Sulfide reductions

Sulfide reduction has an even broader selectivity profile than catalytic hydrogenation or the Bechamp reduction and enables the chemoselective reduction of nitro compounds in presence of C=C, azo, or other nitro groups. The method is insensitive to by-products and high levels of impurities. Depending on pH, different reduction agents with the following stoichiometries are applicable  

The major disadvantages (and the reason it is very seldom used today) are the toxicity and odor of most reducing agents and sulfur-containing organic side-products, and the formation of elemental sulfur. 

---

The industrial processes used for reduction are catalytic hydrogenation, iron reduction (aqueous neutral or acidic, or solvent), and sulfide reduction. 

Bis(4-methylpiperazine-l-yl)-6-nitroquinoxaline (33, R = N02) gave 2,3-bis(4-methylpiperazin-l-yl)-6-quinoxalinamine (33, R = NH2) (Pd/C, H2, 1 atm, dilute HCl, 20°C, h 60%) ° similar treatment of the 5-nitro isomer gave the 5-quinoxalinamine in 15% yield, but sulfide reduction gave a much better yield (cf. analog (45) later in this section). 

Fig. 5.2 The n-Cd(Se,Te)/aqueous Cs2Sx/SnS solar cell. P, S, and L indicate the direction of electron flow through the photoelectrode, tin electrode, and external load, respectively (a) in an illuminated cell and (b) in the dark. For electrolytes, m represents molal. Electron transfer is driven both through an external load and also into electrochemical storage by reduction of SnS to metaUic tin. In the dark, the potential drop below that of tin sulfide reduction induces spontaneous oxidation of tin and electron flow through the external load. Independent of illumination conditions, electrons are driven through the load in the same direction, ensuring continuous power output. (Reproduced with permission from Macmillan Publishers Ltd [Nature] [60], Copyright 2009)...

The above reaction can be driven in the forward direchon by continuously removing hydrogen sulfide from the system. This is accomplished in the sulfide reduction process by incorporating lime, which acts as a scavenger for hydrogen sulfide in accordance with the reaction... 

Two step synthesis of medium-ring ethers through the intermediacy of thionium ions followed by sulfide reduction. 

The chemistry and procedures for modification of the - CO2H groups of PAA hyperbranched grafts on PE powder were analogous to those used for PAA grafts on PE or PP films and wafers. For example, a 90% yield in ester formation was possible using acid-catalyzed Fisher esterification. Likewise, quantitative reduction (ethyl chloroformate activation, borane-dimethyl sulfide reduction) to hyperbranched poly(allyl alcohol)s and amidation all could be carried out using procedures like those used for PAA/Au surfaces. 

The sulfate —> sulfide reduction requires quite low Eh conditions (figure 8.21D). The process takes place through enzymatic mediation (enzymes oxidize organic matter at the Eh of interest). At low pH, the reducing process may result in the formation of native sulfur, as an intermediate step of the process... 

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

Least active 1 Au, Pt Cu, Ag, Hg V, Cr, Mn, Fe, None found in nature as the free metal Roasting of the metal sulfide Reduction of the metal oxide with carbon,... 

In addition to simple CEPT being a favored mechanistic possibility for poly sulfide reduction and formate oxidation, CEPT is almost certainly involved, in all cases, in the reactivation of the molybdenum and tungsten cofactor sites... 

The flash vacuum pyrolysis of the dithienodiazene (145), obtained by sulfide reduction of 4,4 -dinitro-3,3 -dithienyl, gave cyclobuta[c c ]dithiophene (146) <85CC880>. An oxiranocyclo-pentapyrrole undergoes a palladium(0)-catalyzed insertion of carbon dioxide to form a 1,3-dioxole <88JA6123>. 

Both permanganate and ozonolysis break the carbon-carbon double bond and replace it with carbonyl (C=0) groups. In the permanganate cleavage, any aldehyde products are further oxidized to carboxylic acids. In the ozonolysis-reduction procedure, the aldehyde products are generated in the dimethyl sulfide reduction step (and not in the presence of ozone), and they are not oxidized. 

The abundance of tin is 2.1 parts per million and it is about the 48th most abundant element. Tin occurs mainly as cassiterite, Sn02, with other, and minor, ores containing tin sulfides. Reduction of cassiterite is carried out using carbon in a reverberatory fijmace at 1200 1300 °C. The major producers of tin are Malaysia, Indonesia, Thailand, Zaire, China, and Bolivia Brazil, too, is developing its production of tin. 

Germanium 2.0 937 2830 Germinate (mixture of copper, iron, and germanium sulfides) Reduction of Ge02 with H2 or C... 

The main method, both in the laboratory and in technical practice, for the introduction of an amino group into an aromatic compound, is nitration and reduction. Reduction of nitro compounds is accomplished by (1) catalytic hydrogenation, (2) iron reduction (Bechamp method), (3) sulfide reduction, or (4) zinc reduction in an alkaline medium. 

Interest in an old reducing agent, sodium sulfide, was renewed when it was discovered that its reactivity toward nitro groups was sensitive to water. In the absence of water, the aromatic nitro group in (28) can be reduced selectively to (29), without reduction of the aliphatic nitro group, but compounds such as (30), which contain a tertiary aliphatic nitro group eliminate the nitro moiety to yield styrene derivatives (31 Scheme 5). A unique application of the sulfide reduction involves the preparation of isomerically pure substituted aromatic nitro compounds and anilines. ... 

H). The use of sodium borohydride in the presence of platinum, palladium or Raney nickel [96] has been shown to give greater than 50% yields of benzimidazole )V-oxides, but even this reagent is capable of reducing a nitro group to amino, and combined with product loss on work-up, yields of the Af-oxides are often disappointing [97]. Sulfide reduction procedures (c.g. ammonium sulfide) seem better for 1-substituted benzimidazole 3-oxides than for benzimidazole 1-oxides [88, 92]. 

Reductive pathways that are encountered less frequently in dnig metabolism include reduction of Af-oxides to their corresponding tertiary amines and reduction of sulfoxides III sulfides. Reductive cleavage of disulfide linkages and reduction of carbon-carbon double bonds also occur, but constitute only minor pathways in drug metabolism. 

---