Peroxides and Hydroperoxides

0-0 St 1000-800 Mediiun or weak, often doublet, assignment uncertain 

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Most likely singlet oxygen is also responsible for the red chemiluminescence observed in the reaction of pyrogaHol with formaldehyde and hydrogen peroxide in aqueous alkaU (152). It is also involved in chemiluminescence from the decomposition of secondary dialkyl peroxides and hydroperoxides (153), although triplet carbonyl products appear to be the emitting species (132). 

Thermally induced homolytic decomposition of peroxides and hydroperoxides to free radicals (eqs. 2—4) increases the rate of oxidation. Decomposition to nonradical species removes hydroperoxides as potential sources of oxidation initiators. Most peroxide decomposers are derived from divalent sulfur and trivalent phosphoms. 

Isopropyl Ether. Isopropyl ether is manufactured by the dehydration of isopropyl alcohol with sulfuric acid. It is obtained in large quantities as a by-product in the manufacture of isopropyl alcohol from propylene by the sulfuric acid process, very similar to the production of ethyl ether from ethylene. Isopropyl ether is of moderate importance as an industrial solvent, since its boiling point Hes between that of ethyl ether and acetone. Isopropyl ether very readily forms hazardous peroxides and hydroperoxides, much more so than other ethers. However, this tendency can be controlled with commercial antioxidant additives. Therefore, it is also being promoted as another possible ether to be used in gasoline (33). 

For a number of applications curing at room temperature is desirable. This so-called cold cure is brought about by using a peroxy initiator in conjunction with some kind of activator substance. The peroxy compounds in these cases are substances such as methyl ethyl ketone peroxide and cyclohexanone peroxide, which as used in commercial systems tend not to be particularly pure, but instead are usually mixtures of peroxides and hydroperoxides corresponding in composition approximately to that of the respective nominal compounds. Activators are generally salts of metals capable of undergoing oxidation/reduction reactions very readily. A typical salt for this purpose is cobalt naphthenate, which undergoes the kind of reactions illustrated in Reactions 4.6 and 4.7. 

Organic peroxides and hydroperoxides decompose in part by a self-induced radical chain mechanism whereby radicals released in spontaneous decomposition attack other molecules of the peroxide.The attacking radical combines with one part of the peroxide molecule and simultaneously releases another radical. The net result is the wastage of a molecule of peroxide since the number of primary radicals available for initiation is unchanged. The velocity constant ka we require refers to the spontaneous decomposition only and not to the total decomposition rate which includes the contribution of the chain, or induced, decomposition. Induced decomposition usually is indicated by deviation of the decomposition process from first-order kinetics and by a dependence of the rate on the solvent, especially when it consists of a polymerizable monomer. The constant kd may be separately evaluated through kinetic measurements carried out in the presence of inhibitors which destroy the radical chain carriers. The aliphatic azo-bis-nitriles offer a real advantage over benzoyl peroxide in that they are not susceptible to induced decomposition. 

Thermal decomposition of dialkyl peroxides, diacyl peroxides, hydroperoxides and peracids depending on the structure of the peroxidic compound occurs in a measurable rate usually above 60°C. Diacyl peroxides and peracids are considerably less stable than dialkyl peroxides and hydroperoxides. 

A technique is described [213] in which reactive chemical experimental data obtained with peroxides and hydroperoxides are used to define safe design... 

Typical results in the closed cell test for peroxides and hydroperoxides were a pmax of 110 bar and a Tmax of 255°C. From the blowdown test, it was concluded that two-phase blowdown occurred. Furthermore, the peroxide concentration in the residue after blowdown was about twice that of the original concentration. 

Analogous to the reduction of disulfides, peroxides and hydroperoxides, compounds that are generally toxic are readily reduced back to alcohols by peroxidases however, in the process, other compounds including drugs can be oxidized. 

Some times even catalysts can include initiators to decompose into free radicals. In such type of reaction, an electron transfer mechanism is involved. Peroxides and hydroperoxides are decomposed in this way. For example, the decomposition of benzoyl peroxide by an aromatic tertiary amine at room temperature. 

