Volumetric , Viscometric and Excess Properties of Binary Mixtures of 1-Iodobutane with Benzene , Toluene , o-Xylene , m-Xylene , p-Xylene , and Mesitylene at Temperatures from 303 . 15 to 313 . 15

Densities and viscosities have been determined for binary mixtures of 1-iodobutane with benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene at 303.15, 308.15, and 313.15 K for the entire composition range at atmospheric pressure. The excess molar volumes, V, deviations in viscosity, Δη, and excess Gibbs’ free energy of activation flow, ΔG∗E have been calculated from the experimental values. The experimental data were fitted to Redlich-Kister polynomial equation. The variations of these parameters with composition of the mixtures and temperature have been discussed in terms of molecular interactions occurring in these mixtures. Further, the viscosities of these binary mixtures were calculated theoretically from their corresponding pure component data by using empirical relations like Bingham,Arrhenius and Eyring, Kendall andMunroe,Hind, Katti andChaudhari, Grunberg and Nissan, and Tamura and Kurata. Comparison of various interaction parameters has been expressed to explain the intermolecular interactions between iodobutane and selected hydrocarbons.


Introduction
Densities and viscosities of solution are very important properties especially for the chemical design and for the optimization of chemical processes.The study of these properties plays an important role in many industrially interesting systems such as organic synthesis, ion extraction systems, gas adsorption solvents, and mass transfer phenomena.Furthermore, the study of excess thermodynamics and transport properties for binary mixtures gives an important information concerning the deeper understanding of the molecular liquid structure and intermolecular interactions [1].1iodobutane has vast applications at industrial level because it works as an alkylating agent in organic synthesis.Aromatic hydrocarbons are also important organic solvents in organic synthesis and extraction systems.Aromatic hydrocarbons like xylenes were frequently used as octane enhancer in vehicles [2].The excess molar volume and viscosity deviations are properties sensitive to different kinds of association in the pure components and in the mixtures.These properties have been used to investigate the molecular packing, molecular motions, and various types of intermolecular interactions and their strengths, but these properties are influenced by the size, shape, and chemical nature of the component molecules [3][4][5].In view of this significance, it was thought worthwhile to study the binary mixtures of 1-iodobutane, benzene, toluene, o-, m-, and p-xylenes in order to understand the interactions between these components.The lack of information has motivated us to undertake the present investigations.Here, densities and viscosities of the binary mixtures of 1-iodobutane with benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene at different temperatures (303.15, 308.15, 313.15)K are studied.To account more for the interactions between these binaries, some viscosity models, namely, Bingham,

Apparatus and Procedure.
Airtight stopper bottles were used for the preparation of the mixtures and were placed in the dark place.The losses in the mixtures were kept to minimum, as evidenced by repeated measurements of physical properties over an interval of 2-3 days during in which before use time no change in physical properties was observed.The mixtures were well mixed by shaking before use.Binary mixtures were prepared by mass, using an electronic analytical balance (Reptech RA-2012) supplied by Reptechindia Pvt. Ltd., Gujarat, India, with a precision of ±0.0001 g.The uncertainty in mole fraction was estimated to be ±0.0001.
Accurate densities of ±0.0001 g ⋅ cm −3 were measured by using pycnometer having bulb volume of 10 cm 3 and capillary orifice with internal diameter 1 cm 3 .For each measurement, the pycnometer was filled with required liquid and was kept in water bath with thermal stability which was checked by calibrated thermometer at the equilibrium.An average of triplicate measurements was taken into account and their reproducibility was within the range of ±0.3%.The viscosities of pure components and their mixtures have been measured by SV 10, Vibro-viscometer, supplied by A and D instruments Pvt. Ltd., Haryana, India, having measurement range 0.3 m ⋅ Pa ⋅ s-10,000 m ⋅ Pa ⋅ s.Its working vibration frequency is 30 Hz, and the temperature measurement range is 0-160 ∘ C with ±0.1 ∘ C accuracy.Accurate viscosity of ±0.001 m ⋅ Pa ⋅ s was measured by the viscometer.For maintaining the temperature throughout the experiment, NSW 274 water bath supplied by NSW company, India, has been used.The temperature has been measured with accuracy of ±0.01 ∘ C.

Calculations.
The excess molar volumes,   , viscosity deviations, Δ, and excess Gibbs' free energy of activation flow, Δ *  , for binary mixtures were determined using the following equations (Table 4).[4] is calculated by using following equation:

Excess Molar Volumes. Excess molar volume
where   represents the molar volume and   is the mole fraction of th component.The quantity   refers to the molar volume of the mixture which can be calculated from the mixture density,   , and the component molecular weights  1 and  2 as 2.3.2.Viscosity Deviations.The viscosity deviations (Δ) [5] with mole fraction were calculated by the following: where   ,   , and  12 refer, respectively, to the mole fraction and viscosities of th pure components and of the binary mixtures.

