio of the CdWO4 nanorods.
SnO2/SiO2 nanocomposite catalyzed one-pot, four-component synthesis of 2-amino-3-cyanopyridines : research articleSource: South African Journal of Chemistry 65, pp 131 –137 (2012)More Less
An efficient and rapid protocol for the synthesis of 2-amino-3-cyanopyridines by the cyclocondensation reaction of aromatic aldehydes, methyl ketones, malononitrile and ammonium acetate catalyzed by SnO2/SiO2 nanocomposite material at refluxed condition in ethanol was investigated. Nanocomposite (SnO2/SiO2) catalytic material has been synthesized by using the sol-gel method. The prepared catalytic materials were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmer-Teller (BET) surface area, and temperature-programmed desorption of ammonia (NH3-TPD). Advantages of the present method include a simple work-up procedure, high yields of the products, low toxicity and easy recovery and reusability of the catalytic materials.
Dodecatungstocobaltate and Sn (IV)-substituted polyoxometalate : preparation, characterization and catalytic performances in solventless synthesis of bis(indolyl)methanes : research articleSource: South African Journal of Chemistry 65, pp 138 –144 (2012)More Less
Electrophilic substitution reaction of indole with various aldehydes and cyclohexanone were carried out in the presence of electron-transfer (K5CoW12O40.3H2O) and green Lewis acid ([(n-C4H9)4N]3 PMo2W9(Sn4+.H2O)O39) catalysts. These catalysts were characterized by N2-adsorption measurements, FT-IR, UV-Vis, 31P NMR, TGA, cyclic voltammetry and elemental analysis. Mechanisms for their catalytic activity are proposed. Both of these catalysts can be recovered and reused.
Utilization of ionic liquids for the separation of organic liquids from industrial effluents : research articleSource: South African Journal of Chemistry 65, pp 145 –149 (2012)More Less
The recovery of aromatic organic solvents from mixtures containing aliphatic compounds has economic as well as environmental significance. This is so because viable methods have not been established for the recovery from mixtures in which the components of value are 20 % (v/v) or less. In the light of this, we investigated the efficacy of selected ionic liquids to recover aromatic solvents from prepared mixtures. We used 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4] and 1-ethyl-3-methylpyridinium ethyl sulfate [EMpy][EtSO4] to separate and recover aromatic hydrocarbons (less than 10 % (v/v)) from aromatic/aliphatic hydrocarbon mixtures, namely, benzene, toluene, ethyl benzene and o-xylene (BTEX) from n-heptane at 40 °C. The same aromatic components were used with n-hexane as an alkane and 1-ethyl-3-methylpyridinium ethyl sulfate [EMpy][EtSO4] as an ionic liquid. The concentrations of the aromatic components used were in the range of 2.5-10 % (v/v) for the following multi-systems at 40 °C:
- Benzene + toluene + ethyl benzene + o-xylene + n-heptane + [EMIM][EtSO4].
- Benzene + toluene + ethyl benzene + o-xylene + n-hexane + [EMIM][EtSO4].
- Benzene + toluene + ethyl benzene + o-xylene + n-hexane + [EMpy][EtSO4].
Spectral and thermal characterization and antimicrobial effect of 3-(5-H/Me/Cl/NO2-1H-benzimidazol-2-yl)-benzene-1,2-diols and some transition metal complexes : research articleSource: South African Journal of Chemistry 65, pp 150 –158 (2012)More Less
3-(5-H/Me/Cl/NO2-1H-benzimidazol-2-yl)-benzene-1,2-diols (HLX; X=1-4) ligands and HL3 complexes with Fe(NO3)3, Cu(NO3)2, Co(NO3)2, Zn(NO3)2 have been synthesized and characterized. The structural representations of the compounds are proposed on the basis of elemental analysis, molar conductivity,TGA, mass, FT-IR, 1H- and 13C-NMR spectrometry. All of the complexes are 1:1 electrolyte and have 1:1 M:L ratio except that of Cu(II). All of the complexes present fluorescence, the Co(II) complex showing the highest fluorescence intensity and the highest emission wavelength in comparison to the other complexes. Antibacterial activities of the ligands and the complexes formed by the HL3 ligand were evaluated using the disk diffusion method against six bacteria and Candida albicans. HL1, HL2, HL3 and [Cu(HL3)(L3)(H2O)2](NO3)·H2O show considerable antimicrobial activity toward S. epidermidis and C. albicans.
