Oxidation of thiols with 1-butyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate (BABOD) under non-aqueous conditions

Abstract

The oxidative coupling of thiols to their corresponding disulfides under mild conditions is of significant importance from a biological and practical point of view. [1][2][3] Since thiols are among functional groups, which can be over-oxidised, extensive research has been performed to control their oxidation. [4][5][6][7][8][9][10] The oxidation of thiols to disulfides is a characteristic reaction, and further oxidation to disulfide S-oxides (thiosulfinates), 1,1-dioxides (thiosulfonates), and sulfonic acids is possible. The weak S-S bonds in these compounds impart high reactivity, 11 and in natural products, these moieties and related cyclic analogues are associated with interesting biological activity and DNA-cleaving properties. [12][13][14][15] Cr(VI) oxide is an inexpensive, water-soluble and stable oxidising reagent that is commercially available. This reagent is insoluble in non-aqueous solvents; however, the requirement of aqueous conditions had to be overcome. As part of our continued effort to develop new reagents for the oxidation of organic compounds, [16][17] we now wish to report the synthesis of 1-butyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate 1, as a mild, efficient, stable and inexpensive reagent for oxidation of thiols to the corresponding disulfides. This reagent is an orange powder, which is quite soluble in dichloromethane, chloroform, acetone and acetonitrile and insoluble in non-polar solvents such as carbon tetrachloride, n-hexane and diethyl ether. This reagent is readily prepared by the dropwise addition of an aqueous solution of CrO 3 in HCl 3 M to an aqueous solution of 1-butyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide in quantitative yield at room temperature and could be stored for months without losing its potency.At first, the oxidation of thioanisole as the model compound in various solvents was examined. The solvents examined were dichloromethane, chloroform and acetonitrile. The reactions were carried out by stirring the model compound with one molar amount of 1 under reflux conditions. Dichloromethane and chloroform were inferior solvents to acetonitrile, because the reaction stopped at lower conversions in these solvents than in acetonitrile (Table 1 and Scheme 1). A variety of aromatic and aliphatic thiols 2 were converted into symmetrical

Selective oxidation of alcohols to aldehydes by hydrogen peroxide using hexamolybdochromate(III) as catalyst

“…In continuation of our work on organic oxidations catalysed by polyoxometalates [22][23], we now present our studies on a novel system; the oxidation of alcoholic substrates to aldehydes and ketones using hydrogen peroxide catalysed by an Anderson-type polyoxomolybdate, sodium hexamolybdochromate(III) as shown in Scheme 1. The conversion of alcohols into corresponding carbonyl compounds can also be effected by using carcinogenic chromium reagents [24]. However, the present method utilizes the chromium reagent in a catalytic amount rather than stoichiometric amount.…”

Alcohol Oxidation in Ionic Liquid with UHP and Recyclable Amberlite IR-120 Acidic Resin: A Green Approach

“…Oxidative transformation of alcohols to carbonyl and other industrially important molecules such as phenols is one such attractive area due to the wide ranging utility of these products as precursors and intermediates for many drugs, resins, vitamins, fragrances, plasticizers, pharmaceuticals, disinfectant, bis-phenol A, and other uses. Apart from the conventional methods, [1][2][3][4][5] there have been several reports for preparation of such oxidative products using oxygen or hydrogen peroxide as the oxidants under the influence of different metal catalysts. [6][7][8][9][10] On the other hand, phenol is generally prepared by indirect three steps cumene process in which benzene and propylene are first reacted to form cumene which is oxidized with oxygen to hydroperoxide under high temperature and pressure.…”