African Journals Online
South African Journal of Chemistry

Volume 54, 2001
Abstracts

Dirhodium(II) Carbenes: A Rich Source of Chiral Products

Roos, G.H.P.Raab, C.E.

Abstract: The last decade has witnessed enormous growth in the asymmetric synthetic applications of dirhodium(II) carbenes generated from diazo-precursors. Innovative construction of 'designer' catalysts has played an integral role in extending the breadth of the synthetic cascade of non-racemic products now available through a range of cyclopropanation, C-X insertion, aromatic cycloaddition-rearrangement, and ylide-based reaction types. This review, whilst mindful of importance of the catalytic system, focuses primarily on the latter feature of product diversity.

Nonlinear Kinetics and Mechanism of Nile Blue Reaction with Acidic Bromate and with Aqueous Bromine

Jonnalagadda, S.B.Gollapalli, N.R.

Abstract: Nile blue, a dye of the phenoxazine class follows complex kinetics during its reaction with bromate in acidic solutions. The reaction kinetics were investigated using photometric and potentiometric techniques and a stopped flow apparatus. Under excess acid and bromate concentration conditions, nile blue, (NB⁺) initially depletes very slowly. After an induction period, a swift reaction occurs. The overall reaction is NB⁺ + BrO₃^- react to P + CH₃COOH + H⁺ + Br^-, where P is the de-ethylated N-oxide derivative of nile blue. The rapid kinetics of the reaction of bromine direct with nile blue were also reported. A 11-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is described. The role of various bromo- and oxybromo- species is discussed.

Regio- and Stereoselective a-Halogenation of 2-Aryl-1-methylsulfonyl-2,3-dihydroquinolin-4(1H)-ones

Mphahlele, M.J.Hlatshwayo, S.M.Ndlovu, S.M.Fernandes, M.A.

Abstract: 2-Aryl-1-methylsulfonyl-2,3-dihydroquinolin-4(1H)-ones are readily converted into the corresponding 2-aryl-3-iodo- and 2-aryl-3-bromo-1-methylsulfonyl-2,3-dihydroquinolin-4(1H)-ones using iodine in methanol and pyridinium perbromide in acetic acid, respectively. The reactions were found to be regioselective and stereoselective by ¹H NMR spectroscopy, affording in all cases the 2,3-trans isomers. X-ray crystallography was also used to investigate the relative stereochemistry of these 3-halo derivatives.

Determination of Phthalate Esters in the Aquatic Environment

Fatoki, O.S.Noma, A.

Abstract: The use of solid phase extraction and capillary GLC provides the basis for selective determination of phthalate ester plasticizers in rivers and marine water samples. Of the several solvent ratios (methanol in dichloromethane) that were tried for selective elution of phthalate esters from the C18 solid phase glass catridge, the 50/50 ratio, CH₃OH in CH₂Cl₂ (v/v) gave the best result. The method was tested on river and marine water samples that receive effluent from industries that use phthalate esters. The rivers and marine water samples are grossly polluted as several phthalate esters, for example, dimethyl(DMP), diethyl(DEP), dibutyl(DBP) and diethylhexyl(DEHP) were found present at 0.03 – 2 306 ± 9.4 m gl^-1. A study on uncontaminated water was done to establish bank levels.

Stability Constants of the Inclusion Complexes of ß-Cyclodextrin with Various Adamantane Derivatives. A UV-Vis Study

Vashi, P.R.Cukrowski, I.Havel, J.

Abstract: The stability constants for the inclusion complexes of ß-cyclodextrin (ß-CD) with various adamantane derivatives (ADA), namely the amantadinium (AM), rimantadinium (RIM), and memantinium (MEM) cations have been determined by UV-Vis spectrophotometry. All experiments have been performed at a pH of 1.7 and 25 º C on aqueous solutions adjusted to an ionic strength of 0.05 M (Na⁺, H⁺)ClO₄. The competitive binding method has been used whereby methyl orange (MO) is first encapsulated by ß-CD and is then substituted by ADA. It has been shown that the derivatives studied form host-guest type complexes. The calculated stability constants, reported as log K₁, were estimated to be 3.9 ± 0.1, 5.1 ± 0.2 and 3.3 ± 0.1, for AM, RIM and MEM, respectively. The factors that govern the strength of binding ADA with ß-CD have been discussed and an attempt was made to rationalise the variation in the established stability constants for the ADA-ß-CD complexes. General experimental conditions required for the determination of the stability constants of ADA with ß-CD with the use of MO as an auxiliary agent were evaluated. The optimised experimental conditions are recommended. It has been concluded that MO, even though commonly used in this type of study, does not meet the optimal and recommended conditions.