Excess Gibb's Free Energy of Activation of Flow.
The excess Gibb's free energy of activation of flow, Δ *  , for the binary liquid mixture was computed by the following equation: where,  The experimentally determined values of   , Δ and Δ *  for binary mixtures were fitted to the Redlich-Kister equation ( 5) [6]: where   is   or Δ or Δ *  ;  1 denoted the mole fraction of the 1st component in the binary mixture.The coefficient   was obtained by fitting (5) to experimental results using a least squares regression method.The values of coefficient,   , along with the standard deviations, , are presented in Table 6.
(iii) Kendall [9] has modified the equation for viscosity of binary liquid system which is given as where   and   are the mole fraction and viscosity of th component, respectively.
(iv) Grunberg and Nissan [10] have formulated (10) to assess the molecular interactions due to viscosity changes: where  12 is a constant, proportional to interchange energy,  1 and  2 are mole fractions of components 1 and 2, respectively, and  1 ,  2 , and  12 are the dynamic viscosities of component 1, component 2, and binary mixtures, respectively.
(v) Hind et al. [11] have suggested the following (11) for the viscosity of binary liquid mixtures as follows: where  12 is the Hind interaction parameter and is attributed to unlike pair interactions,  1 and  2 are the mole fractions (vi) Tamura-Kurata [12] have developed (12) for the viscosity of binary liquid mixtures as follows: where  12 is the interaction parameter which depends on temperature and composition of the mixtures, and  1 and  2 are the mole fractions of components 1 and 2, respectively. 1 and  2 are the viscosities of component 1 and component 2, respectively, and  1 and  2 are the volume fractions of components 1 and 2, respectively.(vii) Katti et al. [13] have suggested following equation for viscosity of binary liquid system: where  vis is the interaction energy parameter,  is the volume of the mixture,  1 and  2 are the mole fractions, and  1 and  2 are the viscosities of component 1 and component 2, respectively.

