Kinetics and mechanism of the oxidation of ethyl xanthate and ethyl thiocarbonate by hydrogen peroxide

Abstract

Kinetic studies on the oxidation of ethyl xanthate (O-ethyl dithiocarbonate) by hydrogen peroxide have been conducted for a range of ethyl xanthate and hydrogen peroxide concentrations over the pH range 8-12. The initial reaction product is a canonical form of O-ethyl S-oxodithiocarbonate. Further oxidation leads to a bifurcation in the reaction pathway, with the formation of either O-ethyl thiocarbonate or a canonical form of O-ethyl Soxoperoxydithiocarbonate. The partitioning of the reaction between these alternative reaction paths is pH dependent, with the proportion directed towards the O-ethyl thiocarbonate branch increasing over the pH range 10 to12. Further oxidation of O-ethyl thiocarbonate leads to the formation of O-ethyl S-oxothiocarbonate (or a canonical form thereof ), analogous to the initial oxygen addition to ethyl xanthate. For both reaction branches the ultimate sulfur-containing product is sulfate. Apart from the process controlling the bifurcation, the reaction kinetics can be modelled as a series of bimolecular oxygen addition steps. This kinetic model is supported by hydroxyl radical scavenging experiments (using tert-butyl alcohol) that suggest no involvement by OH ؒ . The pH dependence of the rate parameters indicates that reaction occurs exclusively with H 2 O 2 rather than HO 2 Ϫ , consistent with the expected nucleophilic attack at the peroxide oxygen. The process controlling the partitioning between the two alternative pathways is proposed to originate from an oxygen addition adduct of O-ethyl S-oxodithiocarbonate. This work reveals that a range of potential metal ion complexants may be produced in the industrial application of xanthates (primarily sulfide mineral extraction, but also including viscose rayon production and pesticide manufacture), and that the environmental chemistry of these reagents is more complex than has been previously appreciated.

Degradation of Thiol Collectors Using Ozone at a Low Dosage: Kinetics, Mineralization, Ozone Utilization, and Changes of Biodegradability and Water Quality Parameters

“…and CO 3 2− were observed to be readily generated [10,11,31]. Ionized intermediates, such as O-ethyl thiocarbonate (ETC − ) and O-ethyl peroxydithiocarbonate (EPX − ) were also detected in the oxidation of EX by H 2 O 2 [17]. Therefore, the increase of conductivity directly revealed that some ionic intermediates were generated in the ozonation of collectors.…”

“…Recently, advanced oxidation processes (AOPs), involving ozone [10,11], Fenton's reagents [16], hydrogen peroxide [17], persulfate [18], photocatalysis [19], and photoelectrooxidation [20] have been studied to degrade organic flotation reagents, especially xanthates. As hydroxyl radicals (•OH) have an oxidation-reduction potential (ORP) of 2.8 V, the AOPs have exhibited high efficiency in decomposing flotation reagents and their intermediates.…”

“…Thus, the alkalinity of flotation effluents can enhance the ozonation of organic reagents as OH − ions are the catalyst in decomposing O 3 to generate•OH [23,24]. Additionally, from the viewpoints of practical applications, ozone can be generated in situ, using air or oxygen as sources, in mines, avoiding the transportation and storage of dangerous chemical oxidants such as H 2 O 2 [17] and sodium hypochlorite [9]. Therefore, ozonation is considered to be an appropriate technique to treat flotation effluents in mines.…”

Conformational and spectroscopic study of xanthogen ethyl formates, ROC(S)SC(O)OCH2CH3. Isolation of CH3CH2OC(O)SH

“…To the best of our knowledge, there is no previous report of this molecule in the literature. Only its salts were identified as a decomposition product during the flotation process [9]. The matrix-isolation photochemistry of the smallest molecule, CH 3-OC(S)SC(O)OCH 2 CH 3 , was also investigated.…”

Xanthates: Metabolism by Flavoprotein-Containing Monooxygenases and Antimycobacterial Activity

“…Studies of the reactivity of xanthates with oxygen in the presence of metals have shown that the primary oxidation products with hydrogen peroxide are the corresponding sulphines or perxanthates (Silvester et al, 2002).…”