Aspirin transmogrification

The Science & Technology concentrate about a newly discovered aspirin polymorph triggered a lot of nostalgia (C&EN, Nov. 21, 2005, page 50). I tried to explain in a paper the discrepancies associated with the previously published properties of the acetylsalicylamide isomers (Tetrahedron 1967, 23, 863). I determined that O-acetylsalicylamide rapidly and irreversibly rearranges under a variety of conditions to the N-acetyl isomer. Depending on how the N-acetyl isomer was prepared, during melting observed under a microscope along with differential thermal analysis, it was shown to exist in two different needle forms as well as rectangular plates over a fusion-solidification temperature range of 137-148 ^oC. Perhaps the salicylic acid system has a general proclivity to transmogrify.

Arnold J. Gordon
Greenwich, Conn.