Acoustic and volumetric investigations in aromatic, cyclic and aliphatic ketones with dimethyl sulphoxide at 308.15 K

1 Introduction

Ultrasonic velocities, densities and derived thermodynamic and acoustical parameters are of considerable interest in understanding the intermolecular interactions in binary as well as in ternary liquid mixtures (Armugam et al., 1998; Ali et al., 1999; Bhatt et al., 2000; Thirumaran, 2002; Deepali, 2004; Aralaguppi et al., 1991; Aminabhavi et al., 1999). In the chemical industry knowledge of the thermodynamic properties of non-electrolyte solutions is essential in the design involving chemical separation, heat transfer, mass transfer and fluid flow. Ultrasonic studies can also be used to determine the extent of complexation and to calculate the formation constant values of charge transfer complexes (Prakash, 1980; Kannappan, 2009; Zorebski and Kostka, 2008). Measurement of ultrasonic velocity has been adequately employed in understanding the nature of molecular interaction in pure liquid and liquid mixtures. The practical application of mixed solvents rather than single solvent in industrial and biological process has been recognized all over the world as they provide a wide choice of solutions with appropriate properties (Ali and Nain, 2001).

The present study deals with the thermodynamic study of mixed solvent system at 308.15 K temperature. The liquids under investigation have been chosen on the basis of their industrial applications. These applications have greatly stimulated the need for extensive information on the thermodynamic, acoustic and transport properties of these solvents and their mixtures (Oswal and Desai, 2001; Thirumaran and Karthikeyan, 2011; Rathnam, 2012).

The selected components for the present study are dimethyl sulphoxide (DMSO) and ketone group liquids acetophenone (AP)/cyclohexanone (CH)/3-pentanone (3P). These have wide applicability in various food and pharmaceutical industries. Cyclohexanone and 3-pentanone are used in fragrances. Acetophenone is commonly used as flavoring in many cherry flavored sweets and drinks.

The common solvent chosen here is DMSO. The present investigation related to thermodynamic properties of binary liquid mixtures containing DMSO, which is aprotic, strongly associated due to highly polar S⚌O group molecule, large dipole moment and dielectric constant. The study of DMSO is important because of its utilization in a broad range of applications in medicine (Jyostna and Satyanarayana, 2005; Gonzalez et al., 2007; Alonso et al., 2011).

Study on thermo physical properties data of binary liquid mixtures containing ketones has attracted considerable interest in the literature (Pereiro et al., 2005a,b, 2006; Iloukhani and Rostami, 2007a,b; Rathnam et al., 2011). Literature survey reveals that Radhamma et al. reported density and ultrasonic velocity data for binary mixtures of DMSO and certain ketones at 303.15 K (Radhamma et al., 2008).

2 Experimental details

High purity Analytical Reagent (AR) grade samples of DMSO (sd fine chemicals), cyclohexanone (Fluka), 3-pentanone procured from Merck and acetophenone procured from Sigma Aldrich were used. Before measurements all the liquids were carefully dried over 0.4 nm molecular sieves and stored in dark bottles. These samples were further purified by standard methods (Vogel, 1989; Riddick et al., 1986). The solutions of binary mixtures of DMSO with AP, CH and 3P have been prepared in the specially designed glass bottles with airtight stoppers and adequate precautions have been taken to minimize evaporation losses. These samples were distilled just before use. The purity of these liquids was ascertained by Gas Chromatography (HP 8610) using a FID detector and the analysis indicated mole per cent purities >99.5%. The weighing of solutions has been made using a METTLER TOLEDO (Switzerland make) ABB5-S/FACT digital balance with an accuracy of ±0.01 mg. The uncertainty in the mole fraction is 10⁻⁴. The ultrasonic velocities (u) of pure liquids and liquid mixtures have been measured using an ultrasonic interferometer (Mittal type, Model M-82) working at 2 MHz fixed frequency with an accuracy of ±0.01 m s⁻¹. Densities (ρ) of pure liquids and their mixtures have been determined by using a 10 cm³ two stem double-walled Parker & Parker type pycnometer (Parker and Parker, 1925). The procedure for measuring u and ρ has been described in our previous papers (Nayeem et al., 2014a,b,c). The reproducibility in the measured parameter of density is 3 in 10⁴ parts and in mole fraction it is ±0.0002.

