Copper based nanomaterials for oxidation catalysis
| dc.contributor.advisor | Steyl, Gideon | |
| dc.contributor.advisor | Roodt, Andreas | |
| dc.contributor.author | Muller, Theunis Jacobus | |
| dc.date.accessioned | 2015-11-20T11:41:21Z | |
| dc.date.available | 2015-11-20T11:41:21Z | |
| dc.date.copyright | 2009-11 | |
| dc.date.issued | 2009-11 | |
| dc.date.submitted | 2009-11 | |
| dc.description.abstract | English: The aim of this study was the synthesis simple O,O-bidentate ligand copper complexes of the type [Cu(Memal)2], [Cu(Etmal)2], [Cu(Trop)2] and [Cu(TropBr3)2], where Memal = 2- methyl-3-hydroxy-4-pyrone, Etmal = 2-ethyl-3-hydroxy-4-pyrone, Trop = Tropolonato and TropBr3 = tri-bromotropolonato and to do an evaluation of the oxidation catalysis of 3,5-ditert- butylcatechol to the 3,5-di-tert-butyl-1,2-benzoquinone and study the kinetics associated therewith. The ligands were selected to provide a systematic range of electronic and steric variation at the Cu(II) metal centre. Characterisation of the complexes was done by infrared spectroscopy (IR) and elemental analysis, as well as an X-ray crystallographic structure determination of selected compounds i.e., [Cu(TropBr3)2(DMSO)2] and 3,5-di-tert-butylcatechol. [Cu(TropBr3)2(DMSO)2] crystallised in the monoclinic space group C2/c with Z = 4 in the unit cell dimensions a = 18.002(7) Å, b = 20.351(7) Å, c = 7.578(3) Å, = 108.331(2) ° and the data were collected at -173 °C. Least-squares refinement led to a value of the conventional R1 index of 0.0320 and Rw = 0.0571 for 2873 reflections having I > 2 (I). The copper ion is coordinated by four oxygen atoms from two tri-bromotropolonato ligands. In addition there are two oxygen atoms from the two dimethylsulphoxide molecules coordinated to the copper centre in the axial positions, ensuring an overall octahedral geometry. The Cu-O(DMSO) bond lengths in the axial positions are significantly longer than the Cu-O bonds in the equatorial positions due to Jahn-Teller distortions. The 3,5-di-tert-butylcatechol crystallised in the triclinic space group P1 with Z = 4 in the unit cell dimensions a = 9.101(5) Å, b = 11.394(5) Å, c = 13.203(5) Å, = 83.653(5) °, = 79.601(5) °, = 85.091(5) °; and the data were collected at -173 °C. Leastsquares refinement led to a value of the conventional R1 index of 0.0124 and Rw = 0.3548 for 5675 reflections having I > 2 (I). The tert-butyl group on the 5 position of the phenyl ring crystallises in a 45:55 % statistically disordered position. A kinetic investigation was conducted to study the catalytic oxidation of 3,5-di-tertbutylcatechol to 3,5-di-tert-butyl-1,2-benzoquinone by the copper complexes listed above. The reaction was studied by two techniques namely, UV-Vis and GC in order to characterise the final product. All four complexes have the ability to oxidize 3,5-di-tert-butylcatechol, but there is a significant difference in the rate of oxidation between the complexes. [Cu(Memal)2] and [CuEtmal)2] have comparable rates and it is much faster than the rate of [Cu(Trop)2] and [Cu(TropBr3)2]. Different solvents also have an effect on the rate of the reaction: in acetonitrile the reaction only proceed to 14% completeness, but in methanol a 52% conversion is achieved in 24 hr under the same conditions. The rate of the reaction exhibits a limiting relationship with respect to molecular oxygen concentration. The catalytic mechanism that best describes the kinetics consists of five reversible steps. The first steps involves the coordination of 3,5-di-tert-butylcatechol to the copper followed by a second 3,5-di-tert-butylcatechol coordinating to the copper in the subsequent step. The third step involves the interaction with oxygen and the loss of one 3,5-di-tert-butylcatechol. A limiting value for the rate constant of the copper complex with molecular oxygen, k2 = 3.4(3) s-1 for [Cu(Memal)2] was determined. The fourth step is the rate determining formation of 3,5-di-tert-butyl-1,2 benzoquinone, defined by rate constants k3 and k-3, for [Cu(Memal)] is determined to be 3.7(6) x 10-5 M-1 s-1 and 2(5) x10-6 s-1. The fifth step completes the catalytic cycle and regenerates the starting complex i.e. the coordination of the Memal to the copper. The rates of the reaction seem to be both sterically and electronically dependent. TON and TOF values of 70.4 and 2.93 h-1 were observed for [Cu(Memal)2]. | en_ZA |
