Sibusiso Mtongana - Academia.edu (original) (raw)

Papers by Sibusiso Mtongana

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes

The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR' moiety results in ... more The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR' moiety results in unsymmetrical dialkyl-substituted N-alkyl-N-alkyl(aryl)-N'-acylthioureas, R"C(O)NHC(S)NRR' (HL) displaying E,Z configurational isomerism in solution. The isomerism manifests itself by the duplication of resonances of the N-alkyl groups in the 1 H and 13 C NMR spectra. In one class of these ligands where R and R' groups are non-equivalent alkyl groups the isomerism is easily observable at 298 K in chloroform. In the other class where R' is still an alkyl group and R is a para-substituted phenyl group the isomerism is only observable at much lower temperatures due to a lower barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond (X = O-CH 3 , H and NO 2). The electron-withdrawing nature of the nitro group in N-methyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthiourea, HL 3A and N-pentyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthiourea, HL 3D result in the E,Z isomerism of these ligands not observable even at 198 K in dichloromethane. The distribution of E and Z isomers of the unbound ligands vary depending on these R and R' groups. Several E isomers of these ligands have been isolated and structurally characterised and the (S)C-NRR' bond falls in the range [1.343(3)-1.329(3) Å] which shorter than the average C-N single bond of 1.472(5) Å. The E,Z configurational isomerism in the unbound ligands is passed on to the Pt(II) chelates derived from these ligands. The presence of cis-[Pt(ZZ-L-S,O) 2 ], cis-[Pt(EZ-L-S,O) 2 ] and cis-[Pt(EE-L-S,O) 2 ] is readily observable by means of 195 Pt NMR spectroscopy which shows three well resolved resonances, and this can be confirmed by 1 H and 13 C NMR spectra of these complexes. The 195 Pt nuclei are spatially linked to the 13 C nuclei, four bonds away resulting in 4 J(195 Pt-13 C) couplings with N-CH 2-or N-CH 3 carbons in a W pathway. The 195 Pt NMR spectra are also linked to N-CH 2-or N-CH 3 proton resonances by means of the ZZ, EZ and EE isomer distributions. Assignment of these configurational isomers was then achieved by means of a combination of low magnetic field 13 C NMR spectra and high-resolution gHSQC (1 H/ 13 C) NMR experiments. 1 H NMR rotational dynamics study showed that the barrier to rotation, ΔG ≠ , around the (S)C-N(Me)(para-X-Ph) bond in cis-bis(N-methyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1A-S,O) 2 ]; cis-bis(N-methyl-N-phenyl-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 2A-S,O) 2 ] and cisbis(N-methyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 3A-S,O) 2 ] complexes was observed to follow the order: (electron-withdrawing group) NO 2 < H < (electron-donating group) O-CH 3. The ZZ isomer was observed to be favoured over the EZ and EE isomers in this order of the para-substituent on the Nphenyl group. The 1 H dynamic NMR trends about the barrier to rotation, ΔG ≠ , around the (S)C-N(Me)(para-X-Ph) bond were also complemented by DFT linear transit calculations. The isomer distributions were also influenced by solvent polarity and the temperature at which the distributions are determined apart from the electronic influence of the para-substituent of the N-phenyl group. The ZZ, EZ and EE isomers of complexes derived from N-alkyl-N-(para-X-Ph)-N'-acylthioureas with varying Nalkyl substituent (methyl, isopropyl, cyclohexyl and n-pentyl) were determined from the 195 Pt NMR spectra which http://scholar.sun.ac.za/ were measured under identical conditions. The ZZ isomer was observed to be favoured over the EZ and EE isomers upon methyl group substitution with a bulkier alkyl group in the order: methyl < isopropyl < cyclohexyl < n-pentyl. Qualitatively it has been shown that a bulkier N-pentyl group increases the barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond over the N-methyl group and this leads to higher concentrations of the ZZ isomer over the EZ and EE isomers. The combined effects of the electron-donating substituent (X = O-CH 3) on the N-(para-X-Ph) group and the bulkier N-alkyl group (n-pentyl) result in highest ZZ concentration (76 %) over EZ and EE isomers in the complex cis-bis(N-pentyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1D-S,O) 2 ]. The lowest concentration ZZ (27 %) is obtained in the complex cis-bis(N-methyl-N-(4-nitro-phenyl)-N'-2,2dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 3A-S,O) 2 ] when the coordinated ligand has both N-methyl group and N-(4-nitro-Ph) group which both lower the barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond. A crystal of the complex cis-bis(N-pentyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1D-S,O) 2 ] has been isolated and structurally characterised and was shown to be in the ZZ configuration, which is the major component (76 %) in chloroform. This is the first example of Pt(II) chelates with asymmetrically disubstituted ligands to be reported.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry, 2003

