Properties and Derivatives of α-Lipoic Acid

Although a-lipoic acid polymerizes when heated, it has been purified by distillation.

In short-path distillations where the distillate solidifies rapidly, pure DL-a-lipoic acid is obtained.When the distillate is collected in such a manner that it remains liquid, little or no monomer is obtained.

In a distillation where the distillate was collected in a relatively warm (ca., 70") portion of the receiver, only an insoluble rubbery mass was obtained.

In the 50-hour period, the solution protected from light showed no change in ultraviolet absorption. The solution exposed to light, however, shows the characteristic decreasing absorption
at 330 mp and increasing absorption in the 250 mp region.