Peroxyformic acid alkene epoxidation

TABLE 3. B3LYP/6-31G(d) activation barriers (A , kcal mol ) for the epoxidation of a series of alkenes with peroxyformic acid (PFA) and dimethyldioxirane (DMDO). The barriers in parentheses are at the B3LYP/6-31- -G(d,p) level of theory. Other computational approaches are indicated by footnotes. The barriers have been computed with respect to isolated reactants... 

TABLE 7. Summary of the reaction barriers (kcal mol for the epoxidation of simple alkenes with peroxyformic acid (PFA) and dimethyldioxirane (DMDO)... 

The most convincing evidence for an essentially synchronous peracid epoxidation of simple alkenes came from a combined experimental and theoretical study by Singleton, Honk and coworkers. Experimental KIEs for the reaction of m-CPBA with 1-pentene, determined by the clever methodology developed by Singleton and Thomas utilizing the combinatorial high-precision determination of C and H KIEs at natural abundance, confirmed the symmetrical or nearly symmetrical nature of this epoxidation TS. These data were corroborated by B3LYP/6-31G calculations on propylene that supported a synchronous transition state for peroxyformic acid epoxidation. 

TABLE 8. Differences (A) in the O—Cl and O—C2 calculated distances of transition structures for the epoxidations of alkenes with peroxyformic acid using different methods... 

TABLE 9. Activation barriers and reaction enthalpy changes (kcal mol ) for the epoxidation of alkenes with peroxyformic acid calculated at various computational levels... 

A systematic examination of the transition structures for the peroxyformic acid epoxidation at various levels of theory confirms the above suggestion that the MP2 method does provide adequate geometries for a conjugated carbon-carbon double bond in 1,3-butadiene (Figure 23). However, the inverse KIEs measured by HanzUk and Shearer " for 4-vinylbiphenyl are specific to conjugated alkenes and should not be used as evidence of an asynchronous epoxidation TS for simple nonconjugated aUcenes. ... 

Epoxidations of methyl-snbstituted alkenes and o ,/ -unsaturated systems as 1,3-bntadiene and acrylonitrile with peroxyformic acid follow a concerted asynchronous pathway. 

FIGURE 26. Transition structures for the epoxidation of selected cyclic alkenes with peroxyformic acid (PEA), optimized at the B3LYP/6-31+G(d,p) level of theory. The classical activation barriers are given at B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p)... 

High-level calculations of alkene epoxidation reactions with peroxyformic acid, HO—O (C=0)H, which is isoelectronic with peroxynitrous acid [HO—0(N=0)], have indicated... 

A modest increase in the rate of alkene epoxidation by peroxy acid in benzene occurs on addition of TCA or TFA.183 Calculations predict a much lower activation barrier for epoxidation of ethene with fully protonated peroxyformic acid (AE = 6.4kcalmol 1) ... 

Direct anti hydroxylation of an alkene (without isolation of the epoxide intermediate) is possible by using an acidic aqueous solution of a peroxyacid. As soon as the epoxide is formed, it hydrolyzes to the glycol. Peroxyacetic acid (CH3CO3H) and peroxyformic acid (HCO3H) are often used for the anti hydroxylation of alkenes. 

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