Thermal decomposition of di-tert-butyl peroxide at high pressure

Abstract

The thermal decomposition of di-tert-butyl peroxide has been studied in the presence of carbon dioxide at total pressures from 0.05 to 15 at111 and temperatures from 90-130 "C. The first-order rate .constant for the decomposition is independent of total pressure in this range, with Arrhenius parameters E = 37.8 f 0.3 kcal/mole and log A (s-') = 15.8 + 0.2. A reevaluation of previous data on this reaction leads us to recommend E = 37.78k0.06 kcal/mole and log A (s-') = 15.80 F 0.03 over the temperature range 90-350 "C; extension of this range to higher temperatures using a shock tube would be worthwhile.Canadian Journal of Chemistry, 46, 2721 (1968) It has been postulated by Birss (1) and by Bose and Hinshelwood (2) that in the thermal decomposition of di-tert-butyl peroxide (DTBP), a second channel exists between reactants and products which they called induced decomposition. The evidence upon which these arguments are based is in our view not very strong, and we believe that the postulate is unnecessary. It was found that the rate of decomposition at 160 "C increased with pressure between 50 and 600 mm. However, since the explosion limit of the peroxide decomposition is estimated (3) to be around 600 mm at 150 "C, the probable cause of the rise in rate with pressure becomes apparent. It was also found that added gases, namely SF,, CF,, CO,, CCl,, SiF,, and N,O caused an acceleration of the reaction, whereas acetone, 17-hexane, and N2 were without effect. It was recognized later by Archer and Hinshelwood (4) that in the case of CCI,, the acceleration may have been partly a chemical effect involving chloriile atoms. More recently, Flowers, Batt, and Bellson (5) showed that the peroxide decomposition was strongly catalyzed by HC1 by a mechanism involving chlorine atoms, and further evidence for the existence of chlorine atoms in the peroxide/CCl, reaction is available (6). Also, Batt and Cruickshank (7) have shown that CH,F is formed in the peroxide/SF, decomposition. We suggest that all these observed acceleratioils in the presence of CF,, SiF,, CO,, and N,O are due either to chemical reaction of some kind or to the presence of trace quantities of chlorinated impurities; it is reasonable to suppose that the N,, acetone, and hexane used in the above experiments were free from chlorinated impurities. Our own experiments described below show that carefully purified CO, has no effect on the rate of peroxide decomposition up to a pressure of 15 atm, and we believe that the idea of induced decom~osition should not be included in the current theoretical description of unimolecular reactions. Materials and Experimental TechniqueCommercial di-tert-butyl peroxide contains about 0.2% of minor impurities including 0.04% acetone (8); these were removed by preparative scale gas chromatography. Carbon dioxide was made from commercial dry-ice: the gas was condensed onto phosphorus pentoxide it1 vacuo, degassed, and then sublimed into a storage vessel; mass-spectrometer analysis failed to reveal any impurity.Each experiment wa...

Thermal Decomposition of di-tert-Butyl Peroxide in Binary Mixtures near the Critical Point

“…Virtually no tert-butanol was formed in these cases, and in this sense the values of k, shown in Fig. 4 more nearly resemble those determined previously (1) in experiments where only the rate of formation of acetone was measured.…”

“…Rate constants k, were established by measuring the rate of formation of acetone + tert-butanol as described previously (2), and when plotted in Arrhenius form, whether obtained at temDeratures above or below the critical point, were consistent with those obtained previously (1). Since the critical temperature of propane (6) is 96.7 "C, and the reaction becomes too slow (1) for convenient study below 90 "C, the accessible liquid range is somewhat limited; in fact, at our propane concentrations, the gas density is such (7) that two phases would only be present in pure propane below about 93 "C. At the same time, whilst the sum of acetone + tert-butanol formation did not appear to show anomalies at 90 "C, the ratio of acetone/ tert-butanol was only about 50% of that expected by extrapolating the previous gas-phase data (2); unfortunately, at 90 "C, these ratios are quite small, and probably not very reliable.…”

“…The preparation and/or purification of di-rerr-butyl peroxide, carbon dioxide, and propane have been described previously (1,2). Cyclopropane was supplied by Matheson of Canada Ltd: the principal impurities were stated to be air and cyclopropyl chloride; the latter would be expected to have a marked catalytic effect on the peroxide decomposition (I).…”

“…The remainder of the experimental procedures have been described in detail (1,2): in each of the main series of experiments, a total of mol of peroxide was used, together with a propane o r cyclopropane concentration of 3.1 +_ 0.5 mol I-'; departures from these standard conditions are noted below as they arise.…”

Photolysis of Di-tert-butyl Peroxide at High Pressure

“…The preparation and purification of all the materials, the ferrioxalate actinometry, and the methods of analysis used in this work have all been documented adequately in earlier papers (1)(2)(3)(4).…”