Study of Intermolecular Interactions of Acetophenone and Benzene at 303 . 15 , 313 . 15 and 323 . 15

The behaviour of mixture of acetophenone and benzene as a function of temperature and composition has been investigated by measuring sound velocity in conjunction with density at 303.15, 313.15and 323.15 K. Derived parameters computed from density (ρ) and sound velocity (U) have been used to determine excess molar volumes (VM), excess isentropic compressibilities (KS) and excess inter molecular free length (Lf).The excess functions have been discussed in terms of intermolecular interactions between the components of binary mixture. The validity of various theoretical approaches of liquids has been tested for the system by comparing theoretical sound speeds with those experimentally determined over the entire composition range in the temperature range 303.15-323.15K. The computed results have been fitted to the Redlich-Kister polynomial equation to estimate the smoothening coefficients and standard deviations for this system. The validity of various theoretical approaches of liquids has been tested for the system by comparing theoretical sound speeds with those experimentally determined over the entire composition range in the temperature303.15-323.15K.


Introduction
There has been an increasing interest in the study of systems comprising of unlike components with interactions of varying type.The sign and magnitude of excess parameters have been used to investigate the interactions between the components of a system" Venkatesu et al.(1996)".A commercial use of benzene includes synthesis of different intermediate compounds during the process of manufacture of plastic, dyestuffs, detergents and insecticides.An exhaustive survey of literature reveals that studies on the use of acoustic and volumetric properties and their excess functions in order to understand molecular interactions in binary liquid mixtures of acetophenone and benzene have not been studied so far.Hence excess molar volumes, excess isentropic compressibilities and excess intermolecular free length have been calculated at three temperatures at an interval of 10 o C from 303.15 to 323.15 K. Experimental measurements of sound velocity and density are used to calculate various acoustical parameters viz.intermolecular free length, acoustical impedance, molar Volume and isentropic compressibility at three different temperatures.These acoustical parameters are further used to calculate excess parameters because excess parameters are a better measure of intermolecular interaction as compared to derived ones.The low magnitude values of V E , K S E and L f E indicate interaction of less strength between the components.The theoretical approaches for liquids namely Free Length Theory (u FLT ), Impedance Dependence Relation (u IDR ) and Vandeal Vangeal ideal mixing relation (u VAN ) applied to binary mixture under investigation at all three temperatures reflect the behavior of the system by measuring the deviation of theoretical values of sound speeds from experimental ones.

Experimental Procedure
All the chemicals used were of analytical grade.Acetophenone -(S.D. fine Chem.Pvt.Ltd.) with 98% purity and benzene -(Merck) with 99% purity were used after drying by standard procedures " Reddich et al. (1986), Dean (1987)".The densities of pure liquids and mixtures were measured using a precalibrated bicapillary pyknometer, the accuracy of data being within ± 0.06%, sound velocity was measured by single crystal ultrasonic interferometer (Mittal Enterprises, New Delhi) at 2 MHz frequency and data were accurate upto ± 0.07%.All measurements were made in a thermostatically controlled water bath with temperature accuracy of ± 0.1 o C.The purity of the components was ascertained by comparing their densities and velocities, with the corresponding literature values at 303.15K.(Table.1)

Theory
The experimentally measured density (ρ), and sound velocity are used to evaluate derived parameters like molar volume (V M ), intermolecular free length (L f ) and isentropic compressibility (Ks) using well established relations.
Excess parameters have been calculated from following equation.
All the excess parameters of binary liquid mixtures are fitted to Redlich -Kister " Redlich-Kister, (1948) Where Y represents is V M E , K S E and L f E in corresponding equation .Coefficients A i were obtained by fitting equation to experimental values using a least square regression method.Where X 1 and X 2 are mole fraction of acetophenone and benzene respectively.The standard deviation is calculated by using the following relation.
Where n is the total number of observations and p is the degree of fitting.The theoretical values of sound speeds are evaluated using the following relationships: Sound speed by Jacobson's free length theory "jacobson.(1952)" is calculated using the following formula.
Where K is the Jacobson's constant (K= (93.875+0.375T) 10 -8 ) and depends only on temperature and L f(mix) is intermolecular free length of mixture.
Where x 1 and x 2 are mole fractions and u1 and u2 is speed of sound of acetophenone and benzene respectively.The sound speed in the mixture is given by impedance dependence relation"Shipra and Parsania.(1995)"as Where χ i, Z i and ρ i are the mole fractions ,impedance and density of the i th component respectively

