Electrochemical oxidation of dibenzothiophene compounds on BDD electrode in acetonitrile–water medium

Abstract

The electrochemical oxidation of dibenzothiophene and two derivatives, namely 4methyldibenzothiophene and 4,6-dimethyldibenzothiophene, was investigated either separately or as a mixture, on a BDD anode in a miscible acetonitrile (87.5% v/v)-water (12.5% v/v, 0.01 M NaNO 3) solution. Linear sweep voltammetry, cyclic voltammetry, chronoamperometry and bulk electrolysis under potentiostatic conditions suggested the probable occurrence of two pathways: direct electrochemical oxidation and indirect reaction with hydroxyl radicals and other reactive oxygen species formed at the BDD anode surface during water discharge. The products extracted upon electrolysis at 1.5 and 2.0 V vs. SCE were analyzed by Fourier-transform infrared spectroscopy, gas chromatography-mass spectrometry and ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry (UHPLC-ESI-Q-TOF-MS). The main molecules identified were the corresponding sulfoxides or sulfones, depending on the applied anodic potential. Possible oxidation routes for the dibenzothiophene compounds are proposed.

Recent Advances and Challenges in Developing Technological Methods Assisting Oxidative Desulfurization of Liquid Fuels: A Review

“…Various types of electrolytes, such as acids (H 2 SO 4 /HClO 4 and acetic acid), bases (NaOH ,, and KOH), salts (NaCl and cerium nitrate Ce­(NO 3 ) 3 , ), acid/salt (H 2 SO 4 /chromium sulfate hexahydrate (Cr 2 (SO 4 ) 3 ·6H 2 O)), acetonitrile/water, and ionic liquids, have been used in the ECODS process. The anode catalysts, such as CeO 2 /activated carbon, β-PbO 2 /activated carbon, β-PbO 2 /Ti, AAO-CeO 2 , boron-doped diamond (BDD), graphite, , iron, copper, platinum, and glassy carbon electrodes modified with gold-polyaniline (Au-PANI), and cathode catalysts, such as copper pillar, platinum, graphite, , nickel, stainless steel, etc., have been applied in this process. The anode materials and electrolytes have the most important role in the ECODS.…”

Study of the electrochemical oxidation of 4,6-dimethyldibenzothiophene on a BDD electrode employing different techniques

“…Binary mixtures tend to be more useful than pure solvents for practical application or better detection. The application of cyclic voltammetry (CV) in pure acetonitrile (ACN) has shown the irreversibility of the oxidation of DBT, 4-methyldibenzothiophene (4-MDBT) and 4,6-DMDBT [46][47][48], whereas the presence of water in this medium influences the mechanism of the electrochemical oxidation [27,47,49]. The study of the electrochemical oxidation of…”

“…To clarify the mechanism involved, it is necessary to characterize the behavior of the sulfoxide during the bulk electrolysis of 4,6-DMDBT using a BDD electrode. Despite its high cost, BDD shows a high reproducibility in the electrochemical response, stability, resistance to corrosion and low surface fouling related to adsorbed oxidation products [49], which justifies its use.…”

“…5 that, when E > 1.7 V was applied, 4,6-DMDBT was directly transformed into 4,6-DMDBTO2 with the participation of two water molecules and the exchange of four electrons and release of four protons. At high anode potentials (E ˃ 1.7 V), the participation of oxidizing species [O], like hydroxyl radical, generated upon electrolysis of water cannot be discarded either in the oxidative process [49].…”

“…with a concomitant decay of the Ip(I) value (see Fig.2c). This behavior can be attributed to the selective oxidation of 4,6-DMDBT to 4,6-DMDBTO2 (4,6dimethyldibenzothiophene sulfone) through 4,6-DMDBTO (4,6-dimethyldibenzothiophene sulfoxide) in the presence of water[49], as will be demonstrated below. Based on these results, a DPV curve was recorded in ACN (93.5% v/v)-water (6.5% v/v, 0.010 M LiClO4) matrix, i.e., ensuring a large excess water.Fig.…”