Organic tetroxides and mechanism of peroxy radical recombination

Abstract

The chemical properties of organic tetroxides, that is, compounds of a general formula ROOOOR (R = H or organic radical) are discussed. The following tetroxides are considered: hydrogen tetroxide HOOOOH, dialkyl tetroxides ROOOOR, hydrotetroxides ROOOOH, and five‐membered cyclic tetroxides—tetroxolanes. Hydrogen tetroxide is formed via self‐reaction of HOO · radicals on singlet PES; hydroperoxy radical interaction plays an important role in the chemistry of atmosphere. The formation and subsequent decay of tetroxides are discussed in detail. Similar self‐reaction of alkylperoxy radicals leads to organic tetroxides. Its irreversible transformation occurs in two directions depending on the tetroxide structure: the facile homolysis of ROOOOR bond or the induced by αCH bond radical decomposition of tetroxide into hydroperoxy, alkoxy radicals, and carbonyl compound. The latter interaction is the key step in the new mechanism of peroxy radical recombination suggested on the base of extensive analysis of available literature. Hydrotetroxides show properties similar to both HOOOOH and dialkyl tetroxides. A possibility of tetroxolane generation in the reaction of ozone with carbonyl compounds is discussed.

The specific features of the liquid-phase oxidation of saturated esters. Kinetics, reactivity and mechanisms of formation of destruction products

“…The recombination mechanism of secondary and primary ROO • radicals is shown in Scheme 6. 64 It explains all known experimental features of the peroxyl radical recombination: kinetic isotope eff ect, the existence of a non-terminating channel (escape of radicals from the solvent cage), the set of the recombination molecular products, the temperature eff ect on the latter. 64 The specifi city of the occurrence of terminating (Scheme 6, pathway d) and non-terminating (Scheme 6, pathway c) channels in the transformation of ester peroxyl radicals will be considered below.…”

“…[54][55][56]63 In the initiated oxidation of aromatic and aliphatic esters, recombination of peroxyl radicals occurs both with (see Scheme 1, reaction (4), rate constant k t ) and without involvement of chain termination (reaction (9), rate constant k´). Reaction ( 9) is well known for recombination of tertiary peroxyl radicals of hydrocarbons 63,64 .…”

“…Besides, the participation of trioxyl radicals in the formation of the observed product set is unlikely because of utterly low stability of these radicals, and the only channel of their consumption is their decomposition with formation of oxyl radicals and oxygen molecules. 64 Based on the high-level DFT and ab initio calculations, 64 an assumption was made about the occurrence of self-induced decay (Scheme 6, pathway a) of tetroxide via fi ve-membered transition state 13, which is more energetically favorable than other transformations such as, for instance, the O-O decomposition of teroxide (Scheme 6, pathway b). The recombination mechanism of secondary and primary ROO • radicals is shown in Scheme 6.…”

“…Cross recombination of peroxyl radicals such as RCH(OO • )R´ and HOO • (pathways of formation o f these radicals are shown in Schemes 3 and 4) leads through the singlet channel to hydrotetroxide 39 (Scheme 18, reaction (33), pathway а) or through the triplet channel to secondary peroxide (Scheme 18, reaction (33), pathway b). 64 According to the mechanisms shown in Scheme 6, transformations of hydrotetroxide 39 can involve chain termination (reaction (34), pathway с) or avoid chain termination (reaction (34), pathway d). 64 Scheme 18…”

“…64 According to the mechanisms shown in Scheme 6, transformations of hydrotetroxide 39 can involve chain termination (reaction (34), pathway с) or avoid chain termination (reaction (34), pathway d). 64 Scheme 18…”