Physical characterization of the polymorphic variations of magnesium stearate and magnesium palmitate hydrate species

The anhydrate, dihydrate, and trihydrate phases of chemically pure magnesium stearate and magnesium palmitate have been prepared and characterized as to their structural characteristics. The magnesium palmitate materials were obtained as significantly larger crystals than were the magnesium stearate materials, and the crystals of the dihydrate phase of either material were found to be the most fully developed. The crystal structures of all materials were judged to be very similar to each other, differing primarily in the magnitude of the long (001) crystal spacing. Thermal analysis studies revealed that the water of hydration contained within the dihydrate phases of either magnesium stearate or magnesium palmitate was more tightly bound than was the water of hydration within the corresponding trihydrate phases. These findings provide further support for the structural picture where the water contained in these lattice structures is present between the intermolecular planes.