Stepwise Oxidation of Thiophene and Its Derivatives by Hydrogen Peroxide Catalyzed by Methyltrioxorhenium(VII)

Abstract

The oxidation of thiophene derivatives by hydrogen peroxide is catalyzed by methyltrioxorhenium(VII) (CH(3)ReO(3)). This compound reacts with hydrogen peroxide to form 1:1 and 1:2 rhenium peroxides, each of which transfers an oxygen atom to the sulfur atom of thiophene and its derivatives. Complete oxidation to the sulfone occurs readily by way of its sulfoxide intermediate. The rates for each oxidation step of dibenzothiophenes, benzothiophenes, and substituted thiophenes were determined. The rate constants for the oxidation of the thiophenes are 2-4 orders of magnitude smaller than those for the oxidation of aliphatic sulfides, whereas the rate constants are generally the same for the oxidation of the thiophene oxides and aliphatic sulfoxides. The rate constant for conversion of a sulfide to a sulfoxide (thiophene oxide) increases when a more electron-donating substituent is introduced into the molecule, whereas the opposite trend was found for the reaction that converts a sulfoxide to a sulfone (thiophene dioxide). Mechanisms consistent with this are proposed. The first trend reflects the attack of the nucleophilic sulfur atom of a thiophene center on a peroxide that has been electrophilically activated by coordination to rhenium. The second, more subtle, trend arises when both sulfoxide and peroxide are coordinated to rhenium; the inherently greater nucleophilicity of peroxide then takes control.

Ruthenium catalyzed selective oxidation of aryl thiophenes using hydrogen peroxide

“…In the case of the sterically hindered DMDBT, reaction kinetics allow for the observation of the sulfoxide intermediate. A similar behaviour was already observed by other authors [13].…”

“…Hydrogen peroxide was found to be the most suitable stoichiometric oxidant, although t-BuOOH was also used to oxidise DBT in the presence of Mo catalysts supported on Al 2 O 3 (16%) [7]. H 2 O 2 was used Scheme 1. together with organic acids to generate peroxoacids [4,8,9], Na 2 WO 4 /C 6 H 5 PO 3 H 2 /Me(n-octyl) 3 NHSO 4 [10], Mo(VI) and W(VI) catalysts [11], methyltrioxorhenium (MTO) [12,13], polyoxometalates [8], tungstophosphoric acid [14,15], TiO 2 -supported V 2 O 5 [16], Pd, Cr 2 O 3 , Mn oxides, Co-Mo/Al 2 O 3 [17], TS-1, Ti-beta, Ti-HMS [18]. Solid bases such as hydrotalcites and MgLa mixed oxides as catalysts and nitriles or methanol as solvents were also used to oxidise DBT to DBTSO 2 ; the efficiency of the process was hampered by the basecatalyzed H 2 O 2 unselective decomposition, thus requiring an excess of oxidant [19].…”

“…H NMR (δ, CD 3 OD, 200.13 MHz): 7.90 (dd, 4H, J HH = 4.9 Hz, J HH = 1.8 Hz, H1 and H1 ); 8.65 (dd, 4H, J HH = 7.8, 4.9 Hz, H2 and H2 ); 9.36 (dd, 4H, J HH = 7.8, 1.8 Hz, H3 and H3 )13 C { 1 H} Scheme 2. NMR (δ, CD 3 OD, 50.32 MHz): 126.7 (s, 4C, C2 and C2 ); 127.3 (s, 4C, C4 and C4 , nulls in the 13 C DEPT-135 NMR spectrum); 137.9 (s, 4C, C3 and C3 ); 154.3 (s, 4C, C1 and C1 ); 165.6 (s, 4C, C6 and C6 ); δ 175.0 (s, 4C, C5 and C5 ).…”

Selective Catalytic Oxidation of Organosulfur Compounds with tert‐Butyl Hydroperoxide

“…H 2 O 2 reacts with thiophenic compounds at near ambient temperatures with HCOOH, CCl x COOH (x = 1-3), CF 3 COOH, [4,5] methyltrioxorhenium(vii), [6] phosphotungAbstract: Rates and selectivities for the oxidation of various organosulfur compounds with tert-butyl hydroperoxide were measured on CoAPO-5 (APO = aluminophosphate;…”

Polyoxometalate–Organic Hybrid Molecules as Amphiphilic Emulsion Catalysts for Deep Desulfurization

“…H 2 O 2 , an environmentally benign oxidizer, has been used widely for hazardous waste disposal, oxidation desulfurization, and organic synthesis 9. Thiophene, the most inert compound against an oxidizing agent among all its derivatives, is poisonous to living bodies, the environment, and noble metal catalysts for oil reforming in the petroleum industry 10. However, thiophene is immiscible with aqueous solution of hydrogen peroxide, making the oxidation of thiophene by H 2 O 2 very difficult.…”