Synthesis of calix[4]arene containing crown ether and urea for anion recognition

Abstract

A calix[4]urea compound, 5,17-diphenylurea-25, 27-dihydroxy-26, 28-dimethoxycalix[4]arene (13) was synthesized from a coupling reaction between 5,17-diamino-25, 27-dihydroxy-26, 28-dimethoxycalix[4]arene (12) and phenyl isocyanate. Two calix[4]crown urea compounds, 5,17-diphenylurea-25, 27-tetraethylene glycoloxy-26, 28-dimethoxycalix[4]arene (17) and 5,17-dihexylurea-25, 27-tetraethylene glycoloxy-26, 28-dimethoxycalix[4]arene (19) were synthesized from coupling reactions between 5,17-diamino-25, 27-tetraethylene glycoloxy-26, 28-dimethoxycalix[4]arene (16) with phenyl isocyanate and hexyl isocyanate, respectively. 1H-NMR titrations of 13, 17 and 19 with anions in DMSO-d6 showed that 1:1 complex and formed complexes with Cl-, Br-, NO3- and H2PO4- to a different extent. The association constants of 13 and 17 towards anions were calculated and found to vary as H2PO4- > Cl- > Br- > NO3- but those of compound 19 were found to vary as H2PO4- > Br- > NO3-> Cl-. The three compounds cannot bind with I-. However, compared to 13 the presence of the crown unit in 17 and 19 resulted in a lower affinity to bind H2PO4-. Upon addition of Na+ and K+, the binding ability of 17 towards H2PO4- was increased due to the cooperative ion-pair enhancement. However, compound 19 did not show the cooperative ion-pair binding effect