Molecular Interaction between Benzoic Acid and Florite and Complex Formation

The molecular interaction between benzoic acid and florite R (porous calcium silicate) in solid state was studied by using powder X-ray diffraction analysis, infrared (IR)-spectroscopy, differential scanning calorimetry and thermogravimetric analysis. It was found that the mixing ratio, relative humidity and heating significantly affected the molecular behavior of benzoic acid in the physical mixture. In low mixing ratios (up to 30% benzoic acid), benzoic acid was almost transformed to amorphous calcium benzoate within a few hours after mixing. Storage of the physical mixtures containing benzoic acid in the ratio of 40—60% at high relative humidity, or heating them in sealed ampules, accelerated the rate of transformation of benzoic acid to amorphous calcium benzoate and also allowed the formation of a crystalline complex of the following composition: (C6H5COO)2 Ca*C6H5C00H*H20. The same complex was successfully prepared using benzoic acid and calcium benzoate trihydrate in a 1:1 molar ratio by coprecipitation from an aqueous solution, by mechanical grinding and by heating in sealed ampule at 100 °C. © 1992, The Pharmaceutical Society of Japan. All rights reserved.