Character autocatalytic

Several alkali chlorates and perchlorates undergo fusion during the onset of decomposition, the autocatalytic character of reaction then being attributable to the greater rate of reaction in the melt. Khorunzhii and II in [849], from work on the reactions of Na+ and K+ salts of chloric and perchloric acids, conclude that surface and grain boundary diffusion exert an essential role in decomposition rate control. 

According to Sanko and Stefanovskii the reaction between arsenic(III) and chlorate is autocatalytic in character and at constant hydrogen ion concentration the rate is given by... 

In part B, supersaturation is low and the distribution curve is broad, since induction times are spread over the whole aggregation delay. Thus, the autocatalytic character is lost in the resultant kinetics. According to the width of the induction time distribatior , flat or irregular curves can be obtained (Figure 10).It is a region of random growth of the domains. 

The solvent action of sulfite on silver bromide and the resultant tendency to isolate latent image nuclei from the grain accounts for the failure of sulfite itself to act as a direct developer in spite of the autocatalytic character of its reduction of silver ion. The active nuclei simply are isolated from the grain before development gets under way. The same phenomenon enters to prevent sulfite-containing hydroquinone solutions of low pH (e.g., 8.5) from developing readily even though the thermodynamic conditions are suitable for reaction and the hydroquinone develops readily at the same pH when sulfite is absent. 

The epoxy-oligomer curing with amines has an autocatalytic character due to the accumulation of hydroxyl groups during the reaction [cf. Scheme (1)]. 

The first viewpoint contradicts the autocatalytic character of the reaction, conductometric measurements in the polymerization system and some other facts (see below). Scheme (33) can be considered as completely experimentally substantiated. The following important proofs were obtained A direct experimental discovery of a quaternary ammonium alcoholate in the reaction system, 42) a full agreement of the nature of the active propagating site with all the existing kinetic and structural data l4,149 153 157 I58) establishment of the ionic behaviour of the propagating sites by comparison of the kinetic curves of the process with the character of the electric... 

The same reaction also occurs at a lower temperature. 0.665 % of the substance decomposed at 20°C to form benzotrifuroxane in 3 years 2.43% at 35°C in one year 0.65% at 50°C in 10 days and at 100°C the substance underwent complete change in 14 hr. This decomposition is not, however, autocatalytic. This reaction — the formation of furoxane derivatives from aromatic azides with nitro group in the or/Ao-position — is of a general character (Boyer al. [160]). Despite the ease with which it decomposes trinitrotriazidobenzene has not been rejected for use as an initiator. In some countries large scale experiments are in progress to examine the possibilities of developing its practical application. 

As well as deceleratory reactions, kineticists often find that some chemical systems show a rate which increases as the extent of reaction increases (at least over some ranges of composition). Such acceleratory, or autocatalytic, behaviour may arise from a complex coupling of more than one elementary kinetic step, and may be manifest as an empirically determined rate law. Typical dependences of R on y for such systems are shown in Figs 6.6(a) and (b). In the former, the curve has a basic parabolic character which can be approximated at its simplest by a quadratic autocatalysis, rate oc y(l - y). 

It is necessary to take into consideration the fact that the decomposition of nitric esters has an autocatalytic character water and nitrogen dioxide formed during the decomposition lead to the formation of nitric and nitrous acids which accelerate the reaction of decomposition of the nitric ester. The influence of nitric acid on the rate of decomposition of nitroglycerine was studied by Roginskii [79] and is described below. 

The initial period was followed for many expls by a period of acceleration , which was autocatalytic in character. This resulted in complete decompn of the expl. The temp of this final stage of decompn was designated as T,7" for decompn at atm pressure and for that at pressure of 25000kg/cm2 as Tp Results of tests are given in table... 

The curve obtained with PVC prepared by suspension polymerization generally indicated autocatalytic thermal dehydrochlorination, and the time required for 0.1 mole % decomposition was usually less than 35 minutes (Figure 1). When PVC was prepared by bulk polymerization, the dehydrochlorination plot was generally slightly more linear, showed little autocatalytic character, and the time for 0.1 mole % decomposition was approximately 40 minutes (Figure 2). 

