A Simple and Convenient Method for Crystallization ot Thermally Unstable or Highly Soluble Compounds The usual crystallization procedure of organic compounds reported in textbooks and lab manuals involves heating the solid compound in the least amount of the proper solvent in order to obtain a real solution a t high temperatures. This conventional procedure requires two attributes of the crystallized compound:
(1) The compound t o be crystallized should he sparingly soluble or, better, insoluble in the crystallization solvent a t room temperature but should dissolve well a t high temperatures. (2) The compound does not decompose or rearrange by heating in the crystallization solvent. It is, however, possible t o crystallize compounds that do not meet these conditions. Heat-liable or compounds that are highly soluble a t room temperature have been crystallized in our laboratories by the following simple technique. A highly concentrated solution of the compound to he crystallized is prepared in a solvent having a very low freezing point, such as dichloromethane (m.p., - S I T ) . The clear concentration solution, preferably in a n Erlenmayer flask, is then cooled in a proper cold bath, using liquid nitrogen and acetone, or isopropanol, or something else appropriate t o the freezing point of the crystallization solvent. The cooled solution is scratched by a stirrer t o inhance crystallization. The crystallized material is then filtered quickly using cooled filtering apparatus. Many heat-liable compounds or highly soluble materials (i.e., soluble in all ordinary crystallization solvents) such as some N-substituted isoimides were crystallized by this technique.
Thanun M. Pyrladl University of Baghdad Baghdad, Iraq
Volume 64
Number 9
September 1987
813
