Spontaneous decomposition rate

If the rate constant kd for spontaneous decomposition of the initiator is known, the efficiency / of initiation may be determined. (This is a refinement of the molecular weight method set forth in Sec. Ic) The spontaneous decomposition rate of benzoyl peroxide in styrene, according to the work of Swain, Stockmayer, and Clarke is 3.2X10- sec. at 60°C. Hence the efficiency of initiation of the polymerization of styrene by benzoyl peroxide at 60°C is indicated to be about 0.60. 

The rate of copolymerization in a binary system depends not only on the rates of the four propagation steps but also on the rates of initiation and termination reactions. To simplify matters the rate of initiation may be made independent of the monomer composition by choosing an initiator which releases primary radicals that combine efficiently with either monomer. The spontaneous decomposition rate of the initiator should be substantially independent of the reaction medium, as otherwise the rate of initiation may vary with the monomer composition. 2-Azo-bis-isobutyronitrile meets these requirements satisfactorily. The rate Ri of initiation of chain radicals of both types Ml and M2 is then fixed and equal to 2//Cd[7], or twice the rate of decomposition of the initiator I if the efficiency / is equal to unity (see Chap. IV). The relative proportion of the two types of chain radicals created at the initiation step is of no real importance, for they wall be converted one into the other by the two cross-propagation reactions of the set (1). Melville, Noble, and Watson presented the first complete theory of copolymerization suitable for handling the problem of the rate. The theory was reduced to a more concise form by Walling, whose procedure is followed here. 

On the other hand, (case ii) if the reaction of the donor with the metalloporphyrin is faster than its spontaneous decomposition rate, the metalloporphyrin reacts directly with the donor, accelerating its decomposition rate and forming the corresponding nitrosyl complex by azanone transfer to the metal center. For these cases, almost no free HNO is produced, as evidenced by the quantitative formation of the nitrosyl product even for equimolar metalloporphyrin to donor ratios. In these cases, the Uobs against [Donor] plot gives a straight line from which the bimolecular cat(Donor) rate constant can be obtained. 

If the spontaneous decomposition rate of benzoyl peroxide is 3.2 x mVmol-s , calculate the initial rate of polymerization. 

The solvents listed in Table 2.1 were chosen to cover a broad range in solvent properties. In fact hexane was initially also among them, but unfortunately the rate of the reaction in this solvent is extremely low. It turned out that in this solvent spontaneous decomposition of 2.4a competes with the Diels-Alder reaction. 

A few details have been reported on the slow reductions of 8303 by As(ni) and T1(I) . In the anaerobic reductions by As(III) the reaction is first-order in 820 and although As(III) certainly catalyses decomposition, the dependence of the rate on [As(III)] is small. Aeration leaves the rate of spontaneous decomposition of 820g unaffected, but the As(III)-catalysed route is accelerated by a factor of ten, the kinetic law remaining unchanged. The oxygen effect is interpreted in terms of the chain reaction... 

Organic peroxides and hydroperoxides decompose in part by a self-induced radical chain mechanism whereby radicals released in spontaneous decomposition attack other molecules of the peroxide.The attacking radical combines with one part of the peroxide molecule and simultaneously releases another radical. The net result is the wastage of a molecule of peroxide since the number of primary radicals available for initiation is unchanged. The velocity constant ka we require refers to the spontaneous decomposition only and not to the total decomposition rate which includes the contribution of the chain, or induced, decomposition. Induced decomposition usually is indicated by deviation of the decomposition process from first-order kinetics and by a dependence of the rate on the solvent, especially when it consists of a polymerizable monomer. The constant kd may be separately evaluated through kinetic measurements carried out in the presence of inhibitors which destroy the radical chain carriers. The aliphatic azo-bis-nitriles offer a real advantage over benzoyl peroxide in that they are not susceptible to induced decomposition. 

If the rate constant kd for the spontaneous decomposition of the inhibitor is known, and its efficiency has been established, the important ratio kl/kt may then be evaluated. With greater generality, Eq. (8) may be combined with (12) to give... 

