0023-1584/04/4506- © 2004 MAIK “Nauka /Interperiodica” 0809 Kinetics and Catalysis, Vol. 45, No. 6, 2004, pp. 809–812. Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 859–862. Original Russian Text Copyright © 2004 by Grabovskiy, Antipin, Kabal’nova. INTRODUCTION Dioxiranes, which are highly reactive three-mem- bered cyclic peroxides, can hydroxylate the C–H bonds of aliphatic hydrocarbons under mild conditions. Oxi- dation with the participation of dioxiranes occurs with high regioselectivity. Studies on the mechanism of oxi- dation by dioxiranes are of continuous interest. Several opinions on the mechanism of dioxirane reactions with alkanes have formed to date: the “inser- tion” of an oxygen atom [1–3], the homolysis of diox- irane at the O–O bond followed by hydrogen abstrac- tion from the substrate by the resulting biradical or the homolysis of dioxirane by the alkane molecule [4, 5], the simultaneous occurrence of the above mechanisms [6], and the parallel occurrence of two reactions (through the same [7] or different transition states). One of these reactions results in molecular products, whereas the other produces a radical pair in a solvent cage [7–9]. Data on the oxidation of compounds con- taining cyclopropane fragments, which can undergo isomerization with high rate constants with the forma- tion of radicals at the β-position with respect to the cyclopropane ring [1, 10], demonstrated the domina- tion of the “insertion” reaction. However, note that the direction of the reaction depends on the structure of the substrate oxidized and the conclusions made are true only for the test compounds. The extension of the mechanism found for these specific alkanes to other substrates is somewhat premature. The kinetics and the products of adamantane oxida- tion by dioxirane were studied in the most detail [11, 12]. It was concluded that the reaction occurs via the insertion mechanism. In this work, we found that adamantane oxidation by dimethyldioxirane (DMDO) occurs with the partici- pation of free radicals. EXPERIMENTAL Acetone (analytical grade) and tetrachloromethane (high-purity grade) were subjected to a single distilla- tion in an efficient column. Oxone (2KHSO 5 · KHSO 4 · K 2 SO 4 ) from Aldrich ® was used without additional purification. DMDO was synthesized using a published procedure [13]. DMDO was extracted into CCl 4 in accordance with a previously developed procedure [14] (the residual amount of acetone was ~0.1 mol/l). The concentration of DMDO in CCl 4 was varied over the range 0.03–0.15 mol/l. Adamantane from Aldrich ® was twice sublimed. The kinetics of the reaction of DMDO with adaman- tane in CCl 4 were measured by spectrophotometry at λ = 335 nm (ε max = 14 l mol –1 cm –1 ) over the tempera- ture range 10.3–69.3°C. The reactor was a thermostat- ted quartz cell (of volume 1.1 ml; l = 0.5 cm) with a ground-glass stopper. Oxygen was passed through the reaction mixture for ~1.5 min before the beginning of an experiment; next, the cell was closed with the stop- per. The concentration of O 2 in the CCl 4 –hydrocarbon binary system was calculated from published data [15]. The initial concentration of adamantane was varied over the range 0.15–0.9 mol/l. RESULTS AND DISCUSSION We studied the kinetics and the products of the reac- tion of adamantane (AdH) with DMDO. The reaction products and their proportions (table) are analogous to data obtained previously in the oxidation of adaman- tane by DMDO in acetone [12] with the exception of The Role of Free Radicals in the Reaction of Dimethyldioxirane with Adamantane S. A. Grabovskiy, A. V. Antipin, and N. N. Kabal’nova Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, 450054 Bashkortostan, Russia Received August 22, 2003 Abstract—The products and the kinetics of the reaction of dimethyldioxirane with adamantane in CCl 4 were studied. It was found that the reaction simultaneously occurred via molecular and radical paths. The contribu- tion of the radical process was 65% at 30.6°C. The activation parameters of the reaction of dimethyldioxirane with adamantane in the presence of an inhibitor were determined: = (7.33 ± 0.14)–(58.5 ± 0.8)/Θ, Θ = 2.3RT(kJ/mol) (10.3–69.3°C). k log PEROXIDES-XI