A Versatile Method of Ambient-Temperature Solvent Removal

Isolation of heat-sensitive reaction products in post-synthesis workup procedures often requires ambient-or low-temperature solvent removal. In the method demonstrated here, solvent evaporation is driven by the pressure gradient between a distillation flask and a chilled receiver in an evacuated closed system containing a minimal amount of residual noncondensable gas. Using an all-glass apparatus, the method is exemplified by evaporation of solvent samples from a distillation flask containing 50 mL of either dimethylformamide, dimethyl sulfoxide (DMSO), or N-methylpyrrolidone (NMP). The distillation flask is suspended in a water bath at temperatures of 18-28 °C, the evaporated solvent is collected in a receiver chilled with liquid nitrogen, and the entire process is completed in 90-140 min. The practicality of this method is further illustrated on a bench-chemistry scale by DMSO and NMP solvent removal from solutions of benzophenone, monitored by gravimetric and ¹H NMR methods. Modification of the demonstrated method to mimic freeze-drying conditions (by reducing heat flow to the distillation flask) can be used for recovery of water-soluble compounds including polymers and biopolymers. We propose the name "cryovap" for this solvent removal method.