Reaction rates peracid alkene epoxidation

The peracid system can also be applied to the oxidation of olefins (31). In dioxane, 90% H2O2 is necessary in order to prevent epoxide hydrolysis to the diol. Operation in a trlphase mode allows the use of 30% H202 Substitution of the double bond increases the epoxldatlon rate, as is expected, though primary alkenes still react. Allylic alcohols such as geraniol and 2-cyclohexen-l-ol are also highly reactive. The reaction workup consists of filtration and separation of liquid layers. The recovered polymer can be used directly in another reaction. Through five recycles with about 1 mol % catalyst no change in reactivity is seen. 

Epoxidation appears to involve electrophilic addition to the alkene, since the reaction is favored by electron-withdrawing groups on the peracid and electron-donating groups on the alkene. The epoxidation reaction is highly exothermic, with an experimental heat of reaction of -38 kcal/mol. The kinetic expression is overall second order, first order in the alkene and first order in the peracid. Steric effects do not appear to be important. The rate constant for the reaction increases with the number of alkyl substituents on the double bond, but the location of the alkyl groups is not important. For example, cis-2-butene, fra s-2-butene, and isobutene have nearly the same reactivity.The rate constant for the reaction is sensitive to strain, with faster rates observed for alkenes that produce greater relief of strain upon epoxidation. For example, frans-cyclooctene is epoxidized about 100 times faster than cis-cyclooctene. ... 

The epoxidation of simple alkenes with peroxycarboxylic acids involves an electrophilic attack of peracid with the formation of a bicyclic or a mono-cyclic transition state (Scheme 6.1), as first proposed by Bartlett [7] or recently suggested by theoretical studies [8] respectively. The reaction takes place readily in nonpolar solvents such as dichloromethane (DCM) and benzene and one can argue that hydrogen-bonding solvents, in particular, should retard the rate by interfering with intramolecular hydrogen bonding... 

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