Butyl peroxide, rate decomposition

The determination of A V is illustrated by data for the thermal decomposition of di-ferf-butyl peroxide.10 The rate constants at 120 °C in toluene are as follows ... 

A plot of the logarithm of the rate constant for the thermal decomposition of di-rm-butyl peroxide with pressure. The data, from Ref. 10, refer to a temperature of 120 °C in toluene. 

The data of the table are of the decomposition of di-t-butyl peroxide to acetone and ethane at 188 C in a tubular flow reactor of 82.4 cc volume. The concentrations are in mol/liter and flow rate is in cc/sec. A carrier gas was used, and any volume change resulting from the reaction may be taken negligible. Find the rate equation. 

The reaction of EtsSiH with [l.l.l]propellane under photolytical decomposition of di-tert-butyl peroxide afforded products 17 and 18 in 1 3 ratio (Reaction 5.15) [36]. A rate constant of 6.0 x 10 M s at 19 °C for the addition EtsSi radical to [l.l.l]propellane was determined by laser flash photolysis [37]. Thus, it would appear that [l.l.l]propellane is slightly more reactive toward attack by EtsSi radicals than is styrene, and significantly more reactive than 1-hexene (cf. Table 5.1). 

The various initiators are used at different temperatures depending on their rates of decomposition. Thus azobisisobutyronitrile (AIBN) is commonly used at 50-70°C, acetyl peroxide at 70-90°C, benzoyl peroxide at 80-95°C, and dicumyl or di-t-butyl peroxide at 120-140°C. The value of the decomposition rate constant kj varies in the range... 

Let us assume that fci is equal to k9, the rate constant for the gas phase decomposition (15), where no cage effect is expected. This assumption does not always hold (15, 18). For example, it is known (18) that di-f erf-butyl peroxide (DPB) decomposes about 30% slower in the gas phase than in solution. We can calculate from our value of k8 and the known value of kg, from the work of Szwarc (7, 21), a value for the fraction of acetoxy radical pairs recombining, fR, where... 

Aliphatic amines have much less effect on the later reactions of the gas-phase oxidation of acetaldehyde and ethyl ether than if added at the start of reaction. There is no evidence that they catalyze decomposition of peroxides, but they appear to retard decomposition of peracetic acid. Amines have no marked effect on the rate of decomposition of tert-butyl peroxide and ethyl tert-butyl peroxide. The nature of products formed from the peroxides is not altered by the amine, but product distribution is changed. Rate constants at 153°C. for the reaction between methyl radicals and amines are calculated for a number of primary, secondary, and tertiary amines and are compared with the effectiveness of the amine as an inhibitor of gas-phase oxidation reactions. 

Action of Aliphatic Amines on Decomposition of tert-Butyl Peroxide. The rate of decomposition of tert-butyl peroxide is not greatly affected... 

Action of Diethylamine on Decomposition of Ethyl tert-Butyl Peroxide. The rate of decomposition of ethyl ferf-butyl peroxide is decreased by adding diethylamine (Figure 7), and the yield of products is altered (Table II). Again, the yield of methane is increased at the expense of ethane and f erf-butyl alcohol is increased at the expense of acetone. Ethanol and acetaldehyde are formed in considerably greater amounts. The yields of carbon monoxide and methyl ethyl ketone are decreased. 

Even large amounts of aliphatic amines do not alter the rate of decomposition of tert-butyl peroxide, but they do slow down the rate of decomposition of ethyl tert-butyl peroxide. 

The half-life time, Tm, of decomposition of di(t-butyl)peroxide at a temperature of 463 K and ambient pressure is 50 s. One may calculate the rate constant and the half-life time for decomposition at 300 MPa and the same temperature, when the activation volume is Av = +13 cm3 mol"1. 

Thne-of-flight (TOF) mass spectrometric analysis of the pyrolysis fragments of di-t-butyl peroxide suggests t-BuCO as the primary product, followed by decomposition of this radical into CHj.253 Elsewhere, the kinetics of the pyrolysis of dimethyl, diethyl, and di-t-butyl peroxides in a modified adiabatic bomb calorimeter have been investigated.254 The lifetime of acyloxy radicals, generated by the photolysis or thermolysis of acetyl propionyl peroxide, have been studied. Chemical nuclear polarization has been used to determine the rate constant for the decarboxylation of these radical intermediates.255... 

Since the thermal decomposition of di-(-butyl peroxide occurs at convenient rates over the temperature range from 130 to 160°C. with relatively little chain character (Batt and Benson12), many workers have... 

Example The gas-phase thermal decomposition of one mole of di-tert-butyl peroxide, in a constant volume apparatus, yields two moles of acetone and one mole of ethane. If life reaction obeys first-order kinetics, develop expression the rate-constant as a function of time, initial pressure and total pressure. 

Although a vast majority of important chemical reactions occur primarily in liquid solution, the study of simple gas-phase reactions is very important in developing a theoretical understanding of chemical kinetics. A detailed molecular explanation of rate processes in liquid solution is extremely difficult. At the present time reaction mechanisms are much better understood for gas-phase reactions even so this problem is by no means simple. This experiment will deal with the unimolecular decomposition of an organic compound in the vapor state. The compound suggested for study is cyelopentene or di-i-butyl peroxide, but several other compounds are also suitable see, for example. Table XI.4 of Ref. 1. 

