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

Abstract

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.

What Are Reactive Oxygen Species, Free Radicals, and Oxidative Stress in Skin Diseases?

“…In the presence of photosensitizers, such as psoralen, porphyrin, and tetracycline, oxygen reaches its highest excited state via photoreaction pathways, resulting in the formation of 1 O 2 , a strong oxidizer [ 1 , 2 , 3 , 4 ]. Since the lifespan of 1 O 2 is very short (10 −6 to 10 −5 s), it is difficult to detect in the living body [ 5 ]; therefore, whether 1 O 2 is universally produced in the living body remains unknown and its direct effects have not yet been clarified. Although 1 O 2 is the first ROS generated in skin exposed to visible light or ultraviolet rays, it is rapidly metabolized to O 2 •− , H 2 O 2 , and • OH, which are considered to have various biological roles in skin.…”

Chemical Recycling of Polystyrene to Valuable Chemicals via Selective Acid-Catalyzed Aerobic Oxidation under Visible Light

“… 53 Therefore, 1 O 2 is able to initiate low-temperature oxidation of various organic molecules, inspiring a wide array of applications in chemical and biochemical reactions as well as treatment of organic wastes and contaminants. 53 − 58 Based on this knowledge, we envisaged that 1 O 2 may be able to abstract hydrogen at the weak tertiary benzylic C–H bond in PS and thereby induce the chemical degradation of PS. Indeed, there are some methods in the literature regarding the 1 O 2 -mediated degradation of PS under light irradiation.…”

Benzaldehyde-mediated selective aerobic polyethylene functionalisation with isolated backbone ketones

“…The mechanism of PE oxidation by benzaldehyde was further probed through a series of experimental and computational studies. Firstly, we ruled out the involvement of triplet carbonyls generated by the irradiation of benzaldehyde in hydrogen abstraction from PE, 32,33 as well as the contributions of singlet oxygen ( 1 O 2 ) produced by photosensitisation in PE oxidation, 34 as repeating the reaction in the dark did not decrease the resulting TF (Table 1, entry 8). Next, we determined that the auto-oxidation of benzaldehyde was responsible for PE oxidation by performing a negative control using furfural.…”