Review of Chemical Reactivity of Singlet Oxygen with Organic Fuels and Contaminants

Singlet oxygen represents a form of reactive oxygen species (ROS), produced by electronic excitation of molecular triplet oxygen. In general, highly reactive oxygen-bearing molecules remain the backbone of diverse ground-breaking technologies, driving the waves of scientific development in environmental, biotechnology, materials, medical and defence sciences. Singlet oxygen has a relatively high energy of about 94 kJ/mol compared to the ground state molecular O₂ and therefore initiates low-temperature oxidation of electron-rich hydrocarbons. Such reactivity of singlet oxygen has inspired a wide array of emerging applications in chemical, biochemical and combustion phenomena. This paper reviews the intrinsic properties of singlet oxygen, emphasising the physical aspects of its natural occurrences, production techniques, as well as chemical reactivity with organic fuels and contaminants. The review assembles critical scientific studies on the implications of singlet oxygen in initiating chemical reactions, identifying, and quantitating the consequential effects on combustion, fire safety, as well as on the low-temperature treatment of organic wastes and contaminants. Moreover, the content of this review appraises computational efforts, such as DFT quantum mechanical modelling, in developing mechanistic (i. e., both thermodynamic and kinetic) insights into the reaction of singlet oxygen with hydrocarbons.