Source: South African Journal of Chemistry 65, pp 159 –164 (2012)More Less
Pollution of the environment with heavy metals can be a serious problem. In South Africa, particularly, there are many sources of heavy metals, often due to smelter and mining activities. This has led to toxic metals in the environment that directly affect air, water and food. The presence of heavy metal residues in foodstuffs is potentially hazardous to humans and animals. Heavy metals accumulate in certain organs, particularly in the liver and kidney. The objective of this study was to determine the levels of V, Cr, Mn, Sr, Cd, Pb and U in bovine organs and tissues obtained from polluted areas of North West Province, South Africa. Bovine liver, kidney, muscle, fat and bone samples were freeze-dried, homogenized and mineralized using a microwave-assisted digestion system. The levels were quantified using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). A bovine muscle (NIST-RM8414) and bovine liver, reference material (NIST-RM1577b), were also analyzed and results agreed with certified values. The study revealed accumulation of Sr in bone, Cd, Pb and U in kidney and bone, Mn in liver and, V and Cr in kidney tissues of cattle.
Electrochemical oxidation of phenol using a flow-through micro-porous lead dioxide/lead cell : research articleSource: South African Journal of Chemistry 65, pp 165 –173 (2012)More Less
The electrochemical oxidation of phenol to benzoquinone followed by the reduction to hydroquinone and catechol was demonstrated by constructing a three-dimensional porous micro-flow cell from lead dioxide and lead. The electrodes were made by using the principles of curing and formation of lead oxide material that are common in the construction of the electrodes used in lead-acid batteries. This resulted in highly porous electrodes that can allow the reactant solution to flow through them in series, without the risk of having the products being oxidized again at the anode that usually occurs in a simple undivided cell. In this study, a 50mM solution of phenol in a 60% acetonitrile and water mixture was used that contained 2% sulphuric acid. The reactant solution would flow through the anode porous material oxidizing the phenol to benzoquinone. The benzoquinone in solution would then flow through the cathode porous material and reduce to catechol and hydroquinone. The study showed that almost all of the phenol could be converted in one continuous flow process in using a relatively low cost electrochemical micro-flow cell that can be easily scaled up to accommodate larger volumes and concentrations by using electrode manufacturing principles used in the lead-acid battery industry.
Source: South African Journal of Chemistry 65, pp 174 –177 (2012)More Less
The reaction between cis-[ReVO2I(PPh3)2] and H3duo (N-(2-hydroxybenzylidene)-5-amino-1,3-dimethyl uracil) led to the formation of the oxofree, imido compound, trans-[ReV(ddd)(Hduo)(PPh3)2]I (1) (H2ddd=5,6-diamino-1,3-dimethyluracil). An oxo complex, cis-[ReV(bcp)OCl2(PPh3)](2) [Hbcp = N-(2-hydroxybenzylidene)-benzothiazole] was isolated from the reaction of trans-[ReOVCl3(PPh3)2]with Hbcp. The crystal structures of the compounds were determined by single crystal X-ray diffraction.
