title: Oxovanadium(IV)-catalysed oxidation of dibenzothiophene and 4,6-dimethyldibenzothiophene.
abstract: The reaction between [V(IV)OSO(4)] and the tetradentate N(2)O(2)-donor Schiff base ligand, N,N-bis(o-hydroxybenzaldehyde)phenylenediamine (sal-HBPD), obtained by the condensation of salicylaldehyde and o-phenylenediamine in a molar ratio of 2 : 1 respectively, resulted in the formation of [V(IV)O(sal-HBPD)]. The molecular structure of [V(IV)O(sal-HBPD)] was determined by single crystal X-ray diffraction, and confirmed the distorted square pyramidal geometry of the complex with the N(2)O(2) binding mode of the tetradentate ligand. The formation of the polymer-supported p[V(IV)O(sal-AHBPD)] proceeded via the nitrosation of sal-HBPD, followed by the reduction with hydrogen to form an amine group that was then linked to Merrifield beads followed by the reaction with [V(IV)OSO(4)]. XPS and EPR were used to confirm the presence of oxovanadium(IV) within the beads. The BET surface area and porosity of the heterogeneous catalyst p[V(IV)O(sal-AHBPD)] were found to be 6.9 m(2) g(-1) and 180.8 Å respectively. Microanalysis, TG, UV-Vis and FT-IR were used for further characterization of both [V(IV)O(sal-HBPD)] and p[V(IV)O(sal-AHBPD)]. Oxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated using [V(IV)O(sal-HBPD)] and p[V(IV)O(sal-AHBPD)] as catalysts. Progress for oxidation of these model compounds was monitored with a gas chromatograph fitted with a flame ionization detector. The oxidation products were characterized using gas chromatography-mass spectrometry, microanalysis and NMR. Dibenzothiophene sulfone (DBTO(2)) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO(2)) were found to be the main products of oxidation. Oxovanadium(IV) Schiff base microspherical beads, p[V(IV)O(sal-AHBPD)], were able to catalyse the oxidation of sulfur in dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to a tune of 88.0% and 71.8% respectively after 3 h at 40 °C. These oxidation results show promise for potential application of this catalyst in the oxidative desulfurization of crude oils.
authors.affiliation: Department of Chemistry, Rhodes University, Grahamstown, South Africa.
authors.forename: Adeniyi S
authors.initials: AS
authors.lastname: Ogunlaja
authors.forename: Wadzanai
authors.initials: W
authors.lastname: Chidawanyika
authors.forename: Edith
authors.initials: E
authors.lastname: Antunes
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Fernandes
authors.forename: Tebello
authors.initials: T
authors.lastname: Nyokong
authors.forename: Nelson
authors.initials: N
authors.lastname: Torto
authors.forename: Zenixole R
authors.initials: ZR
authors.lastname: Tshentu
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013876:Thiophenes / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
chemical_list: C414426:4,6-dimethyldibenzothiophene; D013876:Thiophenes; C075743:oxovanadium IV; D014638:Vanadates; C016366:dibenzothiophene