Effect of substituents on the solubility and the distribution of alkyl-substituted β-diketone iron chelates

The solubilities and the distributions of nine alkyl-substituted β-diketone iron chelates were measured in a number of common organic solvents, in order to establish the effect of substituents. In synthesis of iron chelates, acetylacetone, di-isobutyrylmethane and di-pivaloylmethane chelates were available with red-orange solid, while other chelates were red-orange oil. Using the solubilities and the respective molar volumes of these solid chelates, the solubility parameter values (δM) were calculated. The constancy of the calculated values was taken as evidence of the adequacy of the regular solution concept for explaining the observed solubility trends in the solvents studied. The molar volumes of iron chelates were nearly 1.5 times those of corresponding copper chelates and the solubility parameter values of the former were about the same as those of the latter. In the extraction of iron chelates, the extracted species were identified to be FeA3 (A: β-diketone anion). The extraction constants (Kex) of iron chelates does not depend on the nature of organic solvents. The distribution coefficients (PFe) of iron chelates increase regularly with the increase in the number of additional carbon atoms of the alkyl chain in the chelate molecule. The relationship between the solubilities or the distribution ratios of iron chelates and those of corresponding copper chelates were discussed.