Impact of metals on secondary metabolites production and plant morphology in vetiver grass (Chrysopogon zizanioides) : research articleSource: South African Journal of Chemistry 65, pp 178 –183 (2012)More Less
The impact of selected metals on the production of phenolic compounds was investigated in a pot trial experiment. One-month-old vetiver grass (Chrysopogon zizanioides) seedlings were exposed to different concentrations (0, 10, 50, 100, and 500 ppm) of As, Cr, Cu, Fe, Ni, Pb and Zn. All the plants except for those treated with As tolerated up to 500 ppm as they did not show any signs of stress such as wilting or necrosis. A significant decrease (>35 %) in the length of the plants treated with As, compared to the control, was observed at 50 ppm which further decreased with increasing As concentration. A serious case of phytotoxicity was observed at 500 ppm As as the plant could not survive. Total soluble phenolics content in vetiver plants increased with increasing concentration of metals in the growth medium. The amount of the cell wall-bound phenolics (2.01 to 5.84 mg GAE g-1 DW) was higher than the total soluble phenolics (1.13 to 2.14 mg GAE g-1 dry weight DW) and both increased with increasing metal concentrations. Morphological changes associated with metal-induced stress were also examined with a scanning electron microscope which revealed thickened cell walls, loss of cell shape, reduction of intercellular space and the closure of stomata in leaves of metal-exposed plants.
Ternary complexes of some divalent metal ions with potentially tridentate ligands in dioxane-water mixtures : research articleSource: South African Journal of Chemistry 65, pp 184 –190 (2012)More Less
Chemical speciation of mixed ligand complexes of Ca(II), Mg(II) and Zn(II) with L-histidine and L-glutamic acid have been studied in varying concentrations (0.0-60.0 % v/v) of 1, 4-dioxane-water mixtures maintaining an ionic strength of 0.16 mol L-1 sodium chloride at 303.0 K. Titrations were carried out in the presence of different relative concentrations (M:L:X = 1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5) of metal (M) to L-histidine (L) to L-glutamic acid (X) with sodium hydroxide. Stability constants of ternary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The predominant species detected were ML2XH2, MLXH2 and MLX2 for Ca(II), Mg(II) and Zn(II). The formation and distribution of different species with relative concentrations of metal and ligands with varying pH are represented in the form of distribution diagrams. The influence of the solvent on the speciation is discussed in terms of the dielectric constant of the medium.
FeCl3.nano SiO2 : an efficient heterogeneous nano catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes under solvent-free conditions : research articleSource: South African Journal of Chemistry 65, pp 191 –195 (2012)More Less
A novel, efficient and eco-friendly procedure for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes is described through one-pot condensation of 2-naphthol and dimedone with aryl aldehydes in the presence of nano silica-supported ferric chloride under solvent-free conditions. The present approach offers several advantages such as short reaction times, high yields, easy purification, recovery and reusability of the catalyst.
Preparation of Mg-doped Ce-Zr solid catalysts and their catalytic potency for the synthesis of 5-arylidene-2,4-thiazolidinediones via Knoevenagel condensation : research articleSource: South African Journal of Chemistry 65, pp 196 –201 (2012)More Less
A series of Mg-doped Ce-Zr mixed oxides with different molar ratios were prepared by a simple co-precipitation method. The surface characterization of these materials were investigated by means of XRD, FT-IR, SEM-EDS, CO2-TPD and BET techniques. The catalytic activity of the prepared materials was tested by synthesizing of 5-arylidene-2,4-thiazolidinedione derivatives via a Knoevenagel condensation using aromatic aldehydes and 2,4-thiazolidinedione in ethanol:water medium. The best catalytic activity was obtained with Ce1Mg0.6Zr0.4O2. The particle size or crystallite size was estimated using the Debye-Scherrer equation. Addition of MgO to the Ce-Zr mixed metal oxides affected both particle size and catalytic activity.
Synthesis and antimicrobial activity of the essential oil compounds (E)- and (Z)-3-hexenyl nonanoate and two analogues : short communicationSource: South African Journal of Chemistry 65, pp 202 –205 (2012)More Less
The synthesis of (E)- and (Z)-3-hexenyl nonanoate, known constituents of essential oil containing plants, and two related compounds is reported. These compounds were assembled from nonanoyl chloride or nonanoic acid and the respective alcohols. In particular, it was found that the use of triethylamine as a co-solvent was necessary to avoid acid-mediated isomerization of the alkenes, which resulted in an inseparable mixture of products. The antimicrobial activity of the four hexenyl and hexyl nonanoate compounds was undertaken using microdilution minimum inhibitory concentration (MIC) analysis against eight test microorganisms. All four compounds demonstrated activity, with (E)-3-hexenyl nonanoate 1b having the highest inhibition (MIC value of 0.45 mg mL-1) against Pseudomonas aeruginosa ATCC 27858. Furthermore, this compound demonstrated the highest broad-spectrum activity (mean MIC value of 1.24 ± 0.50 mg mL-1) with noteworthy activity against all pathogens tested.