Results and Discussion
The experimental values of densities and viscosities of the hydrocarbons are compared with the literature values and are presented in Table 1.It was found that the experimental values are in proximity with the literature values.Insufficient data on densities and viscosities of pure 1-iodoobutane is available [14].The densities, , and viscosities, , of binary mixtures were measured at 303.15, 308.15, 313.15 ± 0.01 K as a function of the composition of the corresponding binary mixtures.The results of the study are presented in Tables 2 and 3.
The plots of   , Δ, and Δ *  versus   in respective binary mixtures have been given in Figures 1, 2, and 3 at 308.15 K.
It can be seen from Figure 1 that the values of   are negative for 1-iodobutane + benzene and positive for 1-iodobutane + o-xylene, m-xylene, p-xylene, and mesitylene mixtures over the whole composition range at three temperatures.The shape of the curve is sigmoid for 1-iodobutane +  toluene mixtures, where   changes sign from positive to negative as the concentration of 1-iodobutane in mixtures has increased.
The observed changes in excess molar volumes are discussed in terms of three types of contributions physical, chemical, and structural in general [15].
(i) Physical contribution, that is, nonspecific interaction between the real species present in mixtures and this effect contributes positive value to   .
(ii) The chemical or specific interaction results in a volume decrease and these include charge transfer type forces and other complex forming interactions.This effect contributes negative value to   .
As we move from benzene, toluene, and xylenes to mesitylene, there is an increase in the number of -CH 3 groups.As the number of methyl groups increases, electron donating tendency increases in hydrocarbons but at the same time there may be steric repulsion between methyl groups of 1-iodobutane and hydrocarbons which hinders proper orientation.  values for o, m, p-xylene, and 1, 3, 5 tri-methylbenzene are positive over the whole composition range.The increase in   values with the increase in number of -CH 3 groups implies that dipole-induced dipole interaction is weaker in higher hydrocarbon owing to its decreased polarizabilities with the increase of -CH 3 groups.A similar type of study was reported by Nain et al. [16] for 1,4-dioxane and hydrocarbons.The observed   values are in the order of Addition of two methyl groups in benzene ring in xylenes further exceeds the electron donating capacity, when compared to toluene, but at the same time steric (hindrance) repulsion between methyl groups of 1-iodobutane which hinders proper orientation that is expected to be more.
The stereo regularity of methyl groups in o-xylene is such that steric repulsion is maximum; so   values for    o-xylene are found to be higher than the m-xylene and p-xylene.Moreover,   values are found to be positive indicating existence of weak interactions of dipole-induced dipole because of the large difference in dipole moments of polar iodobutane and nonpolar hydrocarbons.The observed   values are due to cumulative effect of (i) the specific interaction of the electron donor acceptor between vacant 2p level of iodine atom of butyl iodide and n- elector cloud of aromatic hydrocarbons and of (ii) disruption in the orientation order of the two components.The increase in   values (positive effect) with increase in temperature suggests for declustering of components at higher temperatures and corresponding increase in kinetic energy.
The values of Δ are negative for all the selected binary mixtures and regularly decrease with an increase in -CH 3 groups from benzene to mesitylene.The deviations in viscosity of binary mixtures are essentially due to two factors (in general).
(i) The depolymerization of the associated entities like hydrocarbons and formation of monomeric moieties on mixing make a negative contribution to Δ values.
(ii) Replacement of like contents in pure components by unlike contents in mixture makes positive contributions to Δ values.
Negative values of Δ throughout the whole composition range and at all temperatures suggest that the intermolecular interaction becomes weaker on mixing of components, also indicating that the dispersion type [17] of forces is predominant in these mixtures.The negative Δ values support the positive   values and account for dispersive forces in these binaries.Δ values are also expected to be negative because of vast different in viscosities of pure components (see Table 1).The negative values of Δ at equimolar concentrations of 1-iodobutane and hydrocarbons mixtures are in the following order: benzene Theoretical calculations of viscosities are carried out by using Bingham, Arrhenius-Eyring's, Kendall-Munroe, Grunberg and Nissan, Hind, Tamura-Kurata, and Katti and Chaudhari equations.It is evident from Table 3 that amongst all, 1iodobutane + benzene, + toluene, + o-xylene, + m-xylene, + p-xylene, and + mesitylene systems, Bingham relation gives better results in comparison to other theoretical relations.The differences observed are higher between experimental and theoretical values for other relations studied here.The positive values of  12 may be attributed to the presence of strong interactions between the components, while the negative values of  12 indicate for the dominance of dispersion forces [18].The negatives values of interaction parameters  vis are also suggesting for weak interactions and positive values for strong interactions [19].In the present study,  12 values are positive for benzene and both positive and negative for toluene mixtures and negative for the remaining hydrocarbons.The values of interaction parameters,  12 and  12 , do not differ appreciably from each other.This is in agreement with the view put forward by Fort and Moore [20] in regard to the nature of parameters  12 and  12 .
The Δ *  values are positive for 1-iodobutane + benzene mixtures, positive to negative for 1-iodobutane + toluene, and negative for 1-iodobutane + o-, m-, p-xylenes, and mesitylene mixtures for the entire composition range selected here (shown in Figure 3).Δ *  parameter can be considered as a reliable criterion to detect and interpret the presence of interactions between unlike molecules [21,22].Δ *  values at equimolar concentration of 1-iodobutane and hydrocarbon mixtures show the following order benzene > toluene > o-xylene > m-xylene > p-xylene > mesitylene.
Nain et al. [23] had made similar observations from their Δ *  studies of Tetrahydorfuran with Benzene, Toluene, o-Xylene, m-Xylene, p-Xylene, Mesitylene binary mixtures.Δ *  values for all the selected mixtures decrease with the increase in temperature.

Conclusion
The excess molar volumes,   , deviations in viscosity, Δ, and excess Gibbs' free energy of activation flow, Δ *  , have been calculated from the experimental values at three temperatures for iodobutane, benzene, toluene, o-, p-, m-xylenes, and mesitylene binary mixtures.The sign and magnitude of these quantities have been discussed in terms of the molecular interactions between the mixing components.Negative   , negative Δ, positive Δ *  , and positive  12 are observed for iodobutane + benzene mixtures; both negative and positive   and Δ *  values and only negative Δ values are observed for the toluene mixtures.However, positive   , negative Δ, and positive Δ *  values are obtained for xylenes and mesitylene binary mixtures.Interaction parameters  12 and  vis also support the   and Δ values in explaining the molecular interactions (Table 5).The expansion and contraction in volumes cannot be explained on the basis of simply considering   and Δ values.Any observed property is combined effect of interaction part and size effect.The size effect can be due to free volumes and dipole moments of components.The size effect can be compared with interaction part and this may reverse the trend of interaction parameters.So, in iodobutane + benzene mixtures, strong interactions are reported; in toluene binaries, weak to strong interactions are observed; for other binaries of xylenes and mesitylenes, weak dispersion type of interactions is reported here.In all binaries, these interactions become weaker with increase in content of iodobutane and with rise of temperature.

Table 1 :
Comparison of experimental density and viscosity of pure liquid with the literature values.
ln   V  ,

Table 6 :
Estimated parameters of excess functions for the binary mixtures.