Cyclopentylperoxyl and Cyclohexylperoxyl Radicals in Aqueous Solution: A Study by Product Analysis and Pulse Radiolysis

Article abstract of DOI:10.1021/j150667a026

Radiolysis of N2O/O2 (4:1 v/v) saturated aqueous solutions of cyclopentane generates cyclopentylperoxyl radicals which decay by a second-order rate process (2k = 1.5*10⁷ M^-1s^-1) and give rise to the following products (G values in parentheses): cyclopentanone (1.7), cyclopentanol (0.8), glutaraldehyde (1.2), 5-hydroxypentanal (0.8), organic peroxidic material (0.5), and H2O2 (1.7); oxygen is consumed with G=5.0.The corresponding data for cyclohexane solutions are as follows (2k = 1.2*10⁷ M^-1s^-1): cyclohexanone (2.5), cyclohexanol (0.9), total aldehydes (0.8), organic peroxidic material (0.9), H2O2 (1.6), and oxygen uptake (4.0).During the bimolecular decay of the cycloalkylperoxyl radicals small amounts (G ca. 0.5) of HO2^. (H⁺ + O2^-. are formed.It is proposed that in the rate-determining step a short-lived tetroxide is formed which breaks up by four main routes: (i) O2, cycloalkanol, and cycloalkanone, (ii) H2O2 and two molecules of cycloalkanone, (iii) O2 and two ο-formylalkyl radicals (from which the acyclic aldehydes are formed), and (iv) O2 and two cycloalkoxyl radicals.The cycloalkoxyl radicals undergo a 1,2-H shift, a reaction which eventually leads to the formation of the intermediate O2^-..In the cyclopentane system the fragmentation (mainly the concerted process iii) is the most important single process (40 percent) whereas in the cyclohexane system this route does not exceed 15 percent.A fragmentation of the acyclic radicals is not observed.