Scielo RSS <![CDATA[South African Journal of Chemistry]]> http://www.scielo.org.za/rss.php?pid=0379-435020080001&lang=en vol. 61 num. lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Preparation, structure characterization and thermal decomposition process of the dysprosium(III) m-methylbenzoate 1,10-phenanthroline complex</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100001&lng=en&nrm=iso&tlng=en A dinuclear complex [Dy(m-MBA)3phen]2-H2O was prepared by the reaction of DyCl3-6H2O, m-methylbenzoic acid and 1,10-phenanthroline in a 1:3:1 molar ratio, where m-MBA = m-methylbenzoate and phen = 1,10-phenanthroline. The complex was structurally characterized by single crystal X-ray diffraction, elemental analysis, UV and IR spectroscopy, molar conductance and TG-DTG techniques. It crystallizes in the monoclinic space group Cc with a =15.962(16), b = 18.505(18), c = 22.547(2) Ǻ; a = 90 °, β = 97.9820(10) °, y = 90°; z = 4. The unit cell contains a dinuclear molecule of the title compound. Each Dy(III) ion is eight-coordinated to one 1,10-phenanthroline molecule, one bidentate carboxylate group and four bridging carboxylate groups. The carboxylate groups are bonded to the dysprosium ions in two modes: chelating bidentate and bridging bidentate. The thermal decomposition process of [Dy(m-MBA)3phen]2-H2O has been followed by thermal analysis. <![CDATA[<b>Straightforward synthesis of a new series of </b><b>α</b><b>-(arylamino thiocarbonyloxy) hydrocarbylphosphonates</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100002&lng=en&nrm=iso&tlng=en A convenient, straightforward, two-step reaction of α-hydroxyhydrocarbylphosphonates with arylisothiocyanates in the presence of catalytic amounts of sodium methoxide in 1,2-dichloroethane as solvent produced various new α-(arylamino thiocarbonyloxy) hydrocarbylphosphonates in excellent yields. Their structures have been confirmed by their IR, ¹H NMR and 31P NMR spectra and by elemental analysis. The preliminary antisepsis activity and protein activity of some of the compounds were identified. <![CDATA[<b><i>N,N'</i></b><b>-dibromo-<i>N,N'</i>- 1,2-ethanediylbis(benzenesulphonamide) (BNBBS): A safe, neutral and efficient reagent for the oxidation of primary and secondary alcohols to corresponding carbonyl compounds under mild conditions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100003&lng=en&nrm=iso&tlng=en Efficient oxidation of various types of structurally diverse alcohols to the corresponding carbonyl compounds can be carried out with N, N,-dibromo-N, N,-1,2-ethanediylbis(benzenesulphonamide) in good to high yield of products in CH2Cl2 at room temperature. Primary (aliphatic, benzylic and allylic) alcohols are oxidized with no over-oxidation to carboxylic acids. <![CDATA[<b>Thienyl-containing β-diketones: Synthesis, characterization, crystal structure and keto-enol kinetics</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100004&lng=en&nrm=iso&tlng=en 1-phenyl-3-(2-thenoyl)-1,3-propanedione, Hbth, pKa' = 9.006(8) and 1,3-di(2-thenoyl)-1,3-propanedione, Hdtm, pKa' = 8.893(3) were prepared by the Claisen condensation of ethyl 2-thiophenecarboxylate with an appropriate ketone under the influence of lithium diisopropylamide (LDA). The group electronegativity of the thienyl group is 2.10 (Gordy scale) as calculated from a linear group electronegativity vs. methyl ester IR carbonyl stretching wavenumber relationship. A crystal structure determination of Hbth (orthorhombic, Pbca, Z = 8, R = 0.0290) shows asymmetrical enolization on the side of the phenyl group. The preferred enol isomer of β-diketones containing more than one aromatic moiety that crystallizes in the solid state is determined by the resonance driving force stabilization of the thienyl or any other aromatic group, rather than the stabilization by resonance due to the phenyl group. The slow conversion of the enol isomers to the keto-enol equilibrium position was followed in CDCl3 solution by NMR spectroscopy. <![CDATA[<b>Preparation of MAl<sub>2</sub>O<sub>4</sub>: Eu<sup>2+</sup>, Sm<sup>3+</sup> (M = Ca, Sr, Ba) phosphors by the combustion method and their luminescent properties</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100005&lng=en&nrm=iso&tlng=en A series of MAl2O4:Eu2+,Sm3+ (M = Ca, Sr, Ba) phosphors was prepared by the combustion method, and the influence of these alkaline earth metals on the structure and luminescent performances for these phosphors was investigated. A relationship was established between their composition, crystallization capacity and luminescent properties. The results show that the CaAl2O4: Eu²+,Sm³+ and SrAl2O4:Eu²+,Sm³+ phosphors exhibit monoclinic crystal systems and that the BaAl2O4:Eu²+,Sm³+ phosphor exhibits a hexagonal structure. The alkaline earth metal has a positive