Empirical radical initiating rate

By a comparison of the calculated values for the OH° concentration according to equation 5-4 and 5-6 in connection with 5-11 it was shown that the initiation term was not negligible and the simplified model not appropriate. Thus, the authors defined a hydroxyl radical initiating rate 8 that includes all possible initiating reactions, calculated by the OH° concentration difference between the experiment and the model. 

The scavenger term X kSi c(S,-) was calculated by known values. If only carbonates are present it is calculated with 

With the help of this correction term the atrazine concentration could be calculated with a precision of 15 %. The B-term showed no trend, no general considerations were possible. The prediction of the dissolved ozone concentration was only possible in the presence of scavengers. The effect of ozone consumption due to direct reactions with the intermediates was estimated. 

In general, the model from Beltran et al. uses 6 as a kind of correction factor. Without experimental data from which (3 can be calculated, no prediction is possible. 

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The empirical dependence of v on v/ makes it possible to determine the parameter a = kp 2kf, which characterizes the rate of the chain process. Knowing this parameter, one can find the Ap value, if the rate constant k, or the ratio kp/2k, are known or measured by the independent method (see Section 15.3.2). The parameter a allows one to measure the initiation rate for a non-studied radical source. If this source is the initiator I, then v, = A,p], and A, is determined from a series of experiments with different initial concentrations of the initiator using the equation... 

The experiment is performed as follows (Fig. 13.1). The reaction mixture is placed in a thermostatted vessel 6 with transparent planar-parallel walls. The vessel is irradiated with the light with such a wavelength that generates radicals. Disk 4 is placed in the point where the beams are focused and is rotated. The reaction rate is measured by this or another method from experiment to experiment, and the empirical dependence of the v/v ratio on logrj is plotted, td is found from the rotation velocity of the disk and the ratio between the sizes of the dark and light sectors (usually r - 3). This empirical dependence is compared with the theoretical one, and 2k, is determined by comparison, and from this 2k, is calculated. The initiation rate is measured by the methods of inhibitors (see above) or through the chain reaction rate and the kp/2k, ratio. 

Initiators are introduced into the reactant, as a rule, in very small amounts. The initiator produces free radicals, most of which react with the reactant or solvent or recombine with other free radicals. Radicals formed from the initiator or reactant react with the initiator very negligibly. However, systems (initiator reactant) are known where free radicals induce the chain decomposition of initiators [4,13-15]. Nozaki and Bartlett [16,17] were the first to provide evidence for the induced decomposition of benzoyl peroxide in different solvents. They found that the empirical rate constant of benzoyl peroxide decomposition increases with an increase in the peroxide concentration in a solution. The dependence of the rate of peroxide decomposition on its concentration was found to be... 

Much of the work with labelled initiators in radical polymerizations is quite independent of determinations of molecular weights, attention being focussed on kinetic chain lengths instead of on molecular chain lengths (10). In a sensitized polymerization, the rate of initiation is identified with the rate at which initiator fragments are incorporated in the polymer to calculate the rate of initiation, it is necessary only to determine the empirical formula shown previously for the recovered polymer and the overall rate of polymerization. No assumptions are required concerning the mechanism of termination or the frequency of transfer processes involving monomer, solvent or polymer. Errors can arise from three causes ... 

According to Bolshakov and Tolkachev [1976] and Zaskulnikov et al. [1981], the kinetics of radical conversion in glassy matrices consists of an initial part determined by the rate constant k T) described above and a subsequent conversion of the remaining molecules which obeys the empirical Kolrausch law ... 

The overall reaction of pyridinyl radical and dibromomethane leads to pyridinium bromide and dihydropyridines. The variation in the reaction rate constant with a solvent, using the empirical solvent polarity parameter, the Z-value" (see below), as a criterion reveals that the rate-limiting step is atom-transfer. The rate constants listed in Table 4 show almost no change over a wide range of solvent polarity (dichloromethane (Z 64,0) to ethanol (Z 79.3). The transition state for the reaction and the initial state have then similar degrees of charge-separation. 

Kinetics of initiated radical polymerization of styrene is well studied at the initial stages. At the high-conversion of polymerization the growth of viscosity of media- influences the mechanism and kinetics of process greatly (12),In our research we have attempted to obtain tne empirical dependence of some rate constants of initiated polymerization of styrene on conversion with the aim of using them at mathematical simulation of the process. 

Oxidation rates of I ascorbic add (ASA) in a low dielectric solvent (MeOH) were determined, and initial autoxidation products were separated and identified. Mechanisms of ASA autoxidation were studied using the semi-empirical molecular orbital (MO) method. In this solvent, MeOH and in the absence of metals, ASA reacts with triplet oxygen yielding very similar to or nearly identical reaction products as those observed with singlet oxygen, suggesting the formation of ascorbate-2-peroxy-anion type intermediate.Mechanisms of ASA autoxidation including the formation mechanism of superoxide anion radical were proposed, which were supported by die MO calculation. 

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