Cumylperoxy

PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18) Cumylperoxy derivatives... 

Tn 1955 Russell showed that mixtures of cumene and small amounts of - Tetralin oxidized at rates considerably below the rates of oxidation of either of the pure hydrocarbons (26). Russell suggested that this decrease in rate was caused by the fact that tetralylperoxy radicals terminate oxidation chains much more readily than cumylperoxy radicals. The mixtures, therefore, oxidize at a lower rate than pure cumene because of... 

Hydrogen Atom Transfer from Hydroperoxides to Peroxy Radicals. The reaction of cumylperoxy radicals with Tetralin hydroperoxide (Reaction 10) can be studied at hydroperoxide concentrations below those required to reduce the oxidation rate to its limiting value. The rate of oxidation of cumene alone can be represented by ... 

The rate constants of a-hydrogen atom abstraction from four hydrocarbons by cumylperoxy, tetralylperoxy, and 9,10-dihdroanthracyl-9-peroxy radicals and by the normal chain-carrying peroxy radicals are compared in Table VIII. The results show that the reactivities of peroxy radicals are affected by the nature of the organic group. The relatively low propagation constant for the oxidation of pure cumene may be caused by the low reactivity of the cumylperoxy radical. 

Several other types of antioxidants can inhibit oxidation by donating a hydrogen atom to a peroxy radical. Howard (15) has described the interesting case of inhibition by a second hydrocarbon or its hydroperoxide. In the particular case he discussed, the inhibition of the oxidation of cumene by Tetralin (TH) or Tetralin hydroperoxide (TOOH) occurs because the tetralylperoxy radical (T02 ) reacts with a cumylperoxy radical (CO2 ) much more rapidly than two cumylperoxy radicals react with one another. The inhibition sequence can be represented by the following reactions. 

The self-recombination reactions of HOj, CF3CFHO, and CF3O) have been studied using pulse radiolysis/time-resolved UV absorption spectroscopy.215 The addition of the cumylperoxy radical to a range of alkyl-substituted biphenyls has been studied and the rate constants compared with reactions with related monosubstituted benzenes.216... 

In recent years much emphasis has been placed on studies of co-oxidations, since they can provide quantitative data about fundamental processes (such as the relative reactivities of peroxy radicals toward various hydrocarbons48-50), which are difficult to obtain by other methods. Co-oxidations are also quite important from a practical viewpoint since it is possible to utilize the alkylperoxy intermediates for additional oxidation processes instead of wasting this active oxygen. That the addition of a second substrate to an autoxidation reaction can produce dramatic effects is illustrated by Russell s observation51 that the presence of 3 mole % of tetralin reduced the rate of cumene oxidation by two-thirds, despite the fact that tetralin itself is oxidized 10 times faster than cumene. The retardation is due to the higher rate of termination of the secondary tetralyl-peroxy radicals compared to the tertiary cumylperoxy radicals (see above). 

Tetralyl hydroperoxide Cumylperoxy 6-7m cumene in chlorobenzene 30 30 Howard el al. (1968)... 

Under some experimental conditions, including low hydrocarbon concentration and high rate of radical formation, the interaction of methyl-peroxy and cumylperoxy radicals rather than self-reaction of cumyl-peroxy radicals accounts for most of the terminating interactions. The competing reaction for methylperoxy is abstraction from cumene, viz. 

The term a is the fraction of terminations per self-reaction of two cumylperoxy radicals. When there are no methylperoxy radicals, a equals 0.1 at 60° C. At high rates of initiation and low [RH], the value of a increases and in principle could reach 2.1 if every cumoxy is converted to methylperoxy and terminates with another cumylperoxy radical. Thus kt can range only from fe38 to 2.1 k3S. 

The rate coefficients for the reactions of cumylperoxy radicals with carboxylic groups (fej) and a-C—H Bonds (ft2), and a-hydroperoxycarboxylic acid decomposition (63) with acids in oxidizing cumene (125—145°C) [215,299]... 

In addition to decarboxylation, the oxidation of acids yields hydro-peroxy, hydroxy, keto groups, lactones, and mono- and dicarboxylic acids of lower molecular weight. The mechanism of the oxidation of acids is similar to that for hydrocarbons. The reactivity of mono- [300] and dicarboxylic acids [216] with respect to cumylperoxy radicals was measured by oxidation in the presence of cumyl hydroperoxide as source of R02 (see Table 15). The reactivities of methylenic groups in mono- and dicarboxylic acids and in rc-paraffin acids are close. For example, at 100° C, feCH2 X 102 (1 mole-1 s-1) = 4.8 (n-decane), 10.0 (glutaric, sebacic, j3,7 groups), 6.4 (a-CH2 of dibasic acids), 8.0 (for monocarboxylic acids), and 11.0 (>CH2 for propionic acid). 

Rate coefficients for reactions of cumylperoxy radicals with mono- [300] and dicarboxylic [216] acids in chlorbenzene... 

Values of the ratio kp/ /2kt are given in Table 18. The absolute rate coefficients of cumylperoxy radical reactions with various esters were measured by Agabekov et al. (see Table 19). It is of interest to note that the reactivity of the esters of monocarboxylic acids is much greater than that of dicarboxylic esters (compare, for example, propionates and glutarates). 

The rate coefficients of reaction of cumylperoxy radicals with some esters... 

Effect of f-butanol on the rate coefficient of the exchange reaction between tetrallyl hydroperoxide and cumylperoxy radicals at 30°C [260]... 

Comparison of rate coefficients, experimental (k) and calculated according to the additivity rule (Sfe ), of cumylperoxy radical reactions with esters at 140°C [322,323]... 

Fiikuzumi and Cuo have very recently concluded that the termination reaction for oxidation of c miene with manganese dioxide or cobalt oxide supported on silica ( ) and during autoxidation of cumene initiated by reaction of cumene hydroperoxide with lead oxide ( ) is strictly first-order with respect to the concentration of cumylperoxy radicals. These workers proposed an unprecedented 1,3-methyl shift followed by 0-0 bond cleavage to account for these inusual kinetics. 

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