Organic phase characteristics:

If one looks at the organic phase characteristics, it has been observed that the extraction power changes with the class and solvent molecule. In other words, the solvent efficiency remains a specific characteristic of any particular system. For example, generally ethers are better extractants than ketones for hexavalent actinide nitrates while trend is opposite for tetravalent metal halides from aqueous solutions. Within a homologous series, there is a lowering of metal extraction on increasing the hydrocarbon character of the organic solvent. This means that the lengthening of alkyl chain in alcohols, ketones and ethers by introducing methylene group, will cause a decrease in the extractive power. The dipole moments of ethers and ketones are affected by the symmetry of the molecules. As a rule, asymmetric ethers and ketones have a greater efficiency than the symmetric ones. The greater dipole of asymmetric extractants leads to an increased electron density at the donor oxygen and thus, increased tendency to coordinate. The distribution ratio of metal decreases with increasing branching of the alkyl group, the effect is particularly marked when the branching is near the active oxygen.

As of today, the phosphorus bonded oxygen donor extractants have completely phased out the ethers and ketones from technological applications.