Homogeneous gas phase pyrolysis of N-isopropylacetamide

Abstract

The gas phase pyrolysis of N-isopropylacetamide (IPA) has been studied in a static system at temperatures between 430 and 480°C. The decomposition occurs by a unimolecular mechanism to yield propene and acetamide. This was accompanied by a bimolecular decomposition to give isopropylamine, propene, acetic acid and acetonitrile. The latter reaction was also catalysed by the acetic acid formed. The rate constants for the unimolecular (k₁), bimolecular (k₂) and the catalysed reaction (k₃) are defined respectively by the Arrhenius equations k₁= 10^{12.07 ± 0.33} exp [(–54 000 ± 1100) cal mol^–1/RT] s^–1, k₂= 10^{13.75 ± 0.85} exp [(–42 200 ± 2900) cal mol^–1/RT] cm³ mol^–1 s^–1, k₃= 10^{13.66 ± 0.30} exp [(–35 800 ± 990) cal mol^–1/RT] cm³ mol^–1 s^–1, where R= 1.987 cal mol^–1 K^–1, 1 cal = 4.187 J.

The relative rates of unimolecular elimination of acetamide in the N-substituted acetamides are compared with those for the elimination of carboxylic acid from the esters. The greater mesomeric effect in the amide than in the ester group is responsible for a relatively smaller effect of α-methyl-substitution in the N-alkyl substituted acetamides. The acetic acid catalysed decomposition of N-alkyl substituted acetamides is similar to that of the catalysed decomposition of acetamide.