Strongly basic macrocyclic triamines, 1,5,9-triazacyclododecanes for solvent extraction of gold(I) cyanide

Solvent extraction of gold(I) dicyanide anion from alkaline gold(I) cyanide solution using unusually basic amine extractants was conducted. 1,5,9-Triazacyclododecane (4) is known as an unusually basic macrocyclic amine having pKa=12.3–12.7, and is thus a good candidate as a basic amine extractant. Three lipophilic derivatives of 4 expected to stay in the organic phase during gold solvent extraction were synthesized. N-Dodecyl-1,5,9-triazacyclododecane (3) was prepared from 1,5,9-triazacyclododecane-2,4-dione (1) by N-alkylation with n-dodecyl iodide and then reduction with BH3-THF. N,N′-Didodecyl-1,5,9-triazacyclododecane (5) and N,N′,N′′-tridodecyl-1,5,9-triazacyclododecane (6) were efficiently synthesized by selective di-alkylation of 4 with n-dodecyl iodide, and by reductive alkylation of 4 with n-dodecanal, respectively. The extractants 3 and 6 showed pH50=10.5, which is the minimum value required for practical application.