Ultrasonic and thermodynamic effects of self-association of aliphatic alcohols in cyclohexane. III. Secondary and tertiary butanols

The ultrasound velocities in and densities of mixtures of
cyclohexane with 2-butanol
{x₁sec-C₄H₉OH+(1-x₁)C₆H₁₂} and with 2-methyl-2-propanol
{x₁tert-C₄H₉OH+(1-x₁)C₆H₁₂}
have been measured at 293.15K. The adiabatic compressibility coefficients,
β_s=-1/V(∂V/∂p)_s,
and compressibilities, κ_s=-(∂V/∂p)_s,
as well as the excess molar volumes, V^E,
and free intermolecular lengths, L, were determined in the whole concentration
range for both the systems studied. Using the measurement results in
connection with literature data, the isothermal compressibility
coefficients, β_T=-1/V(∂V/∂p)_T, and isochoric
molar heat capacities, C_v, for the pure components were calculated.
The above values were used to estimate the excess adiabatic
compressibilities, κ_s^E, of the mixtures under test
accoring to the thermodynamically rigorous definitions recommended by Benson
et al. The dependences of those excess functions on the mixture
composition, reproduced by the Redlich-Kister equations, were
compared and discussed in terms of the free intermolecular length and
other factors affecting the self-association of alcohols (molecular
geometry of the hydro-carbon chain and position of the OH group).