Abstract
The formation of solid complex of theophylline and aliphatic organic dibasic acid was tried in aqueous solution. Consequently, solid complexes were formed from theophylline with oxalic acid in a molar ratio of 2 : 1, and with maleic acid, malonic acid and glutaric acid in a molar ratio of 1 : 1. However, no solid complexes with succinic acid or adipic acid were formed. The type of bonding of theophylline with an organic dibasic acid was considered to be an intermolecular hydrogen bond between the carboxyl group of the organic acid and nitrogen at the 9-position of theophylline. The reasons that 1 : 1 complexes tend to be formed were presumed. With a decrease in pKa, organic acid had a tendency to be stabilized thermally by the formation of its solid complex and the heat of reaction to form solid complex from crystals of its component also increased except maleic acid.