Development and application of solid phase extraction method for polycyclic aromatic hydrocarbons in water samples in Johannesburg area, South Africa : research articleSource: South African Journal of Chemistry 65, pp 206 –213 (2012)More Less
A solid phase extraction (SPE) technique has been developed for the quantitative determination of polyaromatic hydrocarbons (PAHs) in aqueous samples. The SPE technique involved extraction of PAHs from a 100mL sample containing 10% methanol as a modifier onto C18 cartridges. 40% methanol in water was used as conditioning solvent, and 3 mL acetone:THF (1:1) as eluting solvent. After eluting, the extract was reduced to 1mL under nitrogen and then analyzed by GC-MS. The extraction was optimized for the addition of organic modifier, sample load volume, conditioning solvent, washing solvent and eluting solvent. In order to evaluate the practical applicability of SPE technique, water samples were spiked with the PAHs to give final sample concentrations between 3 and 7 µg L-1. Enrichment factors of 81-135 were achieved with relative standard deviations (RSDs) of less than 6%. Recoveries obtained ranged from 81 to 135%. Detection limits ranged from 20.0-52.0 ng L-1. The optimized method was validated by analyzing certified reference materials. The optimized method was then applied to spiked real river samples in and around the Johannesburg area, South Africa. The concentrations obtained varied from 22.0 to 1040.0 ng L-1. The RSDs were between 2.3 and 13%. The overall order of PAHs levels was: phenanthrene > acenaphthene > naphthalene > fluoranthene > pyrene.
Source: South African Journal of Chemistry 65, pp 214 –222 (2012)More Less
Bis(diphenylphosphino)amine ligands were supported on Merrifield's resin and tested in catalytic ethylene oligomerization reactions with a chromium source. The supported ligands were characterized via IR, solid-state NMR, SEM and TGA-DSC. In order to compare activity of the supported and unsupported ligands, homogeneous bis(diphenylphosphino)amine ligands were synthesized and characterized via NMR, elemental analysis, IR and GC-MS. Oligomerization reactions were carried out in a Parr pressure reactor using Cr(acac)3 as the precursor and MMAO-3A as the activator. The system with the homogeneous ligands proved active in the tetramerization of ethylene, with the selectivity of 1-octene in the C8 fraction being comparable with that mentioned in literature (>98 wt%). When comparing the homogeneous ligands with their heterogeneous counterparts, the latter showed a four-fold drop in activity compared to their homogeneous counterparts. The selectivity towards the main product, 1-octene, was less than 10 wt%. These supported ligands created a system that favoured the formation of C6 products more than any other product, with C6 cyclics (methylcyclopentane and methylenecyclopentane) being the most dominant, probably due to steric effects caused by the polymer chain.
Source: South African Journal of Chemistry 65, pp 223 –227 (2012)More Less
New heterocyclic 2-Aryl-9-chloro-5,6,7,8-tetrahydrothieno[3,2-b]quinoline derivatives [Aryl-CTTQ] (2a-e) and 5-aryl-thieno[3,2-d][1,3]thiazol-2-amine derivatives [Aryl-TZA] (6a-e) were achieved in good yields starting from 5-aryl-3-aminothiophene-2-carboxylic acid (1a-c).
A convenient and direct route to 1,2-dichlorovinylphosphine oxides via copper-catalyzed addition of H-phosphine oxides to 1,2-dichloroethyne : short communicationSource: South African Journal of Chemistry 65, pp 228 –230 (2012)More Less
An efficient, convenient and inexpensive CuI-catalyzed method for the synthesis of 1,2-dichlorovinylphosphine oxides from substituted phosphites, diphenylphosphine oxide and 1,2-dichloroethyne has been developed in moderate-good yields, and the reactions provided mainly regioselective anti addition products.