The kinetics of coupling a diazonium salt (D) with naphthol (N) to form a dye (A) is complicated to a minor extent by spontaneous decomposition of D to form inert products P. Bata of A, but not of other participants, are in the table (Hanna et al, JACS 96 7222, 1974). Temperature was 0 C, N0 = 0.01 mols/liter, D0 - 0.0001. Find the specific rates. 

These catalytic effects are usually signaled by irreproducible behavior. If it is suspected that traces of metal ions may be causing peculiar rate effects, a strong ligand may be added to sequester the metal ion. The spontaneous decomposition of H2O2 has been reported as 4.7 X 10 M s at pH 11.6 and 35°C. This is the lowest recorded value and is obtained in the presence of strong chelators. In a similar way the decomposition of permanganate in alkaline solution (3.6) is markedly slowed when the reactants are extensively purified... 

For very many years, the alchemist s dream of changing base metals into gold was ridiculed even by the most reputable of scientists. Although it was known that the nuclei of certain atoms undergo alteration in the course of natural radioactive decay, researchers inability to exercise any control over the nature or rate of these spontaneous decompositions probably did much to foster the belief that the nucleus of the atom was inviolate. However, in the year 1919 the English physicist Ernest Rutherford accomplished the first transmutation of an element, and this notable discovery was quickly followed by other equally significant developments. 

For the spontaneous decomposition of nitramide (NH2N02) the transition state is assumed to have formula 8, on the supposition that the rate-limiting step is base-catalysed removal of a proton from the (less stable) aci-tautomer (NH N02H). This suggestion is made in the... 

Insufficient mixing may easily result in a low nitration rate owing to the small interfacial area. It can also lead to a non-uniform nitration process. Owing to inadequate construction of the stirrer, too low a speed of rotation, or an interruption in stirring, so-called dead spaces may easily be formed in which non nitrated or not fully nitrated substances accumulate. If a rather large quantity of the mixture is stirred suddenly, rapid extension of the interfacial area takes place, followed by the generation of large amounts of heat and a rise in temperature. This may cause a spontaneous decomposition of the reaction mass in the nitrator, and then an explosion. 

This spontaneous decomposition of radioactive elements is remarkable, because the chance of a particular atom decomposing is independent of its age. The atoms disappear just as the population of a country would disappear if there were no births and a death rate independent of age. The number of deaths on any day is proportional to the population on that day. For example, if half the atoms remain after one hour, then one-quarter will be left after two hours, one-eighth after three hours, one-sixteenth after four hours, and so on. We do not know what decides which particular atoms shall decompose, so we usually say that it is merely a matter of chance. All the atoms appear to be exactly alike and do not change in any way until they suddenly decompose. Some decompose at once and some last for thousands of years, for no obvious reason so far as we can see. 

Although radical chain processes occur spontaneously at moderate temperatures, it is usually desirable to faciliate the chain propagation by addition of an initiator. 2,2 - Azobi-sisobutyronitrile (AIBN = 2,2 -dimethyl-2,2 -azobis[propanenitrile]) is an ideal initiator, its decomposition rate is solvent independent. Such a reaction is described for a prototype 5-hexenylbromide with tributyltin hydride initiated by In [23] as an illustration in Scheme VII/10. 

A distinction must be made between chemical and physical stability. While physical stability is important, particularly in the evaluation of solid propellants, the chemical stability is of prime importance in the estimation of the course of decomposition of nitrate esters. The nitrate esters which are processed for use as propellants - unlike nitro compounds, which are relatively stable under these conditions - undergo a steady decomposition, which is due to imperfect purification of the starting materials and to the effect of other parameters such as temperature and air humidity. The rate of this decomposition is auto-catalyzed by the acidic decomposition products and may in certain cases produce spontaneous ignition. In order to reduce the decomposition rate as much as possible, suitable stabilizers are added to the powders, which are capable of accepting the acid cleavage products with formation of the corresponding nitro compounds (- Stabilizers). The stability is controlled by means of several tests (- Hot Storage Tests). 

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