Peroxyacids, reaction with

Perhaps the most common method for the epoxidation of simple alkenes is their reaction with peroxyacids, which has occasionally been referred to as the Prilezhaev (Prileschajew) reaction. O This reaction does not require transition metal catalysis and the yield of epoxide is often high. Peroxyacids such as 156 are prepared by reaction of carboxylic acids with hydrogen peroxide. An equilibrium is established during the reaction that favors the peroxyacid, although several alternative methods are available.279 in general, strong... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Treatment of the following alkene with a peroxyacid yields an epoxide different from that obtained by reaction with aqueous Br2 followed by base treatment. Propose structures for the two epoxides, and explain the result. 

Hydroxy-terminated polybutadiene (8) (HTPB) has been treated with dinitrogen pentoxide in methylene chloride. The product (9) is an energetic oligomer but is unlikely to find application because of the inherent instability of /3-nitronitrates." Initial peroxyacid epoxidation of some of the double bonds of HTPB followed by reaction with dinitrogen pentoxide yields a product containing vtc-dinitrate ester groups and this product (NHTPB) is of much more interest as an energetic binder (see Section 3.10)." ... 

Peroxyacids are powerful oxidants and so side reactions are to be expected. Ketones are known to undergo Baeyer-Villiger " oxidation to the carboxylic acid ester on treatment with peroxyacids and so these by-products can be observed if oxime hydrolysis occurs during the oxidation. Paquette and co-workers " " observed such a by-product (61) during the oxidation of the dioxime (59) to the dinitro compound (60) with m-CPBA in hot acetonitrile. 

Much of what is understood today about the influence of solvent on rates of oxidation reactions with hydrogen peroxide, alkyl hydroperoxides and peroxyacids can be attributed to the seminal studies by Edwards and his collaborators over thirty years ago " . They provided convincing experimental data that showed that a hydroxylic solvent (e.g. ROH) can participate in a cyclic transition state where a proton relay can in principle afford a neutral leaving group attending heterolytic 0-0 bond cleavage (equation 13). 

Peroxyacids oxidize the imine group in (236) and related compounds to the nitrone. The 1,4-benzodiazepine (178) and its 4,5-dihydro analogue can be oxidized to the 2-oxo derivatives with chromium(VI) oxide. The benzodiazepinone (236) can be hydroxylated at the 3-position via a two-step process firstly reaction with LTA gives the 3-acetoxy derivative and this can then be hydrolyzed in high yield using sodium methoxide in methanol/methylene chloride. The 3-acetoxy derivative may also be prepared via bromina-tion with NBS and reaction with sodium acetate in situ (79JHC1449). 

Alkenes react with peroxyacids (RCO3H) followed by hydrolysis to give trans-1,2-diols. The products are always anft-diols, since the reaction occurs with anti addition. 

A convenient general method for the conversion of aliphatic and aromatic carboxylic acids into the corresponding peroxyacids involves reaction with 70 per cent hydrogen peroxide in the presence of methanesulphonic acid.33... 

CAUTION All preparations and reactions with hydrogen peroxide and organic peroxyacids must be conducted behind a safety screen, because these reactions sometimes proceed with violence. 

Carboxylic Acids. The peroxyacids formed may be unstable and explosive.13 Ketones. Hazardous reaction with acetone and nitric acid other ketones yield shock-and heat-sensitive explosive peroxides.14... 

In early attempts to produce an iron-oxo species (20) from typical porphyrins like chloro-a,/3,y,8-tetraphenylporphinatoiron(III) [Fe(III)TPP-Cl] and chloroferriprotoporphyrin(IX)[Fe(III)PPIX-Cl], we examined the reaction of t-butyl hydroperoxide and peroxy-acids with alkanes and olefins in the presence of these catalysts. With peroxyacids, decomposition of the porphyrin ring was observed, while with the f-butyl hydroperoxides, product distributions were indistinguishable from free-radical chain reactions initiated photochem-ically in the absence of any metals. 

Reaction with a peroxyacid to yield an epoxide (Secs. 7.8, 18.5)... 

Another route to the preparation of a-hydroxy derivatives consists of the transformation of enolates into silyl enolates and their subsequent oxidation. Oxidation of triaLkylsUyl enolates with peroxyacids, most frequently cpba, has been applied for preparation of a-hydroxy- and a-acetoxy aldehydes or ketones. Reactions require mild conditions and generally give good yields of the expected compound . Mechanistic investigations suggest the intermediate formation of epoxides which evolve to the final products via 1,4-sUyl group migration. 

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