Unsymmetrical, dialkyl‐substituted N,N‐dialkyl‐N′‐acyl(aroyl)thioureas show E,Z configurational i... more Unsymmetrical, dialkyl‐substituted N,N‐dialkyl‐N′‐acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis‐[Pt(ZZ‐L‐S,O)2], cis‐[Pt(EZ‐L‐S,O)2] and cis‐[Pt(EE‐L‐S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long‐range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis‐[Pt(ZZ‐L‐S,O)2], cis‐[Pt(EZ‐L‐S,O)2] and cis‐[Pt(EE‐L‐S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis‐bis[N‐methyl‐N‐(tert‐butyl)‐N′‐(2,2‐dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of Characterisation of Combustion Chamber Deposits Formed in Direct Injection Spark Ignition (DISI) Engines during an On-Road Vehicle Trial

SAE Technical Paper Series, Oct 25, 2010

Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the S... more Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the South African and global vehicle pares. South Africa is in a unique position because a significant portion of all liquid fuels consumed are synthetically produced from coal and gas. These fuels are mainly supplied into the inland regions, particularly the Gauteng province, the economic heartland of South

Research paper thumbnail of Unambiguous assignment of the E, Z configuratonal isomers of platinum complexes of N, N-dialkyl-N'-acyl (aroyl) thioureas by means of 1 H detected 13 C-195 Pt correlation NMR spectroscopy

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes

The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR’ moiety results in ... more The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR’ moiety results in unsymmetrical dialkyl-substituted N-alkyl-N-alkyl(aryl)-N’-acylthioureas, R”C(O)NHC(S)NRR’ (HL) displaying E,Z configurational isomerism in solution. The isomerism manifests itself by the duplication of resonances of the N-alkyl groups in the H and C NMR spectra. In one class of these ligands where R and R’ groups are non-equivalent alkyl groups the isomerism is easily observable at 298 K in chloroform. In the other class where R’ is still an alkyl group and R is a para-substituted phenyl group the isomerism is only observable at much lower temperatures due to a lower barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond (X = O-CH3, H and NO2). The electron-withdrawing nature of the nitro group in N-methyl-N-(4-nitro-phenyl)-N’-2,2-dimethylpropanoylthiourea, HL and N-pentyl-N(4-nitro-phenyl)-N’-2,2-dimethylpropanoylthiourea, HL result in the E,Z isomerism of these ligands not obse...

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of Corrosion challenges and prevention in Ethyl Acetate (EA) production and related processes – An overview

Ethyl Acetate (EA) production plants are among the many industrial facilities where corrosion is ... more Ethyl Acetate (EA) production plants are among the many industrial facilities where corrosion is a major concern. EA plant suffers from various forms of corrosion because of the simultaneous use of strong mineral acids, high temperature and flow environment, presence of aqueous environment, and feedstock contamination. Stainless steels, which are mostly used in EA plants, owed their protective characteristics to their metallurgical composition and the characteristic to form a thin passive oxide layer upon exposure to the atmosphere. However, mineral acids and chloride attacks and the subsequent breakdown of passive films have resulted in continuous corrosion challenges in EA plants. The involvement of various corrosive factors in EA plants has worsened the corrosion problems and often complicate understanding the sources/causes of corrosion. This review article discusses the various corrosion problems, causes, mechanisms, as well as control and preventive strategies in ethyl acetate...

