Tetrafluoroboric Acid oxidation

A compound with tetrafluoroboric acid, previously claimed to be a useful safe oxidant, proved not to be on preparation at 0.5 molar scale. It exploded spontaneously while drying in vacuo at room temperature. Chem. Abs. (112 98095p) identifies it with this title compound, which was claimed to be too unstable to explode by the original users. It seems more likely that the explosive was the anhydride , oxybisphenyliodonium tetrafluoroborate. Several related compounds have also proved to be explosive. 

Acid-catalyzed dealkoxylation is particularly suitable for the preparation of highly reactive, cationic iron(IV) carbene complexes, which can be used for the cyclopropanation of alkenes [438] (Figure 3.11). Several reagents can be used to catalyze alkoxide abstraction these include tetrafluoroboric acid [457-459], trifluoroacetic acid [443,460], gaseous hydrogen chloride [452,461], trityl salts [434], or trimethylsilyl triflate [24,104,434,441,442,460], In the case of oxidizing acids (e.g. trityl salts) hydride abstraction can compete efficiently with alkoxide abstraction and lead to the formation of alkoxycarbene complexes [178,462] (see Section 2.1.7). 

OXYAMINATION Mercury(ll) oxide-Tetrafluoroboric acid. Trioxn(/-butyl-imido)osmium (VIII). 

Conjugated dienes afford either allylic amines or saturated diamines (equation 159).204,219 When mer-cury(II) oxide plus tetrafluoroboric acid is employed, dihydropyrroles are formed instead (equation 160).220... 

In those cases where a hydroxyethyl substituent is attached to the cyclohexadiene ting, an oxidative cyclization procedure has been developed to effect conversion to cyclohexadienyliron complexes.14 Thus, treatment of complex (52) with manganese dioxide gives the cyclic ether (53) which can be converted to the dienyl complex (54 Scheme 7) by treatment with tetrafluoroboric acid in acetic anhydride. 

The reaction of 82 with protic substrates HX can follow different pathways, as depicted in Scheme 23. In most of the cases studied so far, simple oxidative addition takes place leading to compounds of the type (Me5C5)2Si(H)X190. The reaction of 82 with tetrafluoroboric acid leads to elimination of pentamethylcyclopentadiene and to the formation of a cyclotetrasilane derivative, via several intermediates with divalent silicon from which the dimeric pentamethylcyclopentadienyl(fluoro)silylene was proved by Si NMR spectroscopy191,192. In contrast, an HF-oxidation product is formed in the reaction of 82... 

S)-(—)-Menthyl p-toluenesulfmate, 312-315 Mercury(II) acetate, 315-316 Mercury(II) nitrate, 317-318 Mercury(II) oxide-boron trifluoride, 318 Mercury(TI) oxide-tetrafluoroboric acid, 318-319... 

Diphenyl-1,2,4-triazine-3-diazonium tetrafluoroborate 2-oxide, 3670 Disodium 5,5 -azoxytetrazolide, 1015 Fulminic acid, 0380... 

Oxidation of iodoarenes was also effective with NaB03 H20 in Ac20/H2S04. The bromides were converted into the more useful ionic nitrates, trifluoroac-etates or tetrafluoroborates by oxidative anion metathesis, using the corresponding acid and 30% hydrogen peroxide, and refluxing the mixtures in methanol any liberated bromine was trapped by cyclohexene [20]. 

Hydrogen peroxide has been estimated to be more than 106 times less basic than H20. However, on addition of concentrated H202 to tetrafluoroboric acid in tetrahydrothiophene 1,1-dioxide (sulfolane) the conjugate cation (H302) can be obtained. The solutions are very powerful, but unselective, oxidants for benzene, cyclohexane, and other organic materials. 

Conversion of CflsiCHjf Si— to —< //. This useful conversion can be effected in two steps. Reaction with tetrafluoroboric acid. omplexed with diethyl ether results in conversion to a dimethylfluorosilyl group, which on oxidation with m-chloroperbenzoic acid (excess) in the presence of triethylamine or KF is converted into a hydroxyl group with retention of the original configuration. 

Mercury(II) oxide-Tetrafluoroboric acid, HgO-HBp4, white, hygroscopic solid. 

Diphenyl Methyl Telluronium Tetrafluoroborate 0.5 g (1.2 mmol) of diphenyl methyl telluronium iodide are dissolved in water. An aqueous solution eontaining 0.23 g (1.2 mmol) of silver tetrafluoroborate is prepared by reacting equivalent amounts of silver oxide and tetrafluoroboric acid. The solutions are mixed, stirred for 1 h at 20°, heated under reflux for 4h, and concentrated. Silver iodide is filtered off and the product crystallized m.p. 135°. 

Miscellaneous reactions. The sulfides are oxidized by an excess of e.g. hydrogen peroxide or 3-chloroperoxybenzolc acid to the corresponding sulfones. A controlled addition of peroxide yields a mixture of sulfoxide and sulfone products. The use of nitronium hexafluorophosphate or tetrafluoroborate to oxidize dlalkyl, aryl alkyl or dlaryl sulfides yields only the corresponding sulfoxide under extremely mild conditions (224). Sulfoxides may be further oxidized to the corresponding sulfones In good yield by the nitronium salts as well (225). 

---