Identification of an unexpected peroxide formed by successive isomerization reactions of the n-butoxy radical in oxygen

Abstract

A previously unreported peroxide, C₄H₈O₃(5), has been identified and its mechanism of formation proposed. It is generated by two successive isomerization reactions of n-C₄H₉O radicals in O₂. These radicals are produced by di-n-C₄H₉O—OC₄H₉ pyrolysis at 480 K in a wall-passivated quartz vessel. The peroxide is collected, among other end-products, on a liquid-nitrogen trap and recovered in liquid acetonitrile. Analysis was carried out by GC–MS, GC–MS–MS [electron impact (EI) and NH₃(or ND₃)–chemical ionization (CI) conditions] and GC–FTIR. After micropreparative GC separation of the titled peroxide, ¹H NMR and high-resolution EIMS were also obtained. The compound was identified as 3α-hydroxy-1,2-dioxane. The hydroperoxybutyraldehyde OHC—(CH₂)₂—CH₂O₂H is proposed to be initially formed in the gas phase and to be in equilibrium with its cyclic form (six-membered ring peroxide), by far predominant in the liquid phase at room temperature. The implications of this hydroperoxybutyraldehyde in atmospheric pollution (due to the peroxide producing capability of radicals) and in combustion are discussed.