Peroxycarboxylic acids alkenes

Direct Oxidation with Stoichiometric Oxidants. Discovered by Prilezhaev in 1909,211 the typical epoxidation reaction of alkenes is their oxidation with organic peracids. Of the large number of different peroxycarboxylic acids used in... 

Alkenes can be oxidized with peroxycarboxylic acids, RC03H, to give oxacy-clopropanes (oxiranes, epoxides), which are three-membered cyclic ethers ... 

The most important method of preparation involves oxidation, or epoxidation, of an alkene with a peroxycarboxylic acid, RC03H. This reaction achieves suprafacial addition of oxygen across the double bond, and is a type of electrophilic addition to alkenes (see Exercise 15-53) ... 

The reaction of alkenes with peroxycarboxylic acids to produce epoxides was discovered by Prilezhaev over 80 years ago.14 It is still the most widely used method for epoxidation, and considerable work has been carried out to elucidate the mechanism. The commonly accepted explanation for oxirane formation involves a cyclic polar process where the proton is transferred intramolecularly to the carbonyl oxygen, with simultaneous attack by the alkene rc-bond. This concerted process was suggested by Bartlett,15 and because of the unique planar transition structure it is referred to as the butterfly mechanism (Figure 3.2). 

Figure 3.2 Bartlett butterfly mechanism for the epoxidation of alkenes with peroxycarboxylic acids.

The epoxidation of alkenes with peroxycarboxylic acids gives the corresponding oxirane by an electrophilic 1,1-addition mechanism as outlined in Eq. (5-31) [77, 86, 86a, 87, 516]. 

Anti hydroxylation of an alkene is readily achieved with peroxycarboxylic acids. - Acid-catalyzed ting opening of the initial product, an oxirane (epoxide), forms the monoester of a 1,2-diol, hydrolysis of which affords the parent diol. Alternative reagents which are often used for anti hydroxylation of alkenes are hydrogen peroxide with oxides of timgsten - or selenium, - and iodine-silver benzoate (Prdvost reaction). ... 

In general, attack of the peroxycarboxylic acid on an alkene will occur from the less hindered ir-face and ring opening of the oxirane usually occurs to place the acyloxy group on the more substituted carbon atom. 

The most widely used and, presumably, the most chemoselective reagents for the epoxidation of nucleophilic C—C double bonds are the peroxycarboxylic acids (see Houben-Weyl, Vol. IV/ 1 a, p 184, Vol. Vl/3, p 385, Vol. E13/2, p 1258). Using chloroform as solvent, epoxidation rates are particularly high79. Reactive or acid/base sensitive epoxides can often be obtained with dimethyldioxirane (see Houben-Weyl, Vol. R13/2, p 1256 and references 15, 16, 87-90), peracid imides (see Houben-Weyl, Vol. IV/1 a, p 205, Vol. VI/3, p 401, Vol. E13/2, p 1276) (prepared in situ from nitriles and hydrogen peroxide), hydroperoxy acetals (see Houben-Weyl, Vol. El3/2, p 1253) or peroxycarbonic acid derivatives (see Houben-Weyl, Vol. IV/la, p 209 and references 17-19) as oxidants. For less reactive alkenes, potassium hydrogen persulfate is a readily available reagent for direct epoxidation20. 

It is noteworthy that selenium, arsenic and boron compounds are also effective catalysts for the selective epoxidation of alkenes by H2O2 (equations 34-36). It is generally thought that peroxyselenic and peroxyarsonic acids act as reactive intermediates in a way similar to that of peroxycarboxylic acids. Metaboric acid, HBO2, acts as both an epoxidation catalyst and a dehydrating agent. The resulting orthoboric acid can be dehydrated back to metaboric acid. ... 

Alkenes undergo reaction with peroxycarboxylic acids (RCO3H) to give three-membered-ring cyclic ethers called epoxides. For example, 4-octene reacts with a peroxyacid to yield 4,5-epoxyoctane ... 

Prilezhaev reaction Oxidation of alkenes to epoxides using peroxycarboxylic acids. 362... 

Epoxides are three-membered cyclic ethers. The simplest, ethylene oxide is prepared from ethylene and oxygen. Epoxides are prepared more generally from alkenes using a peroxycarboxylic acid. 