3 Results and discussion

The experimentally measured values of ultrasonic speed (u) and density (ρ) at 308.15 K of all pure liquids have been compared with the literature values (Palani et al., 2008; Rathnam et al., 2014) in Table 1 and these values have been used to evaluate the various volumetric and acoustic properties such as molar volume, V_m, isentropic compressibility, k_s, intermolecular free length, L_f, acoustic impedance, Z, using their standard relations. The measured values of ρ, and u have been presented in Table 2. In order to understand the nature of the molecular interactions between the components of the liquid mixtures, it is of interest to discuss the same in terms of excess properties rather than actual values. Non-ideality arises from the differences between interactions in mixtures and pure components. The difference between the properties of the real mixture (Y_real) and those corresponding to an ideal mixture (Y_ideal = ∑x_iY_i) values, namely excess/deviation parameters (Y^E) have been computed by the relation

The deviation in isentropic compressibility, Δk_s has been calculated from the following equation (Ali et al., 2003):

Since k_s is not additive on mole fraction but is additive on volume fraction (Nayeem et al., 2015), hence, such values have been calculated using volume fraction (Φ)

The excess/deviation values are also tabulated in Table 2. The excess/deviation properties have been fitted to a Redlich–Kister type polynomial equation (Redlich and Kister, 1948) as follows:

The values of Δk_s have been fitted to Redlich–Kister type polynomial with volume fraction (Φ) instead of mole fraction (x) in the above polynomial and A_i are the adjustable parameters of the function and are determined using the least square method. In the present investigation ‘i’ values have been taken from 0 to 4. The corresponding standard deviations σ(Y^E) have been calculated using the expression:

In DMSO, the group (S⁺—O⁻) plays vital role in chemical reactions. Ketones are organic compounds that contain a carbonyl group and two aliphatic or aromatic substituents containing the chemical formula RCOR¹. Here, R and R¹ may be same or different incorporated into a ring (alkyl, aryl and heterocyclic radicals). The chemical reactivity of the carbonyl group (C⚌O) plays vital role in chemical reactions and is influenced considerably by steric effects. The greater electro negativity of O⁻ and high dipole moment makes ketones polar. The structures of the ketones in the present study i.e., AP, CH and 3P are also shown below.

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Fig. 1 represents the variation of $V_m^E$ with mole fraction of DMSO. The excess molar volume is the resultant contribution from several opposing effects, namely chemical, physical and structural (Sankar et al., 2014). The chemical or specific interactions result in volume contractions, leading to negative excess molar volume and these include charge-transfer complexes, dipole–dipole and dipole-induced dipole interactions and H-bonding between component molecules. The physical interactions or non-specific interactions are weak and these include breaking of the structure of one or both of the components in the solution, i.e. the loss of dipolar association between the molecules (dispersion forces), steric hindrance of the molecules and H-bond rupture. The structural contributions are mostly negative and arise from several effects such as interstitial accommodation and geometrical fitting of one component into another due to the differences in the molar volumes between components. In the present investigation, the variation of $V_m^E$ is found to be positive over the entire composition range. Further, it is noticed from Fig. 1 that the values of $V_m^E$ become more positive as we move from AP to 3P i.e., over the entire composition range of DMSO, positive values of $V_m^E$ follow the order: (DMSO + AP) < (DMSO + CH) < (DMSO + 3P). Further, positive $V_m^E$ indicate the possibility of existence/dominance of weak interactions (Nayeem et al., 2014a,b,c; Aralaguppi et al., 1992) and strength of weak interactions follows the order: (DMSO + AP) < (DMSO + CH) < (DMSO + 3P).

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Figure 1 Plots of excess molar volume V m E against mole fraction, x₁ of DMSO for the binary mixtures of DMSO + AP (♦), DMSO + CH (■) and DMSO + 3P (▴).

