Ultrasonic Relaxation and Molecular Parameters of Ethyl Formate

The ultrasonic absorption of pure ethyl formate was measured with the pulse method in the frequency range from 100 kHz to 130 MHz, over the temperature range from 15 °C to 35 °C. In determining absorption coefficients at low frequencies, where the diffraction loss as well as the wave guide effect are appreciable, the appropriate corrections to be subtracted from the measured attenuation were found experimentally. From the derived values of the relaxation parameter, velocity dispersion and molecular parameters of ethyl formate were calculated. The value of the relaxation absorption parameter A was found experimentally to be 180 000×10⁻¹⁷ s² cm⁻¹ at 25 °C, much smaller than the extrapolated value of Subrahmanyam and Piercy. The estimated values were (8.2±0.3) kcal mole⁻¹ deg⁻¹ for the activation enthalpy and (3.2±0.5) kcal mole⁻¹ deg⁻¹ for the enthalpy difference between trans- and cis-isomers of ethyl formate.