The reaction of alkenes with peroxycarboxylic acids (or peracids) leads to the formation of epoxides in a concerted addition reaction. The peroxycarboxylic acid donates an oxygen atom to the double bond in a syn- addition reaction. 

Another early discovery was that CALB accepts H202 as nucleophile to produce peroxycarboxylic acids from esters or carboxylic acids (perhydrolysis activity can also be found in other serine hydrolases) [46, 47]. The in situ formed peracid can subsequently be used to epoxidize an alkene by (non-enzymatic) Prileshajev epoxidation. Hence, oleic acid incubated with CALB and H202 will produce 9,10-epoxyoctadecanoic acid [48]. Other alkenes can be epoxidized by H202 and a catalytic amount of carboxylic acid (and CALB) (Scheme 13.2) [49],... 

The oxidation of saturated hydrocarbons in the presence of iron- or manganese-containing catalysts can be achieved by using a variety of oxidants including alkyl hydroperoxides, peroxycarboxylic acids, iodosyl-benzene, dihydrogen peroxide, and dioxygen (9-11). It has been shown that chiral iron- and manganese-porphyrin complexes catalyze the asymmetric epoxidation of unfunctionalized alkenes (75). Except for a number of experiments in which up to 96 % enantiomeric excess (ee) has been reported (16,17), in most epoxidation reactions with chiral porphyrins only a low to moderate enantiomeric excess of the product is obtained (18,19). In association with these catalysts, alkyl hydroperoxides and iodosylbenzene are often used as primary oxidants (18,19). 

These sections present several reactions that attach oxygen to both the double-bonded carbons of alkenes. Each reaction is an example of a concerted process, in which several bonding changes occur in one step. Peroxycarboxylic acids such as MCPBA contain an electrophilic oxygen... 

Step G involves a question of both chemical and stereochemical selectivity. The trisubstituted double bond must be oxidized in preference to the endocyclic double bond. This preferred substitution does occur, largely because of the increased reactivity of the more highly substituted alkene linkage in peroxycarboxylic acid oxidations. The double bond oxidized presents two nonidentical (diastereotopic) faces to the oxidant. The observed (and desired) stereochemistry results because of... 

The most common laboratory method for the synthesis of epoxides from alkenes is oxidation with a peroxycarboxylic acid (a peracid), RCO3H. One peracid used for this purpose is peroxyacetic acid ... 

The key feature of an epoxidation reaction of an alkene and a peroxycarboxylic acid is the formation of an epoxide with retention of stereochemistry about the reacting C—C double bond. This means that the relative stereochemistry of all groups about the double bond must be the same in the product epoxide as shown in the acyclic and cyclic examples. 

To predict the product of a peroxycarboxylic acid and an alkene, convert its C — C double bond to a C—C single bond in which both carbons are bonded to the same oxygen in a three-membered ring. 

Unfortunately, direct epoxidation of alkenes by metal-free haloperoxidases led to racemic epoxides [1331, 1332]. Since the reaction only takes place in the presence of a short-chain carboxylic acid (e.g., acetate or propionate), it is believed to proceed via an enzymatically generated peroxycarboxylic acid, which subsequently oxidizes the alkene without the aid of the enzyme. This mechanism has a close analogy to the lipase-catalyzed epoxidation of alkenes (Sect 3.1.5) and halogenation reactions catalyzed by haloperoxidases (Sect. 2.7.1), where enzyme catalysis is only involved in the formation of a reactive intermediate, which in turn converts the substrate in a spontaneous (nonenzymatic) foUowup reaction. 

The most general reagents for conversion of simple alkenes to epoxides are peroxycarboxylic acids. w-Chloroperoxybenzoic acid (MCPBA) is a particularly convenient reagent, but it is not commercially available at the present time. The magnesium salt of monoperoxyphthalic acid has been recommended as a replacement. Potassium hydrogen peroxysulfate, which is sold commercially as oxone, is a convenient reagent for epoxidations that can be done in aqueous methanol. Peroxyacetic acid, peroxybenzoic acid, and peroxytrifluoroacetic acid have also been used frequently for epoxidation. All of the peroxycarboxylic acids are potentially hazardous materials and require appropriate precautions. 

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