Metal complexes as antioxidants. 9. Application of the spin scavenging technique to the reaction of transition metal dialkyldithiophosphates and dialkyldithiocarbamates with tertiary alkyl hydroperoxides

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Abstract
The spin scavenging technique has been applied to the initial homolytic reaction between tertiary alkyl hydroperoxides and zinc and nickel complexes of dialkyldithiophosphoric acids and dialkyldithiocarbamic acids using low concentrations of Galvinoxyl and 2,2,6,6-tetramethyl-4-oxo-1-piperidinyloxyl as radical scavengers. This method has demonstrated that these transition metal complexes react with hydroperoxides at 303 K to generate free-radicals. Quantitative kinetic data have been obtained from zero-order scavenger decays and the efficiency with which the transition metal complexes generate free-radicals increases in the order Zn[R2NCS2]2 < Zn[(RO)2PS2]2 < Ni[(RO)2PS2]2 < Ni[R2NCS2]2. Deviations from zero-order scavenger decay have been observed, particularly at high complex concentrations, and have been attributed to reaction of the complex with transient radicals to give products which do not react rapidly with the scavenger.

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