Photooxidation of Dibenzothiophene and 4,6-Dimethyldibenzothiophene Sensitized by N-Methylquinolinium Tetrafluoborate:  Mechanism and Intermediates Investigation

Abstract

Photooxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) sensitized by N-methylquinolinium tetrafluoborate (NMQ(+)BF4-) has been investigated in O2-saturated acetonitrile solutions. Nearly 100% oxidation of DBT and DMDBT was observed, and the oxidized products are predominantly composed of sulfoxides and sulfones, which are formed via photoinduced electron transfer (ET). Such ET processes were studied with fluorescence quenching of NMQ+, time-resolved transient absorption measurement, and ESR experiments. The fluorescence of NMQ+ is efficiently quenched by DBT and DMDBT via diffusion-controlled processes, with bimolecular quenching constants of 1.6 x 10(10) M(-1) s(-1) for DBT and 2.3 x 10(10) M(-1) s(-1) for DMDBT. The electron-transfer nature of the quenching is evidenced by the transient absorption measurement of the neutral radical NMQ*, which is formed by electron transfer from the substrates (DBT or DMDBT) to the excited singlet state of NMQ+. The ESR spectra of the superoxide radical anion (O2*-) trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in the photooxygenation of DBT and DMDBT as well as their sulfoxides manifest that O2 traps an electron from NMQ* to form O2*-. The fact that the formation of sulfoxides and sulfones is greatly suppressed in the presence of benzoquinone (BQ), an efficient electron trap for NMQ* and O2*-, further indicates an ET process in the photooxidation of DBT and DMDBT. As inferred from the control experiments, the role of singlet oxygen (1O2) in the photooxidation is negligible. The intermediates responsible for the formation of sulfoxides and sulfones have been examined in detail.

Assessing the hydroxyl radical and volatilization roles in aquatic fate estimations of sulfur heterocycles: Dibenzothiophene derivatives

“…The degradation of DBT by hydroxyl radicals generated via photolysis of hydrogen peroxide was reported by Shemer et al [8]. Dibenzothiophene and 4,6-dimethyldibenzothiophene (C2-DBT) were degraded when irradiated in the presence of N-methylquinolinium tetrafluoborate in oxygensaturated acetonitrile, with sulfoxides and sulfones as the major products [9].…”

Selective photocatalytic reactions with organic photocatalysts

“…110 It should be noted that bromination of thiophenes is particularly important in the preparation of oligothiophenes and polythiophenes, [111][112][113][114][115][116][117][118][119][120][121][122][123] which have many applications as conductive, semiconductive, nonlinear optical and liquid crystalline materials. 124 Visible light irradiation of [Acr + -Mes]ClO 4 -(λ max = 430 nm, 0.20 mM) in an oxygen-saturated MeCN solution containing 1,2,4-trimethoxybenzene (TMB, 4.0 mM), 50 % aqueous HBr ([HBr] = 20 mM, [H 2 O] = 100 mM) with a xenon lamp attached with color glass filter (λ < 320 nm) for 20 min resulted in formation of a brominated product, 2,4,5trimethoxybromobenzene.…”

Monitoring of Remaining Thiophenic Compounds in Liquid Fuel Desulphurization Studies Using a Fast HPLC-UV Method

“…A comprehensive review has listed most of the published methods. However, all these methods are reported as monitoring tools where neither analytical performance characteristics are provided, nor validation criteria are applied [25,34].…”