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 K

Abstract

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^𝐸, 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 and Munroe, Hind, Katti and Chaudhari, 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.

1. 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]. 1-iodobutane 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 [3–5]. 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, Arrhenius and Eyring, Kendall and Munroe, Hind, Katti and Chaudhary, Grunberg and Nissan, and Tamura and Kurata are studied.

2. Experimental

2.1. Chemicals/Materials

1-iodobutane, benzene, toluene, o-xylene, and p-xylene were supplied by Sd Fine-Chemicals Ltd., Mumbai, India, with purity 99.5%. m-Xylene was supplied by Spectrochem Pvt. Ltd., Mumbai, India, with 99.5% purity. Mesitylene was supplied by CDH Ltd. New Delhi, India, with 99.5% purity.

2.2. 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 cm³ and capillary orifice with internal diameter 1 cm³. 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.

2.3. Calculations

The excess molar volumes, 𝑉^𝐸, viscosity deviations, Δ𝜂, and excess Gibbs’ free energy of activation flow, Δ𝐺^∗𝐸, for binary mixtures were determined using the following equations (Table 4).

2.3.1. Excess Molar Volumes

Excess molar volume [4] is calculated by using following equation: 𝑉^𝐸=𝑉_𝑚−²_𝑖=1𝑉_𝑖𝑥_𝑖, (1) where 𝑉_𝑖 represents the molar volume and 𝑥_𝑖 is the mole fraction of 𝑖th component. The quantity 𝑉_𝑚 refers to the molar volume of the mixture which can be calculated from the mixture density, 𝜌_𝑚, and the component molecular weights 𝑀₁ and 𝑀₂ as 𝑉_𝑚=𝑀₁𝑥₁+𝑀₂𝑥₂𝜌_𝑚. (2)

2.3.2. Viscosity Deviations

The viscosity deviations (Δ𝜂) [5] with mole fraction were calculated by the following: Δ𝜂(m⋅Pa⋅s)=𝜂₁₂−²_𝑖=1𝑥_𝑖𝜂_𝑖, (3) where 𝑥_𝑖, 𝜂_𝑖, and 𝜂₁₂ refer, respectively, to the mole fraction and viscosities of 𝑖th pure components and of the binary mixtures.

2.3.3. Excess Gibb’s Free Energy of Activation of Flow

The excess Gibb’s free energy of activation of flow, Δ𝐺^∗𝐸, for the binary liquid mixture was computed by the following equation: 𝐺^∗𝐸Jmol⁻¹=𝑅𝑇ln𝜂𝑉−𝑥₁ln𝜂₁𝑉₁−𝑥₂ln𝜂₂𝑉₂, (4) where, 𝑉₁, 𝑉₂, and 𝑉 are the molar volumes of component 1, component 2, and mixture, respectively. 𝜂₁, 𝜂₂, and 𝜂 are viscosities of the component 1, component 2, and mixture, respectively. 𝑅 and 𝑇 have their usual meaning.

The experimentally determined values of 𝑉^𝐸, Δ𝜂 and Δ𝐺^∗𝐸 for binary mixtures were fitted to the Redlich-Kister equation (5) [6]: 𝑌^𝐸_𝑚=𝑥₁1−𝑥₁^𝑛_𝑖=0𝑎_𝑖2𝑥₁−1^𝑖, (5) where 𝑌^𝐸 is 𝑉^𝐸 or Δ𝜂 or Δ𝐺^∗𝐸; 𝑥₁ denoted the mole fraction of the 1st component in the binary mixture. The coefficient 𝑎_𝑖 was obtained by fitting (5) to experimental results using a least squares regression method. The values of coefficient, 𝑎_𝑖, along with the standard deviations, 𝜎, are presented in Table 6. ∑𝑌𝜎=^𝐸exp−𝑌^𝐸_fit²𝑛−𝑝^1/2. (6)

2.4. Interaction Parameters

Several equations have been put forward to correlate viscosity of binary liquid mixtures in terms of their pure component data. Some of these equations are discussed here.

(i) Bingham [7] proposed the following equation, which gives ideal viscosity of the mixture: 𝜂=𝑥_𝑖𝜂_𝑖, (7) where 𝑥_𝑖 and 𝜂_𝑖 are the mole fraction and viscosity of 𝑖th component, respectively.

(ii) Arrhenius’ [8] model for the viscosity of pure liquid and mixtures can be modified as ln𝜂𝑣=𝑥_𝑖ln𝜂_𝑖𝑣_𝑖, (8) where 𝑥_𝑖, 𝜂_𝑖, and 𝑣_𝑖 are the mole fraction, viscosity, and volume of 𝑖th component, respectively.

(iii) Kendall [9] has modified the equation for viscosity of binary liquid system which is given as ln𝜂=𝑥_𝑖ln𝜂_𝑖, (9) where 𝑥_𝑖 and 𝜂_𝑖 are the mole fraction and viscosity of 𝑖th component, respectively.

