Excess Molar Quantities of Binary Mixture of Dipropyl amine with Aliphatic Alcohols at 298 . 15 K

Refractive indices (nD), viscosities (η) and densities (r) were deliberated for the binary mixtures created by dipropyl amine with 1-octanol, 1-heptanol, 1-hexanol, 1-pentanol and tert-pentyl alcohol at temperature 298.15 K over the perfect installation extent. The function of Redlich-Kister were used to calculate and renovated of the refractive index deviations (∆nD), viscosity deviations (ηE), excess molar Gibbs free energy (∆G*E) and excess molar volumes(Vm E). The standard errors and coefficients were respected by this function. The values of ∆nD, η E, Vm E and ∆G*E were plotted against mole fraction of dipropyl amine. In all cases the obtained ηE, ∆G*E, Vm E and ∆nD values were negative at 298.15K. Effect of carbon atoms number in the chain of alcohol and hydroxyl groups' position on molecular interactions in these mixtures has also been discussed.


INTRODUCTION
The familiarity of the excess parameters of organic liquid blends is salutary in industrial enforcements and is highly significant for understanding the molecular interactions between the components this as well assist to develop theoretical patterns [1][2][3] .The experimental conclusions are adduced in this paper for the binary system of dipropyl amine with 1-alkanols and tert-pentyl alcohol at 298.15 K.These conclusions expose the cross-association between alkanol and amine molecules down the identical conditions [4][5][6] .Also the conclusions display the steric hindrance of methyl groups.Alcohols are polar and self-associated through hydrogen bonding in the state alcohols are multilateral solvents used in the division of saturated and unsaturated hydrocarbons and in medicinal synthesis and serve as solvents for numerous polymers 7 .A survey of the literature detects sundry on the excess properties of binary mixtures including amines and alcohols [8][9][10][11][12][13] .The thermodynamic properties of multicomponent systems are some major parameters for the layout and optimization of chemical process.Although many surveys on density and viscosity have been recorded [14][15] .
Alcohols are highly paramount solvents in a numeral of processing procedures and have sundry enforcements as reagents or solvents, hand sanitizers, antifreeze, and antiseptics as well as keeper in learning and métier 16 .Amines are compounds contain on basic nitrogen atom carried a lone pair.Derivatives of ammonia are known amines, which contains one or more hydrogen atoms have been replaced by substituent such as an alkyl or aryl group.Amines are highly paramount several enforcement for example; dipropyl amine is a secondary amine whose belongs to the class of dialkyl amines.It is multilateral medium with a diversity of enforcements.Most paramount enforcements are found in the field of agricultural chemicals; however, also substantial volumes are wasted for the produce of other non-agricultural chemicals.

Liquid materials
The following liquid materials were used are:

Density measurement
Densities of pure components and liquidliquid mixtures were measured with an Anton paar digital densimeter (Model DMA 60/602) with an accuracy of ± 10 -5 g.cm -3 .Air and double distilled water used for the calibration of the densimeter.At least three times for each composition in experimental were generally repeated and the results were treatment.

Viscosities measurements
By using a suspended-level ubbelohde viscometer in a bath controlled to ± 0.01 K at 298.15 K was determined the viscosities.To give the final values the experimental were repeated at least three times and the results were corrected.

Refractive index measurements
By using a digital Abbe refractometer (Model: BOE 32400) were determined the refractive indices of pure components and their liquid-liquid mixtures.The measuring refractive indices of double distilled water and toluene were used to calibrate the refractometer at 298.15 K.

