Epoxidations with peroxyacetic acid

Explain why 3,4-dimethyl-3-hexene undergoes epoxidation with peroxyacetic acid faster than does 3-hexene. 

Relative Rates of Epoxidation of Some Representative Alkenes with Peroxyacetic Acid... 

Epoxidation of alkenes is a stereospecific syn addition Which stereoisomer of 2 butene reacts with peroxyacetic acid to give meso 2 3 epoxybu tane Which one gives a racemic mixture of (2/ 3/ ) and (25 35) 2 3 epoxybutane ... 

Esters. The monoisobutyrate ester of 2,2,4-trimethyl-1,3-pentanediol is prepared from isobutyraldehyde ia a Tishchenko reaction (58,59). Diesters, such as trimethylpentane dipelargonate (2,2,4-trimethylpentane 1,3-dinonanoate), are prepared by the reaction of 2 mol of the monocarboxyhc acid with 1 mol of the glycol at 150—200°C (60,61). The lower aUphatic carboxyHc acid diesters of trimethylpentanediol undergo pyrolysis to the corresponding ester of 2,2,4-trimethyl-3-penten-l-ol (62). These unsaturated esters reportedly can be epoxidized by peroxyacetic acid (63). 

N-Protected azonines 87 and 88 are smoothly transformed into epoxides 89 and 90, correspondingly, when reacted with peroxyacetic acid (Scheme 15) <1999CC309>. 

The trioxolane was also shown to effect epoxidation of olefins86). This was differentiated from the peracid pathway by generating the intermediate at — 100 °C. Warming this system to — 50 °C in the presence of olefins resulted in the formation of epoxides. The corresponding experiment with peroxyacetic acid at — SO °C showed no epoxidation of the olefins. The trioxolane was also shown to effect hydroxylation of tert-butylphenol to tert-butylcatechol, in agreement with an oxene transfer mechanism. 

The answer is B. In this reaction, 2-butene is reacted with peroxyacetic acid. This reagent converts the alkene into an epoxide, which is a compound that has a three-sided ring with an oxygen atom in the ring. 

The reaction of peroxyacids with alkenes is illustrated by the experiment that reacts cyclopentene with peroxyacetic acid (83). There are two isolated products cyclopentene oxide (88) in 57% yield and acetic acid (89). The yield is only 57% because the remainder of the 100% is unreacted alkene. Labeling experiments (replacing the natural isotope with the less abundant isotope 1 0) show that the oxygen atom of the epoxide in 88 comes from the OH oxygen in the peroxyacid (labeled in red in 83 and 88). 

Reviews discuss the advantages of heterogeneous and homogeneous catalytic oxidations for organic synthesis, and catalytic oxygen atom transfer reactions. The new Cr(VI) reagent (51) catalyses the oxidation of secondary alcohols to ketones with peroxyacetic acid. The tetra(diperoxotungsto)-phosphate(3-) anion has been structurally characterised it catalyses stereospecific olefin epoxidations. ... 

Peroxyacetic acid in acetic acid is used in industrial epoxidation reactions. Peroxyacetic acid is produced from the reaction of hydrogen peroxide with acetic acid. 

Figure 7 7 shows why equal amounts of (R) and (5) 1 2 epoxypropane are formed m the epoxidation of propene There is no difference between the top face of the dou ble bond and the bottom face Peroxyacetic acid can transfer oxygen to either face with equal facility the rates of formation of the R and S enantiomers of the product are the same and the product is racemic... 

Toxicity. The peroxy acid is highly toxic and may cause death or permanent injury after very short exposure to small quants (Ref 12) Uses. Peroxyacetic acid is the most important epoxidation reagent used today because of its economical availability and ease of use with a wide variety of reactants (Ref 10). It also finds wide usage as an organic oxidizing agent (Ref 11) Refs 1) Beil 2, 169, (78), [174] [379 ... 

Further studies were conducted to improve this scheme to the A-ring unit, particularly, with respect to cost and scale-up practicality. Replacement of expensive meta-chloroperoxybenzoic acid by 30-40% peroxyacetic acid in acetic acid (four equivalents at 0°C) gave a 94% yield of epoxides 3a,b in a 9 1 ratio. 

Another method of making epoxides is the electrophilic reaction of alkenes with a peroxy acid such as peroxyacetic acid (sometimes simply peracetic acid). Thus, cyclohexene may be converted into the epoxide in a single reaction. 

---