EFFECTS OF TETRAALKYLAMMONIUM HALIDES ON THE AQUEOUS SOLUBILITIES OF DISPERSE DYES

Abstract

The solubililities of disperse dyes such as azobenzene and p-hydroxyazobenzene in water and aqueous tetraalkylammonium halide (R4NX) solutions were determined at 5°C intervals from 5°C to 40°C. The tetraalkylammonium halides used in this work are tetramethylammonium bromide (Me4NBr), tetraethylammonium chloride (Et4NCl), tetraethylammonium bromide (Et4NBr), tetraethylammonium iodide (Et4NI), and tetra-n-butylammonium bromide (n-Bu4NBr). All experiments were carried ou_??_ below the critical micell concentration of R4NX.From the results the thermodynamic parameters for the process (A) which consists of the transfer of one mole of the solute from a water environment to an aqueous R4NX solution have been calculated from the equations (1), (2) and (3).Process (A): disperse dye in water (mole fraction N0)→ disperse dye in aqueous R4NX solution (mole fraction N)In any case the solubilities of disperse dyes in aqueous R4NX solutions increase regularly with the R4NX concentration for any particular R4NX. It is to be noted that the effects of R4NX on the solubilities are in the follwing order, Me4NBr<Et4NCl<Et4NBr<Et4NI<n-Bu4NBr. This fact indicates that an increase in the solubitity by addition of R4NX is largely dependent on the alkyl chain length of the added R4NX and suggests that the hydrophobic portion of R4NX plays an important role in enhancement of the solubilities of disperse dyes in water. This salting-in maybe explained in terms of an interaction between the dye and the tetraalkylammonium ion, which is induced by the increase in the structure of water near large nonpolar parts of the dye and the organic ion.The resulting ΔSu•trans• are positive for any particular R4NX and ΔHtrans• are positive except for-p-hydroxyazobenzene in aqueous Me4NBr and Et4NI solutions, so it is clear that the favorable transfer of the disperse dye from a water environment to an aqueous R4NX solution comes from the contribution of entropy term. This result strongly suggests that the increase in the solubilities of disperse dyes is the result of the binding of the nonpolar portions of the tetraalkylammoniumm ion to the disperse dye molecule and that this binding comes from the hydrophobic interaction between the hydrocarbon portions of the R4NX and the nonpolar portions of the disperse dye.