Ethanethiol oxidation

Thiirane 1-oxide undergoes acid-catalyzed ring opening by ethanethiol to give ethyl 2-ethylthioethyl disulfide. Treatment of thiirane 1,1-dioxide with thiolate anions, sodium sulfide or thiourea gives /3-mercaptosulfinic acid derivatives (75S55). Thiiranium ions are attacked at carbon by most sulfur nucleophiles (79ACR282), but see Section 5.06.3.4.3 for exceptions. 

The action of nitrous acid on the benzodiazepine A -oxide 38 gives the nitrosoamino derivative 39,234 which reacts with alcohols, ethanethiol and various amino compounds, such as hydrazines and guanidine, by replacement of the methyl(nitroso)amino group.235 Reaction with aziridine affords the aziridinyl compound 40f or the 2-(aziridin-l-yl)ethylainino derivative 40g, depending on the conditions. 

Epoxypropane, see Propylene oxide 2.3- Epoxy-l-propanol, see Glycidol Ethanethiol, see Ethyl mercaptan Ethane 12.1... 

Reaction of 3,4-bis(phenylsulfonyl)-l,2,5-oxadiazole oxide isomers with ethanol and ethanethiol in basic medium gave the expected alkoxy- and alkylthio-substituted (benzenesulfonyl)furoxans, respectively <1996JHC327, 1997FES405>. Nucleophilic substitution of the sulfonyl group of 3,4-bis-(benzenesulfonyl)furoxan 222 in the presence of aqueous NaOH in tetrahydrofuran (THF) furnished the corresponding 3 -0-(3-benzenesulfonylfur-oxan-4-yl) derivative 223 in 79-92% yield (Equation 44) <2004JME1840>. 

Tirey et al. (1993) evaluated the degradation of phorate at three different temperatures. When oxidized at temperatures of 200, 250, and 275 °C, the following reaction products were identified by GC/MS ethanol, ethanethiol, methyl mercaptan, 1,2,4-trithiolane, 1,1-thiobisethane, 1,1 -(methylenebis(thio))bisethane, 1,3,5-trithiane, 0,0-diethyl-5-pentenyl phosphorodithioic acid, ethylthioacetic acid, diethyl disulfide, 2,2 -dithiobisethanol, ethyl-(1-methylpropyl) disulfide, sulfur dioxide, carbon monoxide, carbon dioxide, sulfuric acid, and phosphine. 

Based on pseudo-first-order kinetics of phorate hydrolysis, the following half-lives were reported 52 h at pH 5.7, 61 h at pH 8.5, 62 h at pH 9.4, and 33 h at pH 10.25. The major hydrolysis product is ethanethiol which quickly oxidizes to diethyl disulfide. In addition, diethyl dithiophosphate and diethyl phosphorothioate are potential products of phorate hydrolysis (Hong and Pehkonen, 1998). 

There is also an expectation that thiols can be directly oxidized through to disulfides (RSSR in Fig. 4.4B) (Mestres et ah, 2000 Rauhut et ah, 1996), a mechanism also suggested for the case of 3MH (Murat et ah, 2003) where a protective effect from anthocyanins present in the wine was noted. In one study, the concentrations of both ethanethiol and the related oxidized form of diethyl disulfide in a red wine were found to decrease over a 60-day period, and at a greater rate under aeration (Majcenovic et ah, 2002). However, in a survey of wines over five vintages, the older wines were shovm to contain higher concentrations of diethyl disulfide, and lower concentrations of ethanethiol (Fedrizzi et ah, 2007). 

Experiments were carried out on the oxidation of ethanethiol using a wide variety of metal catalysts. Some typical results are shown in Table I from which it is evident that adding metal salts always results... 

Table I. Oxidation of Ethanethiol Catalyzed by Metal Ions at Standard Conditions...

Using the ethanethiol system as a model, we investigated the dependence of the oxidation rate on the concentration of thiol, of oxygen, and of hydroxide ion. The results for the copper- (10"5M), cobalt-(10"3M), and nickel- (10 3M) catalyzed oxidations, together with the comparable system in the absence of added catalysts are recorded in Table V. 

Oxidation of cyclo(Pro-Pro) with lead tetraacetate afforded the trans-diacetoxy compound (121) in 32% yield. These acetoxy groups could be displaced by sulfur nucleophiles. Thus, with ethanethiol and ZnCl2, it gave the c -3,6-bis(ethylthio) derivative (120) solvolysis by dilute aqueous acid followed by treatment with H2S/ZnCl2 gave the m-dithiol (73CB396), which can be directly oxidized to the episulfide. 