Syntheses, protonation constants and antimicrobial activity of 2-substituted N-alkylimidazole derivatives : research articleSource: South African Journal of Chemistry 65, pp 231 –238 (2012)More Less
A series of N-alkylimidazole-2-carboxylic acid, N-alkylimidazole-2-carboxaldehyde and N-alkylimidazole-2-methanol derivatives [alkyl = benzyl, methyl, ethyl, propyl, butyl, heptyl, octyl and decyl] have been synthesized and the protonation constants determined. The antimicrobial properties of the compounds were tested against Gram-negative (Escherichi coli), Gram-positive (Staphylococcus aureus & Bacillus subtilis subsp. spizizenii) bacterial strains and yeast (C. albicans). Both the disk diffusion and broth microdilution methods for testing the antimicrobial activity showed that N-alkylation of imidazole with longer alkyl chains and the substitution with low pKa group at 2-position resulted in enhanced antimicrobial activity. Particularly, the N-alkylimidazole-2-carboxylic acids exhibited the best antimicrobial activity due to the low pKa of the carboxylic acid moiety. Generally, all the N-alkylimidazole derivatives were most active against the Gram-positive bacteria [S. aureus (MIC = 5-160 µg mL-1) and B. subtilis subsp. spizizenii (5-20 µg mL-1)], with the latter more susceptible. All the compounds showed poor antimicrobial activity against both Gram-negative (E. coli, MIC = 0.15 to >2500 µg mL-1) bacteria and all the compounds were inactive against the yeast (Candida albicans).
Fabrication of perovskite-type oxide BaPbO3 nanoparticles and their efficiency in photodegradation of methylene blue : research articleSource: South African Journal of Chemistry 65, pp 239 –244 (2012)More Less
BaPbO3 perovskite was prepared by the sol-gel method. The physical and chemical properties of catalyst were characterized by XRD, TEM, SEM, EDX and IR techniques. The photocatalytic activity of the sample was evaluated by photocatalytic decomposition of methylene blue (MB) dye under UV irradiation. The results of XRD indicate that the perovskite-type oxide (BaPbO3) is crystal at 700 °C. The XRD, TEM and SEM revealed that BaPbO3 particles are prepared in the nano-size regime. The results show that the degradation efficiency of methylene blue (MB) by BaPbO3 is higher than rutile under similar conditions.
The use of an experimental design approach to investigate the interactions of additives used in the making of the negative plate in lead-acid batteries : research articleSource: South African Journal of Chemistry 65, pp 245 –257 (2012)More Less
When a conventional starting, lighting and ignition (SLI) lead acid battery is exposed to a high rate partial state of charge (HRPSoC) cycling, it would experience a build-up of irreversible PbSO4 on the negative plate, resulting in capacity loss and electrode damage. The addition of certain graphites to the negative paste mix has proven to be successful in reducing this effect. This study looked at using statistical design of experimental (DoE) principles to observe interactions between two graphite types and a nanocarbon together with other additives, such as BaSO4 and Vanisperse, to a negative paste mixture. The response factors considered were in relation to their effect on the battery's cold cranking ability (CCA) at -18 °C, the HRPSoC and its active material utilization. Typical flooded nominal 8Ah test cells were assembled in a reverse ratio build,with three positive and two negative plates, with three types of added carbons (flake graphite, natural graphite and nanocarbon) added to the negative paste mixture at a two-level design. The study showed the usefulness of a statistical DoE approach in the effective use of additives that are included to the negative plate paste mixture, where there are interactions between the amounts of added carbon, BaSO4 and Vanisperse, with respect to the responses of CCA and HRPSoC, that do not necessarily act independently - based on their amounts - on the performance of the active material. The study also showed that there are correlations between certain response factors, such as the number of achievable cycles within a HRPSoC test sequence, and the type of added carbon.