I got a higher extraction of aromatic compounds in BMIM NTF2 than BMIM Pf6.
What interaction is possible between ionic liquids and aromatic compounds, what helps with the extraction?
HPLC results are not showing any change in retention time of aromatic compounds.
if you have any solution please share.
A possible reason might be the higher delocalisation of the charge in the BTA salt.
the interaction between the extracting solvent (Ionic liquid) and solutes is determinant. Since the aromatic nitro-compounds are highly polar, the dipole-dipole interaction with BMIM] NTf2 (that is more polar than BMIM] PF6) is better and stronger. It should be noted that the exact meaning of “polarity” for ILs is complex, since both cations and anions can have their own distinct interactions. i think, in BMIM NTF2, negative charge is localised across the S–N–S moiety but in the case of BMIM Pf6, symmetrical shape and low charge density of the anion may results lower nucleophilisity and perhaps, polarity
On polarity scale, BMIMPF6 is more polar than BMIMNTf2. So higher polarity of aromatic nitro compound can't be correlated with the polarities of ionic liquids. However, [NTf2] is least nucleophilic anion than [PF6] because of its more delocalized negative charge than [PF6]. Thus, possibly BMIMNTf2 is offering more pie-pie interaction with aromatic compounds than BMIMPF6. Another reason might be that nitration of aromatic compound increases acidity of the compound and [NTf2] because of its more basic nature can effectively bind with aromatic nitro compound than less basic [PF6] anion.
I can give an example as a fundamental clue to the point: Our recent classical and Car-Parinello MD simulations [1] have revealed that [BMIM]PF6 ionic liquid form ion pairs leading to no solubility in water. On the contrary, in [BMIM]BF4 anion interact effectively with water. The reason leis on the fact that the charge on the anion is distributed over 6 F atoms in PF6 (6 F-0.18) but over only 4 F atoms in BF4 (4 F-0.33). Astonishingly, water solvent in both cases involves molecules with two H atoms each having the same but positive charge as F atoms in BF4 e.g., (2 H+0.32). This plus other evidences, which have been found by the Car-Parinello MD simulations and ab initio quantum chemical calculations, offer the key point to pursue and explore the extent of solubility of matters in hydrophoblic and hydrophilic ionic liquids.
[1] M.H. Ghatee, A.R. Zolghadr, J. Phys. Chem. C, 2013, 117, 2066–2077
Maybe the lower viscosity of BMIM NTf2 is responsible for a better mass transfer of your aromatic compunds into the IL compared to the BMIM PF6. That should result in an increased extraction efficiency, independent of polarity properties.
Before an equilibrium between the phases has been reached, the lower viscosity of BMIM NTf2 compared to BMIM PF6 should lead to higher mass transfer rate of the aromatics in the NTf2 salt. You can thus ignore the viscosity only when the equilibrium has been reached. Have the experiments been performed to reach equilibrium? How long did you run the extractions and from what solvent and temperature?
Yes, i did
40 min run the extraction from water at room temperature
I would suggest to run the experiment again, over night or longer and check if the difference is still observed. 40 minutes might be not enough time for the equilibrium...
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