Ion Pair Formation between Tertiary Aliphatic Amines and Perchlorate in the Biphasic Water/Dichloromethane System

The ability of aliphatic amines (AAs), namely, tripropylamine (TPrA), trisobutylamine (TisoBuA), and tributylamine (TBuA), to form ion pairs with perchlorate anion (ClO4−) in biphasic aqueous/dichloromethane (CH2Cl2) mixtures containing ClO4− 0.1 M has been demonstrated by GC with flame ionization (FID) and mass detectors (MS) and by NMR measurements. The extraction efficiency of the AAs to the organic phase was modeled by equations that were used to fit the experimental GC data, allowing us to determine values for KP (partition constant of the free AA), KIP (formation constant of the ion pair), and KPIP (partition constant of the ion pair) for TPrA, TisoBuA, and TBuA at 25 °C. Ion pairs were shown to form in CH2Cl2 also when ClO4− is replaced by other inorganic anions, like NO3−, ClO3−, Cl−, H2PO4−, and IO3−. No ion pairs formed when CH2Cl2 was replaced by n-hexane, suggesting that aliphatic amine ion pairs can form in polar organic solvents but not in nonpolar ones.