Cumene hydroperoxide rate constants

The methods of co-oxidation and oxidation of hydrocarbon (RiH) in the presence of hydroperoxide (ROOH) opened the way to measure the rate constants of the same peroxyl radical with different hydrocarbons. Both the methods give close results [5,9]. The activity of different secondary peroxyl radicals is very close. It is seen from comparison of rate constants of prim-R02 and, v -R02 reactions with cumene at 348 K [9],... 

The experiments on emulsion cumene oxidation with AIBN as initiator proved that oxidation proceeds via the chain mechanism inside hydrocarbon drops [17]. The presence of an aqueous phase and surfactants compounds does not change the rate constants of chain propagation and termination the ratio (fcp(2fct)-1/2 = const in homogeneous and emulsion oxidation (see Chapter 2). Experiments on emulsion cumene oxidation with cumyl hydroperoxide as the single initiator evidenced that the main reason for acceleration of emulsion oxidation versus homogeneous oxidation is the rapid decomposition of hydroperoxide on the surface of the hydrocarbon and water drops. Therefore, the increase in the aqueous phase and introduction of surfactants accelerate cumene oxidation. 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

Tetralin hydroperoxide has little or no effect on the thermally or photochemically initiated oxidation of Tetralin, nor are the absolute rate constants for the oxidation of Tetralin (1.7M in chlorobenzene) affected by adding 0.1M [TOOH] (Table I). [Hydrogen-bonded peroxy radicals are either unimportant in this system or have the same reactivity as the peroxy radicals formed in the absence of hydroperoxide. A similar conclusion applies to propagation in cumene and cumene-COOH mixtures (see Table I).]... 

This difficulty has now been overcome. Howard, Schwalm, and Ingold (24) show that the rate constant for reaction of any alkylperoxy radical with any hydrocarbon can be determined (by the sector method) by carrying out the autoxidation of the hydrocarbon in the presence of >0.1 M hydroperoxide corresponding to the chosen radical. All the absolute propagation and termination constants for the co-oxidation of cumene and Tetralin were thus determined. Our Tetralin-cumene work suggests that their results agree well with the best we have been able to get... 

The measured rate constants show some inconsistencies in relation to other work. The most noticeable is the low ratio of kceric/kphotoiysis at 30°C. for f erf-butyl hydroperoxide and cumene hydroperoxide compared with estimates, —5 to 10 for k /k2, obtained from studies of the induced decomposition of these hydroperoxides (22, 46, 48). The photolytic rate constant for cumene hydroperoxide is considerably larger than the termination constant for the oxidation of cumene containing cumene hydroperoxide as determined by the rotating sector (25, 26, 27, 28). It is not clear whether these differences represent some unappreciated features... 

The kinetic conclusions of Obolentsev and Gryazev (3,4), of Ballod et al. (5,6), and of Topchieva and Panchenkov (7) are in doubt because of the method of study used, i.e., variation of space velocity at constant pressure. In addition, as will be shown below, the probability is high that either the rates of reaction observed in their studies were diffusion limited or the cumene used by them contained cumene hydroperoxide. In the study of Corrigan et al. (8) the presence of large diffusion effects has already been demonstrated. 

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. ... 

When either by design or accident the cumene hydroperoxide content is not completely removed, the adsorption constant determined for inhibitors added to this cumene will be incorrect if in the calculation the inhibitor originally present is neglected. When very impure cumene is used, this error may be an order of magnitude or more. When the rate of cracking of pure cumene is known, however, a correction can be applied to obtain the true adsorption equilibrium constant for the added inhibitor. 

The rates of reaction of cumene in the presence of various added substances were determined by use of a differential reactor. The operational procedure is described elsewhere (4). The catalyst used was that described in Section III-l and for which the parameters k Bo and G were determined by Prater and Lago (4). The adsorption constant Kp for the added substance was determined by substituting ksBo, G, and the measured value of dn/dt in Equation (2). When the particular cumene sample used was not completely freed of cumene hydroperoxide, as shown by comparing the... 