N,1-Dialkyl-7-(alkylamino)-4-(alkylimino)-1,4-dihydroquinoline-3-carboxamides and Their 4-Oxo Derivatives: Synthesis and Properties

Van Es, T.Staskun, B.

Abstract: Methods are described for accessing the little known class of 4-alkyliminoquinoline-3- carboxamide title compounds 4; viz., from 4-oxoquinoline-3-carboxylic acids treated successively with thionyl chloride and amine, from 4-oxoquinoline-3-carboxylic esters treated likewise, and from the hydrogen chloride salt of a 4-alkyliminoquinoline-3-carboxylic ester and amine. Mechanistic aspects of the syntheses are discussed, and some spectroscopic and chemical properties of the title compounds are presented.

The Design of Group 4 Cyclopentadienyl, Olefin-Polymerisation Catalysts

Grimmer, N.E.Coville, N.J.

Abstract: This review focuses on Group 4 metallocenes and their use in the polymerisation of _-olefins. A brief overview of their history as well as theories concerning the mechanistic details of the polymerisation reaction precedes a discussion on the design of these polymerisation catalysts. This latter section will cover what effect metal, ligand and bridge choice has on polymerisation activity and the physical properties of the polymer produced. A major drawback to the use of these catalysts in industrial processes is related to the cost of their synthesis, the major problem here being the formation of an unwanted diastereomer during the synthetic process. The techniques employed to overcome these problems are therefore also reviewed. Lastly, the large volume of literature dealing with these catalysts makes it difficult to compare the polymerisation data of different catalysts and laboratories. The review therefore contains tables that attempt to collect the details of the most important polymerisation studies in a comparable and easy to reference manner.

FTIR Spectroelectrochemical Studies on [Ru₃(CO)₁₂] and fac-[Re(Cl)(CO)₃(4bzpy)₂] (4bzpy = 4-benzoylpyridine)

Fatoki, O.S.Mzimba, P.

Abstract: Incorporation of wire mesh platinum electrodes into a standard infrared solution cell yielded an inexpensive and easy to maintain optically transparent thin layer electrochemical (OTTLE) cell, well suited for IR analysis of species with half-lives of seconds to minutes. As test bed, two reactions were investigated, which are discussed in the literature: (i) for [Ru₃(CO)₁₂] evidence was found for at least partial reversibility in the two-electron reduction process to [Ru₃(CO)₁₁]^2- , and (ii) for fac-[Re(Cl)(CO)₃(4bzpy),sub>2] (4bzpy = 4-benzoylpyridine) additional information concerning the two-step electron reduction of the two benzoylpyridine ligands (again partially reversible) could be obtained.

Crystal Structure of [Rh(cacsm-kN,kS)(CO)(PPh₃)].CH₃COCH₃, (cacsm=methyl 2- (cyclohexylamino)-1-cyclopentene-1-dithiocarboxylate) and Kinetics of Iodomethane Oxidative Addition.

Steyn, G.J.J.Roodt, A.

Abstract: The preparation of the acetone solvate of the title complex (methyl 2-(cyclohexylamino)-1- cyclopentene-1-dithiocarboxylato)- kN, kS)carbonyltriphenyl-phosphinerhodium(I), is described. The X-ray structure of the complex, [Rh(cacsm)(CO)(PPh3)].CH3COCH3 was determined and a final R-value of 4.52% resulted from refinement of 5059 observed reflections. The [Rh(cacsm)(CO)(PX3)] complexes (1), with X = phenyl (Ph), para-chlorophenyl (p-Cl-Ph), para-methoxyphenyl (p-MeO-Ph) and cyclohexyl (Cy), undergo oxidative addition by iodomethane, forming the Rh(III)-alkyl species (2) via an equilibrium step, followed by the formation of the Rh(III)-acyl species (3) according to the reaction

Chemical Speciation of Chromium in Various Matrices in South African Terrestrial Water Using an Optimised Adsorptive Stripping Voltammetric Procedure Cukrowska, E.Dube, A.

Abstract: Optimization of analytical procedure for the determination of chromium (III)/(VI) speciation is described. A very sensitive adsorptive-catalytic stripping voltammetry method in the presence of diethylenetriaminepentaacetic acid (DTPA) is used for chromium speciation study in surface and ground water with in very different matrices. The effects of various parameters (pH, ligand concentration, potential, collection time, equilibration time,) on the response are optimized. Concentration ratio of chromium (III)/(VI), and interferences from other metals and anions, typical for South African waters, are considered. Results for total chromium determination are compared with atomic absorption spectrometry (AAS) measurements.