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.

The oxidation of dibenzothiophene using oxidovanadium(IV)-containing nanofibres as catalyst

“…V 4+ species exhibit a hyperfine structure derived from the interaction of free electrons (3d 1 ) with the magnetic nuclear moment of 51 V (I = 7/2), and the EPR signal should split eightfold. 26 The additional splitting displayed by the catalyst, VO-fibre and recycled VO-fibre, was due to the anisotropic nature of the magnetic moment of vanadyl on the polymer support. 36 A slightly different splitting pattern was observed on the spectrum of the recycled catalyst (Fig.…”

“…The 26 functionalized nanofibres (Scheme 1) presented a low nitrogen as well as vanadium content. The low nitrogen content was also observed by Fayemi et al 34 upon functionalizing PVBC with triethylenetetramine (TETA) and tris-(2-aminoethyl) amine (TAEA).…”

“…The reaction was observed to produce an overall conversion of less than 17 % in the absence of the catalyst. 26 The turnover frequency (TOF) for dibenzothiophene decreased from 441 to 113 h -1 (Table 1). A plot of mass of catalyst (vanadium + support) against % conversion (Fig.…”

“…To 26 dissolved in 10 mL methanol, 1 g of PVBC nanofibres was added, and the resulting mixture was then shaken on a mechanical shaker for 48 h (Scheme 1). The functionalized nanofibres were then removed, washed with excess methanol, and then dried in air.…”

“…[18][19][20][21][22][23][24][25] The activity and selectivity of metal complexes immobilized on polymer microspheres have been reported in our previous studies to be as efficient as unsupported metal complexes. [26][27][28][29] In an attempt to improve the surface area of the polymeric support, electropsun polymer fibres have also been reportedly employed as an alternative. [30][31][32][33] This paper describes the development of oxidovanadium(IV) catalyst immobilized on 2,2'-(1E,1'E)-(1,2-phenylenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)bis(4-aminophenol)-PVB electrospun nanofibres for the oxidation of dibenzothiophene.…”