Polymorphic Phase Transitions in Carbamazepine and 10,11‐Dihydrocarbamazepine

Temperature‐induced phase transitions in carbamazepine (CBZ) and 10,11‐dihydrocarbamazepine (DHC) were studied by simultaneous differential scanning calorimetry–X‐ray diffraction in this work. The transitions generally involve a transitional melt phase which is quickly followed by recrystallisation. The expansions of the unit cell as a function of temperature could be quantified and allow us to determine a directional order of stability in relation to the lattice constants. Dihydrocarbamazepine form II undergoes a conversion to form I by a localised melt phase. Carbamazepine (CBZ) form IV converts to form I at 182 °C, again by a localised intermediate melt phase. CBZ form II converted to form I at 119 °C by a pathway that appears to have included some melting, and form III underwent a part melt‐recrystallisation and a part sublimation‐recrystallisation to form I.