D-Galactose was converted by ethanethiol and hydrochloric acid into crystalline D-galactose diethyl dithioacetal, which was acetonated with acetone-zinc chloride. The product (15) was reduced to the L-fu-citol derivative (16) with Raney nickel. The overall yield of 16 was 29%, and it was characterized as the crystalline 6-p-toluenesulfonate 17. Oxidation of 16 by the Pfitzner-Moffatt reagent55 proceeded readily and, after O-deacetonation, and purification of the product by chromatography on a column of silica gel, L-fucose (18 13% overall yield from D-galactose) and L-fucitol (19 1% yield) were isolated (see Scheme 3). 

The chapter by C. J. Swan and D. L. Trimm, which also emphasizes the effect on catalytic activity of the precise form of a metal complex, shows too that, depending on the metal with which it is associated, the same ligand can act either as a catalyst or inhibitor. The model reaction studied was the liquid-phase oxidation of ethanethiol in alkaline solution, catalyzed by various metal complexes. The rate-determining step appears to be the transfer of electrons from the thiyl anion to the metal cation, and it is shown that some kind of coordination between the metal and the thiol must occur as a prerequisite to the electron transfer reaction (8, 9). In systems where thiyl entities replace the original ligands, quantitative yields of disulfide are obtained. Where no such displacement occurs, however, the oxidation rates vary widely for different metal complexes, and the reaction results in the production not only of disulfide but also of overoxidation and hydrolysis products of the disulfide. 

The effects of adding various metal ions and metal complexes on the rate of a model oxidation reaction have been studied in some detail The model reaction chosen—the oxidation of ethanethiol in aqueous alkaline solution in the presence of metal-containing catalysts—involves the transfer of an electron from the thiol anion to the metal The catalytic activity of additives depends upon the solubility of the particular metal complex and varies according to the nature of the ligand attached to the metal ion. In conjunction with different metals, the same ligand can act either as a catalyst or as an inhibitor. The results are discussed in the light of proposed reaction mechanisms. 

The model reaction chosen, the metal-catalyzed oxidation of ethanethiol to diethyl disulfide by molecular oxygen, is of considerable academic (13, 21) and industrial (11) interest. The over-all reaction may be represented by the scheme... 

Since the oxidation of thiols is known to be strongly catalyzed by traces of metal ions, all experimental techniques were designed to prevent the introduction of extraneous metal ions. Control experiments involving the uncatalyzed oxidation of ethanethiol (5) were used to confirm that contamination was negligible. 

All results reported refer to the oxidation of 0.5M ethanethiol in 2Af sodium hydroxide solutions (50 ml.) under a constant pressure of 750 mm. 

Striking confirmation of this can be seen by inspecting results reported in Table I. Tfce oxidation of ethanethiol by simple metal salts in the presence of 0.25M cyanide occurs slowly and proceeds to a final oxygen uptake of 300% when compared with the theoretical amounts calculated in terms of the reaction... 

A practical consideration in working with ethanethiol is the pervasive stench of this and other volatile thiols, especially as such thiols are used in minute concentration as odor markers for natural gas. It is not easy to perform the standard preparative procedures, during which transfer and filtration operations are performed, in a closed system, and vapors carried through a venting system are detectable at considerable distances, hr small-scale operations, it may be possible to employ a sodium hypochlorite trap to convert the thiols into nonvolatile, oxidized products. 

For alcohol additions, mono- and dicarbene complexes have been synthesized, for palladium, platinum (487-489), and gold (475, 490- 493), from methanol, ethanol, or ethanethiol (494) additions to the isocyanide precursor. The stability of the gold(I) carbenes can be gauged from reactions with halogens which gave the oxidative addition product without loss of the carbene ligand (492). 

Reaction of styrene oxide with sodium ethanethiolate completes the synthesis. 

Next step of this synthesis consisted in the conversion of alcohol (17) to pisiferic acid (1) and this has been described in Fig. (3). The alcohol (17) in hexane was treated with Pb(OAc)4 in presence of iodine at room temperature to obtain the epoxy triene (19) (51%) whose structure was confirmed by spectroscopy. Treatment of (19) with acetyl p-toluene-sulfonic in dichloromethane yielded an olefinic acetate (20) and this was hydrogenated to obtain (21). The compound (22) could be isolated from (21) on subjection to reduction, oxidation and esterification respectively. The conversion of (22) to (23) was accomplished in three steps (reduction with sodium borohydride, immediate dehydration in dichloromethane and catalytic hydrogenation). Demethylation of (23) with anhydrous aluminium bromide and ethanethiol at room temperature produced pisiferic acid (1). Similar treatment of (23) with aluminium chloride and ethanethiol in dichloromethane yielded methylpisiferate (3). 

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