Peroxyacetyl

Peroxyacetyl refers to a chemical moiety derived from acetyl that contains a peroxide bond, most commonly described in the acylperoxy radical CH3COOO•. The term is also used to denote the peroxyacetyl group in compounds such as peroxyacetyl nitrate (PAN), CH3C(O)OONO2, where the peroxyacetyl fragment is bound to a nitrate moiety. In atmospheric and organic chemistry, peroxyacetyl denotes the RCOOO– fragment with R = CH3 in the acetyl case.

Formation and occurrence: In the atmosphere, peroxyacetyl radicals are formed during the oxidation of acetaldehyde and other acetyl-containing volatile organic compounds in the presence of oxygen. They are highly reactive and short-lived, acting as key intermediates in radical chain processes that govern oxidation pathways of small carbonyls.

Reactions and role: Peroxyacetyl radicals participate in reactions with nitric oxide and nitrogen dioxide, contributing to the formation of stable peroxyacyl nitrates such as PAN. PAN acts as a reservoir for nitrogen oxides, influencing NOx distribution, ozone formation, and overall air-quality chemistry. Peroxyacetyl species can also engage with other RO2 radicals and HO2, propagating radical cycling and producing secondary organic products.

Significance: In atmospheric chemistry, peroxyacetyl species link VOC oxidation to the formation and transport of PAN, affecting regional air quality and photochemical smog dynamics. They also appear in combustion chemistry as transient intermediates in oxidation sequences of acetyl-containing compounds.

Detection and study: These species are highly reactive and short-lived, so their presence is inferred from indirect methods, including monitoring PAN levels and using spectroscopic and kinetic studies to characterize their formation and reactions.