effect on the crystallization process, the heat treatment procedure and the luminescent properties of the corresponding phosphors. According to the order Ca > Sr > Ba, the maximum emission wavelengths of the corresponding phosphors are found at 505 nm, 490 nm and 478 nm, and the relevant colours of emitted light are between blue and green, which indicates that there is a clear blue shift in the emission spectra, but their excitation spectra show almost no difference. The decay curve shows that the afterglow intensity and time are not only related to the activating processes and the hole transport, but also to the phase structure and the grain size, which is in the order Sr > Ca > Ba. <![CDATA[<b>Synthesis and antimicrobial activity of novel 3-[1-(3-nitrophenyl)-ethyl]-1-(indole-1-yl) substituted aryl/alkyl-phosphinoyl/thiophosphinoyl/ selenophosphinoyl-1<i>H</i>-indole derivatives</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100006&lng=en&nrm=iso&tlng=en Syntheses of novel 3-[1-(3-nitrophenyl)-ethyl]-1-(indole-1-yl) substituted aryl/alkyl phosphinoyl/thiophosphinoyl/ selenophosphinoyl-1H-indole derivatives were accomplished in two steps. The synthetic route involves the cyclisation of equimolar quantities of 3-[1H-3-indolyl(3-nitrophenyl)methyl]-1H-indole with dichlorophenyl phosphine/ethyldichlorophosphite in the presence of triethylamine in dry acetonitrile at room temperature. These compounds were further converted to the corresponding oxides, sulphides and selenides by reacting them with hydrogen peroxide, sulphur and selenium, respectively. The structures of the novel products were established by elemental analyses, IR, ¹H, 13C and 31P NMR and mass spectroscopy. They were screened for antibacterial and antifungal activity against Staphylococcus aureus/Klebsiella pneumoniae and Pellicularia solmanicolor/Macrophomina phaseolina, respectively. <![CDATA[<b>Reduction of α,β-unsaturated ketones using a Zn/NiCl<sub>2</sub> system in aqueous media in the presence of anionic and cationic surfactants</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100007&lng=en&nrm=iso&tlng=en The reduction of aromatic and aliphatic α,β-unsaturated ketones, namely acetophenone (1) and (-)-carvone (3) with a Zn/NiCl2 system in H2OorH2O/EtOH media in the absence or presence of anionic and cationic surfactants have been investigated and have shown remarkable results. The anionic sodium dodecyl sulphate (SDS), the cationic cetyltrimethylammonium bromide (CTAB) and the non-micelle-forming didodecyldimethylammonium bromide (DDAB) surfactants were utilized. The reduction of acetophenone in H2O medium gave only a low yield of 1-phenyl ethanol (2) in comparison with the yields which resulted when a H2O/EtOH medium was employed. The yields increased relatively in a H2O medium in the presence of cationic surfactants which showed a gradual increase at low concentrations following different patterns and sharp increases at 60 °C and pH 9. The reduction of (-)-carvone (3) with the same system in H2O medium gave relatively higher yields than that of acetophenone. In the presence of cationic surfactants CTAB and DDAB in aqueous medium the total reduction yield increased appreciably and sometimes reached 100 % in the presence of DDAB at a concentration of 0.98 X 10-2 mol L-1 at 60 °C. The effects of pH, combined metallic salts and different surfactant concentrations on the reduction of (-)-carvone have been also investigated. This paper focuses on the application of surfactants in the reduction of α,β-enones by metal/metallic chloride/H2O systems in the absence of organic solvents. This method displays regioselectivity and stereoselectivity. This method may also be considered as a contribution to the antipollution process by means of the elimination of organic solvents from the chemical process. <![CDATA[<b>Synthesis, characterization and activity of sulphate-modified V<sub>2</sub>O<sub>5</sub>/SnO<sub>2</sub> catalysts</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100008&lng=en&nrm=iso&tlng=en Sulphate-modified V2O5/SnO2 catalysts were prepared by a simple impregnation method and characterized using different physicochemical techniques, such as EDX, BET-SA, XRD, FT-IR, TGA and 51V NMR spectroscopy. A simple, effective and environmentally friendly method for the gas phase conversion of cyclohexanone oxime to E-caprolactam by these modified catalysts is presented. The optimal protocol allows ε-caprolactam to be synthesized in excellent yields. NH3-TPD and cumene conversion reactions were used to determine the acid structural properties of the catalysts. Definite correlation was observed between the concentration of medium strength acid sites or Bronsted sites and the E-caprolactam selectivity. Time-on-stream studies showed fast decline in the activity of