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes /

Dissertation (PhD)--University of Stellenbosch, 2006. Bibliography.

Research paper thumbnail of Characterisation of Combustion Chamber Deposits Formed in Direct Injection Spark Ignition (DISI) Engines during an On-Road Vehicle Trial

SAE Technical Paper Series, 2010

Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the S... more Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the South African and global vehicle parcs. South Africa is in a unique position because a significant portion of all liquid fuels consumed are synthetically produced from coal and gas. These fuels are mainly supplied into the inland regions, particularly the Gauteng province, the economic heartland of South Africa and the most densely populated area in the country. It is important to understand the performance of synthetic fuels in the latest generation engines, in order to ensure that these fuels are fit for use in these new applications. The latest generation DISI gasoline engines (also known as Gasoline Direct Injection™ and Fuel Stratified Injection™) differ significantly in operation to older Port Fuel Injected (PFI) engines. Although there is literature available on the relationship between crude-derived fuel composition and the composition of DISI engine deposits, no such information exists on the possible effects of synthetic fuel composition on such deposits. An on-road vehicle trial was conducted to assess and compare the effect of synthetic and crude-derived fuels on such engine deposits. During the on-road trial, four similar Volkswagen FSI vehicles were tested under similar conditions over a distance of 20 000 km in order to determine the relative performance of the fuels evaluated. Some of the fuels evaluated during this trial were synthetic fuels (one additised with a detergent additive and two unadditised Fischer-Tropsch fuels), while the fourth fuel was a conventional crude-derived fuel. Comprehensive characterisation of these fuels by Nuclear Magnetic Resonance spectroscopy (NMR) and two dimensional GC analysis (GCxGC-TOFMS) showed very significant differences in fuel composition between the synthetic and the crude-derived fuels. The engine deposits were characterised using various solid-state 13 C NMR techniques, thermogravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). This study confirmed that the methodologies developed for the characterisation of deposits from PFI engines could also be applied to DISI engines, which is consistent with previous literature findings. The species Page 2 of 30 identified in these DISI deposits were shown to be similar in nature to the deposits formed in PFI vehicles. Similarly, it was shown that the deposits formed during the combustion of synthetic gasoline were similar in composition to those formed during operation on a crude-derived fuel. Some differences in the quantity of the deposits formed were observed between the vehicles that ran on synthetic fuels and those that ran on crudederived fuels. Despite the differences in composition between the synthetic and crude-derived fuels, the bulk chemical composition of the deposits generated from these fuels are not significantly different. Moreover, the overall performance of these DISI-equipped test vehicles were unaffected by the fuel composition over the 20 000km test period. However, it must be kept in mind that although vehicle preparation, driving conditions and fuel compositions were well controlled, ambient conditions were not controlled. Results are therefore considered to be comparative.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry, 2003

ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configur... more ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long-range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis-bis[N-methyl-N-(tert-butyl)-N′-(2,2-dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry - MAGN RESON CHEM, 2003

ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configur... more ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long-range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis-bis[N-methyl-N-(tert-butyl)-N′-(2,2-dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes

