Microwave dielectric spectra and molecular relaxation in formamide–N,N-dimethylformamide binary mixtures

The dielectric dispersion and absorption spectra of formamide (FA), N,N-dimethylformamide (DMF) and their binary mixtures are investigated in the frequency range of 500 MHz to 20 GHz at 30 °C in view of the organic synthesis by microwaves heating using amides solvents. The concentration dependent values of molecular reorientation relaxation times lower than that of the ideal mixing behaviour have been attributed to the cooperative dynamics of H-bonded FA–DMF structures. The molar ratio of stable adduct is 2:1 of FA to the DMF, which is determined from the concentration dependent excess static dielectric constant and the relaxation time plots of these binary mixtures. Electrode polarization effect and ionic conduction in FA and DMF were investigated from their dielectric dispersion spectra in the low frequency region of 20 Hz to 1 MHz.

The non-linear behaviour of static dielectric permittivity and dielectric relaxation time revealed the formation of H-bonding between DMF and FA molecules.Figure optionsDownload as PowerPoint slideHighlights
► Significant dielectric loss at microwave frequencies confirms the suitability of FA + DMF mixed solvents in microwaves assisted organic synthesis.
► Dielectric constant and molecular reorientation relaxation time study confirm that FA + DMF form stable adduct of molar ratio 2:1 of FA to DMF.
► The DMF molecules apt to coalesce in H-bonded FA structures, which results cooperative FA + DMF domains of enhanced molecular dynamics.
► Dielectric study of FA + DMF confirms their use in design of mixed solvents of required solvating power in biological and pharmaceutical preparation.