Difference between extractants types:

A major difference between these extractants types  is the role of water. Strongly polar organophosphorus compounds compete favourably with water and can replace water molecules in the inner coordination sphere of the metal ion. With ethers and ketones, water is a necessary part of the complex. Take the example of extraction of uranyl nitrate; it is transferred to dibutyl carbitol with four molecules of water while it goes all alone in TBP. Moreover, when phosphorus compounds are used as extractants, it is easier to evaluate the degree of solvation while in the case of class (i) extractants, it is difficult. In the latter case really, a number of mixed hydrates - solvates coexist in equilibrium. In this regard a typical case, worth mentioning is the variation in the water molecules in the extracted species when iron (iii) chloride is extracted in ether.

With the above background, we should now look into important specific characteristics of the two categories of solvating extractant.