Study of Refractive Indices and Its Theories for Mixtures of N, N- Diethylethanamine and Acetates

This paper reports the refractive indices ( n ) of N,N-diethylethanamine + methyl acetate, ethyl acetate, propyl acetate, butyl acetate and pentyl acetate at 298.15 K and at different composition range. The various empirical correlations like Arago-Biot (AB), GladstoneDale (GD), Lorentz-Lorenz (L-L) Heller (H), Weiner (W), Newton (Nw) and Erying-John (E-J) were applied to experimental data for estimating theoretical value of refractive indices. For an equimolar mixture, the predicted deviation in refractive index values is consistent well with the experimental data. It has been found that the interactions between amine and different esters decrease when carbon chain length in ester increases. Also refractive indices are affected with change in temperature. To evaluate the standard deviation, RK polynomial equation was fitted to the measured refractive indices data.


Introduction
The excess functions are very useful to understand the nature and magnitude of deviations from ideality and as the non-ideality is directly linked with the intermolecular interactions [1,2].
Recently, we have reported some thermodynamic functions of binary mixtures of aliphatic amine and aliphatic esters [3,4]. Deviation in refractive index of binary mixtures reveals significant information about the structure and molecular interactions [5][6][7]. From recent research work it was found that some of the polymers in polymer chemistry which are insoluble in pure solvent can be dissolved in a solvent mixture [8]. Also N,Ndiethylethanamine is a very good additive for gasolines. Binary mixtures are used to refine the petroleum product which is very toxic if we use the binary mixtures then we can increase the efficiency of fuel and decrease the toxicity. N,N-diethylethanamine is a clear colorless liquid having fish-like odour. Its vapours are heavier than air also and are used as a food additive. Esters are clear liquid, flavouring ingredient. They can act as a nonpolar (lipophilic) as well as weakly polar (hydrophilic) aprotic solvent. It is used as adhesives, sealant chemicals, intermediates, lubricants, lubricant additives, electrical, electronic products, paint, coating additives, floor coverings, plasticizers, lubricants and also used as solvents for cleaning and degreasing. Since the components of these binary mixtures have both proton-donating/accepting abilities, significant interaction through hydrogen bonding between unlike molecules is expected.

Experimental
The specifications of all the chemicals are given in Table 1. All the chemicals were purified by standard procedure and their purities were confirmed by comparing the measured density and refractive index (at 298.15 K) data with literature [7][8][9][10][11][12] are given in Table 2. Refractive indices were measured with refractometer (Anton Paar Abbemat-200) having temperature controlled within ±0.01 K with an accuracy of ±1×10 -4 . The samples were prepared by using electronic balance (CAUW 220 D) with a precision of ±0.005 mg.

Results and Discussion
Deviation in refractive index ( n  ) is reported in Table 3 and was calculated as: A are the adjustable parameters and calculated by fitting n  data in Eq. (2). Experimental n  data at 298.15 K for the studied system together with smoothing curves from Eq. (2) is shown in Fig. 1. Similar trend were observed at all the other temperatures. For quantitative determination of refractive indices following mixing relations were used: From these mixing rules standard deviation were also calculated. Refractive index values along with deviation in refractive index over the entire composition are given in Table 3. Figs. 1 and 2 show the variations of n and n  versus 1 for the binary systems studied at 298.15 K respectively.  From Fig. 1 it can be seen that as we increase the concentration of esters in N, Ndiethylethanamine, the interactions becomes appreciable. Also it can be noted that the interactions are maximum for methyl acetate and minimum for pentyl acetate i.e. the interactions decreases as we go from methyl acetate to pentyl acetate. These interactions are due to rupture of self-association of amine molecule as well as ester molecule and orientation of antiparellel spin of ester molecule to amine [13][14][15][16][17]. The n values for the   Fig. 3 shows the standard deviation of predicted values of refractive index using various correlations for the binary mixtures at 298.15 K. From these results, it can be seen that Lorentz-Lorentz correlation well explain these binary systems and as the carbon chain is increasing these correlations fits well also Lorentz-Lorentz has minimum standard deviation among all the correlations used.

Conclusion
From refractive index data we have measured (∆n) for binary liquid mixtures of amine and aliphatic acetates (methyl acetate, ethyl acetate, propyl acetate, butyl acetate and pentyl acetate) at temperature of 298.15 K over the entire composition range. The n  results for all the binary mixtures are negative. The negative magnitude of n  values shows the presence of specific interactions. Also, the predicted result from various correlation of n  also supports experimental data. Various mixing rules applied for the theoretical estimation of refractive index and have good correlation with experimental data. The interaction decreases as we increase the number of carbon atoms in esters (methyl acetate to pentyl acetate).