Thermophysical properties of Ethyl acetate with 1-Alkanol binary mixtures at 303.15 K.

Introduction

In continuation of our studies on thermodynamic, acoustic and transport properties of some binary mixtures of ethyl acetate with 1-alkanols the present paper reports the excess molar volume (V_m^E) and excess molar refraction (R_(m )^E) for binary solvent mixtures containing ethyl acetate, 1- methanol, 1-ethanol, 1-propanol, 1-butanol, 1-hexanol, 1- octanol over the entire mole fraction range at 303.15 K. Density, refraction index and speed of sound represent thermo physical properties of a fluid that characterize each pure substance in the liquid state, as well as their mixtures. Knowledge of these properties is very important for design and operation of separation processes and equipment in the chemical industry, calculation of heart exchangers, fluid transport, as well as for the development of new thermodynamic models. Theoretical significance of the investigation of thermodynamic as well as transport properties of liquid mixtures is reflected in extension of the database with new experimental values [1]. Various substance and their mixtures are used in the industry and for many of them literacy values of thermodynamic properties and related quantities do not exist. On the other hand, density and the excess molar volume, primarily, but also other deviation properties, are the best indicators of molecular interactions, structural changes and packing effects in mixtures. Ethyl acetate is highly miscible with all organic compounds, such as glycols, ketones, alcohols, and esters [2]. It is most commonly used in mixtures with alcohols, and a combination with 20% ethanol found application as an excellent solvent for cellulose acetate. Alkanols are considered as amphiphilic materials of biological and industrial importance is a high energy reaction solvent having a wide range of application. Alkanols are self-associated through hydrogen bonding [3].

Therefore, interesting result may be obtained regarding molecular interaction between these component molecules in the binary mixtures. In this paper we report measured density (ρ), ultrasonic velocity (u) and refractive indices (n) of the binary mixtures of ethyl acetate with 1-methanol, 1- ethanol, 1- propanol, 1- butanol, 1- hexanol and 1- octanol along with those of the pure liquids at 303.15 K, covering the entire composition range expressed by the mole fraction (X1) of ethyl acetate. From the experimental values of ρ, u and n the molar refraction (Rm), excess molar refraction (R_m^E), and excess molar volume (VE) have been calculated. Refractive index is one of the most important properties of liquid. The measurement of the refractive index of liquids is in important work in engineering and science [4]. Transmission and refraction detections near critical angles related to total internal reflection are common methods in refractive index measurement. When a ray of light passes from one medium to another, it suffers refraction, that is change in direction. If it passes from a less dense to a denser medium, it is refracted towards the normal so that the angle of refraction (r) is less that the angle of incidence (I) the refractive index (n) of the medium is the ratio of velocity of light in vacuum to the velocity of light in the medium. Refractive index is an important additive property of the structural arrangement of atom in molecule refractive index can be measured easily with high degree of accuracy.

Materials and Methods

The studies of refractive indices are being increasingly used as tools for investigation of the physical properties of pure components and the nature of intermolecular interaction between the liquid mixture constituents. Refractive indices measurements of binary liquid mixtures are essential for determination of composition of binary mixtures usually for non-ideal mixtures where experimental measurements are performed directly over the entire range of composition. The review of literation on acoustical studies of solution reveals that refractive indices measurements are also used to estimate the different elastic properties of the molecule from which the type of molecular interactions can be very well understood [5].

Pandey have made refractive indices measurements in liquid mixtures and have suggested that such studies are very much helpful for understanding of the molecular interaction in the components of the mixtures. A relatively new method has been used for the estimation of excess molar volumes of binary mixtures from the known experimental values of refractive indices and densities of pure liquids and refractive indices of their mixtures.

Experimental

The chemicals (AR grade) employed were supplied by Merck. Chem. Ltd. India, Their purities (in mass percent) were ethyl acetate 99.4%, 1- methanol 99.27%, 1-ethanol 99.2%, 1-propanol 99.2%, 1-butanol 99.5%, 1- hexanol 99.3% and 1-octanol 99%. All chemicals was stored over sodium hydroxide pellets for several days and fractionally distilled twice. All the chemicals were purified by a method given in the literature. Ethyl acetate was dried over K2CO3 filtered and distilled were discarded. All the chemicals were stored to minimize adsorption of moisture. The purity of the liquids was also checked by measuring their densities, refractive indices and ultrasonic velocities at 303.15 K and were in agreement with the literature values are depicted in (Table 1).

