Preparation and properties of (1-hydroxyethylidene) diphosphonic acid aminium salts

An overview of the preparation methods and properties of (1-hydroxyethylidene) diphosphonic acid aminium salts is presented. (1-Hydroxyethylidene) diphosphonic acid with monoethanolamine forms a crystalline compound, which, according to the elemental analysis and XRD data, is ternary C(CH3)(OH)[P(O)O-NH3+CH2CH2OH]3[P(O)(OH)] amine salt. A characteristic feature of the derivatives of (1-hydroxyethylidene) diphosphonic acid and tris (hydroxymethyl)aminomethane is the formation of glassy and resinous products. Their composition Н4L∙4NH2C(CH2OH)3 corresponds to 4 base molecules per 1 tetrabasic acid molecule. The addition of 4 molecules of the primary amine occurs both when the ratio of the initial reagents is 1: 4 and 1: 3. The polymer structure and the presence of strong hydrogen bonds in the Н4L∙4NH2C(CH2OH)3 compound lead to its very low solubility in organic media and good solubility in water. The solubility of Н4L∙4NH2C(CH2OH)3 in methanol is 1.8 g per 100 mL. The reaction of (1-hydroxyethylidene)diphosphonic acid with para-aminobenzoic acid leads to the formation of bis(4-carboxyphenylamine)(1-hydroxyethylidene)diphosphonate C(CH3)(OH)[P(O)(OH)O-NH3+C6H4С(О)ОН]2. In a crystal, this compound consists of the anion of the double-deprotonated (1-hydroxyethylidene)diphosphonic acid C(CH3)(OH)[P(OH)(O)O-]2 and two amine cations NH3+C6H4С(О)ОН. The tetrabasic acid binds 3 molecules of morpholine, giving tris(morpholinium)(1-hydroxyethylidene)diphosphonate H4L·3HN(CH2CH2)2O in the form of a white powder that dissolves well in water, methyl and ethyl alcohols. The solid complex of morpholine with (1-hydroxyethylidene)diphosphonic acid does not crystallize from various solvents, which may be caused by the oligomeric form of morpholine included in the molecule of the complex with H4L.