(iv) Grunberg and Nissan [10] have formulated (10) to assess the molecular interactions due to viscosity changes: ln𝜂₁₂=𝑥₁ln𝜂₁+𝑥₂ln𝜂₂+𝑥₁𝑥₂𝐺₁₂, (10) where 𝐺₁₂ is a constant, proportional to interchange energy, 𝑥₁ and 𝑥₂ are mole fractions of components 1 and 2, respectively, and 𝜂₁, 𝜂₂, and 𝜂₁₂ 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: 𝜂=𝑥²₁𝜂₁+𝑥²₂𝜂₂+2𝑥₁𝑥₂𝐻₁₂, (11) where 𝐻₁₂ is the Hind interaction parameter and is attributed to unlike pair interactions, 𝑥₁ and 𝑥₂ are the mole fractions of components 1 and 2, respectively, and 𝜂₁ and 𝜂₂ are the viscosities of component 1 and component 2, respectively.

(vi) Tamura-Kurata [12] have developed (12) for the viscosity of binary liquid mixtures as follows: 𝜂=𝑥₁𝜙₁𝜂₁+𝑥₂𝜙₂𝜂₂+2𝑥₁𝑥₂𝜙₁𝜙₂^0.5𝑇₁₂, (12) where 𝑇₁₂ is the interaction parameter which depends on temperature and composition of the mixtures, and 𝑥₁ and 𝑥₂ are the mole fractions of components 1 and 2, respectively. 𝜂₁ and 𝜂₂ are the viscosities of component 1 and component 2, respectively, and 𝜙₁ and 𝜙₂ 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: ln𝜂𝑉=𝑥_𝑖ln𝑉_𝑖+𝑊_vis𝑥𝑅𝑇¹𝑥₂, (13) where 𝑊_vis is the interaction energy parameter, 𝑉 is the volume of the mixture, 𝑥₁ and 𝑥₂ are the mole fractions, and 𝜂₁ and 𝜂₂ are the viscosities of component 1 and component 2, respectively.

3. 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].

Table 1 

Comparison of experimental density and viscosity of pure liquid with the literature values.

The densities, 𝜌, and viscosities, 𝜂, 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.

Table 2 

Mole fraction (𝑥₁), density (𝜌₁₂), and excess molar volume (𝑉^𝐸) for 1-iodobutane + hydrocarbons binary mixtures at different temperatures.

Table 3 

Mole fraction (𝑥₁), experimental and theoretical viscosities (𝜂) for 1-iodobutane + hydrocarbons binary mixtures at 303.15, 308.15, and 313.15 K.

Table 4 

Mole fraction (𝑥₁), viscosity deviations (Δ𝜂), and excess Gibbs’ free energy of activation flow (Δ𝐺^∗𝐸) for 1-iodobutane + hydrocarbons binary mixtures at 303.15, 308.15, and 313.15 K.

The plots of 𝑉^𝐸, Δ𝜂, and Δ𝐺^∗𝐸 versus 𝑥_𝑖 in respective binary mixtures have been given in Figures 1, 2, and 3 at 308.15 K.

Figure 1 

Excess molar volume (𝑉𝐸) with mole fraction (𝑥1) for 1-iodobutane + benzene (■), 1-iodobutane + toluene (●), 1-iodobutane + o-xylene (▲), 1-iodobutane + m-xylene (▼), 1-iodobutane + p-xylene (♦), and 1-iodobutane + mesitylene (▸) at 308.15 K.

Figure 2 

Viscosity deviations (Δη) with mole fraction (𝑥1) for 1-iodobutane + benzene (■), 1-iodobutane + toluene (●), 1-iodobutane + o-xylene (▲), 1-iodobutane + m-xylene (▼), 1-iodobutane + p-xylene (♦), and 1-iodobutane + mesitylene (▸) at 308.15 K.

Figure 3 

Excess Gibbs’ Free energy of activation of flow (Δ𝐺∗𝐸) with mole fraction (𝑥1) for 1-iodobutane + benzene (■), 1-iodobutane + toluene (●), 1-iodobutane + o-xylene (▲), 1-iodobutane + m-xylene (▼), 1-iodobutane + p-xylene (♦), and 1-iodobutane + mesitylene (▸) at 308.15 K.

