Caroat

The triple salt is better known by the trademarks Caroat (Degussa), OXONE Monopersulfate Compound (Du Pont), and Curox (Laporte). It is also known as potassium caroate. It has been made on a commercial scale siace the 1950s, and the world market ia 1994 was several thousand tons. It is made commercially by Peroxid-Chemie (Germany), Degussa (Germany), Du Pont (United States), and Migas (Japan). In 1994, the United Kingdom price was J1.80/kg ( 2.67/kg). 

In the late 1970s, evidence showed that diaLkyl dioxiranes were generated in ketone—caroate, 2KHSO KHSO K SO, systems (106) and the mechanism of the reaction was determined (88,90) ... 

In the mid-1980s a convenient and relatively safe procedure was developed for vacuum codistillation of dimethyldioxirane and acetone from acetone—caroate systems (107). The resulting acetone solution of dimethyldioxirane could be used in subsequent oxygenation reactions (92). 

The epoxidation of nonfunctionalized alkenes may also be effected by chiral dioxiranes. These species, formed in situ using the appropriate ketone and potassium caroate (Oxone), can be formed from C-2 symmetric chiral ketones (29)[93], functionalized carbohydrates (30)[94] or alkaloid derivatives (31)[95]. One example from the laboratories of Shi and co-workers is given in Scheme 19. 

The synthetically most useful method for the preparation of dioxiranes is the reaction of appropriate ketones (acetone, trill uoroacetone, 2-butanone, cyclohexanone etc.) with Caroate, commercially available as the triple salt of potassium monoperoxysul-fate (KHSOs). The catalytic cycle of the dioxirane formation and oxidation is shown in Scheme 1 in general form. For acetone as the ketone, by simple distillation at a slightly reduced pressure ca 100 torr) at room temperature ca 20 °C), Jeyaraman and Murray successfully isolated dimethyldioxirane (DMD) as a pale yellow solution in acetone (maximally ca 0.1 M). This pivotal achievement in 1985 fomented the subsequent intensive research activity in dioxirane chemistry, mainly the synthetic applications but also the mechanistic and theoretical aspects. The more reactive (up to a thousandfold ) fluorinated dioxirane, methyl(trifluoromethyl)dioxirane (TFD), was later isolated in a similar manner by Curd, Mello and coworkers". For dioxirane derived from less volatile ketones, e.g. cyclohexanone, the salting-out technique has been developed by Murray and coworkers to obtain the corresponding dioxirane solution. 

The dioxirane stmcture was postulated by Baeyer and ViUiger as a reactive intermediate in the Caroate oxidation of menthone. ... 

Although the parent formaldehyde-derived dioxirane (H2CO2) was the first of this intriguing class of cyclic peroxides to be prepared and spectrally characterized in 1976, the conversion of aldehydes into the corresponding dioxiranes by treatment with Caroate was deemed difficult because of the expectedly facile Baeyer-Villiger oxidation of the aldehydes to their carboxylic acids. Most gratifyingly, however, is that it was recently demonstrated that optically active aldehydes may also serve as promising catalysts for asymmetric epoxidations. For example, ee values up to 94% were obtained with the aldehyde 14 as dioxirane precursor. 

SCHEME 11. Mechanism for the singlet-oxygen formation in the catalytic decomposition of Caroate by ketones... 

Also, potassium superoxide (KO2) decomposes DMD in acetone solution to release singlet oxygen, as has been detected by the characteristic infrared chemiluminescence . Furthermore, a catalytic amount of n-Bu4NI decomposes TFD into oxygen gas and triflu-oroacetone in high yield . Analogous to the Caroate decomposition by ketones, also the catalytic decomposition of peroxynitrite by ketones, e.g. methyl pyruvate, is rationahzed in terms of peroxynitrite oxidation by in-situ-generated dioxirane. ... 

The enantioselective oxidation of prochiral sulfides with DMD has been achieved by using bovine serum albumin (BSA) as the chiral inductor Moderate to good enan-tioselectivities have been reported in the presence of this protein, for which a typical example is shown in equation 22 . As yet, however, no enantioselective oxidation of a prochiral sulfide has been documented by employing an optically active dioxirane. We have tried the enantioselective oxidation of methyl phenyl sulfide with the dioxirane generated from the ketone 7 (Shi s ketone), but an ee value of only ca 5% was obtained. One major hurdle that needs to be overcome with such enantioselective dioxirane oxidations is the suppression of the background oxidation of the sulfide substrate by Caroate, an unavoidable feature of the in-situ mode. 

Caroate is also known as Qxone (DuPont) and Curox (Peroxidchemie). 

As early as 1899 Baeyer and Villiger165 postulated a dioxirane intermediate in the KHSO5 oxidation of menthone to its lactone (equation 23). The first real contribution to dioxirane chemistry was made Montgomery166. Careful studies on the decomposition of the caroate ion permitted him to observe the acceleration of the reaction by the addition... 

Epoxidation of ketones is carried out by the oxone reagent. The actual oxidizing agent is the caroate ion (equation 24). 

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