Suppes and McHugh studied the effects of different surfaces on the decomposition of cumene hydroperoxide in supercritical krypton, xenon, CO2, propane, and CHF2CI. They reported that the observed first-order rate constants were strongly dependent on the metals present. Gold and 316 stainless-steel surfaces gave larger rate constants than did Teflon-coated surfaces [68]. The authors also observed that the different SCF solvents influenced the reaction rate. 

In this equation, ki is the rate constant in the initiating stage, kp the constant of the chain reaction, kt the constant of the radical termination, 1 cumene, and ROOH the hydroperoxide. 

Structural acrylic adhesives contain monomer, and cure is by a redox system which generates free radicals which cause cure by addition polymerization. Redox systems have two components, one being dissolved in the adhesive and the other in the hardener or catalyst. Once mixed cure is rapid. Examples are cumene hydroperoxide and N,N-dimethyl aniline. Should the peroxide be in the adhesive, then it will slowly decompose to give free radicals, which will cause cure and eventually terminate the shelf life, which is typically 12 months. Chemical reactions obey the Arrhenius relation (O Eq. 18.1). Here k is the rate constant. 

The measure of oxidizability of the RH substance is the parameter 2kp 2k,) which includes the characteristic of the reactivity of RH and R02- with respect to RH and k,. To characterize the reactivity of RH in the reaction with R02-, it is necessary to measure the rate constants of a series of hydrocarbons R/H with the peroxyl radical of the same type. In 1962, J. Thomas and C. Tolman established that the introduction of tetralyl hydroperoxide in oxidized cumene retards its oxidation. They explained the retardation effect of ROOH by the fast exchange reaction of cumylper-oxyl by tetralylperoxyl radicals, which rapidly into the disproportionation reaction. Later, the method using this effect was developed (J. Howard, K. Ingold, 1967). 

Acrylonitrile [271] polymers were prepared in bulk in high yields under controlled conditions at room temperature to 60°C in 30-90 min using radical catalysts with decomposition rate constants >1 hr Thus, 1600 g of acrylonitrile containing 300 ppm water was kept at 50 C, and 3.2 g of cumene hydroperoxide, 23.2 g of dimethyl sulfite, and 18.1 g of magnesium methylate in 150 cm of MeOH were added. The conversion achieved in 15 min represented a final conversion of 11% in a continuous polymerization system. 

The rate of oxidation of 6.7M cumene in chlorobenzene at 30°C. was found to be decreased to a constant value by adding 0.1M Tetralin hydroperoxide. At this point, all the COO radicals are being converted into TOO radicals without undergoing any other reactions. Hence, the TOO radicals are propagating and terminating the chain. The propagation constant is the cross constant kp (Reaction 5) and the termination constant is kt. The rate is given by... 

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. 

It is known that manganese salts cause oxidation of hydrocarbons, like cumene, by initiating free radical chain reactions. However, this is normally done by catalytic decomposition of trace amounts of hydroperoxides found in the hydrocarbons. In our case, the catalyst does not seem to decompose CHP, as demonstrated in an independent experiment (see above). If it did, the rate of decomposition should increase in time as the reaction progresses leading to an increase in the autoxidation rate. While we do observe for cumene an initiation period up to the accumulation of 3-5% hydroperoxide, from that point on up to greater than 50% CHP accumulation, the oxidation rate is constant. This initiation period may be due to surface activation of the catalyst. 

Alkylaromatic hydrocarbons, such as tetralin, ethylbaizene, and cumene, are oxidized in a solution of acetic acid in the presence of cobalt acetate via somewhat different mechanism. In these systems, after some rather short acceleration period, a constant oxidation rate v [RH] is established it is independent of either the catalytic concentration, or the partial oxygen pressure. The stationary concentration of hydroperoxide [ROOHJst ([RH]/[C< ]) corresponds to the constant oxidation rate. In a nitrogen atmosphere the hydroperoxide decomposes with the rate v = k[ROOH][Co(Ac)2]. These results agree with the following scheme of chain oxidation ... 

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