the catalyst resulting from the basic nature of the reactant and product molecules. <![CDATA[<b>Synthesis and antimicrobial activity of 3-[(4-substituted) (2-oxo-1,3-oxazolidin-3-yl) phosphoryl]-1,3-oxazolidin-2-ones</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100009&lng=en&nrm=iso&tlng=en <![CDATA[<b>Critical self-assembly concentration of bolaamphiphilic peptides and peptide hybrids determined by fluorescence measurements</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100010&lng=en&nrm=iso&tlng=en The study of the self-assembly properties of peptides and proteins is important for the understanding of molecular recognition processes and for the rational design of functionalbiomaterials. Novel bolaamphiphilic peptides and peptide hybrids incorporating non-natural aminoacids were designed around a model lysine/leucine-rich peptide with the intention to study their self-assembly behaviour. Steady-state fluorescence measurements using pyrene as fluorescent probe were adapted to the determination of the critical self-assembly concentrations (CSACs) of these amphiphilic peptides and peptide hybrids. Different experimental conditions were studied. The morphology of the peptide aggregates was evaluated by scanning electron microscopy (SEM). Concentration and pH have been revealed to play a key role in the control of the process. Peptides presented different three-dimensional supramolecular arrangements that were correlated with their aminoacid compositions (specifically considering the presence of tyrosine and proline) and CSAC values. <![CDATA[<b>Synthesis and antioxidant activity of 3,3'-diselanediylbis (N,N-disubstituted indolizine-1-carboxamide) and derivatives</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100011&lng=en&nrm=iso&tlng=en A series of novel diselenides 5a-e were synthesized from α-haloketones, α-picoline alkenes and various secondary amines under a dry nitrogen atmosphere. The structures of these compounds were established by means of their spectral data and they were screened for scavenging activity against 1,1-diphenyl-2-picryl-hydrazyl (DPPH.). The results of this research showed that two of these compounds (5e and 5d) exhibited reasonable antioxidant activity. The intermediate, methyl 5-methylindolizine-1-carboxylate was prepared by condensation of methyl acrylate with 1-(carboxymethyl)-2-methylpyridinium halide, which was prepared from a-picoline and chloroacetic acid by using the Tschischibabin reaction. <![CDATA[<b>Students' competence in intellectual strategies needed for solving chemistry problems</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100012&lng=en&nrm=iso&tlng=en Many students' difficulties in solving chemistry problems are due to lack of competence in a few widely applicable skills and strategies. The competence of 300 first year chemistry students at North-West University, South Africa, in four intellectual strategies (clarification and clear presentation of the problem; focussing on the goal and identifying a strategy for moving towards the goal; identification of the principles needed for solution; proceeding step by step) was investigated, over a period of four years, by comparing their performance in 'standard' questions and 'hint' questions. The 'standard' and the 'hint' questions were the same but the 'hint' questions, in addition, suggested the strategies which should be used to solve the problems. Performance in all test items was poor, but improved in the 'hint' questions. The results indicate that about 80 % of the students were unable to use the required strategies, and also that many students who have the competence to use the strategies did not recognize the necessity for doing so. The results also suggest negative attitudes and lack of self-confidence in problem solving. There is therefore a need for specific training of students in the use of intellectual strategies. This should be integrated with the learning of subject content. <![CDATA[<b>A simple, rapid and efficient one-pot protocol for the synthesis of 2-substituted benzothiazole derivatives and their antimicrobial screening</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100013&lng=en&nrm=iso&tlng=en A rapid and efficient condensation reaction of 2-aminothiophenol with various fatty acids in solvent-free conditions with or without microwave irradiation was carried out to afford the corresponding 2-substituted benzothiazole derivatives in good to excellent yields. The structures of the new products were established by elemental analyses, IR, ¹H NMR, 13C NMR and mass spectral data. All the title compounds were screened for their antibacterial and antifungal activity. Most of the compounds exhibited good antimicrobial activity. <![CDATA[<b>The ligand substitution reactions of hydrophobic vitamin