A Mild and Environmentally Benign Oxidation of Thiols to Disulfides

Abstract

Thiols were effectively oxidized into disulfides by reacting with hydrogen peroxide in the presence of a catalytic amount of iodide ion or iodine.The controlled oxidative coupling of thiols to disulfides is important in organic synthesis, and a wide range of methods have been developed for this transformation. 1 Thiols are among the functional groups which can be easily over oxidized, therefore, extensive studies have been carried out for their controlled oxidation with molecular oxygen, 2 peroxide, 3 metal oxidants, 4 halogens and derivatives, 5 sulfoxide, 6 and N-oxide. 7 In particular, the methods of oxidative coupling of disulfides with halogens such as I 2 , 5a I 2 /HI, 5b and Br 2 /KHCO 3 5c were carried out under mild reaction conditions, and gave the disulfides in good yields. However, these reactions require a stoichiometric amount of oxidants and long reaction times. Oae and co-workers developed the oxidative coupling of thiols to disulfides by dimethyl sulfoxide in the presence of a catalytic amount of molecular iodine. 5b Although this reaction affords the products in high yield under very mild reaction conditions, there are still some problems such as the requirement of a long reaction time and the production of foulsmelling dimethyl sulfide as a waste product.To develop an environmentally benign oxidative coupling of thiols, we planned to use hydrogen peroxide as a cooxidant for the oxidation of thiols with molecular iodine, because the iodide ion (iodoanion) is easily oxidized to molecular iodine by hydrogen peroxide.Hydrogen peroxide itself can oxidize thiols to the corresponding disulfides; however, alkaline conditions were required. 3a Recently, Bégué et al. reported that disulfides can be efficiently prepared from thiols using 30% hydrogen peroxide in fluoroalcohols at ambient temperature under neutral conditions. 3b Although this method provides the desired compounds in high yields in most cases, fluoroalcohols are expensive for industrial use. Furthermore, the thiols, which are less soluble in the fluoroalcohols, produced the desired disulfides in poor yields. In this paper, we describe a method for the oxidation of thiols 1 to disulfides 2 using 30% hydrogen peroxide catalyzed by iodide ion (Scheme 1). Scheme 1

Sensitive colorimetric assays for α-glucosidase activity and inhibitor screening based on unmodified gold nanoparticles

“…The oxidation of cysteine catalyzed by I -/H 2 O 2 is attributed to the sequence of reactions outlined in Figure 1 [35]. In the primary step, α-glucosidase and GOD catalyze the aerobic production of H 2 O 2 (eqs.…”

“…A color change from wine red to violet can be observed. However, in the presence of iodide ions and H 2 O 2 , cysteine is oxidized to cystine and the oxidation product cystine cannot lead to aggregation of AuNPs [35]. In this work, maltose is used as the nature substrate of α-glucosidase to conduct our proposed sensing approach.…”

Transition metal-free graphene framework based on disulfide bridges as a Li host material

“…The disulfide bond formation method reported by M. Kirihara et al was adopted [53]. First, 100 mg of SHGO was dispersed in 30 ml ethyl acetate (CH 3 CO 2 C 2 H 5 , EtOAc).…”

7.28 Oxidation of Sulfur, Selenium, and Tellurium

“…45 Hydrogen peroxide and peroxyacids are commonly used reagents to oxidize thiols to disulfides, although it is easy to observe byproducts at various oxidation states. 46 A number of selective protocols of oxidation such as water solution of hydrogen peroxide in alcohols as media, 47 48 and catalytic NaI with a stoichiometric amount of 30% hydrogen peroxide 49 have been developed. The hydrogen peroxide urea adduct, UHP, is activated toward the oxidative coupling of thiols by maleic anhydride, whereas aromatic cyclic seleninate esters and spirodioxyselenuranes mediate the oxidation of thiols to disulfides in the presence of H 2 O 2 .…”