Effect of alkyl substituents in hydrophobic 8-quinolinol on the extraction of gallium(III) and applications to the separation of gallium(III) from aluminum(III)

The extraction of gallium(III) with newly prepared 5-alkyloxymethyl-8-quinolinol derivatives with alkyl substituent at the 2-position in 8-quinolinol moiety has been studied. The Ga(III)-5-octyloxymethyl-8-quinolinol (HO(8)Q), Ga(III)-2-methyl-5-octyloxymethyl-8-quinolinol (HMO(8)Q), Ga(III)-2-methyl-5-hexyloxymethyl-8-quinolinol (HMO(6)Q), and Ga(III)-2-n-butyl-5-hexyloxymethyl-8-quinolinol (HNBO(6)Q) complexes extracted in heptane from a perchloric acid medium were Ga(O(8)Q)(3), Ga(OH)(H2O)(MO(8)Q)(2) Ga(OH)(H2O)(MO(6)Q)(2) and Ga(OH)H2O)(NBO(6)Q)(2), respectively. The 2-tert-butyl-5-hexyloxymethyl-8-quinolin did not exhibit any reactivity toward gallium(III). The extraction constants for Ga(O(8)Q)(3) (K-ex=[Ga(O(8)Q)(3)](org) [H+](3)/[Ga3+][HO(8)Q](3)(org)), Ga(OH)(H2O)(MO(8)Q)(2) (K-ex=[Ga(OH) (H2O)(MO(8)Q)(2)](org) [H+](3)/[Ga3+][HMO(8)Q](2)(org)), Ga(OH)(H2O)(2)(MO(6)Q)(2) and Ga(OH)(H2O)(NBO(6)Q)(2), which were extracted in heptane from an acidic solution, are 10(3.21+/-0.12), 10(-4.24+/-0.16), 10(-3.84+/-0.16) and 10(-4.07+/-0.07), respectively at I = 0.1 M and 25 degrees C. HNBO(6)Q exhibited very high selectivity toward gallium(III) in the presence of aluminum(III). Even in the presence of a 100 fold excess of aluminum(III) to gallium(III) (1.43 x 10(-5) M), gallium(III) was completely extracted and the distribution ratio of aluminum(III) was found to be less than 2.0 x 10(-3).