Li-selective calix[4]arene with trialkyl-monoacetic acid groups: effect of three alkyl branches and t-octyl groups at p-position on selectivity for Li extraction

Abstract

Trialkyl-monoacetic acid derivatives of p–t-octylcalix[4]arene and calix[4]arene were prepared to investigate the effect of the alkyl branches attached to the phenoxy oxygen atoms and the p-position on the selective extraction of Li⁺ over Na⁺. Alkyl branches on the phenoxy oxygen atoms remarkably affected the Li⁺ selectivity, whereas those at the p-position had less effect. The former can contribute to excluding Na⁺ extraction while enabling Li⁺ extraction. Optimal selection of the alkyl branch improves the Li⁺ selectivity of calix[4]arene. However, sterically-hindered p–t-octylcalix[4]arene with three 2-ethylbutyl branches exhibited opposite selectivity.