DIFFUSION-COEFFICIENTS OF SUBSTITUTED BENTENES AND ALCOHOLS AT HIGH DILUTION IN OCTAN-1-OL

Interdiffusion coefficients D-ao in octan-1-ol of benzene, toluene, ch lorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, bromobenzene, 1 ,2-dibromobenzene, and 1,4-dibromobenzene have been measured at 25 deg rees C at average solute mole fractions from 0.001 to 0.000 05 using t he Taylor dispersion technique. The D-ao values range from 0.5 x 10(-9 ) m(2)/s to 0.3 x 10(-9) m(2)/s with standard deviations below 4% in a ll but the highest dilutions and show only minor (and statistically in significant) variations with solute concentration. In addition, corres ponding interdiffusion coefficients of methanol, ethanol, propan-1-ol, butan-1-ol, 2-methylpropan-2-ol and phenol were determined at average mole fractions around 0.0004. For both groups of compounds, distinct but separate dependencies of D-ao on molecular size were observed. The results are discussed from the viewpoint of the Stokes-Einstein equat ion, and in comparison with literature data for the corresponding diff usion in water. The analysis reveals different dependencies of the int erdiffusion coefficients on solvent viscosity for the two classes of c ompounds. Current chemical engineering correlations to predict D-ao at high dilution (D-ao(infinity)) yield only moderate agreement for the benzenes and perform particularly poorly for the alcohols, suggesting that additional experimental work is needed to better understand molec ular diffusion in more viscous media.