Diffusion and thermodynamic studies in amide solutions

Abstract

(A) Diffusion Studies A study has been made on the effects of some selected halide salts on the structure of formamide by measuring molecular diffusion coefficients, A neutral molecule, ferrocene v/as allowed to diffuse in pure formamide and in halide salts solutions of formamide and its diffusion coefficients were determined, A test molecule was chosen rather than a test ion in order to avoid electrostatic effects due to ion--ion and ion-dipole interactions. Graphs of diffusion coefficient versus concentration of salts were drawn and the shapes of these curves have been discussed in terms of the "microscopic" and "macroscopic" effects of these salts on formamide structure. Use of two diffusion techniques was made - (i) an electrochemical diffusion method based on the Cottrell equation and (ii) a diaphragm-cell method based on steady-state diffusion. Only the latter was successful. A number of experimental methods were investigated in order to find a suitable analytical method for determining ferrocene (necessary for the diaphragm-cell measurements). A method for preparing radioactive ferrocene and a successful radiometric analytical technique were developed. (B) Thermodynamics Studies In this section the vapour pressures of binary mixtures of water-formamide, water-N-methylformamide and water-dimethylformamide were measured using a Zimmerli manometric gauge over several temperatures. The graphs of partial pressures of water (determined by a transpiration technique) vorsus mole fractions of water are given and explained in terms of the nature of interactions of water and the amides. Bj' means of the Clausius-Clapeyron equation the enthalpies of vaporization of water were calculated and the results versus water mole fractions are shown in graphs. In the case of water-formamide, the enthalpies of vaporization and the enthalpies of viscous flow are compared.