Cumene radical decomposition

Table III. Polar and Radical Decomposition of Cumene Hydroperoxide Induced by Organic Sulfur Compounds (16)...

Radical involvement is indicated also by the inhibitory effect of radical trapping agents and product analysis, since 10-15% of the products from cumene hydroperoxide decomposition induced by the organic sulfur compounds result from free-radical processes (2). Acids will... 

Thus, it has been proposed that the homolytic decomposition of hydroperoxides can be induced by sulfenic acid (12,13). There is evidence that various carboxylic acids can promote radical formation from hydroperoxides at elevated temperatures (II, 14). The intermediate thiosul-furous acid (Reaction 7) itself may function as the source of radicals, since sulfinic acid is known to initiate the radical polymerization of vinyl monomers at 20°C (15). Based on the AIBN-initiated oxidation of cumene, Koelewijn and Berger (16) proposed that pro-oxidant effects arise from catalysis of the radical decomposition of hydroperoxides by intermediate compound formation between the hydroperoxide and sulfoxide. However, under our conditions hydroperoxide was stable in the presence of sulfoxide alone. 

CNTs improve radical initiation from pure cumene, increase decomposition rate of CHP, and allow oxidation at lower temperatures, with the advantage of higher space-time yield. However, any improved selectivity could not be proved [46,47]. Because of the increased CHP decomposition rate, new safety issues arise, as an uncontrolled decomposition is more probable. This risk becomes even more dangerous as the decomposition rate also depends on the CNT concentration, that... 

Quaternary ammonium salts exhibit high catalytic activity in radical-chain reactions of hydrocarbons liquid phase oxidation by [1, 2]. Tetraalkylammonium halides accelerate radical decomposition of hydroperoxides [3,4] that are primary molecular products of hydrocarbons oxidation reaction. Reaction rate of the hydroperoxides decomposition in the presence of quaternary ammonium salts is determined by the nature of the salt anion [4] as well as cation [5]. The highest reaction rate of the tert-butyl hydroperoxide and cumene hydroperoxide decomposition has been observed in the case of iodide anions as compared with bromide and chloride ones [4]. tetraalkylammonium bromides tetraethylammonium... 

Effects other than those of purely viscometric origin were seen to be significant in a schematic study by McHugh and co-workers of the free radical decomposition of cumene hydroperoxide [48], and subsequent oxidation of cumene (isopropyl benzene) [49, 50] in a range of supercritical and liquid solvents. The effective non-catalysed rate coefficients for cumene hydroperoxide decomposition in non-polarisable supercritical fluids (krypton, xenon) were greater than that for non-polar liquid cyclohexane, as expected a priori on the basis of viscosities. Yet, liquid 1-octene and 1-hexanol gave similar... 

Colorless composites with good mechanical properties can be obtained with either -butyl perbenzoate, cumene- or -butyl hydroperoxide and ascorbic acid or ascorbyl palmitate systems (50). Mechanisms for the free radical formation are given in Fig. 4. Addition of trace amounts of transition metals in their higher oxidation state (Cu", Fe" ) to the perester component further speeds up the polymerization. On admixture with the ascorbic acid derivative the metal cation is reduced to its lower oxidation state which, because it is a potent one electron reductant and will rapidly activate the free radical decomposition of the perester, which it in turn is reoxidized to its higher oxidation state. Means for prevention of oxidation of ascorbic acid or its derivatives on prolonged storage must be developed for these formulations to be suitable for dental application. 

The thermal decomposition of thia2ol-2-yl-carbonyl peroxide in benzene, bromobenzene, or cumene affords thiazole together with good yields of 2-arylthiazoles but negligible amounts of esters. Thiazol-4-ylcarbonyl peroxide gives fair yields of 4-arylthiazoles, but the phenyl ester is also a major product in benzene, indicating reactions of both thiazol-4-yl radicals and thiazol-4-carbonyloxy radicals. Thiazole-5-carbonyl peroxide gives... 

The decomposition of carboxyl radical occurs very rapidly, and C02 is formed with a constant rate in the initiated co-oxidation of cumene and acid [104]. 