B<sub>12</sub> derivatives. Reaction of cobyric acid heptapropyl ester with heterocyclic <i>N</i>-donor ligands</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100014&lng=en&nrm=iso&tlng=en The hydrophobic cobyrinic acid heptapropyl ester corrinoids XCbs-Pr (axial ligandX = CN-,SO3(2-),CH3- and CH3CH2-) have been prepared from vitamin B12 by hydrolysis of the amide side chains and their conversion to propyl esters. Both the position of the y-band and the general shape of the UV-visible spectra of these complexes show significant solvent dependence as the polarity of the solvent is varied. The equilibrium constants, K, for the reaction of five-membered heterocyclic nitrogenous bases (the azoles imidazole, pyrazole and 1,2,4-triazole) with displacement of coordinated H2O in aquacyanocobyrinic acid heptapropyl ester, and coordination by the predominantly five-coordinate complexes sulphitocobyrinic acid heptapropyl ester, ethylcobyrinic acid heptapropyl ester and methylcobyrinic acid heptapropyl ester, have been determined spectrophotometrically at 25 °C in water, methanol, acetonitrile, ethyl acetate and toluene. Values of K are dependent on the identity of the trans ligand (X = CN- &gt;SO3(2-) &gt; CH3- &gt;CH3CH2-); they increase with the basicity of the azole (pyrazole < 1,2,4-triazole < imidazole); and they increase as the solvent polarity increases (toluene < ethyl acetate < acetonitrile < methanol < H2O). Molecular mechanics calculations suggest that these effects are largely electronic in origin. <![CDATA[<b>The binary boron trifluoride-hydroxylamine molecular complex: N-bound or O-bound?</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100015&lng=en&nrm=iso&tlng=en Boron trifluoride acts as a classical Lewis acid in forming molecular complexes with a variety of electron donors. Recent computational results on a number of complexes with some oxygen and nitrogen bases have indicated relationships between the properties of the adducts, such as the interaction energies and the wavenumber shifts of some of the modes of the boron trifluoride sub-molecule, and some physical properties of the bases. Hydroxylamine represents an example of a base containing two potential sites of electron donation, the nitrogen and the oxygen atoms. Predictions based on our earlier investigations of systems of this type suggest that hydroxylamine would bind to boron trifluoride preferentially through its nitrogen atom. Whether such a complex adopts an equilibrium structure in which the NO bond of hydroxylamine lies cis or trans to one of the BF bonds of boron trifluoride is more difficult to predict. This paper investigates the relative binding properties of N-bound versus O-bound complexes of boron trifluoride with hydroxylamine, and explores the conformational preferences and vibrational spectra of both types of adduct. <![CDATA[<b>Modelling of the blood plasma species of biguanide derivatives exhibiting potential as diagnostic radiopharmaceuticals</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100016&lng=en&nrm=iso&tlng=en 99mTc-DMSA (DMSA=dimercaptosuccinic acid), the gold standard for static renal imaging, has a long uptake time, which is a limiting factor in diagnostic procedures and also leads to a relatively high radiation dose to patients. The ligands dimethyl biguanide (DMBG), biuret (BIU), 2-imino-4-thiobiuret (ITB) and carboxy-biguanide (CBIG) have nitrogen donor atoms, which are able to complex transition elements. The formation constants needed in order to establish a blood plasma model for these ligands were determined by potentiometry and the results are reported herein. Based on blood plasma modelling, it was shown that the ligands had selectivity for 99mTc over blood plasma metal ions at physiological pH and it was therefore hypothesized that the Tc-ligand complex would survive in blood plasma. Furthermore, no or few side effects related to the mobilization of blood plasma metal ions by these ligands are expected, once the radiopharmaceutical has been administered. It is also expected that these ligands should clear rapidly from the blood plasma. <![CDATA[<b>Silica sulphuric acid as an efficient catalyst for the catalytic and metal-free oxidation of aromatic amines to their corresponding nitro compounds with sodium perborate under micellar media</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100017&lng=en&nrm=iso&tlng=en Electron-donating substituted anilines were converted to their corresponding nitro compounds with sodium perborate in the presence of a catalytic amount of silica sulphuric acid under micellar media in moderate to good yields. <![CDATA[<b>Synthesis and antimicrobial activity of new </b><b>α</b><b>-aminophosphonic acid esters</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100018&lng=en&nrm=iso&tlng=en