Synthesis of water-soluble manganese(II) (1-hydroxyethylidene)diphosphonates

Two methods for obtaining water-soluble coordination compounds of manganese(II) from MnSO4, (1-hydroxyethylidene)diphosphonic acid (HEDP) H4L, and monoethanolamine have been proposed. The first method involves precipitation of manganese carbonate from an aqueous solution of MnSO4 and its conversion to sparingly soluble (1-hydroxyethylidene)diphosphonate H2MnL.3H2O by adding H4L. The subsequent reaction with monoethanolamine results in the formation of highly soluble bis(monoethanolamine) (1-hydroxyethylidene)diphosphonate manganese(II) dihydrate (H3NCH2CH2OH)2MnL.2H2O. In the second method, monoethanolamine is added to a solution of manganese sulfate and HEDP. The resulting mixture of manganese(II) (1-hydroxyethylidene) diphosphonate (H3NCH2CH2OH)2MnL with bis(monoethanolamine) sulfate (H3NCH2CH2OH)2SO4 forms a strong solution that is stable during storage. Carbon dioxide released in the reaction of manganese carbonate with HEDP reduces the reactivity of monoethanolamine as a result of the formation of a complex with carbon dioxide HOCH2CH2NHCOO-+NH3CH2CH2OH, which leads to inhibition of the interaction of (1-hydroxyethylidene) diphosphonate H2MnL.3H2O with monoethanolamine. Heating and stirring the reaction mixture obtained by the interaction of manganese carbonate with HEDP for 1 h causes the removal of carbon dioxide, as a result, the subsequent addition of an aqueous solution of monoethanolamine leads to the formation of a transparent solution of manganese(II) bis(monoethanolaminium) (1-hydroxyethylidene) diphosphonate dihydrate (H3NCH2CH2OH)2MnL.2H2O. Inhibition of the reaction by monoethanolamine is thus excluded. An attempt to use an aqueous solution of ammonia instead of monoethanolamine has been unsuccessful. A poorly soluble product of the composition 2(NH4)HMnL·H2MnL is obtained in the reaction of manganese(II) sulfate with the tetraammonium salt of HEDP. The thermal behavior of the obtained compounds has been studied in the temperature range of 25-640°C.