Activation energy ester decomposition

Nitrocellulose is among the least stable of common explosives. At 125°C it decomposes autocatalyticaHy to CO, CO2, H2O, N2, and NO, primarily as a result of hydrolysis of the ester and intermolecular oxidation of the anhydroglucose rings. At 50°C the rate of decomposition of purified nitrocellulose is about 4.5 x 10 %/h, increasing by a factor of about 3.5 for each 10°C rise in temperature. Many values have been reported for the activation energy, E, and Arrhenius frequency factor, Z, of nitrocellulose. Typical values foiE and Z are 205 kj/mol (49 kcal/mol) and 10.21, respectively. The addition of... 

A kinetic study of the previously reported substitution of aromatic nitro groups by tervalent phosphorus has established an aromatic 5n2 mechanism. Similarities in values of activation energies, and in relative reactivities of phosphite and phosphonite esters, between this displacement and the Arbusov reaction suggest a related mechanism (31), while the lack of reactivity of p-dinitrobenzene is attributed to the need for intramolecular solvation (32). The exclusive formation of ethyl nitrite, rather than other isomers, is confirmed from the decomposition of triethoxy-(ethyl)phosphonium fluoroborate (33) in the presence of silver nitrite. A mechanism involving quinquevalent phosphorus (34) still seems applicable, particularly in view of the recent mechanistic work on the Arbusov reaction. ... 

This retro-ene reaction is accepted as the primary mode of ester decomposition. For olefins, it has been investigated both directly (8) and via the reverse reaction, the ene reaction (9). The best estimates for 1-hexene and 1-heptene are that the reaction proceeds with an activation energy of about 54 kcal/mol and a preexponential factor of 1012 sec-1. 

This ester resembles its methyl homologue in possessing three modes of decomposition [131]. It also supports a self-decomposition flame, the multiple reaction zones of which are clearly separated at low pressures [122, 123, 125]. Temperature and composition profiles in the low-pressure decomposition flame have been measured [133]. The products include formaldehyde, acetaldehyde and ethanol with smaller amounts of methane and nitromethane. The activation energy derived from the variation of flame speed with final flame temperature was 38 kcal. mole", close to the dissociation energy of the RO—NO2 bond. The controlling reaction is believed to be unimolecular in its low pressure regime, and the rate coefficient calculated from the heat-release profile is... 

The increase in rate with increase of temperature for all the cyclopentane-1,2-diols in Table 2 is small and corresponds to apparent activation energies in the range 1-5 kcal.mole . Each rate coefficient is probably the product of the rate coefficient for decomposition of the cyclic ester and one or more equilibrium constants. The latter could well decrease with increase of temperature, and bring about low overall activation energies. 

Trifluoroacetic acid at 300-390 °C produces mainly carbon dioxide, difluoro-methyl trifluoroacetate, carbon monoxide and trifluoroacetyl fluoride. Blake and Pritchard propose that the decomposition proceeds through the elimination of hydrogen fluoride, followed by the formation of difluorocarbene which largely adds to trifluoroacetic acid to form the difluoromethyl ester. The kinetic order is about 0.5 and the overall activation energy for the formation of carbon dioxide and the difluoromethyl ester is about 45 kcal.mole" ... 

Kinetic results are given in Table 9. The toluene carrier technique often yields low values of the activation energies and 4-factors. Results for the benzyl esters, however, appear to be reasonably good. Note that the estimated reaction enthalpies compare favorably with the observed activation energies and that -factors are reasonable (AS 5 cal.deg mole ). Since only absolute decomposition rate coefficients were reported for the allyl esters, we have estimated the Arrhenius parameters on the assumption that the -factors were all 10 sec The activation energies so obtained are reasonable, since they compare quite favorably to those estimated by group additivities and the accepted heats of formation of the product radicals (Column 3, Table 9). 

The /-butane chemical ionization spectra of benzyl acetate and t-amyl acetate have been investigated at a number of temperatures, and the rate constants for the decomposition of the protonated esters to benzyl and r-amyl ions, respectively, have been obtained at the several temperatures from (41) to (42). It is found that the rate constants obey the Arrhenius relationship, and this is illustrated in Fig. 5. Activation energies and frequency factors obtained from the Arrhenius plots are given in Table XIV. 

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