The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR' moiety results in ... more The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR' moiety results in unsymmetrical dialkyl-substituted N-alkyl-N-alkyl(aryl)-N'-acylthioureas, R"C(O)NHC(S)NRR' (HL) displaying E,Z configurational isomerism in solution. The isomerism manifests itself by the duplication of resonances of the N-alkyl groups in the 1 H and 13 C NMR spectra. In one class of these ligands where R and R' groups are non-equivalent alkyl groups the isomerism is easily observable at 298 K in chloroform. In the other class where R' is still an alkyl group and R is a para-substituted phenyl group the isomerism is only observable at much lower temperatures due to a lower barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond (X = O-CH 3 , H and NO 2). The electron-withdrawing nature of the nitro group in N-methyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthiourea, HL 3A and N-pentyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthiourea, HL 3D result in the E,Z isomerism of these ligands not observable even at 198 K in dichloromethane. The distribution of E and Z isomers of the unbound ligands vary depending on these R and R' groups. Several E isomers of these ligands have been isolated and structurally characterised and the (S)C-NRR' bond falls in the range [1.343(3)-1.329(3) Å] which shorter than the average C-N single bond of 1.472(5) Å. The E,Z configurational isomerism in the unbound ligands is passed on to the Pt(II) chelates derived from these ligands. The presence of cis-[Pt(ZZ-L-S,O) 2 ], cis-[Pt(EZ-L-S,O) 2 ] and cis-[Pt(EE-L-S,O) 2 ] is readily observable by means of 195 Pt NMR spectroscopy which shows three well resolved resonances, and this can be confirmed by 1 H and 13 C NMR spectra of these complexes. The 195 Pt nuclei are spatially linked to the 13 C nuclei, four bonds away resulting in 4 J(195 Pt-13 C) couplings with N-CH 2-or N-CH 3 carbons in a W pathway. The 195 Pt NMR spectra are also linked to N-CH 2-or N-CH 3 proton resonances by means of the ZZ, EZ and EE isomer distributions. Assignment of these configurational isomers was then achieved by means of a combination of low magnetic field 13 C NMR spectra and high-resolution gHSQC (1 H/ 13 C) NMR experiments. 1 H NMR rotational dynamics study showed that the barrier to rotation, ΔG ≠ , around the (S)C-N(Me)(para-X-Ph) bond in cis-bis(N-methyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1A-S,O) 2 ]; cis-bis(N-methyl-N-phenyl-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 2A-S,O) 2 ] and cisbis(N-methyl-N-(4-nitro-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 3A-S,O) 2 ] complexes was observed to follow the order: (electron-withdrawing group) NO 2 < H < (electron-donating group) O-CH 3. The ZZ isomer was observed to be favoured over the EZ and EE isomers in this order of the para-substituent on the Nphenyl group. The 1 H dynamic NMR trends about the barrier to rotation, ΔG ≠ , around the (S)C-N(Me)(para-X-Ph) bond were also complemented by DFT linear transit calculations. The isomer distributions were also influenced by solvent polarity and the temperature at which the distributions are determined apart from the electronic influence of the para-substituent of the N-phenyl group. The ZZ, EZ and EE isomers of complexes derived from N-alkyl-N-(para-X-Ph)-N'-acylthioureas with varying Nalkyl substituent (methyl, isopropyl, cyclohexyl and n-pentyl) were determined from the 195 Pt NMR spectra which http://scholar.sun.ac.za/ were measured under identical conditions. The ZZ isomer was observed to be favoured over the EZ and EE isomers upon methyl group substitution with a bulkier alkyl group in the order: methyl < isopropyl < cyclohexyl < n-pentyl. Qualitatively it has been shown that a bulkier N-pentyl group increases the barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond over the N-methyl group and this leads to higher concentrations of the ZZ isomer over the EZ and EE isomers. The combined effects of the electron-donating substituent (X = O-CH 3) on the N-(para-X-Ph) group and the bulkier N-alkyl group (n-pentyl) result in highest ZZ concentration (76 %) over EZ and EE isomers in the complex cis-bis(N-pentyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1D-S,O) 2 ]. The lowest concentration ZZ (27 %) is obtained in the complex cis-bis(N-methyl-N-(4-nitro-phenyl)-N'-2,2dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 3A-S,O) 2 ] when the coordinated ligand has both N-methyl group and N-(4-nitro-Ph) group which both lower the barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond. A crystal of the complex cis-bis(N-pentyl-N-(4-methoxy-phenyl)-N'-2,2-dimethylpropanoylthioureato)platinum(II), cis-[Pt(L 1D-S,O) 2 ] has been isolated and structurally characterised and was shown to be in the ZZ configuration, which is the major component (76 %) in chloroform. This is the first example of Pt(II) chelates with asymmetrically disubstituted ligands to be reported.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry, 2003

