THERMOLYSIS AND CHEMILUMINESCENCE OF MONOCYCLIC 1,2,4-TRIOXAN-5-ONES

The 3,6-substituted 1,2,4-trioxan-5-ones 11-14, on heating to 170-200 degrees, underwent unimolecular thermolysis to generate electronically excited singlet ketones with an efficiency of ca. 0.2 %. The chemilum inescence quantum yields (phi(CL)) depended on the nature of the 6-sub stituents and increased linearly with temperature. The Arrhenius activ ation energies were obtained by measuring the rate of decay of lumines cence and determined as 22.9, 30.4, 35.6, and 34.2 kcal/mol for 11-14, respectively. Step analysis of the chemiluminescence of 14 afforded a n average activation energy of 44.3 kcal/mol. This latter result is ex plicable in terms of two decomposition paths, higher and lower in ener gy, leading to excited and 'dark' products, respectively. The thermoly sis of trioxanones 12-14 lacking a H-atom at the 6-position is interpr eted as involving successive rupture of the peroxide bond, excision of ketone at the 3-substituted end, and loss of CO2, to finally produce ketone originating from the 6-position (see Scheme 4).