Ternary copolymers of hemin, styrene, and 1‐vinylimidazole or 1‐vinyl‐2‐methylimidazole as cyanide ion exchanger

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Abstract
Ternary copolymers, involving hemin (H) (ferri‐protoporphyrin IX chloride), styrene, and 1‐vinylimidazole (VI) or 1‐vinyl‐2‐methylimidazole (VMI) in the different proportions, were synthesized by radical copolymerization. All the copolymers obtained were insoluble in aqueous solvents. No dissolution of H from the copolymers was observed even when the extraction with 0.5N NaOH or HCl was allowed to continue for a total time of 50 days. To clarify the functional capabilities of the ternary copolymers as a cyanide ion exchanger, the adsorption of cyanide ion onto the copolymers was investigated at different pHs. The amount (Acn) of the adsorbed cyanide ion was found to be dependent on the content of H residue in the copolymer, thus indicating that the adsorption site for the cyanide ion consists of ferri‐protoporphyrin IX (FP). Another important feature is that Acn increases in proportion to the VI or VMI content of the copolymer. This result was discussed in terms of the coordination structure of the FP and also of the coordination reaction of cyanide ion to the FP.