IONIC LIQUID ACT AS SURFACTANT. SOLVATOCHROMIC PROPERTIES AND INTERACTIONS IN MICELLAR SOLUTIONS

C.G. ADAM, P. M. MANCINI, M. V. BRAVO, AND G. G. FORTUNATO

Florianópolis. Brasil

Conferencia; 10th Latin Conference on Physical Organic Chemistry; 2009

Ionic liquids (ILs) are a class of compounds composed entirely of ions, wich are liquids below 373 K. In recent years, ILs have attracted considerable attention due to their unique properties, such as negligible vapor pressure and non-flamability under ambident conditions. This means that common solvent exposure problems can be avoided. Thus, ILs have the potential to become greener industrial solvents for synthesis, catalysis, analysis and separation, and electrochemistry. One of the attractive aspects of ILs bases on the 1-alkyl-3-methylimidazolium cation [Cnmim]+ is their inherent anphiphilic character as surfactans in some conditions. The multiparametric solvent scales of Kamlet, Abboud and Taft, assign different parameters to each particular solvent characteristic (dipolarity/polarizability, p*; hydrogen-bond basicity, b and hydrogen-bond acidity, a) and all of them are necessary to reflect the overall solvation power of the solvent. Of the three solvent polarity parametres, the p* is the particular significance because it represents a measure of polarity without a contribution from hydrogen bonding interactions. El objetivo de este trabajo es determinar the dipolarity/polarizability en sistemas microheterogeneos formados por bromide y tretrafluor fosfato de 1-octyl-3-methylimidazolium [C8mim]+ and 1-decyl-3-methylimidazolium [C10mim]+ como surfactantes. Para ello, se seleccionaron dos indicadores solvatocromicos N,N-dibuthyl-4-nitroaniline (DBNA) y N,N-diethyl-4-nitroaniline (DENA) y se determinaron las longuitudes de onda de absorcion en funcion de la concentracion de surfactante. The presence of the aqueous phase makes it physicallly impossible to directly measure the spectrum of the indicator in the micellar phase free from contributions of the indicator in the aqueous phase. The UV-vis spectrum of an indicator in the solution is (resulta) a concentrated-weighted sum of the indicators’ spectra in both phases. We have used a modification of the curve resolution method of Kubista et al. to obtain the disered micelar spectra, we analyzed using a curve resolution program written in Matlab for Windows. The algorithm upon which the program is bases is similar to the method described by Kubista et al. The model asumes that only two components contribute to the observed spectra, namely, the indicator in the aqueous and micellar phases. Los resultados reflejan que el DBNA interactua con el sistema micelar reflejando cambios notorios en la longuitud de onda. Se puede observar la formacion de micelas en los sistemas formados por Br [Cnmim]+ y de agregados cuando el surfactante es BF4 [Cnmim]+ . The average p*(micellar) shows that the micellar environment of the solubilized indicators is quite polar considering that the p* of other polar aprotic solvents. This high polarity strongly suggests that the indicators are solubilized in the hydrated polar head-group region of the micelles and not in the nonpolar core.