Diazopyrazolones as weak solvent extractants for copper from ammonia leach solutions

Potentially bidentate 4-diazopyrazol-5-one ligands carrying a range of substituents can readily be prepared by coupling arene diazonium salts on to the appropriate pyrazolones. Hydrocarbon-soluble versions are shown to be suitable reagents for the recovery of copper by solvent extraction from ammoniacal leach solutions, and potentially have greater resistance to chemical degradation than the beta -diketones which have been used. Cobalt(III), nickel(II), copper(II) and zinc(II) complexes with 4-(4-tert-butylphenylazo)-3-methyl-1-phenyl-5-pyrazolone (HL) have been characterised by X-ray crystallography. The significant deviations from planar coordination geometry which are observed in [CuL2] and [CuL'(2)], where HL' is 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone, arise from interligand repulsion, and account for the relatively weak complexation and ease of stripping of copper from this class of extractant. The cobalt(III) complex [CoL3]. 3MeOH and the high spin nickel(II) complex [NiL2(MeOH)(2)]. 2MeOH both have approximately octahedral geometries, but show significantly different bite distances in the chelate rings. The zinc complex [ZnL2] has a pseudo-tetrahedral structure.