The theoretical trajectory for the chloride-ion-induced generation of singlet oxygen in the decomposition of dimethyldioxirane

The mechanism of the catalytic chloride-ion-induced decomposition of dimethyldioxirane has been investigated from a theoretical point of view. The geometrical parameters and harmonic vibrational frequencies of the detected stationary points were calculated at the MP2/6-31+G(d) level of theory, the energies of all the stationary points were refined by means of the MP4(SDTQ)/6-31+G(d) approximation. It was found that the chloride ion forms complexes with acetone and dioxirane, the latter transforms to the anionic intermediate 2-chlorooxy-2-hydroxy propane alcoholate (5b) or ClO–C(CH3)2–O−. Electrostatic forces stabilize these complexes, supported by the similar reaction enthalpies (ΔrH°298.15 K) and ion–dipole interaction energy (E). Our results reveal that the chloride-ion-induced decomposition of the peroxide is a four-step process in which the ClO–C(CH3)2–O− anion 5b serves as a chain carrier in contrast to the earlier postulated hypochlorite ion. The critical step for the production of singlet oxygen is the strongly exothermic decomposition of the intermediate by its reaction with dimethyldioxirane. This chemiluminescent process takes place on the singlet potential energy surface (PES), for which spin conservation obliges the generation of electronically excited singlet oxygen. The present results require revision of the previously published mechanism.