DIFFUSION-COEFFICIENTS OF SUBSTITUTED BENZENES AT HIGH DILUTION IN WATER

The interdiffusion coefficient D-aw of six hydrophobic benzene derivat ives (a = chlorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, bro mobenzene, 1,2-dibromobenzene, 1,4-dibromobenzene) in aqueous solution (w) at 25 degrees C is measured at different concentrations below 10( -5) solute mole fractions using the Taylor dispersion technique. On th e basis of the experimental uncertainty around 4%, a distinct concentr ation dependence is not recognizable. Analysis of the interdiffusion c oefficients with the Stokes-Einstein equation shows greater D-aw(infin ity) values than expected from the limit of a complete solute-solvent contact (''stick limit''), and in addition substance-specific deviatio ns. Chemical engineering correlations for D-aw(infinity) presently ava ilable from the literature yield unsatisfactory results for this class of predominantly hydrophobic compounds.