Selenonic acid

There are only few hexavalent selenium compounds of interest to synthetic chemists. Selenonic acids 198 and selenones 199 have found several synthetic applications, whereas the organic synthesis of perselenuranes such as phenylselenenyl pentafluoride 200 still remains unexplored. (Figure 8).344... 

Selenonic acids (45) have been little studied but can be produced by the further oxidation of seleninic acids with potassium permanganate. 

The structures of organic selenium compounds are closely related to those of the homologous sulfur compounds. However, in sharp contrast to organosulfur compounds, most of the organoselenium derivatives contain the divalent, dicoordinate selenium atom. Tetravalent, tricoordinate selenium compounds such as selenoxides, selenonium salts and seleninic acids are much less common. Only a few hcxavalent selenium compounds such as selenonic acids and selenones are known. Thus, asymmetric C —Se bond formation is limited to creation of a carbon — selenenyl bond. 

Selenonic acids 194a and selones 194b belong to the best-known hexavalent, tetracoordinated organoselenium compounds. Moreover, they have found synthetic applications in recent years. 

The formula H2Se03 has been used in the literature for both selenonic acid and selenous acid. The present choice of names for the two structures shown is in accord with the parent names given in Sections P-42.1 and P-42.4 of Ref. 1. 

An analogous sequence appears in trifluoroseleninic acid as compared to -selenonic acid CF3SeO3H resonates at 3 = 981 whereas the Se chemical shift of CF3SeO2H is only 5=1231 The 3-value of benzeneseleninic acid Ph-SeO2H in a chloroform-methanol mixture is 1188 (3=1152, 1182) and its methyl ester 3= 1236 protonation leads to a ca. 20 ppm shielding. Recently, some further arylseleninic acids have been reported with Se chemical shifts between 3=1200 for Ar = 2,4,6-triisopropylphenyl and 3= 1276 for Ar = 2,4,6-triethylphenyl. These were optically resolved, partially to 100% e.g., on a chiral column and their racemization studied. ... 

The first stable arylselenenic acid, Ar-Se-OH (109) as a bridged calix [6]arene, was synthesized and characterized by an X-ray study (Scheme 17) Se chemical shifts of selenenic acids seem to be comparable to those of selenonic acids. This is confirmed by the data of the selenoperacetate 110 (same 5-value for the selenoperbenzoate) and the selenenic anhydride 111. 

The synthetic utihty of selenonic acid (RSeO, ) and its derivatives has, on the other hand, been limited, because of their lower thermal stability. 

Peroxyseleninic acids Selenonic acids Selenous acid esters Selenious acid esters 15... 

The propensity for selenonic acids to react as oxidizing agents has been known for a long time, but this has been regarded more as an interesting contrast between... 

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