Density

The densities of pure liquids and their binary mixtures were measured (303.15 K) using a single-capillary pycnometer, made of borosil glass, having a bulb capacity of 30 cm3. The capillary, with graduated marks, had a uniform pore and could be closed by a well- fitted glass cap. The marks on the capillary were calibrated by using double-distilled water at 303.15 K. The pycnometer was kept for about 30 minute in an electronically controlled thermostate water bath (MSI Goyal Scientific Meerut, India) 303.15 ± 0.02 K and the position of the liquid level on the capillary was noted. The volume of the pycnometer at each mark was calculated by using the literature value of the density of pure water at 303.15K. The volume these obtained is used to determine the density of the unknown liquid. The observed values of densities of pure ethyl acetate, 1-methanol, 1-ethanol, 1- propanol, 1-butanol, 1-hexanol and 1-octanol at 303.15 K were 0.8820, 0.7840, 0.7720, 0.8070, 0.8040, 0.8128 and 0.8242 g-m-3which compare well with corresponding literature values of respectively.

Sound velocity

The ultrasonic velocities were measured using a multifrequency ultrasonic interferometer (Model F-80D, Mittal Enterprises, New Delhi, India) working at 3 MHz. The meter was calibrated with water and benzene at 303.15 K. The measured values of ultrasonic velocities of pure ethyl acetate, 1-methanol, 1-ethanol, 1- propanol, 1-butanol, 1-hexanol and 1-octanol at 303.15K were1125, 1084, 1141, 1182, 1196, 1298 and 1327 m.s- 1 respectively, which compare well with the corresponding literature values.

Refractive index

Refractive indices of pure liquids and liquid mixtures were measure using white light by an Abbe refractometer (Model R- 8 M/S Mittal Enterprises, New Delhi). Refractometer was calibrated with kept constant at 303.15 ± 0.03 K by circulating water of the thermostate with the help of pump through both the prism boxes of the refractometer. Refractive indices of liquid were measured after attainment of constant temperature. An average five measurements was made for each sample. The measured values of refractive indices of pure ethyl acetate, 1- methanol, 1-ethanol, 1-propanol, 1-butanol, 1-hexanol and 1-octanol at 303.15 K were 1.374, 1.351, 1.362, 1.387, 1.398, 1.412 and 1.429 respectively, which compare well with the corresponding literature values. The mixtures were prepared by mixing known volumes of the pure liquids in air tight stoppered bottles. The weights were taken on a single pan electronic balance (K. Roy Company, Varanasi, (U.P.) India) accurate to 0.01 mg.

Results and Discussion

Shows the experimental values of densities (ρ), refractive indices (n) and ultrasonic velocity (u) of pure ethyl acetate, 1-methanol, 1-ethanol, 1- propanol, 1-butanol, 1-hexanol and 1-octanol over the whole composition range at 303.15 K, the derived parameter Rm ( using Lorentz-Lorenz equation) were calculated from the following relation

Rm = (n2mix.− 1) / (n2mix. + 2) Vmix.

Where Vmix. =(X1M1+X2M2)/ρ) is the molar volume of the mixture X1 and X2 are the mole fractions of component 1 (ethyl acetate) and component 2 (alkanols); and M1 and M2 are their molar masses. Results of excess and deviation properties provide insights into the positive or negative deviation from the ideal mixture, indicating which interactions are prevalent in the systems under study. When mixing pure components deviations from the ideal mixture can be smaller or larger depending on the formation of different types of intermolecular bonds and interactions and the packing ability. Dipole-dipole and H-bond interactions between hetero molecules in the mixture lead to negative excess molar volumes, as well as structural effects such as favorable interstitial accommodation and efficient packing. On the other hand, disruption of dipole-dipole interactions and intermolecular hydrogen bonds between molecules of the same substance when put in a mixture.

Alcohols are organic compounds with a highly polar hydroxyl group, which enables interconnection of molecules with strong hydrogen bonds and construction of associated liquids. In mixtures with another organic component, alcohol molecules tend to dissociate from the aggregates and form hydrogen bonds with molecules of another kind. The degree of dissociation from the aggregate depends on the affinity towards the proton of a functional group of another molecule, a proton acceptor.

Ethyl acetate is also a polar compound, which acts as H-bond acceptor, and therefore there is a possibility of intermolecular interactions in mixtures with alcohols. Depending on the strength of these two types of interactions, disruption of bonds between molecules of alcohol and formation of new ones between molecules in the mixture, negative deviation from ideal behaviour can be noticed. Another possibility to interact are dipol-dipol interactions. Since the dipole moment of ethyl acetate is higher than the ones for investigated alcohols, it can be concluded that these interactions are stronger between molecules of acetate than those with alcohol molecules. The molar refraction (R_m) for the pure liquid ethyl acetate, 1-methanol, 1-ethanol, 1- propanol, 1- butanol, 1- hexanol and 1- octanol have been calculated using Lorentz- Lorenz equation. The calculated values for all the liquid are listed in Table II. The molar refraction for six binary liquid mixtures ethyl acetate + 1-methanol, ethyl acetate + 1-ethanol, ethyl acetate + 1-propanol, ethyl acetate + 1-butanol, ethyl acetate + 1-hexanol and ethyl acetate + 1-octanol have been calculated using equation 1 and calculated values are recorded in Table II. The excess molar refraction (R_m^E) have been calculated through molar fraction of the mixture and ideal molar refraction

The value of excess molar refraction (R_m^E) for these system are also enlisted in Table II. The variation of excess molar refraction (R_m^E) with mole fraction (X_1) of ethyl acetate at 303.15 K for the binary mixture of ethyl acetate with 1-alkanol are displayed in Figure 1.