Results and Discussion
The experimental values of density and sound velocity have been used to determine , interaction parameters (ρ) relative association (R A ) for the system under study.The experimental data and derived parameters at 303.15, 313.15 and 323.15K are reported in tables 2-4 respectively.The excess parameters V M E , K S E , L f E and Z E have been plotted against mole fraction of acetophenone in figures 1-4.Table 5 presents the smoothening coefficients and standard deviations at 303.15, 313.15, and 323.15K for the system under investigated.Table 6 presents experimental and theoretical values of sound speed and deviations of these theories from experimental sound speeds at the temperatures take for study.
The deviation of V m E with the mole fraction xi of acetophenone (1) + benzene (2) at 303.15, 313.15 and 323.15 k is represented in figure.1.This shows that the excess molar volumes are always negative for all the studied temperature and for any composition.Roux and Desnoyers"Roux and Desnoyers.(1987)" suggested that V m E is the resultant contribution from several opposing effects.These may be divided arbitrarily into three types, namely, physical, chemical and structural.Physical contributions, that are nonspecific interactions between the real species present in the mixture, contribute a positive term of V m E .The chemical or specific intermolecular interactions result in a volume decrease, and these include charge transfer type forces and other complex forming interactions.This effect contributes negative values of V m E .The structural contribution are mostly negative and arise from several effects, especially from interstitial accommodation and changes of free volume.The negative values for acetophenone + benzene system indicate strong specific interactions through dipolar association between acetophenone and benzene molecules over the entire composition range.
The deviation of isentropic compressibility for acetophenone and benzene system with temperature is recorded in tables 2-4.The excess isentropic compressibility data over the entire composition range are shown in figure.2 at three temperatures taken for the study.K S E increases with rise in temperature but the magnitude of increase is very-very less.The intermolecular free length as shown in tables 2-4 decreases with increase in concentration of acetophenone which implies strong interactions between the components.
The excess intermolecular free length becomes increasingly negative with increase in concentration of acetophenone.Negative L f E values as shown in figure .3exhibit strong interaction.The lessening of interactions at higher temperatures is expected in accordance with the decrease in the negative value of L f E with rise in temperatures.The values of L f E are supported by the variation of K S E which also exhibits insignificant interactions in the system of acetophenone and benzene.
The deviation of excess acoustic impedance Z E are found to be positive as shown in fig. 4. The effect of an increase in the temperature appears to increase the excess properties, suggesting the presence of specific molecular interactions.As the temperature increases the values of K S E and L f E become more negative and Z E becomes more positive this may be due to thermal dissociation of hetero aggregates in liquid mixtures and more interstitial accommodation of one component into another.Relative association is found to increase with the molar concentration of acetophenone +benzene system.Relatively higher values of R A for the acetophenone +benzene system signifies that unlike interactions are relatively strong compared to like interactions.
The experimental data are correlated with composition according to Redlich Kister polynomial equation and the smoothening coefficients obtained using least square method and the standard deviation are listed in table 5.The values of interaction parameter (α) are reported in tables 2-4 for the three temperatures taken for the study.The interaction parameter is positive over the entire range of composition at all the three temperatures.The less positive values of the interaction parameter suggest that dispersion forces are prevalent in the system but the magnitude of these forces is very less which is in support of the results as explained above.