N,N-Dialkyl-amides thermal degradation at low temperatures

The N,N-di-(2-ethylhexyl) 3,3-dimethylbutanamide (DEHDMBA) thermal degradation seemed to be complex. The thermal degradation study of N,N-dialkyl-amides, which present similar structures to DEHDMBA, has then been necessary. Four compounds are chosen, the N,N-diethylpropionamide (DEP), the N,N-diisopropyl-acetamide (DIPA), the N,N-diethyldodecanamide (DEDD), and the N,N-dimethyl-benzamide (DMB). These N,N-dialkyl-amides heated at 215 deg. C essentially produce acids, ketones, imides, and amides substituted or not. The atmosphere oxygen level is the most influent factor on amides thermolysis. Thus, after one hour under oxygen atmosphere, the amide residual yields are close to 20%. These same yields are included between 60% and 70% after one hour of thermolysis under ambient air. A thermal oxidation mechanism is therefore probably involved. The initial rates of the amides degradation follow second order kinetics under ambient air atmosphere, and zero order kinetics under oxygen atmosphere. Under nitrogen atmosphere, only the DEHDMBA pyrolysis rate is studied and the reaction follows a second order kinetic. The results show that the two carbon long chains N,N-dialkyl-amides are characterized by a similar thermal behaviour. Moreover, a great number of the degradation products appear whatever the atmosphere and the temperature applied. The acids are often final reaction products, like some primary amides and aldehydes. Secondary amides, sometimes partially degraded, are also identified after two or three hours reaction rimes. Finally, imides are generally intermediate reaction products. This separation between final products and by-products allow to establish a schematic reaction pathway of the N,N-dialkyl-amides thermal degradation. (author)