Refractrometic Studies of Binary Mixtures of Flavoured Compounds and Some Hydrocarbons

Abstract: Refractive indices have been measured for the binary liquid mixtures of n-butylethanoate and 3methylethanoate with cyclohexane, benzene, 1,4-dimethylbenzene and 1,3,5-trimethylbenzene over the entire composition range at 308.15K. From the experimental data, the values of deviation in refractive index ( n), molar refraction (R) and deviation in molar refraction ( R) have been determined. The values of n and R have been fitted to the Redlich Kister polynomial equation to determine the standard deviation.


INTRODUCTION
Physical properties of several esters in their binary mixtures have been already reported [1][2][3][4][5][6][7][8].However, studies in this regard for the determination of refractive indices of the binary mixtures of n-butylethanoate and 3-methylbutylethanoate at 308.15K are still lacking.Esters are an important class of organic compounds having characteristic fruity odour.They are used as component of perfumes and flavourings.Higher esters have low solubility in water and used as extraction solvents for fine chemicals particularly for certain antibiotics.They are also useful in cosmetics and materials for personal care.
3-methylbutylethanoate is used as solvent for old oil colors, perfuming, shoe polish, metallic paints and in photographic films.
In our laboratory refractive index studies have been made on binary systems of bromoalkanes and cyclohexane and aromatic hydrocarbons.Literature reveals that binary systems of esters and aromatic hydrocarbons have rarely been studied employing refractive index measurements.In view of this, binary systems of flavoured compounds viz.1-butylethanoate and 3-methylbutylethanoate and aromatic hydrocarbons viz.benzene, 1,4-dimethylbenzene and 1,3,5-trimethylbenzene having successive methylation and differing in the polarisablity have been selected in the present investigation.Since cyclohexane has a six membered ring without any -electrons, binary mixtures of both the esters with it are also studied at experimental temperature in order to have a reference point for composition of unlike molecular interactions.
Binary mixtures were prepared by weight covering whole mole fractions range in a sealed glass vials and component liquids were injected by means of syringe to minimize evaporation losses during sample preparation.Weights were measured employing single pan analytical balance (Model K-15 Deluxe, K. Roy Instruments Pvt. Ltd.Varanasi) with a precision of ± 0.00001x10 -3 kg.
Densities of the liquids and their binary mixtures were measured employing stem pyknometer having bulb capacity about 12.0 x10  1 and 2 respectively.Measurements of refractive indices were carried out after attainment of constant temperature by the sample.An average of three to four measurements for each sample was taken.

RESULTS AND DISCUSSION
The experimental values of densities and refractive indices at 308.15 K for all the four binary mixtures and   Where n and n 1 , n 2 are refractive indices of the mixtures and the components 1 and 2 are refractive indices of the mixtures and the components 1 and 2 respectively are also recorded in Tables 1 and 2.
Redlich-Kister equation [11] given below Where A, B and C are the coefficients of the equation is generally used by the chemists to analyse thermodynamic data on liquid mixtures.However, Desnoyers and Perron [12] has suggested in agreement with the original statements of Redlich and Kister, that plot of Y E /x 1 (1-x 1 ) is better for this purpose.
In the present investigation Redlich -Kister equation was fitted to the evaluated n values and the coefficients of equation and standard deviation ( n) for all the systems are recorded in Tables (3)(4).
Perusal of Tables 1 and 2 reveals that refractive indices for all the mixtures increases with mole fractions of hydrocarbons.It shows that the order of refractive index for binary mixtures of n-butylethanoate and 3-methylbutylethanoate with hydrocarbons is.Cyclohexane< benzene < 1,4-dimethylbenzene< 1,3,5-trimethylbenzene And this order is shown in Figures (3)(4).Experimental n values are used to evaluate molar refraction, R for all the binary mixtures studied by equation:

Variations of deviation in refractive indices, n for the mixtures studied with concentrations of
Where R is the molar refraction, x 1 and x 2 are mole fractions of components 1 and 2 M 1 and M 2 are the molecular weight of component 1 and 2, is the density, n is the refractive index.
R values for all the mixtures also given in Tables 1  and 2 for both the systems with hydrocarbons variations of R with composition of mixtures are linear for all the binary mixtures.Values of R at equimolar compositions follow the trend similar that of n values as given above and shown in Figures 7 and 8.
Deviation in molar refraction from the linear blending rule ( R) have been defined on mole fraction basis [13,14].Considering molar refraction as isomorphic to the molar volume.However, others [15,16] have defined it on volume fraction basis.In the present investigation R has been evaluated on volume fraction basis as equation 5: Where R 1 , R 2 are the molar refractions of pure components and 1 and 2 are their volume fractions in binary mixtures.The R values with composition for all the systems at experimental temperature evaluated by equation ( 4) are recorded in Tables 1 and 2 It is evident from Figures 5 and 6 that R values are negative for binary systems of n-butylethanoate with all the hydrocarbons.But for the binary systems of 3methylbutylethanoate R values are negative for cyclohexane and benzene positive for 1,4dimethylbenzene and 1,3,5-trimethylbenzene.

CONCLUSION
Refractive index and density of binary mixtures are useful for evaluation of molar refraction.These evaluations give information about molecular interactions between the components of the mixture.

Figure 1 :
Figure 1: Operating Principle of the Abbe Refractometer.
Temperature of the sample was kept constant by circulating water from thermostat at constant experimental temperature with the help of tullu pump through the upper and lower prism boxes of the Abbe Refractometer.The diagram and photograph of the refractometer is shown in Figures