African Journals Online
South African Journal of Chemistry

Volume 56, 2003
ABSTRACTS

Effect of Cobalt Source on the Catalyst Reducibility and Activity of Boron-modified Co / TiO₂ Fischer-Tropsch Catalysts

Li, Jinlin; Coville, Neil J.

Abstract: The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility and dispersion, as well as the catalytic activity of the Fischer-Tropsch (FT) synthesis, of boron-modified titania-supported cobalt catalysts (0.1%B/10%Co/TiO₂) has been investigated. FT studies were performed on both calcined and uncalcined catalysts prepared from the three cobalt sources. The uncalcined nitrate catalyst showed a higher activity for FT synthesis compared to the uncalcined acetate and chloride catalysts. For the calcined catalysts, the acetate and nitrate catalysts exhibited higher FT activity. The low activity associated with the chloride catalyst related to poisoning by residual chloride ions. Calcination was found to enhance the extent of cobalt bulk reduction and FT activity for all three of the catalysts. The FT reaction rate increased with increasing percentage cobalt dispersion while the turnover frequency (TOF) was found be near independent of cobalt source.

Voltammetric Determination of a Benzimidazole Anthelmintic Mixture at a Poly(3-methylthiophene)-modified Glassy Carbon Electrode

Msagati, Titus A.M; .Ngila, J. Catherine

Abstract: The voltammetric determination of benzimidazole anthelmintics at a glassy carbon rotating-disk electrode modified with poly(3-methylthiophene) is presented. The purpose of surface modification was to improve the sensitivity and limits of detection for determination of the compounds in a standard mixture. Thus, five compounds, namely thiabendazole, mebendazole, albendazole, fenbendazole and oxibendazole have been studied using square wave voltammetry. It has been possible to resolve four of the compounds, mebendazole, fenbendazole, oxibendazole and thiabendazole, in a mixture. Investigations of a number of parameters, including the mode of potential application, cathodic reduction versus anodic oxidation, the type of electrode, effect of pH and speed of electrode rotation, among others, are reported.

Spectrophotometric and Thermal Studies of the Reaction of Iodine with Nickel(II) Acetylacetonate

Nour, El-Metwally; Teleb, Said M.; Elmosallamy, Mohamed A.F.; Refat, Moamen S.

Abstract: The reaction of iodine (acceptor) and nickel(II) acetylacetonate (donor) was studied photometrically in different solvents such as chloroform, dichloromethane and carbon tetrachloride at room temperature. The results indicate the formation of a 1: 1 charge-transfer complex in each solvent and the iodine complex is formulated as the triiodide species [Ni(acac)₂]₂I⁺.I₃^-, based on the characteristic electronic absorptions of the I₃^- ion at 361 and 285 nm, as well as on the far infrared absorption bands characteristic of the I₃^- ion with C_2v symmetry. These bands are observed at 132, 101 and 84 cm^-1 and are assigned to n_a(I-I), n_s(I-I) and d(I₃^-), respectively. The values of the equilibrium constant (K), absorptivity (e) and oscillator strength (f) of the iodine complex are shown to be strongly dependent on the type of solvent used. The important role played by the solvent is suggested to be mainly due to the interaction of the ionic complex with the solvent. The proposed structure of the new solid triiodide charge-transfer complex reported in this study is further supported by thermal and mid-infrared measurements.

Analysis of Trace Elements in South African Clinkers using Latent Variable Model and Clustering

Abonyi, Janos; Tamas, Ferenc D.; Potgieter, Sanja; Potgieter, Herman

Abstract: The trace element content of clinkers (and possibly of cements) can be used to identify the manufacturing factory. The Mg, Sr, Ba, Mn, Ti, Zr, Zn and V content of clinkers give detailed information for the determination of the origin of clinkers produced in different factories. However, for the analysis of such complex data there is a need for algorithmic tools for the visualization and clustering of the samples. This paper proposes a new approach for this purpose. The analytical data are transformed into a twodimensional latent space by factor analysis (probabilistic principal component analysis) and dendograms are constructed for cluster formation. The classification of South African clinkers is used as an illustrative example for the approach.