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The nature of existing interaction in a binary liquid can also be analysed by knowing their individual chemical and physical properties (physico-chemical properties). The presence of chemical or specific interactions is certainly absent in the present systems at all temperatures. This is due to the fact that the chemicals which are used in the present investigation lack hydroxyl group and hence formation of H-bond is trifling. With regard to physical or non-specific interactions, according to the authors (Rajagopal and Chenthilnath, 2010a,b), when ketones are mixed with polar molecules, the strength of interaction between the participating molecules depends on the dipole moment/polarizability and geometry (i.e., steric hindrance) of the interacting molecules. It is evident that DMSO and the present ketones are polar and their dipole moment values follow μ_D = 4.06 D > μ_AP = 3.02 D > μ_CH = 2.87 D > μ_3P = 2.70 D. In the present study, positive $V_m^E$ values suggest the possibility of loss of dipolar association (dispersion forces) (Radhamma et al., 2008) between DMSO and ketone molecules. As the difference between dipole moment values of the binary system increases, the strength of interaction decreases (Kondaiah et al., 2013). Therefore in the present investigation strength of interaction follows the order: (DMSO + AP) > (DMSO + CH) > (DMSO + 3P). Further, based on the geometry (i.e., steric effect), the order of strength of weak interaction can be written as: (DMSO + aromatic ring with CH₃ group of AP) < (DMSO + cyclic CH) < (DMSO + aliphatic 3P). This implies that the presence of larger —CH₃—CH₂— chain attached to carbonyl group of aliphatic 3P causes much more steric hindrance to DMSO over the other ketones leading to highest positive values of $V_m^E$ . Thus in the present study, dispersion forces and steric hindrance of physical interactions play vital role in deciding the observed positive values of $V_m^E$ . With respect to structural contribution, the molar volumes of pure components of DMSO, AP, CH and 3P are 7.2029, 11.8550, 10.7528 and 10.4459 (×10⁻⁵ m³ mol⁻¹) respectively at 308.15 K. From these values geometrical fitting of smaller molecules into the voids created by the bigger molecules is most favourable in (DMSO + AP) rather than (DMSO + CH) and (DMSO + 3P) binary systems. Therefore, the observed positive values of $V_m^E$ and the order of strength of weak interactions are due to cumulative effect of all the above mentioned facts. In DMSO + ketone binary systems, the dominance of prevailing physical interactions over the other factors (structural) makes the molecules of the binary liquid move apart leading to the observed positive values of $V_m^E$ . Similar type of study was reported in polar lower alcohol of 2-methyl-2-propanol with aromatic and aliphatic ketone (Rajagopal and Chenthilnath, 2010a,b). Moreover, the same type of positive values of $V_m^E$ trend was observed in N-methyl-2-pyrrolidone with ketones (Gnana Kumari et al., 2009) and in cyclohexane with ethyl acrylate, butyl acrylate, methyl methacrylate, and styrene (Peralta et al., 2002, 2003). Thus, this analysis gives an idea about the participation tendency of aromatic, cyclic and aliphatic ketones in molecular interactions with DMSO.

The existing molecular interactions in the systems are well reflected on the properties of partial molar volumes. Partial molar volume is the contribution that a component of a mixture makes to the overall volume of the solution. Thus, the partial molar volume is a function of mixture composition. The partial molar volumes ${\bar{V}}_{m\text{,}1}$ of component 1 (DMSO) and ${\bar{V}}_{m\text{,}2}$ of component 2 (ketones) in the mixtures over the entire composition range have been calculated by using the following relations:

Using the above equations ${\bar{V}}_{m\text{,}1}^E\text{,}{\bar{V}}_{m\text{,}2}^E$ have been calculated using,

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Figure 2 Plots of excess partial molar volumes of DMSO V ‾ m , 1 E and AP/CH/3P V ‾ m , 2 E against mole fraction, x₁ of DMSO for binary mixtures of DMSO with AP (♦), CH (■), and 3P (▴).

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Furthermore, the partial molar volumes and excess partial molar volumes of the components at infinite dilution respectively, ${\bar{V}}_{m\text{,}1}^{\infty }\text{,}{\bar{V}}_{m\text{,}2}^{\infty }\text{,}{\bar{V}}_{m\text{,}1}^{E\text{,}\infty }$ and ${\bar{V}}_{m\text{,}2}^{E\text{,}\infty }$ were obtained by putting x₁ = 0 in Eq. (8) and x₁ = 1 in Eq. (9).

