Autoxidation of N-alkyl-amides. Part II. N-alkyl-amide hydroperoxides and di-N-alkyl-amide peroxides

Abstract

1-Amido-n-alkyl hydroperoxides are formed during the thermal oxidation of N-n-alkyl-amides. The pure hydroperoxides isolated from thermally oxidised N-ethylacetamide, N-n-propylpropionamide, NN-diethylacetamide, and NN-di-n-propylpropionamide are relatively stable crystalline solids. Rotation about the –CO·N– bond is hindered, and in the cis-configuration 7-membered intramolecular hydrogen-bonded rings are formed. Decomposition of these hydroperoxides in solution in N-alkyl-amide solvents has been investigated. The principal products are (i)N-acyl-amides and water, (ii)N-formyl-amides and alcohols, (iii) primary amides and aldehydes, and (iv)N-alkenyl-amides and hydrogen peroxide. The overall decomposition is first-order for at least one half-life but is then autocatalytic. For the decomposition of 1-propionamidopropyl hydroperoxide, k= 2·3 × 10⁹ exp(–23,700/RT) sec.^–1. Measurement of the rate of removal of added 1-naphthol indicates that only a small proportion of the decomposition is homolytic; the main decompositions are non-radical concerted ones.

Photo-oxidation of N-n-alkyl-amides initiated by di-t-butyl peroxide is non-chain at 0°, and di-(1-amido-n-alkyl) peroxides are found among the products. Photo-oxidation at higher temperatures (75°) proceeds by short chains, and the peroxidic products are mixtures of 1-amido-n-alkyl hydroperoxide and di-(1-amido-n-alkyl) peroxide.