| Abstract: | - Aims and Background. Ionic liquid application in industry will offer several excellent solutions, but it also means that they
will enter the environment sooner or later. Responsible product design should always take into consideration not only technological
demands, but also the risks arising out of possible toxicity and ecotoxicity. In our strategy we are aiming to understand
the fate of these entities through their life cycle in the environment as a complimentary element of their design. This paper
presents results on the lipophilicity of selected imidazolium ionic liquids, a parameter that plays a key role in environmental
and biological distribution. Additionally, the prediction of the most stable metabolite of a 1-butyl-3-methylimidazolium (BMIM)
cation – a congener representative of this group of compounds is presented.
Materials and Methods Lipophilicity was evaluated by means of reversed phase and immobilized artificial membrane chromatography and further compared
to calculated data. Theoretical prediction of lipophilicity was undertaken using fragmental methodology combined with manual
calculations of the geometric bond factor for quaternary ammonium and the electronic bond factor due to the presence of a
charge.
Results and Discussion All the substances studied are characterized by very low partition coefficients, and lipophilicity varies linearly with elongation
of the n-alkyl chain. Prediction of metabolic routes was based solely on thermodynamic data of the radical intermediates formed
during the reaction with the cytochrome P450 system. The energetically most stable radical structure is generated by hydrogen
abstraction from the gamma position of the BMIM cation.
Conclusions and Recommendations. The experimentally measured and theoretically estimated lipophilicity coefficients obtained for all the
compounds studied generally indicate a relatively low lipophilicity and thus preferable partition to the aqueous phase. By
means of thermodynamic data, it was also confirmed that the energetically most stable radical structure is generated by hydrogen
abstraction from the gamma position on the alkyl chain in the 1-alkyl-3-methylimidazolium cation, as a result of which the
C1 atom is preferentially oxidized.
- * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on 'Chemistry and Environment', 29 August
to 1 September 2004, Bordeaux, France. |