The sign and magnitude of Δu play important roles in describing molecular rearrangements as a result of molecular interactions occurring among the component molecules in the mixtures. The variation of deviation in ultrasonic speed (Δu) with mole fraction of DMSO is shown in Fig. 3. Here we observed that the Δu values are negative for all binary systems over the entire range of composition at 308.15 K temperature. Positive deviations in Δu indicate the increasing strength of interaction between component molecules of binary liquid mixtures. If the strong interactions arise among the components of a mixture, it may lead to the formation of molecular aggregates and attains more compact structures, then sound will travel at faster rate through the mixture by means of longitudinal waves and hence the ultrasonic speed deviations with respect to the linear behavior will be positive. If the structure-breaking factor in the mixture predominates resulting expansion then the speed of sound through the mixture will be slower resulting in negative Δu. The negative values in Δu generally indicate the presence of weak interactions (Nain, 2008; Kawaizumi et al., 1977). This negative deviation in u also supports the inference drawn from excess molar volume in all the systems studied.

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Figure 3 Plots of deviation in ultrasonic velocity (Δu) against mole fraction, x₁ of DMSO for the binary mixtures of DMSO + AP (♦), DMSO + CH (■) and DMSO + 3P (▴).

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Fig. 4 represents the variation of deviation in isentropic compressibility (Δk_s) with the mole fraction of the DMSO over the entire composition range. The experimental values of Δk_s may be attributed to the relative strength of effects which influence the free space, defined by the author (Jacobson, 1952). According to this hypothesis addition of ketone molecules to DMSO will induce breaking of clusters of DMSO molecules thereby releasing several dipoles, which interact with dipoles of ketone. This causes an increase in free space, decrease in sound velocity and positive deviation in isentropic compressibility. However, this effect will be counteracted due to the interaction between carbonyl group of ketone and S⚌O group of DMSO, changes in free volume in the real mixtures and interstitial accommodation of component molecules into each other’s structure resulting to negative deviation in compressibility. The actual values of Δk_s, therefore, would depend upon the relative strengths of two opposing effects. The experimental values of the deviation in isentropic compressibility, Δk_s, in the present investigation show that the factors responsible for positive Δk_s are dominant over the entire volume fraction. This supports the inference made from the variation of deviation in all ultrasonic speeds.

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Figure 4 Plots of deviation in isentropic compressibility (Δk_s) against mole fraction, x₁ of DMSO for the binary mixtures of DMSO + AP (♦), DMSO + CH (■) and DMSO + 3P (▴).

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The variation of excess acoustic impedance (Z^E) and excess free length $(L_f^E)$ with mole fraction of DMSO in the mixtures has been presented in Figs. 5 and 6 respectively. From Fig. 5 it has been observed that the values of Z^E are negative over the entire mole fraction range which indicates the decreasing strength of interactions between component molecules of the mixture (Krishna Rao and Sreekanth, 2011). From Fig. 6 it has been observed that the values of $L_f^E$ are positive. The positive $L_f^E$ values should be attributed to the weak dispersive forces (Fort and Moore, 1965). These inferences further support the presence of weak interaction forces in all the present systems studied.

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Figure 5 Plots of excess acoustic impedance (Z^E) against mole fraction, x₁ of DMSO for the binary mixtures of DMSO + AP (♦), DMSO + CH (■) and DMSO + 3P (▴).

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Figure 6 Plots of excess free length L f E against mole fraction, x₁ of DMSO for the binary mixtures of DMSO + AP (♦), DMSO + CH (■) and DMSO + 3P (▴).

