CONTROL OF POLYMORPHISM IN TRIALKYLUREA

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