Most synthetic and natural polymers degrade when exposed to solar ultraviolet (UV) radiation (1-5). In synthetic polymers degradation is generally caused by the presence of photosensitive impurities and/or abnormal structural moieties which are introduced during polymerization or in the fashioning of the finished products. The presence of groups such as ketones, aldehydes, peroxides and hydroperoxides are implicated in polymer degradation (1-5). 

Oxygen-oxygen bond in peroxides and hydroperoxides is cleaved very easily by catalytic hydrogenation over platinum oxide [661,662], over palladium [75, 662, 663, 664] or over Raney nickel [66S. Hydroperoxides yield alcohols... 

Floyd EP, Stokinger HE Toxicity studies of certain organic peroxides and hydroperoxides. Am IndHyg Assoc J 19 205-212, 1958... 

At this stage it may be worth conjecturing as to why some calorimetric smdies of peroxides and hydroperoxides are seemingly unreliable. Recall that an ether that has been left standing too long autooxidizes to a peroxide, which then has a tendency to explode on heating or when shocked. In an experimental combustion process, this same tendency to explode may result in incomplete combustion with attendant carbon build-up. If so, there are thermodynamically ill-defined and irreproducible products that increase the variability and uncertainty in the measurements and essentially invalidate the results derived . 

The application of CPO, HRP and CiP is limited to sterically unencumbered substrates and all these peroxidases produce the same absolute configuration of the chiral hydroperoxide. To overcome this limitation, the semisynthetic enzyme selenosubtilisin, a mimic for glutathione peroxidase, with the peptide framework of the serine protease subtilisin was developed by Bell and Hilvert. This semisynthetic peroxidase catalyzes the reduction of hydrogen peroxide and hydroperoxides in the presence of 5-mercapto-2-nitrobenzoic acid. It was utilized by Adam and coworkers and Schreier and coworkers for the kinetic resolution of racemic hydroperoxides (equation 17) . The results obtained were very promising. 

Chloroprene Peroxide. The efficiency of conversion of oxygen to total peroxides and hydroperoxide at various extents of oxidation was determined by iodometric methods. At up to 12% oxidation the proportion of hydroperoxide was constant at 20% of the whole. Ferrous thiocyanate likewise estimated a constant proportion (40%) of the total peroxide. Direct analysis of oxidates was somewhat difficult since the chloroprene tended to continue oxidizing during manipulation. Total peroxide estimates on chloroprene-free solutions of peroxide in toluene showed that at 20% oxidation 84% of the oxygen absorbed was present as peroxide groups. This is a minimum value since a small amount of the peroxide may have decomposed while chloroprene was being removed at —20°C. 

Many metal peroxides, superoxides, organic peroxides, and hydroperoxides are known, but they are not expected to be significant because of their inferiority to H202 in terms of performance, properties, or stability. 

While such oxidizing agents as chromic acid and nitric acid have been used to convert azo compounds into azoxy compounds, the more recent techniques have involved perbenzoic acid [7, 21-24], peracetic acid or hydrogen peroxide in glacial acetic acid [3, 25-28], and hydrogen peroxide in trifluoroacetic acid [29], Use of the various organic peroxides and hydroperoxides does not appear to have been studied. 

For a review of the synthesis of alkyl peroxides and hydroperoxides, see Sheldon, in Patai The Chemistry of Peroxides,. Wiley New York, 1983. pp. 161-200. 

Peroxide and hydroperoxide ions. A patent disclosure h Barueoh and Payne101 has described addition of teri-bntylliydi- peroxide to ethylene oxide, propylene oxide, and isobutylene oxide in ether, in the presence of either basic or acidic catalysts. The <°rt-Imtylperoxide ion, like other nucleophiles, apparently prefers to uttar. c... 

Figure 4.61 Peroxide and hydroperoxide formation in photo-oxygenation reactions addition of molecular oxygen to anthracene to form the transannular peroxide, and insertion into an olefin...

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