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FTIR spectra for the present pure liquids along with their binaries in equal ratio are shown in Figs. 7–9. Usually in an IR spectrum, the change in the intensity is related to the interaction between solute and solvent. In this spectra, considerable changes in the intensity of transmission/absorption show strong interaction in the system otherwise no or small changes show weak interactions (Rajendran, 1996). Furthermore, intensity of transmission/absorption in an IR spectrum is related to the change in dipole moment that occurs during the vibration (Karunakar and Srinivas, 2013). The characteristic peaks in pure DMSO and binaries (1:1) are tabulated in Table 6. Pure DMSO exhibits peaks at 1436 cm⁻¹, 1406 cm⁻¹, 1311 cm⁻¹ and a broad vibrational mode around 1041 cm⁻¹. The modes at wave numbers 1436 cm⁻¹ and 1406 cm⁻¹ correspond to the antisymmetric bending of CH₃(δ_as CH₃), and the peak at 1311 cm⁻¹ is identified as a symmetric deformation of CH₃(δ_s CH₃) group that is attached to the S atom. A broad vibrational mode around 1041 cm⁻¹ can be assigned to S⚌O stretching (ν SO). From Table 6, it is evident that the symmetric deformation caused by δ_s CH₃ of DMSO is affected reasonably in DMSO + AP system whereas antisymmetric bending vibration δ_as CH₃ of DMSO is not that much influenced in DMSO + 3P. From the FTIR spectra of binary liquids, it is concluded that the order of weak interactions is as follows: (DMSO + aliphatic 3P) > (DMSO + cyclic CH) > (DMSO + aromatic AP) and it also supports the inferences drawn from excess/deviation properties.

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Figure 7 Fourier Transform Infrared spectra of pure DMSO (Blue), DMSO + AP (Green) in the ratio 1:1 and pure AP (Red).

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Figure 8 Fourier Transform Infrared spectra of pure DMSO (Blue), DMSO + CH (Green) in the ratio 1:1 and pure CH (Red).

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Figure 9 Fourier Transform Infrared spectra of pure DMSO (Blue), DMSO + 3P (Green) in the ratio 1:1 and pure 3P (Red).

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In the present study, semi-empirical sound velocities have been evaluated by considering ketones as one component and DMSO as the other component in the binary mixture. Such an evaluation of semi-empirical sound velocity is useful to verify the applicability of various postulates of the theories of liquid mixtures and to arrive at some useful inferences regarding the (strength of) molecular interactions between component liquids in some cases. The semi-empirical values of ultrasonic velocity with percentage deviation are summarized in Table 7 and standard deviations of these empirical values are shown in Table 8.

Nomoto (1958) established the following relation for sound velocity based on the assumption of the linearity of the molecular sound velocity and the additivity of molar volume:

The Impedance Dependence Relation (Baluja and Parsania, 1995) is given as follows:

Van Dael (Van Dael and Vangeel, 1969) obtained the Ideal Mixture Relation

Rao’s (specific sound velocity) (Sreekanth et al., 2011) relation is given by

Junjie’s (Savaroglu and Aral, 2004) equation is given by

Percentage deviation in ultrasonic speed is given by

4 Conclusions

• Densities and ultrasonic velocities for binary liquids of DMSO with AP/CP/3P have been measured experimentally over the entire composition range at T = 308.15 K.

• From the experimental data parameters such as $V_m^E$ , Δk_s, $L_f^E$ , Z^E and Δu have been evaluated. The excess and deviation properties have been fitted to Redlich–Kister type polynomial and corresponding standard deviations have been calculated. In the present binary liquid systems of DMSO+ different geometrical ketones, the observed positive values of $V_m^E$ , Δk_s, $L_f^E$ and negative values of Z^E, Δu clearly indicate the dominance of weak physical interactions (dispersion and steric hindrance). The order of weak interactions is as follows: (DMSO + aliphatic 3P) > (DMSO + cyclic CH) > (DMSO + aromatic AP).

• The observed higher partial molar volumes in the liquid mixture when compared to the respective molar volumes of pure components also support the presence of weak physical interactions in the systems.

• The FT-IR spectra also support the inferences drawn from excess/deviation properties.

• The ultrasonic velocities computed from different velocity theories have been correlated with the experimentally measured ultrasonic velocities and their percentage deviations have been evaluated. Among all the empirical theories Jungie’s relation is found to give the best estimate of experimental values of sound velocity in all the systems investigated.