The standard enthalpies of formation of proline stereoisomers

The combustion calorimetry and differential scanning calorimetry (DSC) techniques have been employed in order to obtain the thermochemical properties of l-, d-enantiomers and racemic mixture of proline.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 250 °C. A combined transformation–melting and decomposition is occurring on heating. The decomposition mechanism is discussed in relationship with the data obtained by means of DSC.

► Enthalpies of combustion and formation of crystalline l-, d- and dl-prolines.
► Melting–decomposition processes occurring on heating investigated by DSC.
► Agreement of our data with literature and calculated ones.
► Discussion of the possible decomposition reactions according to the values of the thermal effects.