O-Ethylperoxycarbonic Acid

[70288-43-6]  · C3H6O4  · O-Ethylperoxycarbonic Acid  · (MW 106.09)

(oxygen atom transfer reagent, useful for the epoxidation of alkenes)

Preparative Method: formed in situ by the reaction of aqueous Hydrogen Peroxide with Ethyl Chloroformate.

Handling, Storage, and Precautions: generated in situ; not stable to storage.

Alkene Epoxidation.

The direct oxidation of an alkene to the corresponding epoxide is most typically accomplished by an organic peroxy acid or by metal-catalyzed oxygen atom transfer from a hydroperoxide.1,2 Alternate methods based upon the utilization of hydrogen peroxide as the oxidant have also been developed, most notably by Payne.3 Although H2O2 itself is not sufficiently reactive to epoxidize a nonconjugated alkene, its propensity for oxygen atom transfer can be markedly enhanced by placing the OOH moiety in conjugation with a multiple bond. Typical examples are peroxy acids (1) and peroxyimidic acids (2). The latter oxidant can be readily formed in situ by the addition of H2O2 to a nitrile. Acetonitrile,3 benzonitrile,3 and trichloroacetonitrile4 have been employed as coreactants in the epoxidation of alkenes. Trichloroperoxyacetamidic Acid is a highly effective oxidant that is competitive with m-Chloroperbenzoic Acid on both a cost effective and reactivity basis. Acetoperoxyimidic acid has been scaled up for the synthesis of epoxides on a multimolar scale.5

O-Alkylperoxycarbonic acids (3) can be formed in situ by the reaction of H2O2 with alkyl chloroformates.6 Although dialkyl esters of peroxycarbonic acid (ROCO3RŽ)7a and peroxydicarbonates (ROCOO)27b are stable isolable compounds, an O-alkylperoxycarbonic acid (3) must be generated in situ. O-Benzylperoxycarbonic acid has been prepared from dibenzyl peroxydicarbonate and alkaline H2O2 in methanol.8 This peroxycarbonic acid (3; R = Bn) is considerably less stable than a peroxycarboxylic acid (1) and has a half-life of about 61 h at room temperature in benzene. However, it is an effective oxidizing reagent and exhibits a reactivity toward (E)-stilbene that is intermediate between that of Perbenzoic Acid and m-CPBA in benzene.

The current procedure utilizes a biphasic solvent system that allows one to utilize the cost and safety advantages of aqueous 30% H2O2 and CH2Cl2 as a second phase. This two-phase system is ideal since the rate of epoxidation of alkenes is maximized in nonpolar solvents like CH2Cl2. O-Ethylperoxycarbonic acid (4) is produced at the interface by the reaction of H2O2 with ethyl chloroformate (eq 1). The epoxidizing reagent should be formed in the presence of a buffer to neutralize the HCl produced since the decomposition of the -CO3H functional group is catalyzed by both acids and bases. When Na2HPO4 is used as a buffer, the reaction medium is slightly acidic and the pH decreases from 6.8 to 4.5 during the course of the reaction. Alternatively, if alkaline conditions are desired because of an acid-sensitive functional group, Na3PO4 may be used as the buffer and the pH maintained between 9.5 and 8.8.6 It should be recalled that aqueous 30% H2O2 is typically stabilized by a strong acid (e.g. H2SO4) and the solution is acidic. m-CPBA has also been used under biphasic conditions.9

The overall procedure for alkene epoxidation with (4) is accompanied by the formation of two innocuous byproducts, carbon dioxide and ethanol (eq 2). Good to excellent yields of epoxides are obtained with a variety of alkenes, with the exception of 1-nonene. Terminal alkenes typically react more slowly with peroxy acids than more highly substituted double bonds.

This synthetic procedure offers the advantage of the in situ generation of a relatively inexpensive oxidant under either mildly acidic or basic conditions. Reaction times vary from 3-24 h at room temperature. The products of oxidation are not contaminated with residual byproducts.

Related Reagents.

Peroxyacetimidic Acid; Trichloroperoxyacetamidic Acid.

1. Sharpless, K. B.; Verhoeven, T. R. Aldrichim. Acta 1979, 12, 63.
2. (a) House, H. O. Modern Synthetic Reactions, 2nd ed.; Benjamin: Menlo Park, CA, 1972; p 292. (b) Swern, D. OR 1953, 7, 378.
3. (a) Payne, G. B.; Deming, P. H.; Williams, P. H. JOC 1961, 26, 659. (b) Payne, G. B. T 1962, 18, 763.
4. Arias, L. A.; Adkins, S.; Nagel, C. J.; Bach, R. D. JOC 1983, 48, 888.
5. Bach, R. D.; Knight, J. W. OS 1981, 60, 63.
6. Bach, R. D.; Klein, M. W.; Ryntz, R. A.; Holubka, J. W. JOC 1979, 44, 2569.
7. (a) Strain, F.; Bissinger, W. E.; Dial, W. R.; Rudoff, H.; Dewitt, B. J.; Stevens, H. C.; Langston, J. H. JACS 1950, 72, 1254. (b) Organic Peroxides; Wiley: New York, 1970; Vol. I, p 68; Vol. II, p 863.
8. Coates, R. M.; Williams, J. W. JOC 1974, 39, 3054.
9. (a) Anderson, W. K.; Veysoglu, T. JOC 1973, 38, 2267. (b) Ishikawa, K.; Charles, H. C.; Griffin, G. W. TL 1977, 427. (c) Ishikawa, K.; Griffin, G. W. AG(E) 1977, 16, 171.

Robert D. Bach

Wayne State University, Detroit, MI, USA

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