As extraction proceeds, acid from the aqueous phase gets reacts with the amines and forms reaction complex. This reaction complex of succinic acid-TOA is soluble in organic phase. At quilibrium the distribution coefficient (𝐾 𝐷 ) is the ratio of concentration acid in the organic phase (𝐶 𝐴 ̅̅̅ ) to the concentration of acid in the aqueous phase (𝐶 𝐴 ) and is given as [18] ,