Sulfonium special

One procedure for the synthesis of these title ring systems appeared recently <2003S1079>. Yadav and Kapoor described that the transformation of some oxadiazole and thiadiazole derivatives bearing specially substituted methylsulfinyl side chain 131, when reacted with thionyl chloride, give ring-closed compounds 134. The reaction was carried out in pyridine under reflux conditions in 74-79% yield. As shown in Scheme 25, the authors assume that the first step is the formation of the sulfonium salt 132 which undergoes cyclization with hydrogen chloride and sulfur dioxide elimination to 133 and, finally, demethylation of this intermediate leads to the final product 134. 

In spite of the large number of dithiolene complexes synthesized, 50 of their derived compounds exhibit a metal-like behavior at a temperature close to RT and within a significant temperature range. These compounds, listed in Tables I-IV, together with the relevant references and some details about their electrical behavior are either NIOS salts or D-A adducts. For the NIOS salts of dmit and mnt complexes, the associated counterions are mostly closed-shell cations such as alkyl-ammonium or sulfonium, or alkaline metal cations. For the D-A adducts derived from dmit and mnt acceptor complexes, the associated donors are TTF-like molecules and Per, respectively. The dddt complexes deserve special mention as the derived metal-like conductors involve M(dddt)2 v - cation radicals (instead of anion-radicals as in dmit or mnt systems). 

A special case of oxidation at the sulfide bridge is in the preparation of the sulfonium salt 184 starting with 183. ... 

Ylide can be viewed as a special carbanion in which the negative charge on carbon is stabilized by an adjacent positively charged heteroatom. The most common ylides are phospho-nium ylides, sulfur ylides (sulfonium and sulfoxonium ylides) and certain nitrogen-based ylides (ammonium, azomethine, pyridinium and nitrile ylides). In addition to synthetically important phosphorus, sulfur and nitrogen, ylides of tin (Sn) and iodine (I) have been developed in recent years. 

Charge cancellation polymerizations must be considered as special cases. Some degree of charge separation already exists in acetonitrile oxide but a base is required to initiate its polymerization. Although linked by a conjugated system ionisation is essentially complete in cyclic sulfonium zwitterion monomers. No initiator is required and monomeric units add at both ends of the p>olymer chain. The initial step in the general scheme above is best considered as part of monomer synthesis. 

The involvement of methionine sulfonium salts in these chemical cleavage reactions may stimulate experiments to show the significance of special methionine residues in the active centers and the catalytic sites of enzymes. Such an important role for a particular methionine has been postulated for the enzymes phosphoglucomutase and chymotrypsin on the basis of photooxidation studies (Ray et al., 1960). 

Reported S -substituents are restricted to oxygen or alkyl groups. Both have the expected reactivity patterns of sulfones or sulfonium compounds. The presence of a ring formed from two substituents on the sulfur atom does not confer any special reactivity to A-substituents. 

In some special cases, an isotopic dilution can occur by exchange (see Chap. 15 in Vol. 2) between the labeled reagent and the solvent or reagents used. Dimethyl sulfoxide, a commonly used solvent in alkylation reactions, might react with [ C] methyl iodide to form labeled oxo-trimethyl-sulfonium iodide. This intermediate can transfer any of the three methyl groups to... 

Ionic liquids (ILs) with their outstanding solvent properties, that is, high conductivity, tunable polarity, zero volatility, and high thermal stability, are of growing interest in different fields of application including as a solvent component in microemulsions [6,7]. Thus, the tunable polar properties are of special interest. Therefore, ILs can be used as polar [8-11] as well as nonpolar solvents [12,13], Moreover, ILs can show amphiphilic behavior [14] and are called IL sirnfactants [15], Their physical properties can be adjusted in a characteristic way by varying the molecular structure of ILs. Since the ILs are sterically mismatched ions, they hinder crystal formation. Different cations, for example, ammonium, phosphonium, sulfonium, imidazolium, pyridinium, or pyrrolidinium, with different anions, for example, chloride, bromide, iodide, fluoroborate, or fluorophosphates, can be selected for a broad range of combinations [6]. 

Most organic corrosion inhibitors used in cleaning solutions will not prevent ferric ion corrosion. Special chemicals were developed to reduce this problem. Alfandry demonstrated that hexamethylenetetramine will protect steel in HCI, but the protection is reduced by the presence of Fe + ions. However, the protection provided to steel in sulfuric acid is improved by the addition of ferric ions to a solution inhibited by phenylthiourea. Streicher reported that ferric ion corrosion of steel in sulfuric acid can be reduced by a mixture of diorthotolylthiourea and an anionic surfactant, such as an alkyl-aryl sodium sulfonate. Sulfonium salts also were used as ferric ion inhibitors. These inhibitors are effective in a variety of mineral and organic acids, but they are most effective in acidic (pH of 5) EDTA solutions. The sulfonium salts were shown to electroreduce at the corrosion potential to form a hydrophobic product (hydrocarbon) that may enhance the protection of the steel from oxidation by the ferric ion. 

Vesicant agents of the mustard type present some special features in their reaction mechanism(s). It is known that the mechanism involves, as a first step, the formation of a cyclic sulfonium ion and the release of chloride (CT). This mechanism is illustrated for the cases of half-mustard and sulfur mustard in Scheme 2. In addition, these vesicant agents are persistent agents, depending on pH and moisture. The mustard is hydrolysed to form HCl and thio-diglycol. Ointment formulation-incorporated spin probes are sensitive to the polarity and fluidity of... 

Cationic polymerizations proceed as chain reactions involving initiation and propagation. In most cases, there is no termination by neutralization, and the growing chains are terminated by nucleophilic impurities. Cationic chain reactions are photoinitiated by special initiators (Table 3.10) which date back to the pioneering studies of Crivello on sulfonium and iodonium salts containing non-nucleophilic anions such as and AsFs ... 

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