Effect of temperature on the kinetics of free radical formation during the pyrolysis of some amino acids

Abstract

Relatively stable free radicals of DL-lysine, DL-aspartic acid and DL-glutamic acid pyrolysates were identified by electron spin resonance (ESR) spectroscopy. The ESR spectral intensity of the amino acid pyrolysates showed that the formation of free radicals on pyrolysis at 473–873 K, during a reaction period that lasted from 0.12 × 10³ to 1.08 × 10⁴ s, depended mainly on the temperature applied, the duration of pyrolysis and the structure of the amino acid.

Based on the shapes, intensities and g-values of the ESR spectra and differential scanning calorimetric and thermogravimetric analysis of the amino acids, it can be concluded that the reaction between degraded and transformed amino acid molecules or byproducts, as intermediates, leads to the formation of different final reaction products and considerably different kinetics of the pyrolysis reactions.