Figure 1: Plots of excess molar refraction (R_m^E) versus mole fraction of ethyl acetate (X1) at 303.15 K for binary mixtures of ethyl acetate with 1- methanol, 1-ethanol,1- propanol, 1- butanol, 1-hexanol and 1-octanol.

A perusal of Table II show that the value of molar refraction increase with increase in mole fraction of the ethyl acetate (X_1). The table also show that the value of excess molar refraction (R_m^E) are negative for all the binary liquid system ethyl acetate + 1-methanol, ethyl acetate + 1-ethanol, ethyl acetate + 1-propanol, ethyl acetate + 1-butanol, ethyl acetate + 1-hexanol and ethyl acetate + 1-octanol at 303.15 K. In the present investigation the negative excess molar refraction (R_m^E) for binary mixtures of ethyl acetate with 1-alkanols may be attributed to hydrogen bond formation through dipole-dipole interaction between 1-alkanol and ethyl acetate molecule to structural contribution arising from the geometrical fitting of component (1-alkanols) in to the other (ethyl acetate) due to difference in the free volume between components

The molar refraction (Rm) increases with the chain length in the homologes series from 1-methanol to 1-octanol while it decreases with an increase in ethyl acetate concentration (Table- II). The average value of Rm for the -CH2 group estimated from the data for 1-methanol, 1-ethanol, 1- propanol, 1-butanol, 1-hexanol and 1-octanol comes out to be constant. This is in good agreement with the value of Rm of C and H, moreover, the value of Rm obtained for the – CH2 group of the present alkanols is in close agreement with the value 4.6440×10-6 m3 mol-1 for the alkanols series reported by Sjoblom et.al 29. The functions, VE are highly sensitive to intermolecular interactions between the component molecules of the mixture. The values of the functions VE were computed using the following relation

V^E = Σ_(i=1)^2 (X_i M_i (1/ρ_1 -1/ρ_2)

Where Mi is molar masses of the ith component respectively. The plots of excess molar volume VE with mole fraction 1 for the binary mixtures of ethyl acetate with 1- methanol, 1- ethanol, 1- propanol, 1- butanol, 1- hexanol and 1- octanol at 303.15 K were depicted in Fig. 2

Figure 2: Plots of excess molar volume (VE) versus mole fraction of ethyl acetate (X1) at 303.15 K for binary mixtures of ethyl acetate with 1-methanol, 1-ethanol, 1- propanol, 1- butanol, 1-hexanol and 1-octanol

The VE values of are negative sign at the temperature for these systems over the whole composition range, Generally, VE values may be explained in term of physical, chemical and structural factors. It is a consequence of the rapture of the hydrogen bonding in the self-associated alkanol molecules on the other hand; the negative VE data are attributed in terms of charge- transfer complex, dipole-dipole interactions and formation of intermolecular hydrogen bonding between component molecules. Further, the sign and magnitude of VE also very with the structural characteristics of the component molecules arising from the geometrical fitting of one component in to the structure of the other component because of the difference in the size, shape, orientation of the components and the free volume. In present investigation chemical interactions are prevailing in the mixture of ethyl acetate with 1- alkanol due to the existence of strong intermolecular hydrogen bond (H-----OH) between the H- atom of the ester group of ethyl acetate and oxygen atom of the O-H group of 1- alkanol. The algebraic value of VE for the mixtures of ethyl acetate with 1-alkanols fall in the order 1- methanol < 1- ethanol < 1- propanol < 1- butanol < 1- hexanol < 1- octanol. The above order indicates the strength of interactions between component molecules decreases due to decrease in polarizability of alkanol molecules.

Conclusion

In this paper, an attempt is made to measure densities (ρ), ultrasonic velocity (u) and refractive indices (n) at 303.15 K over the entire range of mixture composition of ethyl acetate with 1-methanol, 1-ethanol, 1- propanol, 1-butanol, 1-hexanol and 1-octanol out of these measured data, the excess molar volume (VE), molar refraction (Rm) and excess molar reflection (R_m^E) have been calculated. The negative deviations are observed in the case of excess molar volume VE and excess molar refraction[R]_m^E, are observed for all binary mixtures of ethyl acetate with 1-methanol, 1-ethanol, 1-propanol, 1-butanol, 1-hexanol, 1-octanol.The results are analyzed in the sight of molecular interactions between

The components. It may be concluded that the interaction resulting in the interstitial accommodation of ethyl acetate in to 1-alkanols are the predominant factor over dipole-dipole interaction.

Acknowledgements

The authors are very much thankful to the Head of the Department of Chemistry Bundelkhand University, Uttara Pradesh, India. For proving the facilities for Research work.

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