Acylpyrazolones

Acylpyrazolones (24) also form neutral /3-diketonate-type complexes suitable for extraction of a range of metals into organic solvents and have been considered171 as alternatives to LIX 54 for use in ammoniacal leach circuits. Although they are stronger extractants than LIX 54,4,172 the low solubility of their metal complexes has limited their usefulness in Cu recovery.171 The structurally related diazopyrazolones (25) have pHi/2 values, ca. 3.7, and their chemical stability on contact with ammoniacal feeds meets the requirements of the flowsheet outlined above, but their very intense colors may restrict their use as commercial extractants.173,174 The bulk of the arylazo... 

Mundra, S.K. Pai, S.A. Subramanian, M.S. Synergistic extraction of uranyl ion with acylpyrazolones and dicyclohexano-18-crown-6, J. Radioanal. Chem. Articles 116 (1987)203-211. 

Complexation rate constants for tervalent lanthanide-acylpyrazolone complexes in the toluene-water phase pair... 

Significant differences are seen between Cyanex 272 and the acylpyrazolones. The extractibility of the triva-... 

K. Inaba, H. Freiser, and S. Muralidharan, Effect of kinetic factors on the efficiencies of centrifngal partition chromatographic separations of tervalent lanthanides with bis(2,4,4,-trimethylpentyl)phosphinic acid as extractant, Solvent Extract Res. Dev. Japan 1 13 (1994). G. Ma, H. Freiser, and S. Mnralidharan, Centrifugal partition chromatographic separation of tervalent lanthanides using acylpyrazolone extractants, A aZ. Chem. 69 2835 (1997). 

A convenient method of synthesis of acylpyrazolones, reported by Jensen,155-157 is the acylation in the 4-position of A-substituted-5-pyrazolones in basic dioxane with subsequent acidification. 

Okafor synthesized fluorinated acylpyrazolones by interaction of A-substituted-5-pyrazolones and fluorinated anhydrides in pyridine.158,159 Another modified procedure starts from 4-acyl-1,2-oxazolin-5-ones, which react with substituted hydrazine affording 4-acyl-5-pyrazolones.160... 

The archetype of these molecules contains R1 = R3 = Ph and R2 = Me, and modifications generally involved the R3 fragment. Variations in R1 and R3 have also been reported.161-165 The substituents can greatly influence not only the physico-chemical properties of corresponding metal derivatives, such as solubility in water of bis(acylpyrazolonate)diorganotin(IV) when R1 Me,163 but also their crystal structures when R1 = 4-CF3-Ph trans-octahedral bis(acyl-pyrazolonate)diorganotin(IV) can be isolated in either syn or anti isomeric forms.164,165... 

Crown-ether functionalized acylpyrazolones (30) and (31) have been synthesized and found effective as metal-ion-selective extraction agents.192 Two chelating acylpyrazolone moieties were linked to each other by aliphatic chains (32) or aromatic moieties (33) and shown to be able to... 

A similar limitation has been recently reported for the synthesis of unsaturated triple-stranded binuclear lanthanide helicates with bis-bidentate acylpyrazolone ligand strands and some analogues of bis- S-diketonate ligands, for which only the ethyl spacer was found to form the targeted helical complex (Semenov et al., 2008). 

Lanthanide acylpyrazolonates Synthesis, properties and structural features 12UK1159. 

Significant differences are seen between Cyanex 272 and the acylpyrazolones. The extractibility of the trivalent lanthanides is higher with Cyanex 272 than with the acylpyrazolones, where HPMBP shows better extraction than HPMCP. The stability constants of the lanthanides increases from the light to heavy, and the values for the Cyanex 272 and HPMCP complexes are larger than those of HPMBP. The separation factor (or selectivity) for a pair of lanthanides is much better with Cyanex 272 than with HPMBP or HPMCP, which have similar separation factors. 

The lanthanide complexes lack distinct ultraviolet-visible spectra and, hence, kinetic information on their complex formation and dissociation reactions was obtained indirectly by the metallochromic indicator method. These studies indicate that in the case of the Cyanex 272 complexes, the CPC efficiencies are mainly limited by the slow dissociation of the M(HL2)HL complex at the heptane-H20 interface. In the case of the complexes of the acylpyrazolones, the CPC efficiencies are again limited by the dissociation of the lanthanide-pyrazolone complexes at the organic-aqueous interface with the rate-limiting step being the dissociation of the ML complex. It was also shown that because the dissociation reactions are interfacial separations, efficiencies can be dramatically improved by the addition of surfactants like Triton X-100 to the organic phase and by... 

Ma, G. Freiser, H. Muralidharan, S. Centrifugal partition chromatographic separation of tervalent lanthanides using acylpyrazolone extractants. Anal. Chem. 1997, 69, 2835. 

HALF-SANDWICH DERIVATIVES WITH ACYLPYRAZOLONE LIGANDS... 

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