Self-diffusion and molecular association of acetylsalicylic acid and methyl salicylate in methanol-d4 in the temperature range 278–318 K

Abstract

The effect of concentration on the self-diffusion coefficients of acetylsalicylic acid and methyl salicylate in methanol-d4 is investigated in the temperature range of 278–318 K using NMR. It is found that the self-diffusion coefficients increase along with temperature and fall as concentration rises. Within the limit of an infinitely dilute solution, the effective radii of solute molecules, calculated using the Stokes–Einstein equation shrink as the temperature grows. It is shown that the observed reduction of effective radii is associated with an increase in the fraction of solute monomers as the temperature rises. The physicochemical parameters of heteroassociation of acetylsalicylic acid and methyl salicylate with methanol are determined.