Thermal stability of amino acids

Thermal decomposition of L-α-amino acids RCH₂(NH₂)COOH where R = Me₂CH, Me₂CHCH₂, MeEtCH, and C₆H₅CH₂ was studied at temperatures below the melting points of their crystals. From the effective rate constants of the first order reactions energy parameters in the Arrhenius equation were calculated. Correlations between the reaction rate constants k _R and the inductive constants σ* of substituents R and also between the rate constants of the reactions and the dipole moments of amino acids was established. Value of ρ* parameter +8.8 in the Taft equation indicates the heterolytic mechanism of transformation of the amino acids. Chromato-mass spectrometric analysis of decomposition products shows that condensation, decarboxylation, and deamination of the amino acids take place.