Influence of the composition of the chelate ring and the structure of the ligand on the inhibiting activity of metal thiooxinates in the oxidation of hydrocarbons

Abstract

1. The polarographic half-wave oxidation potentials (E1/2) of the thiooxinates and 5-S-alkylthiooxinates of Cu(II), Ni(II), Pb(II) and Co (III), as well as Zn(II) thiooxinate and Cu(II) acetylacetonate, have been determined. A correlation has been established between the ease of the oxidation of the sulfur-containing chelates of the divalent metals and their inhibiting activity in the model reaction of the low-temperature oxidation of ethylbenzene: The more easily is the chelate ring oxidized, the more actively it inhibits. 2. The introduction of an S-alkyl substituent into position 5 of the mercaptoquinoline ring of the ligand slightly alters E1/2 and the inhibiting activity of the thiooxinates. 3. The nonlinear nature of the dependence of the induction period for the oxidation of ethylbenzene on the initial concentration Co of the inhibitor CuTox2 and the corresponding extreme-value dependence of the stoichiometric inhibition coefficient f on Co are attributed to a reaction in the induction period between the conversion products of CuTox2 and 2-cyanopropyl hydroperoxide, which is formed as a result of the dissociation of the initiator in the medium of the oxidized hydrocarbon. 4. The rate constant of the reaction of the conversion products of CuTox2 with the hydroperoxide of ethylbenzene has been evaluated.