Rate constant decompositions

The complete assembly for carrying out the catalytic decomposition of acids into ketones is shown in Fig. Ill, 72, 1. The main part of the apparatus consists of a device for dropping the acid at constant rate into a combustion tube containing the catalyst (manganous oxide deposited upon pumice) and heated electrically to about 350° the reaction products are condensed by a double surface condenser and coUected in a flask (which may be cooled in ice, if necessary) a glass bubbler at the end of the apparatus indicates the rate of decomposition (evolution of carbon dioxide). The furnace may be a commercial cylindrical furnace, about 70 cm. in length, but it is excellent practice, and certainly very much cheaper, to construct it from simple materials. 

Table 6.2 Rate Constants (at Temperature Given) and Activation Energies for Some Initiator Decomposition Reactions...

The problems of monomer recovery, reaction medium viscosity, and control of reaction heat are effectively dealt with by the process design of Montedison Fibre (53). This process produces polymer of exceptionally high density, so although the polymer is stiU swollen with monomer, the medium viscosity remains low because the amount of monomer absorbed in the porous areas of the polymer particles is greatly reduced. The process is carried out in a CSTR with a residence time, such that the product k jd x. Q is greater than or equal to 1. is the initiator decomposition rate constant. This condition controls the autocatalytic nature of the reaction because the catalyst and residence time combination assures that the catalyst is almost totally expended in the reactor. 

The following conditions are stipulated the catalyst decomposition rate constant must be one hour or greater the residence time of the continuous reactor must be sufficient to decompose the catalyst to at least 50% of the feed level the catalyst concentration must be greater than or equal to 0.002 x Q, where the residence time, is expressed in hours. An upper limit on the rate of radical formation was also noted that is, when the rate of radical formation is greater than the addition rate of the primary radicals to the monomers, initiation efficiency is reduced by the recombination of primary radicals. 

Decomposition of diphenoylperoxide [6109-04-2] (40) in the presence of a fluorescer such as perylene in methylene chloride at 24°C produces chemiluminescence matching the fluorescence spectmm of the fluorescer with perylene was reported to be 10 5% (135). The reaction follows pseudo-first-order kinetics with the observed rate constant increasing with fluorescer concentration according to = k [flr]. Thus the fluorescer acts as a catalyst for peroxide decomposition, with catalytic decomposition competing with spontaneous thermal decomposition. An electron-transfer mechanism has been proposed (135). 

Reaction 1 is the rate-controlling step. The decomposition rate of pure ozone decreases markedly as oxygen builds up due to the effect of reaction 2, which reforms ozone from oxygen atoms. Temperature-dependent equations for the three rate constants obtained by measuriag the decomposition of concentrated and dilute ozone have been given (17—19). 

Ozone can be destroyed thermally, by electron impact, by reaction with oxygen atoms, and by reaction with electronically and vibrationaHy excited oxygen molecules (90). Rate constants for these reactions are given ia References 11 and 93. Processes involving ions such as 0/, 0/, 0 , 0 , and 0/ are of minor importance. The reaction O3 + 0( P) — 2 O2, is exothermic and can contribute significantly to heat evolution. Efftcientiy cooled ozone generators with typical short residence times (seconds) can operate near ambient temperature where thermal decomposition is small. 

It was found (32) that in the acid range (pH 4—6) the alkyl group does not influence the rate of decomposition, which is similar for all xanthates. In the alkaline range the rates are markedly influenced by the substitutional group, and the rates could be correlated with the Taft polar substituent constants estabhshed for the various groups. 

The rate-conttolling step to chlorate is the bimoleculat formation of chlorite, which reacts rapidly with hypochlorite. The temperature dependence of the rate constants is expressed by the equations = 2.1 x 10 g-io3.8/i T 3 2 x 10 g-87.o/i T L/(mol-s) (144). The uncataly2ed decomposition to... 

Many researchers have correlated the overall decomposition as an nxh. order reaction, with most paraffins following the first order and most olefins following a higher order. In general, isoparaffin rate constants are lower than normal paraffin rate constants. The rate constants are somewhat dependent on conversion due to inhibition effects that is, the rate constant often decreases with increasing conversion, and the order of conversion is not affected. This has been explained by considering the formation of aHyl radicals (38). To predict the product distribution, yields are often correlated as a function of conversion or other severity parameters (39). 

The kinetics of spinodal decomposition is complicated by the fact that the new phases which are formed must have different molar volumes from one another, and so tire interfacial energy plays a role in the rate of decomposition. Anotlrer important consideration is that the transformation must involve the appearance of concenuation gradients in the alloy, and drerefore the analysis above is incorrect if it is assumed that phase separation occurs to yield equilibrium phases of constant composition. An example of a binary alloy which shows this feature is the gold-nickel system, which begins to decompose below 810°C. 

If the decomposition reaction follows the general rate law, the activation energy, heat of decomposition, rate constant and half-life for any given temperature can be obtained on a few milligrams using the ASTM method. Hazard indicators include heats of decomposition in excess of 0.3 kcal/g, short half-lives, low activation energies and low exotherm onset temperatures, especially if heat of decomposition is considerable. 

The gas phase decomposition A B -r 2C is conducted in a constant volume reactor. Runs 1 through 5 were conducted at 100°C run 6 was performed at 110°C (Table 3-15). Determine (1) the reaction order and the rate constant, and (2) the activation energy and frequency factor for this reaction. 

A gas decomposition reaction with stoichiometry 2A —> 2B -i- C follows a second order rate law rj(mol / m s) = kC, where C is the reactant concentration in mol/m. The rate constant k varies with the reaction temperature according to the Arrhenius law ... 

The differenee in reaction rates of the amino alcohols to isobutyraldehyde and the secondary amine in strong acidic solutions is determined by the reactivity as well as the concentration of the intermediate zwitterions [Fig. 2, Eq. (10)]. Since several of the equilibrium constants of the foregoing reactions are unknown, an estimate of the relative concentrations of these dipolar species is difficult. As far as the reactivity is concerned, the rate of decomposition is expected to be higher, according as the basicity of the secondary amines is lower, since the necessary driving force to expel the amine will increase with increasing basicity of the secondary amine. The kinetics and mechanism of the hydrolysis of enamines demonstrate that not only resonance in the starting material is an important factor [e.g., if... 

Once the order of the reaction is known, the rate constant is readily calculated. Consider, for example, the decomposition of acetaldehyde, where we have shown that the rate expression is... 

It follows that the rate constant is 0.35/min the integrated first-order equation for the decomposition of N205 is... 

A single chlorine atom can bring about the decomposition of tens of thousands of ozone molecules. Bromine atoms can substitute for chlorine indeed the rate constant for the Br-catalyzed reaction is larger than that tor the reaction just cited. 

The first-order rate constant for the decomposition of a certain drug at 25°C is 0.215 month1. 

Dinitrogen pentoxide gas decomposes to form nitrogen dioxide and oxygen. The reaction is first-order and has a rate constant of 0.247 h1 at 25°C. If a 2.50-L flask originally contains N205 at a pressure of 756 mm Hg at 25°C, then how many moles of 02 are formed after 135 minutes (Hint. First write a balanced equation for the decomposition.)... 

The byproducts of decomposition of certain dialkyldiazcncs can be a concern. Consider the case of AIBN decomposition (Scheme 3.13). The major byproduct is the ketenimine (lO).61 100"102 This compound is itself thermally labile and reverts to cyanoisopropyl radicals at a rate constant similar lo that for AIBN thermolysis.59,60 102 This complicates any analysis of the kinetics of initiation/2,60... 

---