Diffusion in n-alkyl benzenes. Diffusion of 1,1,2,2-tetrabromoethane in a homologous series of n-alkyl benzenes

Abstract

The dependence of the product D_0η0(where D₀ is the interdiffusion coefficient at infinite dilution and η₀ is the solvent viscosity) on the solvent molar volume V_m has been investigated for 1,1,2,2-tetrabromoethane diffusing in n-alkyl benzenes at 20, 25, 35 and 45°C.

The experimental results at 20, 25 and 35°C show that D_0η0 is an increasing function of V_m. Anomalous in this respect are the data for benzene and toluene which do not show the progressive increase of D_0η0 with V_m. The dependence of D_0η0 on V_m at these three temperatures was found to be non-linear over the entire range of V_m employed in the present study and no reasonable extrapolation to zero V_m could be carried out.

The plots of D_0η0 against V_m at 35 and 45°C show a discontinuity at C₆/C₇, the effect becoming more pronounced with increasing temperature. A qualitative explanation for this effect is suggested.

The Stokes–Einstein radius (r) at 45°C calculated for 1,1,2,2-tetrabromoethane using the expression (D_0η0)V_m=0 =kT/6πr, for the solvent range C₀-C₆, was identical to the molecular radii obtained by other methods.