Temperature-dependent conglomerate crystallization of carbonatobis(ethylenediamine)cobalt(III) bromide and its application to kinetic optical resolution

Abstract

The binary and ternary solubility diagrams of [Co(CO₃)(en)₂]Br (en = ethylenediamine) have been determined at 5–70°C. It was found that the bromide exists as a racemic compound dihydrate below 15.0 °C and as an anhydrous conglomerate above this temperature. The conglomerate is kinetically resolved by crystallization in the presence of chiral additives, Δ-[Co(glyO)(en)₂]Br₂(glyO = glycinate) and Λ-[Co(ox)(en)₂]Br (ox = oxalate), at room temperature. The same resolutions utilizing racemization of [Co(CO₃)(en)₂]Br were also attempted at 40 °C.