Molecular association between N,N-dimethylformamide and acetonitrile using dielectric relaxation measurements in the microwave region

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Abstract
Using a standing wave X-band microwave technique, the dielectric constant ( epsilon ") and dielectric loss ( epsilon ') of dilute solutions of N,N-dimethylformamide (DMF), acetronitrile (AN) and four binary mixtures of DMF and AN have been measured. Measurements were carried out in benzene solution at 9.885 GHz and 15 degrees C. Similar measurements have also been made on a (DMF+AN) mixture containing 50 mol.% AN at 15, 20, 25 and 30 degrees C. Following the single-frequency concentration variational method, the dielectric relaxation times ( tau ) for all these systems have been evaluated. The variation of relaxation time as a function of AN molar fraction in (DMF+AN) mixtures shows a solute-solute type of molecular association between DMF and AN at all compositions. The energy parameters ( Delta Fepsilon , Delta Hepsilon , Delta Sepsilon ) for the dielectric relaxation of the 50:50 mol.% mixture at various temperatures have been found to be in fairly good agreement with the corresponding energy parameters for the viscous flow. The entropy of activation for the relaxation process and for the viscous flow has been found to be negative.

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