The factor P is called the autocatalytic factor for P = 0, the reaction becomes a single first-order reaction. With increasing P, the autocatalytic character becomes more important. 

This method was validated with over 100 substances and compared with the results of the classical study by isothermal experiments. For apparent activation energies above a level of 220 kj mol"1, 100% of the samples showed an autocatalytic character in isothermal experiments. This method can be used as a screen to distinguish clearly autocatalytic reactions from others that should be studied by isothermal experiments. This reduces the number of isothermal experiments required. 

More work is required to understand the adaptive significance of the small-world character in experiments in which the above explanations can be independently controlled in an evolutionary model of dynamic autocatalytic metabolism. 

These observations can be represented as a special case of the general rate equation derived by the application of order-disorder theory to diffusionless transitions in solids.3 According to this equation, the shape of the rate curve is determined by the relative numerical values of zkp/kn and of c. The larger the factor is relative to c, the more sigmoidal the curves become. This is understandable since the propagation effect which is responsible for the autocatalytic character of the transformation becomes more noticeable when kPlkn is large and c small. Under these conditions some time elapses before a sufficient number of nucleation sites are formed then the... 

Reaction (61) would now be expected to be an equilibrium. The RO2 radicals involved in these types of reactions are likely to have a considerably enhanced stability as a result of the delocalized character of the aromatic rings. The rate of oxidation of p-xylene was found, by Barnard and Ibbison [216], to be very similar to that of toluene. The slow oxidation of all of the xylene isomers and of toluene were found to be autocatalytic [36, 215], and a mechanism through formaldehyde oxidation was proposed, since it was found to be one of the intermediate products. Hydrogen peroxide must also be formed from the predominantly HO2 propagation, and this is likely to be an important contributor to the autocatalysis. 

The autocatalytic character of many solid-state reactions indicates the medium change in the process of transformation [136]. 

The thermal stabilities of the three silver salts decrease [14] in the sequence AgCC04 > AgCCOj > AgC 02, which is also the order of decreasing ionic character. The fusion of AgC 04 well below its melting point is attributed to eutectic formation with AgC during an autocatalytic reaction. The chlorate decomposed at about 80 K above the melting point through disproportionation accompanied by some decomposition. In contrast, the disproportionation of silver chlorite ... 

A further isothermal study [30] confirmed the autocatalytic character of the nickel acetate decomposition. The variation with temperature of the rate of decomposition... 

Finally, we address the question of the reasons for the superiority of Co(II) compounds as the catalysts for the alkene epoxidation by 02/aldehyde system. We have studied the catalytic activity of Co(II) compounds using imKS-stilbene as a model substrate. Kinetic curves for the Iran -stilbene epoxide accumulation are given in Fig. 3. The kinetic curves show autocatalytic character. The time of the complete alkene conversion depends on both the induction time and the rate of the reaction after the completion of the induction period. It should be noted that the induction time increases considerably with decreasing aldehyde concentration and goes through a maximum with increasing Co(II) concentration (in the range 10 - 10 M). One can see from Fig. 3 that the rate of the epoxidation lowers in the order PW1 iCo, CoW 12 > CoNaY, Co(N03)2 >CoPc. 

There have been numerous reports (ref. 13-16) that methanol conversion has autocatalytic character and is accelerated by added olefin (or C3+ alcohol). Espinoza s results indicating that olefin oligomers block the zeolite channels cloud the evidence on autocatalysis. They probably explain why added olefins (or alcohols) accelerate conversion over only a narrow temperature range below that at which complete conversion would occur in the absence of added olefin. 

Equation 3 is often used in the literature to account for the kinetic behavior of several common dicyanate monomers (25, 26). The autocatalytic character of cyanate polycyclotrimerization is now quite well established we noticed that it was especially enhanced in samples with a large surface directly exposed to air (24, 27, 28). The kinetics of DPEDC blends were more difficult to describe because they were perturbed by several residual impurities in the monomer. Together with adventitious air moisture, the latter increased gel conversion with respect to the theoretical value (0.5). 

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