Insights into the dehydration behavior of thiamine hydrochloride (vitamin B1) hydrates: part II.

Thiamine hydrochloride (THCl) can exist as an anhydrate (AH) and as a hemihydrate (HH). AH sorbs water as a function of environmental water vapor pressure to form a nonstoichiometric hydrate (NSH). NSH dehydration is initiated at approximately 40 degrees C to yield AH, an isomorphic desolvate (ID) of NSH (Chakravaty et al., 2009, J Pharm Sci). Upon heating, dehydration of HH occurs only at elevated temperatures (>120 degrees C) and is accompanied by chemical decomposition. When heated at reduced temperature (60-90 degrees C) and pressure (20-760 mTorr), HH was incompletely dehydrated with partial loss of long-range lattice order. Complete dehydration of HH to AH was achieved through a solvent-mediated transformation in ethanol. The crystal structures of NSH and HH exhibit pronounced differences in the hydrogen bonding of water. The dehydration mechanism of NSH and HH can be explained by the "continuous and unified" dehydration model.