The design and utilization of a stirred-flow reactor for kinetic and mechanistic studies of the liquid-phase autoxidation of organic compounds are described. Utilizing a variety of selective reduction, separation, and analytical procedures the primary C16, products derived from the initial stages of the autoxidation of n-hexadecane with molecular oxygen at 120, 160, and 180 °C have been quantitatively determined. These products include isomeric monohydroperoxides, II, isomeric α,γ-and α,δ-dihydroperoxides, IV, two groups of isomeric α,γ-and α,δ-substituted species which consist of mixtures of hydroperoxy ketones, VI, α,α,γ-and α,α,δ-trihydroperoxides, VI11, and/or α-hydroperoxy-α,γ-and α-hydroperoxy-α,δ-cyclic peroxides, IX, and a further group of trisubstituted products with isolated functional groups. With the exception of the group of α,γ-substituted species VI, VIII, and/or IX at 160 and 180 °C, the ratios of the concentrations of these products to the concentrations of monohydroperoxides are constant at a given temperature in the range of conversions studied. These ratios at 180 °C (120 °C) are equal to 0.054 (0.044) for αγ-substituted IV, 0.095 (0.076) for α,δ-substituted IV, 0.103 (0.087) for the groups of α,δ-substituted species VI, VII], and/or IX, and 0.025 (0.017) for trisubstituted products with isolated functional groups. For the group of α,γ-substituted species VI, VIII, and/or IX, the ratio of their concentrations to that of monohydroperoxides is equal to 0.18 at 120 °C. At 160 and 180 °C the ratio decreases with increasing conversion. As will be shown in a later paper of this series, these species are unstable and undergo rapid conversion to secondary products, methyl ketones and carboxylic acids. A reaction scheme consistent with the analytical results is proposed. The scheme consists of a series of consecutive, competitive intra-and intermolecular hydrogen abstraction reactions by hexadecylperoxy radical species. A high percentage of the abstraction reactions from n-hexadecane occur via hydroxyl radicals which are produced concurrently with and/or subsequently to the formation of species VI, VIII, and/or IX. Chain initiation occurs via homolytic decomposition of hydroperoxide species and termination by bimolecular reaction of the chain carrying peroxy radicals. Comparison of the experimentally determined hydroperoxide concentrations with those calculated from the concentrations of the reduced products suggests that greater than 90% of the hydroperoxide products are accounted for in the present study. A discussion of the importance of intramolecular hydrogen atom abstraction by peroxy radicals in both the liquid-and gasphase autoxidations of n-alkanes is presented. It is concluded that the failure of earlier workers to observe the products of such reactions in the liquid-phase systems was due to the limitations of their analytical techniques and to the extended reaction times during which the conversion of VI, VIII, and/or IX species to secondary products occurred. The striking similarities of the results of the present study and gasphase studies at elevated temperatures with regard to the initial distribution of α,γ-and γ,δ-substituted products and their subsequent reactions are also discussed. © 1979, American Chemical Society. All rights reserved.
