The thermochemistry of threonine stereoisomers

• ΔfH of l-, d- and dl-threonine from combustion data: −790.0 ± 3.1, −787.7 ± 3.7, and −778.0 ± 2.8 kJ mol−1, respectively.
• DSC: one peak corresponding to a mix melting–decomposition process in the case of enantiomers in the range 247–258 °C.
• DSC: two neighbor peaks, at lower temperatures than those of enantiomers, for the racemic.
• ΔH = 54 kJ mol−1 from DSC of enantiomers is assigned to the first step of the thermal degradation with formation of dipetide.

Combustion calorimetry and differential scanning calorimetry (DSC) techniques have been employed in order to obtain the thermochemical properties of l- and d-enantiomers and racemic mixture of threonine.The large negative values of the enthalpies of formation of the investigated compounds reveal their high stability. The thermal behavior of the compounds was studied by means of DSC in the temperature range between ambient and 265 °C. A combined transformation – melting and decomposition is occurring on heating. The decomposition mechanism is discussed in relation to the data obtained by means of DSC.