On the origin of decomposition of triphenyl phosphite ozonide accelerated by ammonia or pyridine water solution

The decomposition of triphenyl phosphite ozonide (TPPO) has been well recognized as a potential source of singlet oxygen (O2, 1Δg) for the chemical oxygen-iodine laser. Experimental observations suggested that ammonia or pyridine water solution can accelerate the decomposition of TPPO, and hydroxyl ion is responsible for accelerating singlet oxygen liberation during this decomposition. In this paper, we studied the mechanism of OH−-accelerated reaction using density functional theory (DFT) at B3LYP/6-31+G* levels of theory. The calculations reveal a favorable free energy pathway for hydroxide-accelerated decomposition of TPPO, i.e. nucleophilic addition at phosphorus, followed by elimination of phenoxy group and subsequent liberation of singlet oxygen. The solvent effects were studied using a polarizable continuum model. The frontier molecular orbitals of the ozonides, atom-atom Wiberg bond index and corresponding atomic charges were also investigated to shed further light on the reaction pathway.