Study of the behavior of the methyl orange (MOR) dye in binary mixtures using amphiprotic solvents

The solvents influence on chemical and physical processes, reaction rates, mechanisms, selectivity, chemical equilibrium, position and intensity of spectral absorption bands, liquid chromatographic separations.1 The behavior of MOR in binary mixtures of water (W) (Solvent 1, S1) and methanol (M), ethanol (E), n-propanol (NP), iso-propanol (IP) or t-butanol (NB) (cosolvent or solvent 2, S2) was studied in order to investigate the behavior of the MOR in amphiprotic solvents. The energy transition (ET) values were plotted as a function of the molar fraction of the cosolvent (X2) (Figure 1) and the experimental values for each binary mixture were fitted according equation described to Rosés et al.2 The results (Table 1) show a good nonlinear fit (SD ≤ 0.191). The ET(MOR) values are in agreement with the experimental values. The parameters which define the preferential solvation (f2/1 and f12/1) indicate a tendency for the indicator MOR to be solvated by the cosolvents (S2, R-OH) and by the mixture of solvent 1 (S1, water) with solvent 2 (S12), rather than S1. In mixed solvents the solutes can interact to a different degree with the components of the mixture and this difference in the interactions is reflected in the composition of the solvation microsphere. The results show new potentialities of the methyl orange indicator.