Discovery of New Calcium Etidronates Employing Ultrasound Adapted High-Throughput Methods

The formation of calcium etidronates was investigated employing high-throughput ultrasonic synthesis. In the study of the system CaCl2/H2O3P-C(OH)(CH3)-PO3H2/H2O/KOH three new crystalline products were obtained in dependence of the deprotonation degree of the bisphosphonic acid HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, H2O3P-C(OH)(CH3)-PO3H2) and the sonication time. In a large region of the parameter space and at short reaction times [Ca(HO3P-C(OH)(CH3)-PO3H)(H2O)]·2.5H2O (1) forms. At higher pH [KCa(HO3P-C(OH)(CH3)-PO3)(H2O)]·H2O (2) containing the asymmetrically deprotonated HO3P-C(OH)(CH3)-PO33– ion and [K2Ca(O3P-C(OH)(CH3)-PO3)(H2O)6] (3) with the fully deprotonated ligand are obtained. The crystal structures of 1 and 2 were solved and refined from X-ray powder diffraction data. The thermal decomposition of the compounds was investigated. If exposed to moderate temperatures 1.5 water molecules per formula unit are removed from the crystal structure of 1 and the pseudopolymorphic compound [Ca(HO3P-C(OH)(CH3)-PO3H)(H2O)2] is formed [Uchtman J. Phys. Chem. 1972, 76, 1304−1310]