Hydroperoxides 1,2-diperoxides

One feature of many sulphide oxidations merits particular note. The initially rapid uptake of oxygen soon slackens and autoretardation may be observed to such an extent that oxygen absorption practically ceases after very small extents of reaction. As with hydrocarbon oxidation the reaction appears to be sensitive to free radical promoters and inhibitors (but, surprisingly, not to peroxides) suggesting that a free radical process is operating. Unlike olefin oxidations which yield essentially single primary products (hydroperoxides or diperoxides or hydroperoxide-diperoxides) sulphide autoxidations yield complex product mixtures from the earliest stages of the reaction. 

Most ozonolysis reaction products are postulated to form by the reaction of the 1,3-zwitterion with the extmded carbonyl compound in a 1,3-dipolar cycloaddition reaction to produce stable 1,2,4-trioxanes (ozonides) (17) as shown with itself (dimerization) to form cycHc diperoxides (4) or with protic solvents, such as alcohols, carboxyUc acids, etc, to form a-substituted alkyl hydroperoxides. The latter can form other peroxidic products, depending on reactants, reaction conditions, and solvent. 

Another butadiene oxidation process to produce butanediol is based on the 1,4-addition of /-butyl hydroperoxide to butadiene (108). Cobalt on siHca catalyzes the first step. This is followed by hydrogenation of the resulting olefinic diperoxide to produce butanediol and /-butyl alcohol. 

In order to induce the free-radical chain reaction, a starter compound such as dibenzoyl diperoxide, azo-Zj -(isobutyronitrile) or tcrt-butyl hydroperoxide or UV-light is used. The commercially available, technical grade N-bromosuccinimide contains traces of bromine, and therefore is of slight red-brown color. Since a small amount of elemental bromine is necessary for the radical... 

Experimental evidence is available to show that at room temperature diperoxides are formed in polyethylene, whereas polypropylene and polyvinyl chloride generate hydroperoxides. The temperature at which the peroxides decompose and initiate grafting depends on the type of polymer used. 

In PE, these trapped radicals have been identihed as, mainly, alkyl and allyl radicals with the stmctures (—CH2CHCH2—) and (—CH—CH=CH—) [134,135]. In the presence of oxygen, the polymeric radicals will react to form diperoxides and hydroperoxides, as well as certain amount of less stable peroxy radicals (—CH2OO ). 

Procedures. Chromatographic Purification of Ozonization Products. Ozonization products from ethyl 10-undecenoate and 1-octene were chromatographed on silica gel columns (Baker) and eluted with 15 or 25% ether in petroleum ether (b.p., 30°-60°). Fractions were examined by thin-layer chromatography (TLC) on silica gel G Chroma-gram sheet eluted with 40% ether in petroleum ether. For development of ozonide and peroxide spots, 3% KI in 1% aqueous acetic acid spray was better than iodine. The spots (of iodine) faded, but a permanent record was made by Xerox copying. Color of die spots varied from light brown (ozonide) to purple-brown (hydroperoxide), and the rate of development of this color was related to structure (diperoxide > hydroperoxide > ozonide). 2,4-Dinitrophenylhydrazine spray revealed aldehyde spots and also reacted with ozonides and hydroperoxides. Fractions were evaporated at room temperature or below in a rotary evaporator. 

By analogy with Reaction 2 oxygen should be evolved from alkoxy hydroperoxide oxidation and a nonacidic diperoxide produced (Reaction... 

The peroxidation procedure, which is the least often used of all the irradiation techniques, involves irradiation of the substrate in the presence of air or oxygen. This produces diperoxides and hydroperoxides on the surface of fhe subsfrafe, which are stable, and the substrate can be stored until the combination with a monomer is possible. Monomer, with or without solvent, is then reacted with the activated peroxy trunk polymer in air or under vacuum at elevated temperatures to form the graft copolymer. The advantage of this method is the relatively long shelf life of fhe infermediate peroxy trunk polymers before the final grafting step. ... 

The two products formed in Reactions 16 and 17—i.e., hydroperoxides and diperoxides, respectively—exhibit different properties, and this makes it possible to assign a reaction mechanism to a given peroxidation process if one can establish the nature of the resulting peroxide. Thus, hydroperoxides are usually less stable to heat than diperoxides. 

The concentration of hydroperoxides can often be determined by infrared analysis or by chemical titration. Diperoxides are more difficult to detect experimentally. If both substituents of the peroxide are polymeric radicals, P, the corresponding peroxide POOP can actually be considered as an oxygen bridge between two macromolecules and should therefore behave like a crosslink ... 

It must be noted here that ketone or aldehyde, diperoxides and peroxide oligomers are obtained in non participating solvents whereas alkoxy or alkyl hydroperoxides result from ozonolysis conducted in participating solvents [13]. 

W. D. Wang, J. H. Espenson, Thermal and photochemical reactions of methylrhenium diperoxide Formation of methyl hydroperoxide in acetonitrile, Inorg. Chem. 36 (1997) 5069. 

The most commonly used initiator for anaerobic adhesives is cumene hydroperoxide. Many other hydroperoxides have been disclosed, such as t-butylhydroperoxide (XL), p-menthane hydroperoxide (XLI), diisopropylbenzene hydroperoxide (XLII), pinene hydroperoxide (XLIII), and methyl ethyl ketone hydroperoxide (XLIV) [40]. Some diperoxides, such as di-/-butylperoxide (XLV) and dicumylperoxide (XLVI), have been claimed, but these may function only because of hydroperoxide contamination [41]. 

Isoprene polymers, both of low molecular weight such as squalene, and of high molecular weight such as natural rubber and gutta percha also differ from mono-olefins in that intramolecular reactions can occur because of the multiple unsaturation and the short distances between the double bonds. For such materials it has been shown that a diperoxide-hydroperoxide structure is formed which Holland and Hughes (1949) proposed as ... 

In the Criegee proposals the initial product is stipulated to have a 1,2,3-trioxolane structure (I) which is also known as a molozonide structure. This undergoes a concerted decomposition to give a zwit-terion (II) and a carbonyl compound (III). The decomposition products (II) and (III) in most cases recombine to give the normal ozonide (IV). Other possible reactions include dimerization of the zwitterion to yield a diperoxide (V) or a higher peroxide (VI) whilst in the presence of methanol as a reactive solvent a methoxy-hydroperoxide (VII) may be produced. 

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