The kinetic study of cumyl hydroperoxide decomposition in emulsion showed that (a) hydroperoxide decomposes in emulsion by 2.5 times more rapidly than in cumene (368 K, [RH] [H20] = 2 3 (v/v), 0.1 N Na2C03) and (b) the yield of radicals from the cage in emulsion is higher and close to unity [19]. The activation energy of ROOH decomposition in cumene is Ed = 105 kJ mol-1 and in emulsion it is lower and equals Ed 74 kJ mol 1 [17]. 

Combining thianthrene radical ion(l+) with free radicals to produce thianthrenium salts has also been achieved. Decomposition of various cumene hydroperoxides (83MI6) and of azobis(2-phenoxy-2-propane) (85MI1) gave 5-arylthianthrenium ions together with 5-(propen-2-yl)thianthrenium perchlorate in the latter case. 

Chain Termination in the Oxidation of Cumene. Traylor and Russell (35) assume that the acceleration in the rate of oxidation of CH which is produced by added COOH is solely caused by a chain transfer reaction between CO radicals and COOH. This assumption implies that all CH3OO radicals enter into termination via Reaction 13. However, Thomas (32) has found that acetophenone is formed even in the presence of sufficient COOH to raise the oxidation rate of CH to its limiting value. (The receipt of Thomas manuscript prior to publication stimulated the present calculations.) From this fact, and from a study of the acetophenone formed during the AIBN-induced decomposition of COOH, Thomas concludes that the accelerating effect of added COOH is primarily caused... 

The decomposition of carboxyl radical occurs very rapidly, and C02 is formed with a constant rate in the initiated co-oxidation of cumene and acid [104]. Cumylperoxyl radical attacks the a-CH2 group of the carboxylic acid with the formation of a labile hydroperoxide. The concentration of this hydroperoxide increases during oxidation till it reaches a stationary concentration [RCH(OOH)-COOH]st = pi2[RCH2COOH][CuOO ]/A d. This reaction produces C02 with acceleration during some period of time equal to the time of increasing the a-carboxyhydroperoxide concentration. 

A radical chain oxidation mechanism, involving the formation and decomposition of an intermediate hydroperoxide, is consistent with the observed kinetics in the oxidation of cumene and acenaphthene by oxygen in the presence of alkylammonium perchlorates.128... 

However, a recent kinetic study188 has shown unequivocally that chain initiation proceeds via the usual metal-catalyzed decomposition of the hydroperoxide. Thus, the rate of initiation of the autoxidation of cumene was, within experimental error, equal to the rate of production of radicals in the (Ph3P)4Pd-catalyzed decomposition of tert-butyl hydroperoxide in chlorobenzene at the same temperature and catalyst concentration. Moreover, long induction periods were observed (in the absence of added tert-butyl hydroperoxide), when the cumene was purified by passing it down a column of basic alumina immediately prior to use. Autoxidation of cumene purified by conventional procedures showed only short induction periods. These results further demonstrate the necessity of using highly purified substrates in kinetic studies. 

The use of chemical sensitizers such as benzoyl peroxide, cumene hydroperoxide, or azo-bis-isobutyronitrile, which decompose thermally to give free radicals in a convenient temperature range (i.e., 60 C to 150 C), makes it possible to study polymerizations over an extended temperature range. The form of the rate law with chemical initiations would be given by setting III = 2k (ln)< >i in Eq. (XVI.10.4). Here (In) is the initiator concentration, k I its specific rate constant of decomposition which can usually be measured independently, and is the efficiency with which its radicals initiate chains. The measure of t is subject to the difficulties already indicated in connection with the photolysis systems. ... 

In its relative reactivity toward toluene, ethylbenzene and cumene the more highly substituted 1-methyl-2,2-diphenylcyclopropyl radicaP , derived from the decomposition of the precursor diacyl peroxide, resembles the chlorine radical more than it does the phenyl radical (Table 3). Similarly, comparison of the relative reactivities of primary, secondary and tertiary aliphatic hydrogens toward chlorine atoms (1.0 3.6 4.2) and phenyl radicals (1.0 9.3 44) with the relative reactivities of the C-H bond in the methanol/ethanol/2-propanol series toward the 1-methyl-2,2-diphenylcyclopropyl radical (1.0 2.4 15) further confirms the low selectivity of the cyclopropyl radical. Again, this radical resembles the chlorine atom in its reactivity more than it does the phenyl radical. 

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