A thermochemical study of serine stereoisomers

• ΔfH of serine isomers: l−/−736.1 ± 2.2, d−/−737.0 ± 2.3, dl−/−743.5 ± 1.3 kJ mol−1.
• DSC: two peaks corresponding to melting–decomposition processes for the enantiomers.
• DSC: two peaks, at higher temperatures than those of enantiomers, for the racemic.
• ΔH from DSC are correlated with the possible thermal degradation processes.

The combustion and formation enthalpies in the solid state of serine stereoisomers (l- and d-) and of their racemic mixture, −736.6 ± 2.1, −739.4 ± 2.3, −744.0 ± 1.2 kJ mol−1 are reported and compared to literature and calculated data. The transformation points (melting and decomposition) and the associated thermal effects were determined from the DSC thermograms in the temperature range between 300 K and beyond the melting–decomposition temperatures. The high negative values of the enthalpies of formation (over −700 kJ mol−1 for a molecular formula C3H7NO3) highlight the stability of serine. Important differences between enantiomers and racemic are noticed. The decomposition mechanism is discussed in relation to the data obtained by means of DSC.