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The antioxidant properties of a series of biologically active polysubstituted tetrahydroquinolines containing chromanyl fragments have been experimentally studied in the liquid phase. Probed was the ability of the substrates to kinetically retard the initiator‐induced radical chain oxidation by O2 of the model compounds 1,4‐dioxane or isopropyl alcohol. The oxidation reactions were monitored at 348 K using a manometric technique, measuring under various initial conditions the time‐dependent concentration of oxygen in the gas phase above a reaction mixture containing the radical‐chain initiator azobisisobutylnitrile and the substrates under study. When tetrahydroquinolines were present, the kinetic curves of oxygen absorption exhibited characteristic induction periods (τ) wherein the reaction rate is immeasurably small. The dependence of τ on the initial concentration of the introduced antioxidants has been determined and the results interpreted within the framework of a classical scheme describing the radical‐chain oxidation of organic compounds in the presence of an inhibitor. Values of the stoichiometric coefficient of inhibition, f, which is related to the number of chain propagating radicals destroyed by each antioxidant molecule, is >>2 for all the studied antioxidants. Consistent with the existing literature, it is inferred that the original antioxidant molecule is regenerated from its radical inhibition product during reaction. Previous studies suggest that oxyperoxy radicals play an important role in the inhibitor regeneration process due to their ability to act either as an oxidizer (in chain propagation) or as a reducing agent (in regeneration of the inhibitor from its corresponding radical). In the presently studied systems containing 1,4‐dioxane, it is argued that the source of oxyperoxy radicals is 2‐hydroxy‐1,4‐dioxane. A reaction mechanism that includes the stages of inhibitor regeneration and that is quantitatively consistent with the present results has been developed. It is suggested that the high antioxidant capacity of the tetrahydroquinoline derivatives is due to their large chain breaking rate constants in conjunction with regeneration of the inhibitor during chain termination processes. The relationship of the studied chemical structures and their antioxidant capacity is discussed.

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Using the GUSAR 2013 program, the quantitative structure–antioxidant activity relationship has been studied for 74 phenols, aminophenols, aromatic amines and uracils having lgk7 = 0.01–6.65 (where k7 is the rate constant for the reaction of antioxidants with peroxyl radicals generated upon oxidation). Based on the atomic descriptors (Quantitative Neighborhood of Atoms (QNA) and Multilevel Neighborhoods of Atoms (MNA)) and molecular (topological length, topological volume and lipophilicity) descriptors, we have developed 9 statistically significant QSAR consensus models that demonstrate high accuracy in predicting the lgk7 values for the compounds of training sets and appropriately predict lgk7 for the test samples. Moderate predictive power of these models is demonstrated using metrics of two categories: (1) based on the determination coefficients R2 (R2TSi, R20, Q2(F1), Q2(F2), RmTSi2¯) and based on the concordance correlation coefficient (CCC)); or (2) based on the prediction lgk7 errors (root mean square error (RMSEP), mean absolute error (MAE) and standard deviation (S.D.)) The RBF-SCR method has been used for selecting the descriptors. Our theoretical prognosis of the lgk7 for 8-PPDA, a known antioxidant, based on the consensus models well agrees with the experimental value measure in the present work. Thus, the algorithms for calculating the descriptors implemented in the GUSAR 2013 program allow simulating kinetic parameters of the reactions underling the liquid-phase oxidation of hydrocarbons.

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