Peracids, reaction with olefins

Characterization of Photooxidation Products Formed in Isooctane. Among the lodometncally titratable species formed in the photooxidation of isooctane, a substance, developed in appreciable amounts, was observed which was easily distinguishable from ordinary alkyl-hydroperoxides. This substance is, at room temperature, readily destroyed by addition of olefins to the reaction medium. This is a reaction which is typical and specific for peracids (10) and can be employed for quantitative assessment of peracids in the presence of alkylhydroperoxides. In contrast to alkylhydroperoxides, peracids react with olefins forming the corresponding epoxide, according to the equation... 

In a study of the effects of substituents upon reactivity, it was found that electron-withdrawing groups retarded the reaction while electron-releasing groups assisted it . It is probable that the rate-determining stage, which involves one molecule of peracid and one molecule of acetylene , has similar requirements to that of the analogous reaction with olefins. 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

The reactions of olefins with peracids to form epoxides allows for the selective oxidation of carbon-carbon double bonds in the presence of other functional groups which may be subject to oxidation (for example, hydroxyl groups). The epoxides that result are easily cleaved by strong acids to diols or half-esters of diols and are therefore useful intermediates in the synthesis of polyfunctional compounds. 

Peracids react heterolytically with olefins with the formation of epoxides by the Prilezhaev reaction. So, the co-oxidation of aldehydes with olefins has technological importance. Peracids react with ketones with formation of lactones. These reactions will be discussed in Section 8.2. The oxidation of aldehydes are discussed in monographs [4-8]. 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

Free-radical autoxidation of aldehydes with 02 is facile and affords the corresponding peradds, which are used as oxidants for carbonyl compounds. The peracid can transfer an oxygen atom to a substrate such as an olefin or ketone, resulting in the formation of one equivalent of epoxide or ester and add as a co-produd in the absence of metal catalysts [59]. Kaneda and coworkers have developed several HT materials that are active for heterogeneous Baeyer-Villiger reactions with 02/aldehyde [60]. Combination with Lewis addic metals improved the reaction by allowing coordination of the peracid and the intermediate. 

Oxiranes may also be prepared by the cooxidation of aldehydes and olefins. There are two assumptions as regards the mechanism the oxidation occurs via either an acylperoxy radical or a peracid. The peracid oxidation is stereospecific. Experiments carried out with a view to assessing the radical versus nonradical mechanism indicate that the extent of the radical epoxidation depends on the structure of the olefin and the olefin/aldehyde ratio. Cooxidation in the presence of oxygen was achieved by irradiating the aldehyde and carrying out the reaction with the alkene after a suitable quantity of peracid had been obtained. Enantioselective epoxidation has been described in the reaction of (1-phenyl-alkylidene)malonitriles 63 catalyzed by optically active tertiary amines. ... 

Epoxides are usually prepared in the laboratory by the reaction of olefins with organic peracids or by the reaction of halohydrins with alkali. The mechanism of the first of these processes has not been completely elucidated,170 but the second involves an ionic reaction whose mechanism has already been discussed (p. 96). The synthesis of phenyl-methyl glycidic ester176 appears to proceed by a related sequence ... 

Hpoxidation of olefins. Reif and House worked out the following procedures for I ho preparation of rra/ij-stilbene oxide. Titration of the commercial 40% peracetic acid showed it to contain 0.497 g. of peracid per ml. For reaction with 0.3 mole of t/wi.v-stilbene, 65 ml. (0.425 mole) of reagent was used after addition of 5 g. of Na()Ac-3 H 0 to neturalize the sulfuric acid present. A solution of the hydrocarbon... 

The reaction of olefins with peracids involves firstly the formation of an epoxide, reaction (5.1) in acidic media the epoxide may suffer ring-opening to yield the mono-ester of a glycol, reaction (5.2). ... 

Oxoisophorone 68 can be converted into trimethylcyclohexanone (74), in a series of reduction and elimination steps [82], opening up a new route to p,p-carotene (3) and vitamin A [85,86]. The Cio-epoxide 75 can be obtained by Wittig olefination of 73 with methylene-triphenylphosphorane, isomerization and reaction with peracids. Lewis acid-catalysed rearrangement to give the five-membered ring yields the capsorubin synthon 76 [9]. 

The perhydroxyl anion, HO2 , is quite a powerful nucleophile and, as seen later, will attack substrates such as electron-deficient olefins (e.g. a,P-unsaturated ketones) and aldehydes - reactions with some synthetic utility, and also of value in bleaching and product purification, particularly of natural materials. In addition, HO2 can be used to generate more powerful oxidants by mixing with electron-deficient acyl compounds (giving peracids) or with nitriles (Payne system, see section 9.3.3.3). 

The iodometric method determines the total concentration of hydroperoxides, peroxides and peracids. In order to determine peracids in the presence of hydroperoxides and peroxides, an equal volume of 7-tetradecene solution (2 X 10 M) is added to a given volume used for analysis. Peracids (R—CO—OOH) react with olefins forming a corresponding epoxide, according to the reaction ... 

Epoxidations with peracids can exhibit high degree of chemoselectivity and these generally display preferences for reaction with more nucleophilic alkenes. This phenomenon is illustrated in Vandewalle s work directed towards the total synthesis of the sesquiterpene estafiatin (6, Equation 3) [52]. The final step included selective epoxidation of the trisubstituted olefin from its more accessible convex face (dr =97 3). 

In analogy with the peracid attack on steroidal double bonds, the formation of the bromonium ion, e.g., (81a), occurs from the less hindered side (usually the a-side of the steroid nucleus) to give in the case of the olefin (81) the 9a-bromo-l l -ol (82). Base treatment of (82) provides the 9 5,1 l S-oxide (83). Similarly, reaction of 17/3-hydroxyestr-5(10)-en-3-one (9) with A -bromosuccinimide-perchloric acid followed by treatment with sodium hydroxide and sodium borohydride furnishes the 3, 17 5-dihydroxy-5a,l0a-oxirane. As mentioned previously, epoxidation of (9) with MPA gives the 5, 10 -oxirane. °... 

Alkylsulfonic peracids oxidize olefins to epoxides. The formed sulfonic acid reacts with epoxide to form diols and esters. The yields of epoxides in the reactions of oxidation of two cycloolefins are given in Table 12.4. 

The electron-donating groups, if present in the alkene enhance the rate of the reaction. This is why the reaction is particularly rapid with tetraalkyl olefines. The electron-withdrawing groups in the peracids also increases the reaction rate. The following suggested mechanisms has been accepted for the conversions. 

The reaction of allenes with peracids and other oxygen transfer reagents such as dimethyldioxirane (DM DO) or hydrogen peroxide proceeds via allene oxide intermediates (Scheme 17.17). The allene oxide moiety is a versatile functionality. It encompasses the structural features of an epoxide, an olefin and an enol ether. These reactive intermediates may then isomerize to cyclopropanones, react with nucleophiles to give functionalized ketones or participate in a second epoxidation reaction to give spirodioxides, which can react further with a nucleophile to give hydroxy ketones. 

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