Selenides, diaryl

The isolable and thermally stable selenoxides are, therefore, rather limited. Stable examples are as follows those derived from selenides which have no hydrogen atoms on the -carbon, such as dimethyl sel-enide, aryl methyl selenides, diaryl selenides and benzyl phenyl selenides, those with an intramolecular hydrogen bonding, such as (36) and (37), and those leading to an unfavorable double bond such as (38). Vinylic selenoxides (39) and (40) are also generally isolable. 

For comparison within the chalcogens, the oxidation potentials of the Ph-E-Me series 94, 95b, 96b, and 97b, where E = O, S, Se, Te, respectively, were evaluated by pulse radiolysis.Consistent with the analogous diaryl series, the values for this series indicate that the compounds are increasingly easy to oxidize, with telluride 97b most easily oxidized (0.74 V) and ether 94 least easily oxidized (1.62 V), with these values vs. NHE (Table 10). Eor a broader comparison, series of four or five para-substituted arylmethylsulfides, selenides, and tellurides, 95a-e, 96a-e, and 97a-d were prepared and their values determined in the same manner (Table 10). The same trends were observed, with the thioethers least... 

Unlike the aryl methyl selenides, the alkyl aryl selenides with alkyl groups of two carbons or more are able to undergo scission of the radical cation at the Cgp-Se bond, yielding the ArSe radical (Fig. 35). This can impact product distribution, particularly under conditions in which water is not present to react with the radical cation. Trends in ease of oxidation typically seen in series of chalcogen compounds can still be observed, and are consistent with trends in the diaryl chalcogenides and aryl methyl chalcogenides. 

Aryl trimethylsilylmethyl selenides also yielded the diaryl diselenide as the major product, but possibly through a somewhat different mechanism, due to the increased stability of the initially formed radical cation (Fig. 31) ... 

By the interaction of selenium tetrachloride and benzene in the presence of aluminium chloride. Diaryl selenides and diaryl diselenides are formed as by-products. 

The aryl selenides are crystalline solids or liquids heavier than water. Oxidation by atmospheric oxygen or dilute alkali yields diaryl diselenides. 

For the diaryl selenides, RaSe, a variety of methods of preparation is available ... 

In addition to method (1), mixed diaryl selenides may also be obtained ... 

Most of the simple diaryl selenides are liquids, combining with bromine to yield dibromides. The ditolyl-, benzyl- and dinaphthyl-compounds are solids. 

When diaryl selenides in carbon disulphide, carbon tetrachloride or chloroform solution are treated with bromine, direct addition occurs, yielding dibromides, R2SeBr2. In some cases the dichlorides have been obtained by direct chlorination, but they are usually isolated by the action of hydrochloric acid on the selenoxides or dinitrates. 

Dibenzyl selenide gives an iodide when allowed to react with iodine in chloroform solution. Dinitrates are formed when nitric acid (density 1 4) acts upon diaryl selenides or upon their dibromides. The dihalides have their halogen removed by moist silver oxide, the hydroxides resulting. When sodium hydroxide is used they are transformed to the oxides, R2SeO, which also result when diaryl selenides are oxidised by 46 perhydrol. ... 

Unsymmetrical diaryl sulfides (60 R = 2-NO2, 4-NO2, 2,4-(N02)2 R = H, 4-NMe2) were obtained in 80-97% yields from the reaction under PTC conditions of nitro-activated aryl halides with arenethiolates generated in situ from the reduction of the corresponding diaryl disulfides with aminoiminomethanesul-finic acid (61).192 Arylthiolates carrying electron-withdrawing substituents were not sufficiently reactive. The reaction could also be applied to the synthesis of diaryl selenides, but not of ditellurides. 

The methods of synthesis of diaryl and aryl alkyl selenides have been recently reviewed.215 4-Nitro-phenyl methyl selenide was obtained in 93% yield from the reaction of 4-chloronitrobenzene in DMF with a suspension of MeSeLi in THF, prepared from powdered Se and MeLi.216 Other mixed RSeAr selenides were synthesized via alkylation with RI of ArSe resulting from the nucleophilic substitution of unactivated haloarenes ArCl with MeSeLi in DMF at 120 C, followed by MeSe -induced demethyl-ation.217... 

In a rare example of the use of iodonium salts for heteroatom-heteroatom bond formation, diaryliodonium halides were employed with sodium 0,0-diethyl phosphoroselenolate for a one-pot synthesis of diaryl diselenides (Scheme 9) [27]. These transformations probably occur via arylation of the phosphoroselenolate salt with the diaryliodonium ions, hydrolysis of the resulting aryl phosphoroselenolates with sodium hydroxide, and air oxidation of the arene-selenide ions thus produced. 

Fluorination of diaryl sulfides, selenides, and tellurides leads to the formation of diarylsulfur, selenium, and tellurium difluorides, all of... 

Dialkyl- or 2,5-diaryl-l,3,4-selenadiazoles (176) are prepared from AT1,AT2-diacylhy-drazines (175 Scheme 71) (04JPR(69)509>. Compounds (171) are prepared in low yields by hydrazinolysis of arylselenoamides (Scheme 72) (79JHC365). The parent compound (166) is prepared by the reaction of hydrogen selenide and N,N- dimethylformamide azine (Scheme 73) (70JOC806). 

The oxidation of selenoxides to selenones is slow requiring drastic conditions to be used. Diaryl, aryl methyl and dimethyl selenones are prepared by the oxidation of the ctxresponding selenoxides with prolonged exposure to KMn04 or ozone. The direct oxidation of selenides to selenones by FWO with ruthenium(II) complex catalyst, and C u(Mn04)2 has also been described. Aiyl trifluo-... 

Reaction of diphenyl diselenide or dimethyl diselenide with hydrazine hydrate and sodium hydroxide generates the corresponding selenolates smoothly in solvents like DMF or diethyl ether and in the presence of tetrabutylammonium chloride as a phase-transfer catalyst [13]. The selenolates react with organic halides to give various selenides (Scheme 9). Similar conditions have been applied to the synthesis of aryl vinyl selenides from diaryl diselenides and acetylene [14]. 

Oxidation of elemental sulfur and selenium with SbFs leads to the formation of doubly charged polyatomic cations [26]. These cations can react with polyfluorinated arenes to form diaryl sulfides or selenides (Eq. 12) [27]. 

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