Bis-Aryloxalates as Convenient Unimolecular Sources of Aryloxyl Radicals

Synthesis of a new photochemical unimolecular precursor to aryloxyl radicals is described, the bis-aryloxalate esters (BAO's). These molecules are readily synthesized, are thermally very stable, may be stored under ordinary benchtop laboratory conditions in the dark, make large and well-formed crystals, and are readily photolyzed either in solution or in solid phases. Solid state photochemical experiments may easily be carried out in polymer matrices (PPMA), frozen glassy matrix, microcystalline powders, or in single crystals. Photoefficiency is about half by comparison to analogous aryloxyoxalyl tert- butylperoxide precursors (described in ONR Technical Report 12), but in symmetrical BAO's generated the same number of radicals per unit quantum of photolysis greater than 300 nm. Unsymmetrical BAO's are also readily synthesized from the oxalyl chloride half-esters of 2,4,6-tri-tert-butylphenol. Keywords: Solid state unimolecular photochemical generation, Aryloxyl radicals.