Synthesis of new a-aminophosphonic acid esters (3a-I) was accomplished by the reaction of equimolar quantities of phenyl ethyl glycine and various aryl aldehydes with diethyl/ dimethylphosphite in dry toluene at reflux temperature. All the structures of the newly synthesized a-aminophosphonic acid esters (3a-I) were established by elemental analysis, and IR, ¹H, 13C, 31P NMR and mass spectral data. The antimicrobial and antifungal activities of these compounds were evaluated and they exhibited significant activity. <![CDATA[<b>Methyl iodide oxidative addition to rhodium(I) complexes: A DFT and NMR study of [Rh(FcCOCHCOCf3)(CO)(pph3)] and the rhodium(III) reaction products</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100019&lng=en&nrm=iso&tlng=en A theoretical (DFT) study of the equilibrium geometry of the possible reaction products of the oxidative addition reaction [Rh(FcCOCHCOCF3)(CO)(PPh3)] + CH3I (Fc = ferrocenyl), consistent with experimental observations, revealed that the first alkyl product results from trans addition to RhI. Isomerization via an acyl intermediate leads to a second octahedral alkyl product with the PPh3 group and the iodide above and below the square plane. Theoretical computations also revealed that the thermodynamic acyl product adopts a square-pyramidal geometry with the COCH3 group in the apical position. <![CDATA[<b>Performance and structure of LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> prepared from various Ni precursors for lithium ion batteries</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100020&lng=en&nrm=iso&tlng=en LiNi0,5Mn1,5O4 compounds were prepared through a solid-state reaction using various Ni precursors. The effect of the precursors on the electrochemical performance of LiNi0,5Mn1,5O4 was investigated. LiNi0,5Mn1,5O4 made from Ni(NO3)2 ● 6H2O shows the best charge-discharge performance. The reversible capacity of LiNi0,5Mn1,5O4 is about 145 mA h g-1 and remained at 143 mA h g-1 after 10 cycles at 3.0 to 5.0 V. The XRD results showed that the precursors and dispersion method had significant effects on their structures. Pure spinel phase can be obtained with a high energy ball-milling method and Ni(NO3)2●6H2O as precursor. A trace amount of the NiO phase was detected in LiNi0,5Mn1,5O4 with the manual grinding method when Ni(CH3COO)2●6H2O, NiO and Ni2O3 were used as precursors. <![CDATA[<b>NBS as a powerful catalyst for the synthesis of <i>β</i>-hydroxysulphides with thiolysis of epoxides under mild reaction conditions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100021&lng=en&nrm=iso&tlng=en N-Bromosuccinimide (NBS) catalyses the ring opening of various epoxides with different thiols in CH3CN at room temperature under mild reaction conditions. The corresponding β-hydroxysulphides are obtained in short reaction times and in good to high yields with nearly complete regioselectivity. The catalyst was compared with previously reported catalysts and only one that we have found [B(C6F5)3] gave the same regioselectivity, but the reaction time was much longer (4 h versus 5 min) and the yield was considerably lower. Zn(ClO4)2.6H2O gave slightly lower selectivity but higher yields. The reaction time was about 12 times longer. <![CDATA[<b>Synthesis of some benzimidazole-substituted benzotriazoles</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100022&lng=en&nrm=iso&tlng=en 2-Alkylsubstituted benzimidazoles ( 3A-H: ) were prepared from the acid-catalyzed reaction of 4-methyl-1,2-phenylenediamine with corresponding carboxylic acids. Addition of these benzimidazoles to N-chloromethylbenzotriazole in the presence of sodium amide under reflux conditions gave the novel benzimidazole-substituted benzotriazoles ( 5A-F: ). IR and ¹H NMR spectroscopy and elemental analysis were used for the identification of these compounds. <![CDATA[<b>A coloured spin trap which works as a pH sensor</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100023&lng=en&nrm=iso&tlng=en Nitration of 4-hydroxybenzaldehyde afforded 2,6-dinitro-4-hydroxybenzaldehyde 2, which in the presence of thionyl chloride is converted to 4-chloro-2,6-dinitrobenzaldehyde 3. This compound is very reactive towards nucleophiles, and reacts easily with methoxyamine, affording the intermediate 4-aminomethoxy-2,6-dinitrobenzaldehyde 4. Reaction of 4 with N-t-butyl-hydroxylamine led to a new spin trap of the nitrone type, namely 4-aminomethoxy-3,5-dinitrophenyl-1-f-butylnitrone 6. The spin-trapping capabilities of the new compound have been tested in a classical system, in which short-lived radicals were generated by irradiation. The new compound 6 contains an acidic proton with a pKa value of 7.8, and removal of this by a base induces a colour change, from yellow to green-blue. In a similar way, a new stable