It can be seen from Figure 1 that the values of 𝑉^𝐸 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 𝑉^𝐸 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 𝑉^𝐸. (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 𝑉^𝐸.(iii)The structural contributions arise from several effects, especially from interstitial accommodation and change in free volume. In other words, structural contribution arises due to geometrical fitting of one component into another because of large difference in the free volume and molar volume of components. This effect contributes negative value to 𝑉^𝐸. 𝑉^𝐸 values observed are both negative to positive, in case highly polar 1-Iodobutane and non polar hydrocarbons. 𝑉^𝐸 values are negative for benzene and 1-iodobutane binary mixtures indicating strong interaction between the two components. The observed 𝑉^𝐸 values are both positive and negative for 1-iodobutane-toluene mixtures and shift from positive to negative values at a mole fraction of 𝑥₁=0.6837 for component 1. For remaining binary mixtures, 𝑉^𝐸 values are positive and indicate for involvement of dispersion type of force. The plot of 𝑉^𝐸 versus 𝑥₁ shows maxima near the middle point, that is, 𝑥₁=0.5 confirming the maximum interaction at the equimolar composition.

As we move from benzene, toluene, and xylenes to mesitylene, there is an increase in the number of –CH₃ 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. 𝑉^𝐸 values for o, m, p-xylene, and 1, 3, 5 tri-methylbenzene are positive over the whole composition range. The increase in 𝑉^𝐸 values with the increase in number of –CH₃ groups implies that dipole-induced dipole interaction is weaker in higher hydrocarbon owing to its decreased polarizabilities with the increase of –CH₃ groups. A similar type of study was reported by Nain et al. [16] for 1,4-dioxane and hydrocarbons. The observed 𝑉^𝐸 values are in the order of Benzene < Toluene < p-xylene < m-xylene < o-xylene < MesityleneAddition 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 𝑉^𝐸 values for o-xylene are found to be higher than the m-xylene and p-xylene. Moreover, 𝑉^𝐸 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 𝑉^𝐸 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-π elector cloud of aromatic hydrocarbons and of (ii) disruption in the orientation order of the two components.

The increase in 𝑉^𝐸 values (positive effect) with increase in temperature suggests for declustering of components at higher temperatures and corresponding increase in kinetic energy.

The values of Δη are negative for all the selected binary mixtures and regularly decrease with an increase in –CH₃ 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 Δ𝜂 values. (ii)Replacement of like contents in pure components by unlike contents in mixture makes positive contributions to Δ𝜂 values. Negative values of Δ𝜂 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 Δ𝜂 values support the positive 𝑉^𝐸 values and account for dispersive forces in these binaries. Δ𝜂 values are also expected to be negative because of vast different in viscosities of pure components (see Table 1).

The negative values of Δ𝜂 at equimolar concentrations of 1-iodobutane and hydrocarbons mixtures are in the following order: benzene > toluene > o-xylene > m-xylene > p-xylene > mesitylene.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, 1-iodobutane + 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 𝐺₁₂ may be attributed to the presence of strong interactions between the components, while the negative values of 𝐺₁₂ indicate for the dominance of dispersion forces [18]. The negatives values of interaction parameters 𝑊_vis are also suggesting for weak interactions and positive values for strong interactions [19]. In the present study, 𝐺₁₂ values are positive for benzene and both positive and negative for toluene mixtures and negative for the remaining hydrocarbons. The values of interaction parameters, 𝑇₁₂ and 𝐻₁₂, 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 𝑇₁₂ and 𝐻₁₂.

The Δ𝐺^∗𝐸 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). Δ𝐺^∗𝐸 parameter can be considered as a reliable criterion to detect and interpret the presence of interactions between unlike molecules [21, 22]. Δ𝐺^∗𝐸 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 Δ𝐺^∗𝐸 studies of Tetrahydorfuran with Benzene, Toluene, o-Xylene, m-Xylene, p-Xylene, Mesitylene binary mixtures. Δ𝐺^∗𝐸 values for all the selected mixtures decrease with the increase in temperature.

4. Conclusion

The excess molar volumes, 𝑉^𝐸, deviations in viscosity, Δη, and excess Gibbs’ free energy of activation flow, Δ𝐺^∗𝐸, 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 𝑉^𝐸, negative Δ𝜂, positive Δ𝐺^∗𝐸, and positive 𝐻₁₂ are observed for iodobutane + benzene mixtures; both negative and positive 𝑉^𝐸 and Δ𝐺^∗𝐸 values and only negative Δ𝜂 values are observed for the toluene mixtures. However, positive 𝑉^𝐸, negative Δ𝜂, and positive Δ𝐺^∗𝐸 values are obtained for xylenes and mesitylene binary mixtures. Interaction parameters 𝐻₁₂ and 𝑊_vis also support the 𝑉^𝐸 and Δ𝜂 values in explaining the molecular interactions (Table 5). The expansion and contraction in volumes cannot be explained on the basis of simply considering 𝑉^𝐸 and Δ𝜂 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 5 

Comparison of interaction parameters (𝑇₁₂, 𝐺₁₂, 𝐻₁₂, and 𝑊_vis) for 1-iodoutane + hydrocarbons binary mixtures at 303.15, 308.15, and 313.15 K.

Table 6 

Estimated parameters of excess functions for the binary mixtures.