Unsymmetrical, dialkyl‐substituted N,N‐dialkyl‐N′‐acyl(aroyl)thioureas show E,Z configurational i... more Unsymmetrical, dialkyl‐substituted N,N‐dialkyl‐N′‐acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis‐[Pt(ZZ‐L‐S,O)2], cis‐[Pt(EZ‐L‐S,O)2] and cis‐[Pt(EE‐L‐S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long‐range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis‐[Pt(ZZ‐L‐S,O)2], cis‐[Pt(EZ‐L‐S,O)2] and cis‐[Pt(EE‐L‐S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis‐bis[N‐methyl‐N‐(tert‐butyl)‐N′‐(2,2‐dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of Characterisation of Combustion Chamber Deposits Formed in Direct Injection Spark Ignition (DISI) Engines during an On-Road Vehicle Trial

SAE Technical Paper Series, Oct 25, 2010

Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the S... more Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the South African and global vehicle pares. South Africa is in a unique position because a significant portion of all liquid fuels consumed are synthetically produced from coal and gas. These fuels are mainly supplied into the inland regions, particularly the Gauteng province, the economic heartland of South

Research paper thumbnail of Unambiguous assignment of the E, Z configuratonal isomers of platinum complexes of N, N-dialkyl-N'-acyl (aroyl) thioureas by means of 1 H detected 13 C-195 Pt correlation NMR spectroscopy

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes

The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR’ moiety results in ... more The partial double bond character of the carbon-nitrogen bond of the (S)C-NRR’ moiety results in unsymmetrical dialkyl-substituted N-alkyl-N-alkyl(aryl)-N’-acylthioureas, R”C(O)NHC(S)NRR’ (HL) displaying E,Z configurational isomerism in solution. The isomerism manifests itself by the duplication of resonances of the N-alkyl groups in the H and C NMR spectra. In one class of these ligands where R and R’ groups are non-equivalent alkyl groups the isomerism is easily observable at 298 K in chloroform. In the other class where R’ is still an alkyl group and R is a para-substituted phenyl group the isomerism is only observable at much lower temperatures due to a lower barrier to rotation around the (S)C-N(alkyl)(para-X-Ph) bond (X = O-CH3, H and NO2). The electron-withdrawing nature of the nitro group in N-methyl-N-(4-nitro-phenyl)-N’-2,2-dimethylpropanoylthiourea, HL and N-pentyl-N(4-nitro-phenyl)-N’-2,2-dimethylpropanoylthiourea, HL result in the E,Z isomerism of these ligands not obse...

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of Corrosion challenges and prevention in Ethyl Acetate (EA) production and related processes – An overview

Ethyl Acetate (EA) production plants are among the many industrial facilities where corrosion is ... more Ethyl Acetate (EA) production plants are among the many industrial facilities where corrosion is a major concern. EA plant suffers from various forms of corrosion because of the simultaneous use of strong mineral acids, high temperature and flow environment, presence of aqueous environment, and feedstock contamination. Stainless steels, which are mostly used in EA plants, owed their protective characteristics to their metallurgical composition and the characteristic to form a thin passive oxide layer upon exposure to the atmosphere. However, mineral acids and chloride attacks and the subsequent breakdown of passive films have resulted in continuous corrosion challenges in EA plants. The involvement of various corrosive factors in EA plants has worsened the corrosion problems and often complicate understanding the sources/causes of corrosion. This review article discusses the various corrosion problems, causes, mechanisms, as well as control and preventive strategies in ethyl acetate...

Research paper thumbnail of A multinuclear (1H, 13C, 31P and 195Pt) magnetic resonance spectroscopy study of mixed ligand platinum(II) complexes with new N,N-dialkyl-N'-acyl(aroyl)thioureas as ligands

Research paper thumbnail of A multinuclear magnetic resonance spectroscopy study of E/Z configurational isomers of unsymmetrical N-alkyl-N-alkyl(aryl)-N'-acylthioureas of platinum(II) complexes /

Dissertation (PhD)--University of Stellenbosch, 2006. Bibliography.