nitronyl-nitroxide radical 8 has been obtained from the intermediate 4. <![CDATA[<b>Dissolution kinetics of Icel-Aydincik dolomite in hydrochloric acid</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100024&lng=en&nrm=iso&tlng=en The dissolution of Icel-Aydincik dolomite in aqueous hydrochloric acid solution was investigated with respect to the effects of acid/dolomite mole ratio, solid/liquid ratio, particle size, stirring speed, time and temperature. It was observed that solubility of the dolomite ore increased with increasing acid/dolomite mole ratio, stirring speed, period of time, temperature, and with decreasing solid/liquid ratio and particle size. A kinetic model was applied to describe the dissolution and to analyse the kinetic data. By analysis of the experimental data, it was determined that the leaching process was controlled by the chemical surface reaction. The apparent activation energy of the leaching process was found to be 31.98 kJ mol-1. <![CDATA[<b>Degradation studies of <i>β</i>-cyclodextrin polyurethane polymers using soil burial experiments</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100025&lng=en&nrm=iso&tlng=en Degradation studies of β-cyclodextrin polymers cross-linked with toluene-2,4-diisocyanate (TDI) and hexamethylene diisocyanate (HMDI) were carried out by exposing the polymers to different soil types for up to 120 days. The aim of the study was to determine the fate of these novel polymers in the environment. The polymers were either digested with sulphuric acid prior to performing a soil burial test or buried undigested. Results from the study indicate that the β-CD/TDI polymers with aromatic links underwent a greater mass loss during soil burial when first digested in sulphuric acid (ca. 50 % maximum mass loss). The β-CD/HMDI polymers, on the other hand, underwent the same mass loss for both the digested and undigested polymers (ca. 30 % maximum mass loss). Although the Fourier transform infrared (FTIR) spectroscopy data suggested no changes in the overall polymer structures, the scanning electron microscopy (SEM) micrographs revealed changes in the surface morphology of the polymers. Moreover, results of thermogravimetric analysis (TGA) point to polymer degradation under all conditions tested. <![CDATA[<b>The reduction of nitriles to aldehydes: Applications of Raney nickel/sodium hypophosphite monohydrate, of Raney nickel/formic acid, or of Raney(Ni/Al) alloy/formic acid, respectively</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100026&lng=en&nrm=iso&tlng=en The three title reductant systems have significant advantages in generating aldehydes from nitriles. These include: the utilization of convenient hydrogen sources, namely, sodium hypophosphite monohydrate and formic acid, respectively, and of the relatively inexpensive Raney nickel and Raney (Ni/Al) alloy; the convenience of conducting the reaction(s) in aqueous media at ambient temperatures and pressures, and avoiding the use of trapping agents (except when transforming glycosyl nitriles (vide infra)) and of hydrogen cylinders. Numerous examples of the utilization of the title systems are presented (mostly from the more recent literature) that demonstrate the utility of the respective methods in transforming a solo cyano group, or when accompanied by other chemosensitive functions in a structure, to the corresponding aldehyde. Such substrates include benzonitriles, glycosyl nitriles, O-, N- and S-containing heterocyclic nitriles, aliphatic-aromatic situations, and more complex fused heterocyclic and carbocyclic scaffolds. The review reports modifications of the title methods and several notable steric effects. <![CDATA[<b>Characterization and cardiovascular effects of (13S)-9</b><b><i>α</i></b><b>,13</b><b><i>α</i></b><b>-epoxylabda-6β(19),15(14)diol dilactone, a diterpenoid isolated from <i>Leonotis</i><i> leonurus</i></b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100027&lng=en&nrm=iso&tlng=en A new diterpenoid, (13S)-9α,13α-epoxylabda-6β(19),15(14)diol dilactone (1), was isolated from Leonotis leonurus and the structure determined via NMR analysis. The compound causes significant changes in blood pressure of anaesthetized normotensive rats and exhibits a negative chronotropic effect. <![CDATA[<b>Preparation of ultra-fine calcium carbonate by a solvent-free reaction using supersonic airflow and low temperatures</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502008000100028&lng=en&nrm=iso&tlng=en The treatment of calcium chloride with sodium carbonate under solvent-free conditions with a supersonic airflow and at a low heating temperature leads to the synthesis of ultra-fine calcium carbonate. The reaction not only involves mild conditions, a simple operation, and high yields but also gives a high conversion rate.