a. Epoxides of `alpha,beta`-unsaturated carbonyl compounds can be formed by peroxy acid as well as with `H_(2)O_(2)//O^(Θ)H`. Explain the formation of epoxides in both cases.
b. Acrolein `(CH_(2)=CH-CHO)` is epoxidised much more rapidly with `H_(2)O_(2)//overset(Θ)(OH)` than with a peroxy acid. Explain why.

Explanation

a. i. With peroxy acid, e.g., peroxyacetic acid `(MeCO_(3)H)` or peroxy benzoic acid `(PhCO_(3)H)`, it is electrophilic addition reaction on `(C=C)` bond by the electrophile `(overset(o+)(OH))` generated form the peroxy acid.
`R-overset(O)overset(||)(C)-O-OH hArr underset("Nucleophile")(R-overset(O)overset(||)(C)-O^(Θ))+underset("Electrophile")(overset(o+)(O)H)`
`overset(beta)(CH_(2))=overset(alpha)(CH)-CHO`

Nucleophile portion `(RCOO^(Θ))` removes H form (OH) to give epoxide.
ii. `H-O-O-H+overset(Θ)(OH) rarr underset("Conjugated base")H-O-O^(Θ)+H_(2)O`
The base converts `H_(2)O_(2)` to the conjugate base `HOO^(Θ)`. The latter undergoes a Michael addition reaction with `alpha,beta`-unsaturated carbonyl compounds to give reasonance-stabilised `alpha`-carbanion which removed `overset(Θ)(OH)` form the (HGO) group to give expoxide.

b. Epoxides formation of `alpha,beta`-unsaturated compound with `H_(2)O_(2)//overset(Θ)(OH)` is faster since it proceeds by the formation of resonance-stabilised `alpha`-carbanino.