Substituent Effects on Metal-Ion-Capturing Function of Amidinourea Resins

Abstract

The substituent effects on the metal-ion-capturing function of amidinourea resins were investigated. The metal-ion-capturing function likely depends on the steric effects and/or hydrophilic/hydrophobic properties of the three substituents around the capturing sites. In order to clarify these points, we synthesized eight amidinourea resins having acyclic-and cyclic substituents with various numbers of carbon atoms. The adsorption analysis and the water-solubility test indicated that the hydrophilic/hydrophobic properties are more important for the metal-ion-capturing function than the steric effects. From the results including those with the unsubstituted amidinourea resin, we concluded that the optimized structure for metal-ion-capturing amidinourea resins is one with three methyl substituents.

Ion‐exchange kinetics based on film theory

“…Although substitution by alkyl and benzyl groups (resins 1–6) leads to a decrease in the adsorption efficiency because of the corresponding steric hindrance and hydrophobic regions, substitution by pyrrolidil and piperidil groups (resin 7 and 8) leads to an increase in the adsorption efficiency, in which the spread of hydrophilic region overcomes the steric‐hindrance effects. Moreover, it was found that the adsorption efficiency was approximately proportional to the water solubility of the corresponding substituted amidinoureas . These facts show that boundary films are formed at the surface of resins, and the importance of film diffusion in polymer complexes is implied.…”

“…As introduced previously, the adsorption efficiencies of ion‐exchange resins are highly dependent on the hydrophilic and hydrophobic properties of substituents around the ligands . Moreover, the adsorption efficiencies are also affected by the polarization of the polymer chain .…”

“…Moreover, it was found that the adsorption efficiency was approximately proportional to the water solubility of the corresponding substituted amidinoureas. 13 These facts show that boundary films are formed at the surface of resins, and the importance of film diffusion in polymer complexes is implied. In view of chemical engineering, we should recognize that there is a nontrivial difference between the overall mass-transfer coefficient and the liquid-film mass-transfer coefficient.…”

“…Recently, we showed that the metal‐adsorption efficiency of amidinourea resins are strongly effected by substituents around the ligands. As shown in Figure , the percentage of Cu(II) adsorption is very sensitive to the arrangement of hydrophilic and hydrophobic substituents around the amidino group . These resins adsorb Cu(II) selectively at the Schiff‐base moiety .…”

“…As shown in Figure 1, the percentage of Cu(II) adsorption is very sensitive to the arrangement of hydrophilic and hydrophobic substituents around the amidino group. 13 These resins adsorb Cu(II) selectively at the Schiff-base moiety. 14 Although substitution by alkyl and benzyl groups (resins 1-6) leads to a decrease in the adsorption efficiency because of the corresponding steric hindrance and hydrophobic regions, substitution by pyrrolidil and piperidil groups (resin 7 and 8) leads to an increase in the adsorption efficiency, in which the spread of hydrophilic region overcomes the steric-hindrance effects.…”