Thermal Decomposition of Diacyl Peroxides and Peresters An Undergraduate Laboratory Experiment Using Infrared Absorptions To Monitor Decomposition Rates Michael D. Mosher, Sandra Vinson, Jodi Connagahan, Regina Forsythe, and Melvyn W. Mosher . Missouri Southern State College, Joplin, MO 64801 One of the important goals of an educator is to adapt research techniques to the teaching laboratory. To this end this paper describes a technique originally reported by Tanner ( I ) and others (2) in which the characteristic infrared absorption bands of the carbonyl group are used to monitor the decomposition of either peresters or diacyl peroxide. The experiment better illustrates the thermal decomposition of these compounds than most of the classical methods on this subiect and has been found to he verv successful in . ohvsical. instrumental, and advanced organic teaching laboratories. The kinetically slow step in the thermal decomposition of peroxides and peresters is the first-order homolytic cleavage of the weak oxygen-oxygen bond. This is illustrated by a comparison of the rate constants k2and kg (Fig. I), which are. several orders of maenitude greater than kl (3). When alkanes are used as the solve^, the major product (>98%) arising from the decomposition of benzoyl peroxide is henzene (3). Phenyl benzoate and benzoic acid are also reported as products in trace amounts (3). Figure 1 illustrates these steps for the thermal decomposition of a typical diacyl peroxide. In the infrared spectra, peresters show a characteristic ahsorption near 1780 cm-', while diacyl peroxides show two carhonvl ahsorotions near 1820 cm-' and 1780 cm-' (4). These ibsorptikm have been found to obey Beer's law over the concentration ranee of 0.001 M to 0.025 M. Monitorine these infrared absorp
