Dimesityldioxirane is a substituted dioxirane with two mesityl groups attached to the dioxirane carbon. It is a colorless crystalline substance, indefinitely stable at −20 °C.
Structure In the solid phase, the molecule possesses approximate C2 symmetry; under B3LYP this is predicted to be an exact symmetry, with each mesityl group being twisted away from coplanarity by 54.2°. The bulky mesityl groups cause steric strain, which is compensated for by an increase in the angle from 117° in dioxirane to 119.2° in dimesityldioxirane, together with rotation of the mesityl groups out of plane. This in turn yields a narrower angle and a shorter and stronger bond than in other dioxiranes, stabilizing the molecule.
Synthesis Dimesityldioxirane was first isolated at room temperature in pure as well as in solution form in 1994. It was synthesised by irradiation of , its diazo derivative, in oxygen-saturated trichlorofluoromethane at 183 K to form , which reacts to form dimesityldioxirane via a carbonyl oxide intermediate, with overall yield 50%.
Stability Pure dimesityldioxirane is indefinitely stable at −20 °C in the absence of light, in both solid form and trichlorofluoromethane solution. Upon exposure to blue light, it undergoes photolysis to mesityl 2,4,6-trimethylbenzoate. In solid form at room temperature, it decomposes over a period of weeks to dimesitylketone and mesityl 2,4,6-trimethylbenzoate. In methanol solution at room temperature, it decomposes over a period of hours to days, while also slowly oxidizing the solvent.
Reactions Like other dioxiranes, it is a potent oxygen-transfer reagent, driving characteristic reactions such as the epoxidation of cyclohexene.
See also Difluorodioxirane Dimethyldioxirane Shi epoxidation
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