Organic peroxides and hydroperoxides

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. 

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

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. 

The example demonstrating this type of conjugation is that of organic peroxide and hydroperoxide decomposition induced by radicals. These processes were discussed in Chapter 1. 

Organic peroxides and hydroperoxides, including peroxide-containing solvents, can be treated. However, any solvent capable of forming peroxides from which a solid has crystallized should be handled by personnel trained in handling explosives. Most diazonium salts are not explosive and can be converted into disposable material by the coupling procedure. However, some diazonium salts are explosive when dry and should be carefully moistened before any manipulation is attempted. 

Many organic peroxides and hydroperoxides are known.30 Peroxo carboxylic acids (e.g., peroxoacetic acid, CH3CO OOH) can be obtained by the action of H202 on acid anhydrides. Peroxoacetic acid is made as 10 to 55% aqueous solutions containing some acetic acid by interaction of 50% H202 and acetic acid, with H2S04 as catalyst at 45 to 60°C the dilute acid is distilled under reduced pressure. It is also made by air oxidation of acetaldehyde. The peroxo acids are useful oxidants and sources of free radicals [e.g., by treatment with Fe2+(aq)]. Dibenzoyl peroxide, di-r-butyl peroxide, and cumyl hydroperoxide are moderately stable and widely used as polymerization initiators and for other purposes where free-radical initiation is required. 

Another question to be considered is whether it is in principle possible to affect the course of radical polymerization catalytically. The ions of metals with a variable valence are well known to be capable of catalyzing the monomolecular decomposition of organic peroxides and hydroperoxides. 

Allgrl-substituted phenols are the most widespread inhibitors. The phenoxyl radicals corresponding to them are readily produced by oxidizing the phenols with lead dioxide [3], in photolysis, y and /3 radiolysis, as well as in their reaction with active radicals produced in the thermal or catalytic decomposition of organic peroxides and hydroperoxides [4]. The stability of the radicals formed is determined by the structure of the initial phenol. The most stable radicals are strongly shielded phenols. Thus, 2,4,6-tri-tert-butylphenol (I), when oxidized by Pb02, forms phenoxyl radicals, the EPR spectmm of which is presented in Fig. 34a, in almost 100% yield ... 

In organic solvents, iodide ions reduce organic peroxides and hydroperoxides with the liberation of iodine. The reactions may be schematized as follows ... 

Organic peroxides and hydroperoxides are very commonly used at the laboratory scale as well as at the industrial level. Their instability can be characterized by their half-life time (/1/2)—that is, the time necessary to their half-decomposition at a given temperature —or by the temperature at which they exhibit a given half-life time (see Table 8.2) from these half-life times it is possible to easily And the corresponding value of kd using the kinetic equation of decomposition of the initiator... 

Organic peroxides and hydroperoxides are generally unstable and can decompose spontaneously and explosively under thermal and mechanical stress. Such decomposition may be caused by shock, impact, friction, or the catalytic effect of impurities. To reduce hazards involved during transportation and handling, they are desensitized by the addition of inert inorganic solids or liquids like water, halogenated hydrocarbons. 

The organic peroxides and hydroperoxides cover a wide range of half-life, and can provide an appropriate choice for most normal polymerization temperatures. The... 

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