Epoxidation peroxynitrous acid

Peroxynitrous acid, which has an estimated lifetime of 1-3 s at neutral pH, has been studied through ab initio calculations that suggest that peroxynitrous acid, per-oxyformic acid, and dimethyldioxirane have, despite diverse 0—0 bond energies, similar activation energies for oxygen-atom transfer." The transition-state structures for the epoxidation of ethene and propene with peroxynitrous acid are symmetrical with equal or almost equal bond distances between the spiro oxygen and the carbons of the double bond. 

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

The triplet instability of both RB3LYP and RHF solutions is responsible for the difference in the symmetry of the ethylene-peroxynitrous acid transition structure. In general, an unsymmetrical transition structure with alkene epoxidation when an alternative symmetrical structure is possible, appears to be associated with an unstable wave function. 

FIGURE 8. Geometrical parameters of the nearly symmetrical transition structure (a) for propylene epoxidation with peroxynitrous acid optimized at the QCISD/6-31G and CISD/6-31G (values are in parentheses) levels and unsymmetrical transition structures (b) and (c) resulting from the geometry optimizations at the B3LYP/6-311G and MP2(fuU)/6-31G levels, respectively... 

While it is well established that HO—ONO can be involved in such two-electron processes as alkene epoxidation and the oxidation of amines, sulfides and phosphines, the controversy remains concerning the mechanism of HO-ONO oxidation of saturated hydrocarbons. Rank and coworkers advanced the hypothesis that the reactive species in hydrocarbon oxidations by peroxynitrous acid, and in lipid peroxidation in the presence of air, is the discrete hydroxyl radical formed in the homolysis of HO—ONO. The HO—ONO oxidation of methane (equation 7) on the restricted surface with the B3LYP and QCISD methods gave about the same activation energy (31 3 kcalmol" ) irrespective of basis set size . ... 

---