Abstract
Trialkyl urea exists in three polymorphic modifications, stable A, metastable B and unstable C. In order to produce metastable B, the crystallization behavior of this compound in toluene was investigated using an infrared spectrometer. In the case of crystallization temperature at 318 K and 333 K, B, mixtures of A and B or A crystallized initially corresponding to the degree of supersaturation SB. But crystallized B transformed to A after some elapsed time. C cyrstallized at 298 K independently of SB and transformed to A.
The effects of crystallization conditions on the transformation rate constant κ from A to B and on the waiting time θB for the nucleation of B-form were investigated using a 500-ml crystallizer. Furthermore, the detailed crystallization conditions for large-scale production were determined using a 2l and 200l crystallizers.
On the basis of these results, metastable B free from stable A was produced in a 200 l crystallizer.