Research paper thumbnail of Characterisation of Combustion Chamber Deposits Formed in Direct Injection Spark Ignition (DISI) Engines during an On-Road Vehicle Trial

SAE Technical Paper Series, 2010

Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the S... more Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the South African and global vehicle parcs. South Africa is in a unique position because a significant portion of all liquid fuels consumed are synthetically produced from coal and gas. These fuels are mainly supplied into the inland regions, particularly the Gauteng province, the economic heartland of South Africa and the most densely populated area in the country. It is important to understand the performance of synthetic fuels in the latest generation engines, in order to ensure that these fuels are fit for use in these new applications. The latest generation DISI gasoline engines (also known as Gasoline Direct Injection™ and Fuel Stratified Injection™) differ significantly in operation to older Port Fuel Injected (PFI) engines. Although there is literature available on the relationship between crude-derived fuel composition and the composition of DISI engine deposits, no such information exists on the possible effects of synthetic fuel composition on such deposits. An on-road vehicle trial was conducted to assess and compare the effect of synthetic and crude-derived fuels on such engine deposits. During the on-road trial, four similar Volkswagen FSI vehicles were tested under similar conditions over a distance of 20 000 km in order to determine the relative performance of the fuels evaluated. Some of the fuels evaluated during this trial were synthetic fuels (one additised with a detergent additive and two unadditised Fischer-Tropsch fuels), while the fourth fuel was a conventional crude-derived fuel. Comprehensive characterisation of these fuels by Nuclear Magnetic Resonance spectroscopy (NMR) and two dimensional GC analysis (GCxGC-TOFMS) showed very significant differences in fuel composition between the synthetic and the crude-derived fuels. The engine deposits were characterised using various solid-state 13 C NMR techniques, thermogravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). This study confirmed that the methodologies developed for the characterisation of deposits from PFI engines could also be applied to DISI engines, which is consistent with previous literature findings. The species Page 2 of 30 identified in these DISI deposits were shown to be similar in nature to the deposits formed in PFI vehicles. Similarly, it was shown that the deposits formed during the combustion of synthetic gasoline were similar in composition to those formed during operation on a crude-derived fuel. Some differences in the quantity of the deposits formed were observed between the vehicles that ran on synthetic fuels and those that ran on crudederived fuels. Despite the differences in composition between the synthetic and crude-derived fuels, the bulk chemical composition of the deposits generated from these fuels are not significantly different. Moreover, the overall performance of these DISI-equipped test vehicles were unaffected by the fuel composition over the 20 000km test period. However, it must be kept in mind that although vehicle preparation, driving conditions and fuel compositions were well controlled, ambient conditions were not controlled. Results are therefore considered to be comparative.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry, 2003

ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configur... more ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long-range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis-bis[N-methyl-N-(tert-butyl)-N′-(2,2-dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of Assignment of theE,Z configurational isomers of platinum complexes ofN,N-dialkyl-N?-acyl(aroyl)thioureas by means of triple resonance1H/13C/195Pt PFG correlation NMR spectroscopy

Magnetic Resonance in Chemistry - MAGN RESON CHEM, 2003

ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configur... more ABSTRACT Unsymmetrical, dialkyl-substituted N,N-dialkyl-N′-acyl(aroyl)thioureas show E,Z configurational isomerism at room temperature in solution, which is also expressed in the existence of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes derived from these ligands. These configurational isomers were assigned by means of a double magnetization transfer 1H/13C/195Pt correlation NMR experiment, despite the fact that the long-range 5J(195Pt, 1H) and 4J(195Pt, 13C) scalar couplings are not directly observable in their 1H and 13C spectra at high field. Depending on the ligand structure, the relative amounts of cis-[Pt(ZZ-L-S,O)2], cis-[Pt(EZ-L-S,O)2] and cis-[Pt(EE-L-S,O)2] complexes are in the ranges 40–42% ZZ, 46–47% ZE and 12–13% EE. The cis-bis[N-methyl-N-(tert-butyl)-N′-(2,2-dimethylpropanoyl)thioureato]platinum(II) complex is found to occur exclusively as the ZZ isomer. Copyright © 2003 John Wiley &amp; Sons, Ltd.