Abstract: Six monohexadecyl hydrocarbylphosphonate extractants with highly steric hindrance,R¹ (R²O)P(O)OH, where R² represents -CH(C₆H₁₃) C₂H₄CH(C₂H₅) C₄H₉ or -CHC₆H₁₃)CH₂CH(CH₃)C₆H₁₃, as well as R¹represents CH₃, C₂H₅, i-C₃H₇, cyclo-C₆H₁₁ and C₆H₅, respectively, were synthesized and their extraction behaviours on Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ), Fe(Ⅲ)and Ca were investigated. The structural variation of the hydrocarbyl groups in the extractant molecules has the different influences on the extractability of various metal ions.The compounds with isopropyl and cyclohexyl, having higher steric hindrance, possesshigher separation ability of Co and Ni, and they are a new class of extractants superior tomono-2-ethylhexyl 2-ethylhexyl phosphonate (P-507), which has already been employed inindustry.

Key words: monohexadecyl hydrocarbylphosphonate, NI(Ⅱ), Co(Ⅱ), extraction, organophosphorus compound