Even in those cases where the rate constants, for a reaction in various solvents, are not significantly different, the activation parameters may indicate a significant amount of interaction between solute and solvent, as shown for the unimolecular decomposition of di-tert-butyl peroxide in Table 5-14 [172, 227]. The rate of decomposition of the per-... 

Table 5-14. Rate constants and activation parameters for the decomposition of di-tcrt-butyl peroxide at 125 °C [172, 227].

Tt is well known that HCl can serve as a catalyst in free radical reactions, for example, the thermal decomposition of neopentane (2) and diter-tiary butyl peroxide (3). In these reactions the slow and rate-controlling step is a reaction of the type R + R H — RH -f R where both R and R are polyatomic radicals. The addition of HCl causes the rapid chain process, R -f HCl — RH -f Cl and R H -f Cl - R -f HCl to occur and to accelerate the overall reaction. 

The use of the differential method of data analysis to determine reaction orders and specific reaction rates is clearly one of the easiest, since it requires only one experiment. However, other effects, such as the presence of a significant reverse reaction, could render the differential method ineffective. In these cases, the method of initial rates could be used to determine the reaction order and the specific rate constant. Here, a series of experiments is carried out at different initial concentrations, C q, and the initial rate of reaction, is determined for each run. The initial rate, can be found by differentiating the data and extrapolating to zero time. For example, in the tfi-tert-butyl peroxide decomposition shown in Example 5-1, the initial rate was found to be... 

The decomposition of acetaldehyde, sensitized by biacetyl, was studied at 499 °C by Rice and Walters , and between 410 and 490 °C by Boyer et al. They found the initial rate to be proportional to the square root of the biacetyl concentration and to the first power of the aldehyde concentration. The chains are initiated by the radicals originating from the decomposition of the biacetyl molecule. The decomposition of acetaldehyde can be induced also by di-r-butyl peroxide (at 150-210 °C, about 10-50 molecules decompose per peroxide molecule added), as well as by ethylene oxide (around 450 °C each added ethylene oxide molecule brings about the decomposition of up to 300 acetaldehyde molecules). For the influence of added diethylether, vinyl ethyl ether, ethyl bromide, and ethyl iodide etc., see Steacie °. 

THE EFFECT OF INITIAL CONCENTRATION ON THE RATE OF DECOMPOSITION OF DI-/-BUTYL PEROXIDE IN CUMENE AT I35.0 0.1 °C ... 

The slight effect of solvent upon the rate of decomposition is characteristic of tertiary dialkyl peroxides. For example, the rate of decomposition of di-r-butyl peroxide is altered only slightly by changing from the gas phase through hydrocarbon solvents to tri-n-butyl amine (Table 66). These results indicate that there is little ionic character in the activated complex of the rate-determining step (2). 

In one of the most elegant applications of gas-phase inhibition by nitric oxide, Birss, Danby and Hinshelwood have studied the thermal dissociation of r-butyl peroxide. The low temperatures required for pyrolysis permitted mass spectro-metric determination of t-butyl nitrite, and a fairly complete kinetic analysis of the system was possible. The rate of decomposition of peroxide was related to the consumption of nitric oxide and to the appearance of butyl nitrite during the inhibition period, and curves were obtained which showed the acetone and ethane concentrations as a function of time during and after inhibition. 

The adiabatic time to maximum rate, TMR, gives a measure of the time required to reach, from a given temperature, the maximum selfheating rate for a system under conditions of no heat transfer. A plot of TMR vs. temperature is shown in Figure 1 for the decomposition of di-tert-butyl peroxide. The time to maximum rate is best measured directly rather than calculated because of the very large errors associated with the exponential term involved in the calculations. (2) TMR can be measured directly using an adiabatic calorimeter such as the Accelerating Rate Calorimeter. 

Figure 1. Temperature vs. Time to Maximum Decomposition Rate (TMR) for Di-tert-butyl Peroxide.

The kinetics of the thermal decomposition of di-r-butyl peroxide in toluene were determined by Tou and Whiting (172). They found the kinetic parameters to be E — 37.8 1.1 kcalmol and log A = 16.15 0.61 sec"1. This compares favorably with E = 37.78 + 0.06 kcalmol and log. 4 = 15.80 0.03 sec 1 determined by Shaw and Pritchard (173) from a least-squares treatment of 177 data points obtained by various workers. The highest selfheat rates that the calorimeter can follow without deviation from the... 

To calculate the first-order rate constant for the decomposition of di-f-butyl peroxide in the vapour phase. 

Pincock [Pi 64] characterized solvents on the basis of the solvent dependence of the ionic decomposition of t-butyl peroxyformate. However, not only the rate, but also the mechanism of decomposition of this compound is solvent-dependent. For example, in chlorobenzene it decomposes in a slow unimolecular reaction in which the peroxide bond is split in n-butyl ether the decomposition proceeds via radical attack on the peroxide oxygen atoms and in the presence of pyridine a bimolecular elimination reaction occurs, with the formation of t-butanol and carbon dioxide. Pincock used the solvent dependence of the rate of this latter reaction to characterize the solvent. 

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