Study of the Effects of Acetonitrile on the Alcohol Solutions by Volumetric and Viscometric Measurements

Abstract

Densities and viscosities of binary mixtures of n-Propanol + Acetonitrile, iso-Propanol + Acetonitrile, n-Butanol + Acetonitrile, iso-Butanol + Acetonitrile n-Pentanol + Acetonitrile, iso-Pentanol + Acetonitrile and Propylene glycol + Acetonitrile have been studied over the entire range of composition (0 < x2 < 1) at 298.15- 323.15K with an interval of 5K. The studied alcohols or glycols are found to be dissolved completely in acetonitrile solutions at any composition. The density of alcohols or glycols in equi molefraction of acetonitrile solution was found to be order of Propylene glycols> iso-Pentanol> n -Pentanol > n-Butanol> iso-Butanol > n -Propanol > iso-Propanol. The value of density of alcohols in acetonitrile increases with the increasing of composition of the alcohols. The increase of density with composition of alcohols can be attributed to solute-solvent interaction. The densities of all alcohols increase with the increase of carbon number which may be depend on the molecular weight of alcohols, structural formula and H-bonding of lcohols. The density of Propylene glycol is higher than the studied alcohols owing to the higher degree of —OH and increasing unsaturation. The densities decrease regularly with the increasing of temperature. This is due to the thermal agitation and hence the weaker the dipole-dipole interaction or dissociation of H-bonding are occurred. The excess molar volumes, VE were calculated from the densities of the mixtures at different temperatures. The values of VE for all the systems are positive over the entire range of composition, showing maxima ~ 0.1-0.2 mole fraction of n-Propanol and ~ 0.4 mole fraction of iso-Propanol, ~ 0.4 mole fraction of n-Butanol ~ 0.4 mole fraction of iso-Butanol, ~ 0.3- ~ 0.4 mole fraction of n-Pentanol, ~ 0.5 mole fraction of iso-Pentanol and ~ 0.5 mole fraction of Propylene glycol . The excess molar volume, VE of alcohols in acetonitrile solutions was found to be order of Propylene glycol >n-Pentanol >n-Butanol >n-Propanol and iso-Pentanol > n-Pentanol and iso-Butanol > n-Butanol and iso-Propanol > n-Propanol. The increasing of VE with carbon chain length of alcohol may be related to increase of the size of alcohols. The values of VE for the studied alcohols increase with the increase of temperature. The observed values of VE for the mixtures have been explained in terms of physical, chemical and geometrical contributions. The viscosity coefficients, n of all the above mixtures at all the six different temperatures have also been determined. The viscosities increase initially slowly up to ~ 0.6 mole fraction of n -Propanol, iso-Propanol, n-Butanol, iso-Butanol, n-Pentanol, iso-Pentanol and Propylene glycol and later on, the viscosity increases sharply until the pure alcohol is reached specially at lower temperature. In pure state the viscosity of alcohols has been found to be in the order of, propylene glycol > iso-Pentanol n-Pentanol > iso-Butanol > n-Butanol > iso-Propanol > n- Propanol There is, a marked decrease in the viscosity with increase of temperature for all the studied alcohols. This ascribed that the alcohol solutions are less stable at higher temperature. The increasing of viscosity with carbon number of alcohols ascribed that the solution resistance increases with the increase of carbon chain length. The linear dependence of In77 against 1/T shows for the all studied alcohols. The branched chain isomers are less stable than linear chain isomer at higher temperature. The excess viscosity, ƞE values are found to be negative, indicating that the acetonitrile solutions of alcohols are non ideal. Excess viscosities are negative at all the temperatures over the entire range of composition for all the systems with minima occurring between 0.6-0.9 mole fraction of n-Propanol, iso-Propanol, n-Butanol, iso-Butanol, n-Pentanol, iso-Pentanol and Propylene glycol. The negative excess viscosity, ƞE of acetonitrile + all the studied alcohols indicate that the dissociation of components through dispersive forces or steric hindrance. The position of minima virtually does not change remarkably with the variation of temperature. The values of the minima are in the order: Propylene glycol ~ iso-Pentanol > n-Pentanol> iso-B utanol>n-Butanol > iso-Propanol> n-Propanol The hydrophobic effect increases with the increasing of carbon chain length of alcohols. This indicates that the ƞE decreases with the decrease of carbon number. The positive VE, negative ƞE, and negative ε for the acetonitrile + studied alcohols systems indicate that dispersion force is dominant. Some disruptive force causing volume expansion may be present and it is more than compensated by volume contraction through the segmental inclusion of acetonitrile. The thermodynamic parameters such as free energy (ΔG*E), enthalpy (ΔH*) and entropy (ΔS*) change of activation for the viscous flow for these systems were examined for the entire range of composition. The free energy (ΔG*) were found to be positive in magnitude indicating that the kinetic species involved in forming cavities or holes in the liquid medium is given by the work required in forming the hole against surface tension of the solution. The negative excess free energy, ΔG*E indicate that the strong dispersion force in alcohols-acetonitrile solution is dominant. The excess properties (VE, ƞE, ΔG*E) data have been fitted by the least square method to the four parameter Redlich-Kister equation and the values of the parameter ai and standard deviation have been reported. The volumetric properties are fully consistent with viscometric and thermodynamic properties.