Stabilization of polyamides. V. Thermo-oxidation of hexano-6-lactam in the presence of copper salts

The effect of Cu(I) and Cu(II) salts, halides and acetates on the kinetics and mechanism of the branched chain oxidation of hexano-6-lactam was studied. The effect of Cu salts on the oxidation is independent of the oxidation state of Cu ions and is similar to the effect of alkali metal salts; Cu cations do not seem to be oxidized or reduced in the course of the process. Similarly to alkali metal salts, Cu salts also affect the rates of the initiation and termination reactions of the chain oxidation, namely by their ability to coordinate with hydroperoxides and their peroxy radicals. Thus the Cu salts are able to induce homolysis of 6-hydroperoxyhexano-6-lactam, the branching reaction of the chain oxidation, the bimolecular termination of 6-peroxyhexano-6-lactam radicals leading to adipimide and peroxyadipamic acid, and most probably also the redox reaction of 6-hydroperoxyhexano-6-lactam with the aldehyde O CH(CH 2) 4CONH 2 formed from alkoxy radicals resulting from 6-hydroperoxyhexano-6-lactam homolysis via unstable hydroxy compound. All the above reactions can participate in the final effect of Cu salts on the kinetics and mechanism of N-alkyl amide oxidation.