Auto-catalytic

The azo coupling reaction of the calix[4]arene 12.32 shows an unexpected auto-catalytic effect. If the molar ratio of the diazonium ion (X=N02) to the calix[4]arene is 4 1, the yield of the tetra(arylazo)calix[4]arene 12.33 is 99%, but with ratios 3 1, 2 1, and 1 1 the tetra(arylazo) compound is also a major product (70%, 45%, and 22% respectively). If ratios 3 1, 2 1, and 1 1 are used the yields of the tris- and bis(arylazo) products are in the range of only 1.2-3.4%, and the mono(arylazo) compound is formed with a yield of 5.3-6.0%. Using the ratio 4 1 the bis- and mono(arylazo) products are not found at all, and the tris(arylazo) com-... 

However, the mechanisms by which the initiation and propagation reactions occur are far more complex. Dimeric association of polystyryllithium is reported by Morton, al. ( ) and it is generally accepted that the reactions are first order with respect to monomer concentration. Unfortunately, the existence of associated complexes of initiator and polystyryllithium as well as possible cross association between the two species have negated the determination of the exact polymerization mechanisms (, 10, 11, 12, 13). It is this high degree of complexity which necessitates the use of empirical rate equations. One such empirical rate expression for the auto-catalytic initiation reaction for the anionic polymerization of styrene in benzene solvent as reported by Tanlak (14) is given by ... 

Caution Most selenium compounds are toxic consequently care should be exercised in handling them. The hydrogen peroxide oxidation of selenides is highly exothermic, acid-catalyzed, and auto-catalytic. The procedure given for adding the hydrogen peroxide solution should be carefully followed. 

Many acylation reactions of esters using sodium hydride as base appear auto-catalytic, with considerable potential for runaway, since the active base in solution is an alkoxide and the alcohol is a product of reaction [4], A safe form of sodium hydride (as a solid solution in a halide) for large-scale industrial use has been claimed [3],... 

During evaporation of liquid stibine at — 17°C, a relatively weak and isothermal explosive decomposition may occur. Gaseous stibine at ambient temperature may propagate an explosion from a hot spot on the retaining vessel wall, and it auto-catalytically decomposes, sometimes explosively, at 200°C. 

Recently there has been an increasing interest in self-oscillatory phenomena and also in formation of spatio-temporal structure, accompanied by the rapid development of theory concerning dynamics of such systems under nonlinear, nonequilibrium conditions. The discovery of model chemical reactions to produce self-oscillations and spatio-temporal structures has accelerated the studies on nonlinear dynamics in chemistry. The Belousov-Zhabotinskii(B-Z) reaction is the most famous among such types of oscillatory chemical reactions, and has been studied most frequently during the past couple of decades [1,2]. The B-Z reaction has attracted much interest from scientists with various discipline, because in this reaction, the rhythmic change between oxidation and reduction states can be easily observed in a test tube. As the reproducibility of the amplitude, period and some other experimental measures is rather high under a found condition, the mechanism of the B-Z reaction has been almost fully understood until now. The most important step in the induction of oscillations is the existence of auto-catalytic process in the reaction network. 

Modify the program to study an auto-catalytic reaction (A- B and A+B->2B). 

Modify the existing program to study adiabatic decomposition. Compare the results with those for an adiabatic decomposition of an auto-catalytic reaction. 

This set of reactions is auto-catalytic, i.e., production of B by the second step enhances the reaction rate of the first step. 

In the chain reaction the radical combines with oxygen to form a hydroperoxide (ROOH). This can itself break down to form two radicals (RO + OH ) which can combine further with oxygen. Thus the reaction, once started, continues to stimulate itself (i.e., it is auto-catalytic). In the termination reaction the hydroperoxide is de-activated. 

The gradual accumulation of structures III in the initial stages of the reaction could account for its auto-catalytic character until a "stationary-state" is reached in which the surface of the precipitated polymer available for such association with monomer remains practically constant. A structure such as III could also be responsible for the stereo-control of the propagation step. Indeed, the polymer formed at conversions below 2 per cent exhibits much lower stereoregularity than at higher conversions (see Figure 6). These various peculiar consequences connected with the arizing of structure III will be referred to as "matrix effect". 

Thermal treatment, applied to honey, may destroy vitamins and bionutrients, and produce a simultaneous decrease in diastase activity and an increase in HMF content. Honey treatment temperature and time must be limited when pasteurising and stabilising it both diastase activity and HMF content are national and international parameters used as controls so as to limit thermal treatment application. HMF can be formed by hexose dehydration in acid media or by the Maillaid reaction [11,12]. According to Ibarz et al., HMF formation can be described by a second order kinetics (auto-catalytic), with the following equation as expression model [13] ... 

Shy, S.S., R. H. Jang, and P. D. Ronney. 1996. Laboratory simulation of flamelet and distributed models for premixed turbulent combustion using aqueous auto-catalytic reactions. Combustion Science Technology 113 329-50. 

Figure 1 shows experimental reaction curves obtained in the absence of added catalyst and in the presence of various colloidal catalysts. The reaction has a pronounced induction period in the absence of added catalyst, and the curve shows the typical shape expected for an auto-catalytic reaction. Addition of colloidal silver, gold, palladium, and silver sulfide markedly decrease the magnitude of the induction period. 

Epoxidized soyabean or linseed oils Plasticizers for novolac epoxy resins. Also prevent auto-catalytic decomposition of NG during storage... 

AP is stable at room temperature and it decomposes with a measurable rate at temperatures above 150 °C. Further, it undergoes decomposition due to auto-catalytic reaction of the following type at temperatures below 300 °C (Equation 4.22) ... 

This auto-catalytic reaction stops after about 30% decomposition. This is usually called low temperature decomposition (LTD) and it is believed that the electron transfer mechanism is operative in this region. At temperatures above 350 °C, high temperature decomposition (HTD) takes place usually by proton transfer mechanism and finally AP decomposes into NH3 and 4 (Equation 4.23) ... 

The previous chapters focused on the existence and locus of stationary states. Here their stability to small perturbations is outlined, together with the systematic study of the onset of oscillations in isothermal, auto-catalytic open systems. After careful study the reader should be able to ... 

Kinetic data on the thermal degradation of ABS and PC/ABS blends are available (130,131). Thermogravimetric analysis suggests that the kinetics of the thermal degradation can be modelled by an auto-catalytic process. 

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