| dc.description.abstract | Afrikaans: Die doel van hierdie studie was die sintese van eenvoudige O,O-bidentate ligand koper komplekse van die tipe [Cu(Memal)2], [Cu(Etmal)2], [Cu(Trop)2] en [Cu(TropBr3)2] waar Memal = 2-metiel-3-hydroksie-4-piroon, Etmal = 2-etiel-3-hydroksie-4-piroon, Trop = Tropolonato en TropBr3 = tri-bromrtroplonato en om `n evalueering van die katalitiese oksidasie van 3,5-di-tert-butielkatekol na die 3,5-di-tert-butiel-1,2-bensokinoon en die kinetika daarmee geassosieer te doen. Die ligande is gekies om `n sistematiese reeks elektroniese en steriese verandering op die Cu(II) metaal senter. Karakterisering van die komplekse is gedoen deur middel van infrarooi spektroskopie (IR) en elementele analise, asook X-straal kristallografiese struktuurbepaling van gekose verbindings bv. [Cu(TropBr3)2(DMSO)2] en 3,5-di-tert-butielkatekol. [Cu(TropBr3)2(DMSO)2] het gekristalliseer in die monokliniese ruimtegroep C2/c met Z = 4 in die eenheidsel met dimensies a = 18.002(7) Å, b = 20.351(7) Å, c = 7.578(3) Å, = 108.331(2) °, en die data was by -173 °C gekollekteer. Kleinste kwadraat verfyning het gelei na `n konvensionele R1 indeks waarde van 0.0320 en Rw = 0.0571 vir 2873 refleksies met I > 2 (I). Die koper ioon is gekoördineer deur vier suurstof atome van twee tri-bromotropoloon ligande. Bykomend hiertoe is daar twee suurstof atome van die twee dimetielsulfoksied molekule aan die koper senter gekoördineer in aksiale posisies; dus is die algehele geometrie oktahedries. Die Cu- O(DMSO) bindingsafstande in die aksiale posisies is langer as die Cu-O bindingsafstande in die ekwatoriale posisies as gevolg van die Jahn-Teller effek. Die 3,5-di-tert-butielkatekol kristalliseer in die trikliniese ruimtegroep P1 met Z = 4 in `n eenheidsel met dimensies a = 9.101(5) Å, b = 11.394(5) Å, c = 13.203(5) Å, = 83.653(5) °, = 79.601(5) °, = 85.091(5) ° en die data was by -173 °C gekollekteer. Kleinste kwadraat verfyning het gelei na `n konvensionele R1 indeks waarde van 0.0124 en Rw = 0.3548 vir 5675 refleksies met I > 2 (I). Die tert-butiel groep op die 5-posisie van die feniel ring het uit gekristaliseer in `n 45:55 % statistiese vervormde posisie. `n Kinetiese ondersoek is uitgevoer om die katalitiese oksidasie van 3,5-di-tert-butielkatekol na 3,5-di-tert-butiel-1,2-bensokinoon deur die bogenoemde koper komplekse te bestudeer. Die reaksie is met behulp van twee metodes bestudeer, naamlik UV-Vis spektroskopie en gaskromatografie (GC) ten einde die finale produk te karakteriseer. Al vier komplekse het die vermoë om 3,5-di-tert-butielkatekol te oksideer, maar daar is `n noemenswaardige verskil in die tempo van oksidasie tussen die verskillende komplekse. [Cu(Memal)2] en [CuEtmal)2] het vergelykbare tempos wat aansienlik vinniger is as die tempos van [Cu(Trop)2] en [Cu(TropBr3)2]. Verskillende oplosmiddels beïnvloed ook die tempo van die reaksie: in asetonitriel bereik die reaksie slegs 14% volledigheid maar in metanol bereik die reaksie 52% omskakeling binne 24 uur onder dieselfde reaksietoestande. Die tempo van die reaksie stel `n beperkende verhouding ten toon, ten opsigte van molekulêre suurstof konsentrasie. Die katalitiese meganisme wat die kinetika die beste beskryf bestaan uit vyf omkeerbare stappe. Die eerste stap behels die koördinasie van 3,5-di-tert-butielkatekol aan die koper en `n tweede 3,5-di-tert-butielkatekol wat aan die koper koördineer in die daaropvolgende stap. Die derde stap behels die interaksie van suurstof en die verlies van een 3,5-di-tertbutielkatekol. `n Beperkende waarde vir die tempo konstante van die koper kompleks met molekulêre suurstof, k2 = 3.4(3) s-1 vir [Cu(Memal)2] is bepaal. Die vierde stap is die tempobepalende vorming van 3,5-di-tert-butiel-1,2-bensokinoon gedefinieer deur tempo konstantes k3 en k-3, en is onderskeidelik bepaal as 3.7(6) x 10-5 M-1.s-1 en 2(5) x 10-6 s-1 vir [Cu(Memal)]. Die vyfde stap voltooi die katalitiese kringloop en vorm die begin kompleks, met ander woorde die koördinasie van die Memal aan die koper. Die tempos van die reakse blyk beide steries en elektronies afhanklik te wees. TON en TOF waardes van 70.4 en 2.93 h- 1 was waargeneem vir [Cu(Memal)2]. | af |
| dc.description.sponsorship | University of the Free State, MNS cluster | en_ZA |
| dc.description.sponsorship | Sasol | en_ZA |
| dc.description.sponsorship | Thrip | en_ZA |
| dc.description.sponsorship | National Research Foundation (NRF) | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/1700 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Dissertation (M.Sc. (Chemistry))--University of the Free State, 2009 | en_ZA |
| dc.subject | Nanostructured materials | en_ZA |
| dc.subject | Copper compounds -- Oxidation | en_ZA |
| dc.subject | Catalysis | en_ZA |
| dc.subject | Limiting kinetics | en_ZA |
| dc.subject | Kinetics | en_ZA |
| dc.subject | Crystal structure | en_ZA |
| dc.subject | Steric parameters | en_ZA |
| dc.subject | Electonic parameters | en_ZA |
| dc.subject | Oxidation | en_ZA |
| dc.subject | Copper | en_ZA |
| dc.subject | 3,5-di-tert-butylcatechol | en_ZA |
| dc.subject | 3,5-di-tert-butyl-1,2 benzoquinone | en_ZA |
| dc.title | Copper based nanomaterials for oxidation catalysis | en_ZA |
| dc.type | Dissertation | en_ZA |