Sulfides disulfides, reduction

Types of compounds are arranged according to the following system hydrocarbons and basic heterocycles hydroxy compounds and their ethers mercapto compounds, sulfides, disulfides, sulfoxides and sulfones, sulfenic, sulfinic and sulfonic acids and their derivatives amines, hydroxylamines, hydrazines, hydrazo and azo compounds carbonyl compounds and their functional derivatives carboxylic acids and their functional derivatives and organometallics. In each chapter, halogen, nitroso, nitro, diazo and azido compounds follow the parent compounds as their substitution derivatives. More detail is indicated in the table of contents. In polyfunctional derivatives reduction of a particular function is mentioned in the place of the highest functionality. Reduction of acrylic acid, for example, is described in the chapter on acids rather than functionalized ethylene, and reduction of ethyl acetoacetate is discussed in the chapter on esters rather than in the chapter on ketones. 

Symmetrical 3,5-dialkyl-l,2,4-trithiolanes (178) can be synthesized in reasonable yield by chlorination of dialkyl disulfides (175) to a-chiloroalkyl sulfenyl chlorides (176), which are then reacted with potassium iodide to give di-a-chloroalkyl disulfides (177). Subsequent cyclization with sodium sulfide gave (178) (72T3489). When (176) was treated with one molar equivalent of sodium sulfide, the reductive dimerization and cyclization was effected in one step (78HCA1404). Treatment of perfluoropropene with sodium hydrogen sulfide in THF resulted in the formation of 3,5-bis(2,2,2-trifluoroethyl)-l,2,4-trithiolane (179) (72IZV2517). 

The mechanism of disulfide reduction by phosphines is hypothesized to involve a stable intermediate containing a sulphur-phosphorous bond (6). Beta elimination would yield the phosphine sulfide and dehydroalanine. The formation of relatively stable adducts between cystine-containing peptides and the reagent was confirmed by mass spectrometry for several peptides with the major adduct representing one reagent molecule per cystine residue. 

Figure 27 Proposed mechanism for covalent substantivity of exogenous protein to hair by sulfide-disulfide interchange in permanent waving treatment. The formation of new —SS—bonds between the two species can occur by nucleophilic attack of thiol groups of reduced hair on disulfide bonds of unreduced protein (a), or via contemporaneous reduction of hair and protein derivative (b). A third possible route (not shown) is based on a separate activation of the protein derivative by sulfitolysis with Na2S03 at a concentration sufficient to reduce soluble peptides, but having neghgi-ble effects on the hair.

Diethanolamine (DEA) has replaced MEA as the most widely used amine solvent. High load DEA technologies, such as that developed by Elf Aquitaine, permit the use of high (up to 40 wt % DEA) concentration solutions. The Elf Aquitaine—DEA process allows lower cinculation rates, and has consequent reductions ia capital and utility expenses. DEA tends to be more resistant to degradation by carbonyl sulfide and carbon disulfide than MEA. DEA is, however, susceptible to degradation by carbon dioxide. 

Thiols, the sulfur analogs of alcohols, are usually prepared by Sjv 2 reaction of an alkyl halide with thiourea. Mild oxidation of a thiol yields a disulfide, and mild reduction of a disulfide gives back the thiol. Sulfides, the sulfur analogs of ethers, are prepared by an Sk2 reaction between a thiolate anion and a primary or secondary alkyl halide. Sulfides are much more nucleophilic than ethers and can be oxidized to sulfoxides and to sulfones. Sulfides can also be alkylated by reaction with a primary alkyl halide to yield sulfonium ions. 

Di-o-nitrophenyl disulfide was first prepared by the action of hydriodic acid on o-nitrobenzene sulfochloride.1 It has also been prepared by the reduction of o-nitrobenzene sulfinic acid with hydrogen bromide 2 by the reduction of ethyl-o-nitro-phenylsulfonacetate with ammonium sulfide 3 and by the deamination of 4,4,-diamino-2,2 -dinitrodiphenyldisulfide.4 The procedure given is the method of Blanksma5 as elaborated by Wohlfahrt.6... 

Et3SiH/TFA reduces disulfides to the corresponding mercaptans in modest yields (Eq. 340).564 Naphthyl thio ethers are reduced in rather poor yields to tetrahydronaphthalene with the combination EtjSiH/HF -OfE (Eq. 341).263 There is one report of the reduction of a diaryl sulfide to the hydrocarbon but the yield... 

Carbon is able to bind sulfur to its surface. The reaction of sugar charcoal or wood charcoal with elementary sulfur at temperatures of 400-1000° was studied in detail by Wibaut (118-122). In this reaction some carbon disulfide was formed as well as hydrogen sulfide, if hydrogen was present in the samples. The solid reaction products contained considerable amounts of sulfur, up to 20% by weight. The maximum sulfur uptake was observed at 600°. The sulfur was not completely volatized even by heating in a vacuum to 1000° (122). The sulfur came off in elementary form and as carbon disulfide. Neither could the sulfur be removed from the samples by extraction. It was disposed of by powerful chemical attack, e.g., by oxidation or by reduction with hydrogen at 700°. The formation of hydrogen sulfide started at 460°. 

Electrolytic reduction of H SO /HjSeO mixtures using aluminium electrodes results in the formation of a sulfur-selenium coating at the elwtrode Irradiation of a solution of SCg in carbon disulfide by sunhght for 1-2 hours at 20 °C results in the formation of various cyclic selenium sulfides The formation of Se Sg compounds is also initiated by refluxing the above solution . ... 

The bicyclic sugars 121 and 128-130 should all be capable of some sort of chemical activation to produce glycosyl donors. To date, we have investigated just the related sulfide 133. Treatment of 133 with a range of alcohols, 134-138, in the presence of N-iodosuccinimide and triflic acid, has given rise to intermediate disulfides, e. g. 139 in good yield and capable of reduction (Ra/Ni) to the 6,6 -dideoxy /3-disaccharide 140 [66]. This is truly an excellent result in terms of a direct synthesis of -acarbose. 

The proposed mechanism of the oxidative cleavage of S-protecting groups by the chlorosilane/sulfoxide procedure is outlined in Scheme 8. 95 The first reaction is considered to be formation of the sulfonium cation 9 from diphenyl sulfoxide (7) and the oxygenophilic silyl compound 8. The formation of a sulfonium ion of this type is known and has been utilized for the reduction of sulfoxides. 97 Subsequent electrophilic attack of 9 on the sulfur atom of the S-protected cysteine residue leads to the formation of intermediate 10, whereby the nature of the silyl chloride employed should be the main factor that influences the electrophilicity of 9. The postulated intermediate 10 may then act as the electrophile and react with another S-protected cysteine residue to generate the disulfide 11 and the inert byproduct diphenyl sulfide (12). This final step is analogous to the reaction of a sulfenyl iodide as discussed in Section 6.1.1.2.1. 

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