Structural, Spectroscopic and Thermal Analysis of Cocrystals of Carbamazepine and Piracetam with Hydroquinone

Cocrystals of two important active pharmaceutical ingredients, carbamazepine and piracetam, with hydroquinone are reported. Cocrystal formation between the selected APIs and hydroquinone is investigated with the aid of solid-state grinding methods. Both the crystal structures belong to the triclinic, P (1) over bar space group, with the cocrystal involving carbamazepine and hydroquinone having the unit cell parameters a = 6.9725 (14) , b = 8.8175 (18) , c = 15.083 (3) , alpha = 106.96 (3)A degrees, beta = 92.16 (3)A degrees, gamma = 103.23 (3)A degrees, V = 858.0 (4) (3) and Z = 2; and the cocrystal involving piracetam and hydroquinone has the unit cell parameters a = 6.4909 (13) , b = 6.5410 (13) , c = 11.612 (2) , alpha = 103.92 (3)A degrees, beta = 104.53 (3)A degrees, gamma = 91.06 (3)A degrees, V = 461.59 (18) (3) and Z = 2. Analysis of the cocrystals revealed that they are sustained by an alcohol-carboxamide heterosynthon. In addition, the cocrystal of carbamazepine and hydroquinone features an amide-alcohol heterosynthon and an alcohol-alcohol homosynthon. The cocrystal of piracetam and hydroquinone features an amide-amide dimer synthon. Cocrystal formation was evidenced from the shifts in the vibrational frequencies corresponding to the functional groups present on the cocrystal components.