Characterization of the time-dependent L-asparagine monohydrate crystal phase transition

The high-temperature phase transition of single crystals of L-asparagine monohydrate was investigated by X-ray diffraction in association with Rietveld refinement and dilatometer measurements as a function of annealing time. The X-ray results showed that, for samples annealed at 343 K (or even 333 K) for 5 h, the expected anhydrous L-asparagine phase has been formed, monoclinic system (space group P2₁), with lattice parameters a = 5.0677 (2), b = 6.7657 (2), c = 8.0742 (3) Å and β = 91.276 (4)°. The results obtained from measurements as a function of annealing time confirmed that the phase transition associated with loss of the water molecule is time dependent.