Thermal stability of aliphatic-aromatic polyamide model compounds: Structure-reactivity relationships in the catalyzed thermal reaction of benzamides in the presence of copper halides

The relationship between the structure and reactivity of aliphatic-aromatic polyamides in the presence of CuI in an inert atmosphere was probed by reacting a family of benzamides with varying degrees of substitution on the amide nitrogen. Experiments with benzamide, N-methylbenzamide, N,N-dimethylbenzamide, N-hexylbenzamide, and N,N-dihexylbenzamide allowed comparison of primary, secondary, and tertiary benzamides and identification of the degradation pathways influenced by CuI. The presence of copper iodide enhanced the reactivity of all of the benzamides. Loadings as low as 0.5% led to higher conversion and increased recoverable product yields. Reaction path selectivities were also affected by the addition of CuI. The selectivity to benzene increased for all reactants, and the pathway leading to N-alkylation increased for the reaction of NHB. In all, these results revealed three major reaction pathways influenced by CuI: 1) N - C bond cleavage; 2) N - H bond cleavage; and 3) removal of the amide functional group from the aromatic ring. Kinetic results and visible color changes suggested a direct interaction of CuI with the reactant benzamide. Three electron-rich sites on the reactant benzamide, namely, the lone pairs on the carbonyl oxygen, the lone pair on the amide nitrogen and the aromatic ring, are likely sites of interaction of Cu⁺. Models invoking the subsequent reaction of complexes formed from Cu⁺ ion interaction at each of these sites account for the observed products well.