Phase Diagram and Dissolution Studies of Mepyrizole (DA-398)/Water System

概要

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Mepyrizole (DA-398) was found to have the two crystalline forms of anhydride and dihydrate. Aqueous solution which contain more than 5 per cent of mepyrizole separate into two liquid layers at temperatures above 45°. It was found from the results of thermal analysis that crystal of mepyrizole dihydrate is transformed into anhydrous form at about 46°. Phase diagram of mepyrizole/water system was obtained by summarizing the results of solubility studies, hygroscopic equilibriums and thermal analysis. Such abnormalities in the vicinity of 46°can be explained as based on the transition between mepyrizole anhydride and dihydrate and the mutual solubility of mepyrizole anhydride and water. From the results of calorimetric analysis, the endothermic reaction given after the dissolution reaction is deduced to the hydration reaction of mepyrizole anhydride in solution. Consequently, the dissolution phenomena of mepyrizole anhydride can be explained as follows : mepyrizole anhydride [MP]_<solid> first dissolves quickly in water as anhydride [MP]_<aqueous> and then gradually changes into dihydrate [MP.2H_2O]_<aqueous>. [MP]_<solid>→[MP]_<aqueous>→[MP.2H_2O]_<aqueous>
1971-11-25