Synthesis and antimicrobial activity of new Thiazole-2(3H)-thiones containing 1, 1, 3-trisubstituted Cyclobutane

Ahmedzade, Misir; Kirilmis, Cumhur; Cukurovali, Alaaddin; Dilsiz, Nihat

Abstract: The reaction of potassium salts of RNHCSSK with 2-chloro-1-(3-methyl-3-phenylcyclobutyl)ethan-1-one in ethanol at 78-80°C afforded new 1, 3-thiazole-2(3H)-thiones containing 1, 1, 3-trisubstituted cyclobutane rings at C-4. The antimicrobial activities of these compounds were also investigated against seven different microorganisms, and some of them were found to be active against several of the microorganisms at higher concentrations.

Chromone Studies. Part 12.¹ Fragmentation Patterns in the Electron-impact Mass Spectra of 2-(N, N-Dialkylamino)-4H-1-benzopyran-4-ones and -naphthopyran-4-ones

Kaye, Perry T.; Ramaite, Isaiah D.I.

Abstract: The major electron-impact mass fragmentation patterns exhibited by 2-(N, N-dialkylamino)-4H-1-benzopyran-4-ones and -naphthopyran-4-ones have been explored using a combination of low-resolution, high-resolution and B/E linked-scan data.

Production of 9-thioxo-2, 3, 4, 9-tetrahydro-pyrrolo[3, 4-b]quinolin-1-one derivatives from the aminolysis of 3, 3, 9-trichloro-3H-thieno[3, 4-b]quinolin-1-one

Van Es, Theodorus; Staskun, Benjamin; Fernandes, Manuel A.

Abstract: Treatment of the title substrate with propylamine yielded 2-propyl-9-propylamino-3-propylimino-2, 3-dihydro-pyrrolo[3, 4-b] quinolin-1-one (15%) and a S-containing product (63%). The latter is inferred (from its spectral and chemical properties) to be a (1:1) complex of 2-propyl-3-propylimino-9-thioxo-2, 3, 4, 9-tetrahydro-pyrrolo[3, 4-b]quinolin-1-one (derived via an unusual S-rearrangement) with propylamine. The propylamine in the complex is removed by acid or thermally to provide the aforementioned 9-thioxo component which structure was substantiated froma X-ray crystal analysis. Aminolysis of the title substrate with ethylamine afforded the analogous ethyl-substituted products.

The Surface Chemical Properties of Novel High Surface Area Solids Synthesized from Coal Fly Ash

Pretorius, P. Julius; Woolard, Christopher D.

Abstract: The zeolite, Na-P1, was synthesized from fly ash samples originating from coal-fired power stations in South Africa by hydrothermal treatment of the raw ash with concentrated aqueous NaOH solutions. The zeolite was then further modified by acid leaching at elevated temperatures. This resulted in the formation of a novel high surface-area solid. Spectroscopic and potentiometric investigations into the surface properties of both solids indicate that acid-base properties are most likely due to the presence of =AlOH- and =SiOH-type surface groups. Surface protonation constants for the various solids (unmodified ash, base-modified ash, acid-etched zeolitic product) are reported. Metal sorption studies were performed for cadmium and copper. It is suggested that the zeolitic product sorbs copper and cadmium by an ion exchange mechanism instead of a surface complexation mechanism, whereas the high surface-area solid, formed after acid etching, sorbs these metals via a surface complexation mechanism. Metal adsorption constants for the formation of =XOMOH species on the surface of the last mentioned solid for use in speciation models are reported.

Chlorine- and Sulphur-substituted Pyrrolo[3, 4-b]quinolines and Related Derivatives arising from the Aminolysis of 3, 3, 9-Trichlorothieno[3, 4-b]quinolin-1(3H)-one

Van Es, Theodorus; Staskun, Benjamin

Abstract: The outcome from aminolysis of 3, 3, 9-trichlorothieno[3, 4-b]quinolinone with an alkylamine is dependent on the reaction conditions and extraneous reagents employed. A variety of hitherto unreported products can be obtained and include 4-chloro-2- alkylthiocarbamoyl-quinoline-3-carboxylic acid alkylamides, 9-chloro-2-alkyl-3- alkylimino-pyrrolo[3, 4-b]quinolines, 9-chloro-2-alkyl-3-thioxo-pyrrolo[3, 4-b]-quinolines, 2-alkyl-3-alkylimino-9-thioxo-pyrrolo[3, 4-b]quinolines, and 2-alkyl-9-alkylamino-3-alkylimino-pyrrolo[3, 4-b]quinolines. The spectral (1H NMR, HRMS) and chemical properties and the structures of the products are described and discussed, and possible mechanistic pathways leading to their formation are presented.

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