RESULTS AND DISCUSSION
Table 2 shows experimental viscosities, densities, refractive indices, deviation in viscosity, excess volumes, refractive index deviation and excess molar Gibbs free energy for five binary systems dipropyl amine with some alcohols and tert-pentyl alcohol at 298.15 K.
The excess molar volumes (V m E ) were matured from density data according to: Where r i , X i and Mi are the density, mole fraction and molar mass of the component i, r is the density of mixtures, n is the number of components.The values of excess molar volumes are shown in Figure 1.The excess molar volumesV m E , inspected in project were all negative over the whole range of dipropylamine composition at 298.15 K.These are shown in Fig. 1.This may suggest that volume construction takes place onto mixing dipropylamine with alcohols due to the cross-association between these various molecules 37 .
And the negative values are attributable mainly to the association between amine and alcohols intermolecular hydrogen bonds between the -OH groups in alcohols and the nitrogen atoms in the amine.The strength of the associations arising from interactions between the unlike molecules was stronger than the strength of the association between like molecules 38 .The magnitude of the volume contraction follows the sequence of: The viscosity deviations (η E ) for two compound mixtures can be calculated as: Where η i is the absolute viscosity of pure component i and η is the absolute viscosity of the mixtures.The (η E ) values are also graphically represented as a function of mole fraction at 298.15 K in Figure 2. Excess molar Gibbs free energy of activation of viscous flow was acquired by using: Where R is the universal constant of gases, T is a Kelvin temperature, X 1 , X 2 represent mole fraction of component 1 and 2, V 1 , V 2 are the molar volumes of component 1 and 2, and η 1 , η 2 and η m are the viscosity of component 1, 2 and viscosity of mixture respectively.
V m is obtained from equation: The values excess molar Gibbs free energy is shown in Figure 3.The viscosity deviations (η E ), Fig. 2 and excess molar Gibbs energy (∆G* E ), Fig. 3 are negative over the whole mole fraction range at 298.15 K.These results can be attributed to the laceration of hydrogen bonded between dipropylamine and alcohols which overtake on dipole-dipole molecular interaction between them and become less positive as the length of alkanol chain increased.The necessitation values of deviation in viscosity and excess molar Gibbs free energy for binary liquid mixtures fall in the order: 1-octanol >1-heptanol >1-hexanol >1-pentanol >ter-pentyl alcohol by Brocos et al., 36 were calculated the deviation of refractive index (∆n D ) from the volume fraction average: Where ϕ i , n D , and n Di are the volume fraction, refractive index of mixture, the density of the mixture and refractive index of pure component i respectively.V and V i are the molar volume of the mixture and molar volume of pure component i respectively.The values of ∆n D are shown in Figure 4.
Where Y is ∆G* E , η E , n D , and V m E and p is a degree of polynomial expansion.Standard deviations were calculated by means of the equation:  Where (m) is a number of data points and (n) are a number of estimated parameters.Values of these coefficients and the standard deviation are given in Table 3.
The V m E , ∆n D , ∆G* E and η E were acquired from experimental data and were correlated using Redlich-Kister Polynomial equation.The results assure what has been formerly announced that in the solvents systems investigated, the negative values are attributable to stronger hydrogen bond formations between unlike molecules than those between like molecules and become less positive as the length of alkanol chain increased.

Fig. 3 .
Fig. 3. Curves of excess molar Gibbs free energy (∆G* E ) Vs mole fraction (X 1 ) for the binary mixtures of dipropylamine+1-pentanol(),1-heptanol (∆), tertpentylalcohol(×), 1-hexanol (*) and 1-octanol(♦), at 298.15K The values of refractive index deviation (∆n D ) for the system containing dipropylamine and alcohols are negative values, Fig. 4.These values are due to hetero association of unlike molecules which give rise to formation of cross complexes where O-H-N bonds of the mixtures are stronger than O-H-O and N-H-N bonds of the single component solvents.In case of dipropylamine-ter-pentyl alcohol mixtures (∆n D ) give lowest negative values such behavior may be explained qualitatively by crowdies of methyl groups around the active site of alcohol (OH) and (∆n D ) for these binary mixtures follows the sequence of: 1-octanol >1-heptanol >1-hexanol >1-pentanol > ter-pentyl alcohol The ∆G* E , η E , n D , and V m E values were fitted to a Redlich-Kister-type [39] polynomial equation: Y=

Table 1 :
Comparison of experimental, viscosities (η), densities (r) and refractive index (n D )of pure liquids with literature data at 298.15 K.