Thermal decomposition dialkyl peroxides

Primary and secondary dialkyl peroxides undergo thermal decompositions more rapidly than expected owing to radical-induced decompositions (73). Such radical-induced peroxide decompositions result in inefficient generation of free radicals. 

Thermal or photo-induced decompositions of dialkyl peroxides in the presence of suitable substrates yield various products. For example, with nitric oxides, alkyl nitrites or nitrates are formed and, with carbon monoxide, Z fZ-alkyl esters are obtained (44) ... 

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. 

Methods for detecting whether peroxy compound have been used for cross-linking elastomers have been reviewed. An important application of dialkyl peroxides is as initiators of cross-linking and graft polymerization processes. The success of both processes depends on the ability of the peroxide to produce free radicals and the ability of the free radicals for H-abstraction from a relevant donor substrate. A method for evaluating this ability consists of inducing thermal decomposition of the peroxide dissolved in a mixture of cyclohexane and MSD (225). The free radical X" derived from the... 

The alkenyl hydroperoxides and polymeric dialkyl peroxides are fairly stable at ambient temperature but decompose appreciably at the reaction temperatures studied. Thermal stabilities of the alkenyl hydroperoxides and dialkyl peroxides in the olefin solution were determined by heating the solution at 110°C. under nitrogen. The peroxide numbers were plotted vs. time to estimate the half-lives in solution. The thermal decomposition half-lives of these alkenyl hydroperoxides are compared with values from the literature for acyclic and cyclic hydroperoxides in Table IV. Secondary acyclic alkenyl hydroperoxides appear to be less... 

At Van Sickle s conditions of low temperatures and low conversions, branching routes A and B appear to be dominant since there is little alkenyl hydroperoxide decomposition. In our work above 100°C., the branching routes are supported by the nearly linear initial portions at low conversions for alkenyl hydroperoxide and polymeric dialkyl peroxide curves (see Figures 2, 3, and 4). The polymeric dialkyl peroxides formed under our reaction conditions include those formed by the branching mechanism postulated by Van Sickle (routes A and B) and those formed by the reaction of the alkenoxy and hydroxy radicals from alkenyl hydroperoxide thermal decomposition reacting further and alternately with olefin and oxygen (step C). The importance and kinetic fit of the sequential route A to C appears to increase with temperature and extent of olefin conversion owing to the extensive thermal decomposition of the alkenyl hydroperoxides above 100°C. 

The thermal decomposition of S5mrmetrical dialkyl peroxides such as diisopropyl peroxide in solution has been shown to involve a competition between monomolecular homolysis k ) and an electrocyclic reaction yielding acetone and hydrogen ( h) cf Eq. (5-59) [564]. 

For further examples of dichotomous solvent-influenced radical/ionic perester decompositions, see the base-catalyzed perester fragmentation shown in Eq. (5-39) in Section 5.3.2 [110], as well as the decomposition of t-butyl heptafluoroperoxybutyrate, C3p7-C0-0-0-C(CH3)3 [691]. The relative extent of monomolecular and induced thermal decomposition of disubstituted dibenzyl peroxydicarbonate, ArCH2-0-C0-0-0-C0-0-CH2Ar, is also substantially influenced by the reaction medium [692]. The thermolysis of suitable dialkyl peroxides can also proceed by two solvent-dependent competitive reaction pathways (homolytic and electrocyclic reaction), as already shown by Eq. (5-59) in Section 5.3.4 [564]. 

Kinetics of thermal decomposition of dialkyl peroxides in solution as well as the gas phase have been reviewed by Molyneux and Frost and Pearson . The decomposition of dialkyl peroxides is moderately free from induced decomposition, compared to other types of peroxides. As seen from Table 65, the first-order rate coefficient increases by about 16 % when the initial peroxide concentration is increased about 5 fold at reasonably high peroxide concentrations. The increase in the rate coefficient is attributed to an induced decomposition where hydrogen atom abstraction generates the radical (I). Further reaction of (I) produces isobutylene oxide and the f-butoxy radical, viz. 

Kinetic data for thermal decomposition of the related dialkyl peroxydicarbonates are given in Table 112. Variation of the substituent groups R has little effect on the rate coefficients or the activation energy. In addition the activation energies are in the range of those reported for benzoyl peroxides. This suggests a one-bond homolysis reaction. Activation energies for dialkyl peroxydicarbonates with... 

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