Dialkyl diselenides

Nitric acid oxidises dialkyl diselenides to alkylseleninic acids RSe.SeR + 2HN03 = 2RSe02H + 2NO... 

These compounds are obtained by oxidising dialkyl diselenides by nitric acid (density 1 4), the general equation for the reaction being as follows ... 

Various reducing agents have been used for the generation of selenolates from diselenides or selenocyanates. Alkali metals M (M = Li, Na, K)149,150 or alkali hydrides MH (M = Li, Na, K)151,152 can generate the corresponding selenolate anions such as 80 these are more reactive than the borane complexes of type 77 (Scheme 15). Diaryl diselenides are easier reduced than dialkyl diselenides, but the mechanism for the reduction of selenocyanates is complex and can lead to either diselenides or selenolates.153,154... 

Alkyl selenocyanates diselenldes. Primary alcohols are converted by the reagent into alkyl selenocyanates in about 80% yield. If the reaction mixture is treated with 5% KOH in CH3OH for 2 hours the alkyl selenocyanates are transformed to dialkyl diselenides (about 70% yield). The reagent converts secondary alcohols into selenocyanates and to a lesser extent into isoselenocyanates. It does not react with tertiary alcohols. 

LiHdiaryl diselenides are more easily reduced than dialkyl diselenides. The reactions are faster in DMF than in THF [7a]. 

Dialkyl diselenides. A con ei KSeCN in aq DMF in the presence < and the resulting alkyl selenide 10ns... 

Dialkyl diselenides. The synthesis involves treatment of an alkyl halide with Se and Zn dust in aqueous NaOH under nitrogen at 80°C. Access to dibenzyl dise-lenides by a phase-transfer process (Se, NaOH, polyethyleneglycol-400/benzene, 65°C) is also convenient (9 examples, 73-96%). 

Reduction with only 1 equiv. leads to the dark brownish-red lithium diselenide, which reacts with alkyl halides to form dialkyl diselenides (equation II). ... 

Dialkyl diselenides, 310 Di-f-alkyl ethers, 441 Dialkyl selenides, 310... 

Applications of Crown Ethers.—Crown ethers have been found to form molecular complexes with bromine that can be used as reagents in bromination reactions, e.g. of alkenes. The crown-halogen interaction seems not to be encapsulation but rather to be the formation of a polymeric structure. The complexes of nitro-nium tetrafluoroborate (NO2BF4) with various crown ethers, for example the 1 1 complex with 18-crown-6, have been reported to be selective nitrating agents. A new rapid synthesis of alkylseleno- and alkyltelluro-arenes from arenediazon-ium tetrafluoroborates and dialkyl diselenides or ditellurides employs KOAc and 18-crown-6 as a phase-transfer catalyst a radical mechanism has been suggested. Fluorine-19 n.m.r. evidence has been presented to show that KF forms... 

The diselenides, RSe.SeR, are prepared by the interaction of potassium diselenide and dialkyl sulphates or alkyl halides ... 

A related, but mechanistically different, approach to the dialkyl phospho-roselenolates 10 entails the treatment of diphenyl diselenide with BAIB and... 

Vinyl sulfides(selenides). Dialkyl disulfides or diselenides react in HMPA with vinyl bromides in the presence or absence of Cul to form vinyl sulfides or selenides... 

The lithium alkyltelluroselenolates undergo internal redox reactions below room temperature to form dialkyl ditellurium and the diselenide anion. The phenyl derivative is stable under these conditions2. 

Reduction of elemental selenium with Sml2 leads to the selective formation of Se and Se depending on the reaction stoichiometry, similar to the reduction with NaBH4 and hydrazine (Sects. 2.2.2 and 2.2.3). These inorganic dianions react with alkyl bromides to produce dialkyl selenides and diselenides, respectively, in excellent yields (Scheme 15) [17a]. 

In addition to the selective synthesis of selenides and diselenides, symmetrical dialkyl tellurides [5a, 47-49, 50a, 58] and ditellurides [48a, 51a, c, 59] can be prepared with high selectivity by alkylation of Na2Te and Na2Te2, respectively, with alkyl halides (Scheme 15.20). 

Recently, the synthesis of dithio- and diselenoacetals of formylphosphonates by the BF3 EtjO-catalyzed reaction between dialkyl diazomethylphosphonate and disulfides or diselenides has been reported." The reaction proceeds by the insertion of the dialkoxyphosphorylcarbene moiety into the S-S or Se-Se bonds of the disulfide or diselenide. Preparation of diethyl 1,1 -/ .v(me thylthio )meth-ylphosphonate is generally carried out in methyl disulfide as solvent, and it has been found that both BFj Et2O and disulfide had to be used in excess to produce the expected dithioacetal in a good yield (85%)." ... 

On the other hand, good yields of tetraselenated products have been obtained (87JOC3444) by treatment of 16 with four equivalents of dialkyl (aryl) diselenides. Analogous reactions with dialkyl(aryl) disulfides are also satisfactory, but it was reported in the same paper that the reaction... 

The symmetrical monoselenodiphosphates have also been prepared using dialkyl trimethylsilyl phosphites for the deselenation of diphosphoryl diselenides.An improved synthesis of dialkyl thioxaphosphoranesulphenyl chlorides and bromides lies in the treatment of the sulphenylamides (RO)2 (S)SNR2 with a halogenotrimethylsilane followed by ethanol. 

Dialkyl selemdes dialkyi diselenides. Reaction of selenium with 2.1 equiv. of this hydride in THF gives a suspension of milky white lithium selenide. On addition of alkyl halides dialkyl selenides are formed in 60-95% yield (equation I). 

Reductions. Elemental selenium can be reduced using sodium hydride. The resulting sodium diselenide (Na2Se2) can be used to prepare dialkyl selenides (eq 55). Similarly, elemental sulfur can be reduced to diatomic sulfur by sodium hydride in the presence of a phase transfer catalyst,... 

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