Ultrasonic Investigations of Molecular Interaction in Binary Mixtures of Cyclohexanone with Isomers of Butanol

Ultrasonic speed, u, and density, ρ, have been measured in binary liquid mixtures of cyclohexanone with the isomers of butanol (n-butanol, sec-butanol, and tert-butanol) at 308.15 K over the entire range of composition. Molar volume (V m ), adiabatic compressibility (k s ), intermolecular free length (L f ), acoustic impedance (z), and their excess/deviation along with Δu have been calculated from the experimental data.These values have been fitted to Redlich-Kister type polynomial equation. Positive values of


Introduction
Ultrasonic measurements are very useful in chemical and food processing, pharmaceuticals, material testing, and underwater ranging and cleaning and are also commonly employed in mechanical machinery of materials [1], preparation of colloids or emulsions, the pregermination of seeds, imaging of biological tissues [2], activation energy of metabolic process [3], formation and destruction of azeotropes in petrochemical industries [4], and nondestructive testing (NDT).
Alcohols are self-associated organic liquids, used for the synthesis of other organic compounds.They are also widely used as coupling and dispersing agents in the chemical, pharmaceutical, and household industries and as carrier and extraction solvents for natural products.Cyclohexanone and its derivatives are used for the synthesis of pharmaceuticals, dyes, herbicides, pesticides, plasticizers, and rubber chemicals.Ketones are a class of an organic compound that contains a carbonyl group and two aliphatic or aromatic substituents containing the chemical formula RCOR 1 (general chemical formula of Ketones).The chemical reactivity of the carbonyl group plays vital role in chemical reactions and is influenced considerably by steric effects.The greater electronegativity of O − and high dipole moment value make Cyclohexanone polar.Scheme 1 illustrates this polarity.Further the presence of oxygen with its nonbonding electron pairs makes cyclohexanone H-bond acceptors.Thus a study on thermophysical properties data of binary liquid mixtures containing ketones has attracted considerable interest in the literature [5][6][7][8][9].
Literature survey reveals that Tsierkezos et al. [10] studied molecular interactions in cyclohexanone with methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol at 293.15 K and Sri Lakshmi et al. [11] studied molecular interactions in cyclohexanone with -heptanol, -octanol, and isooctanol at temperatures 303.15, 308.15, 313.15, and 318.15K over the entire range of composition.Keeping these important aspects in mind, the present study deals with ultrasonic and thermodynamic study of cyclohexanone (CH) with the isomers of butanol (-butanol, sec-butanol, and tert-butanol) at 308.15 K.The liquids under investigation have been chosen on the basis of their multifold applications.

Experimental Section
High purity analytical reagent (AR) grade compounds of cyclohexanone (mass fraction purity > 99%) and -butanol, sec-butanol, and tert-butanol (mass fraction purity > 99.5%) obtained from S D Fine Chemicals are used in the present study.The chemicals are further purified by standard methods mentioned in [12,13].The weighing of solutions has been made using 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 speeds of pure liquids and liquid mixtures have been measured using an ultrasonic interferometer (Mittal type, Model F-82) working at 2 MHz fixed frequency with an accuracy of ±0.2%.
The temperature of liquid sample in the interferometer cell is maintained constant by circulating water pumped from constant temperature water bath.In the present study the constant temperature water bath (digital electronic) supplied by Concord Instruments Co. Ltd., Chennai (RAAGA type), has been used.The instrument can maintain temperature to ±0.01 K as per its specifications.Densities of pure liquids and their mixtures have been determined by using a 5 cm 3 two-stem double-walled Parker & Parker type pycnometer [15].This pycnometer is calibrated with triply distilled water.The pycnometer filled with air bubble free experimental liquids was kept in a transparent walled constant temperature bath for 20 to 30 min to attain thermal equilibrium.The positions of the liquid levels in the two arms are recorded with the help of traveling microscope.At least three to four measurements are performed, from which an average value of density of the experimental liquid is determined.The estimated accuracy in the density measurement is 3 in 10 5 parts.The ultrasonic speeds, , and densities, , measured at 308.15 K for the pure liquids used in this investigation are compiled in Table 1 together with the literature data [11,14] available.These results are in good agreement with the reported data.

Theory
Thermodynamic and acoustical parameters such as molar volume (  ), adiabatic compressibility (  ), intermolecular  [14] 1086.00 1086.0 [14] free length (  ), and acoustic impedance () are evaluated using the relations given below: where  eff is given by , where  1 and  2 are the molar masses of pure components, and  is the density of the liquid mixture.The speed of sound () and the density of the medium () are related by using Newton and Laplace equation as Here  is the temperature dependent constant which is equal to  = (93.875+ 0.375) × 10 −8 where  is absolute temperature.Consider 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 parameters rather than actual values.Nonideal liquid mixtures show considerable deviation from linearity in their concentrations and this has been interpreted to arise from the presence of strong or weak interactions.The difference between the properties of the real mixtures ( real ) and those corresponding to ideal mixture ( ideal = ∑     ) values, namely, excess properties (  ), such as excess molar volume (   ), free length (   ), acoustic impedance (  ), and deviations in ultrasonic speed (Δ), is computed by the relation where   =    ,    ,   and Δ;   is the mole fraction and   is the value of the property of the th component liquid of mixture.
The deviation in adiabatic compressibility (Δ  ) has been calculated from the equation where Φ 1 , Φ 2 , and  1 ,  2 are the volume fractions and adiabatic compressibilities of components 1 and 2, respectively.Since   is not additive on mole fraction but is additive on volume fraction, such values are calculated using volume fraction (Φ): The experimentally measured values of ultrasonic speed () and density () and calculated properties of molar volume (  ), adiabatic compressibility (  ), intermolecular free length (  ), and acoustic impedance () and excess/deviation thermodynamic properties    ,    ,   , Δ, and Δ  are presented in Table 2 for all binary systems over the entire composition range of CH.
The excess/deviation properties have been fitted to a Redlich-Kister type polynomial equation [16] where   =    ,    ,   , Δ and Δ  ;  1 is the mole fraction of the solute.
The values of Δ  have been fitted to Redlich-Kister type polynomial with volume fraction instead of mole fraction in the above polynomial and   are the adjustable parameters of the function and are determined using the least square method.In the present investigation "" values are taken from 0 to 4. The corresponding standard deviation (  ) was calculated using the expression where "" is the total number of experimental points and "" is the number of coefficients in (7).The calculated values of the coefficients   along with the standard deviations () have been presented in Table 3.

Results and Discussion
Figure 1 represents the variation of excess molar volume (   ) with mole fraction of CH.The sign of    depends upon the contraction and expansion of volume of the liquids due to mixing.The factors that are mainly responsible for the expansion of molar volume, that is, positive values of    , are the following: (i) breaking of the structure of one or both of the components in a solution, that is, the loss of dipolar association between the molecules (dispersion forces); (ii) Hbond rupture and stretching of self-associated molecules (like alcohols); (iii) the geometry of molecular structures which does not favour the fitting of molecules of one component into void space of another molecule; (iv) steric hindrance of the molecules.The negative values of    are due to the (i) association of molecules through the formation of hydrogen bond, that is, strong specific interactions, and (ii) accommodation of molecules because of large differences in their ) V E m (10 Figure 1: Variation of excess molar volume,    , with mole fraction,  1 , of cyclohexanone in (X), -butanol/(◼), sec-butanol/(), and tert-butanol at 308.15 K and Tsierkezos et al. [10] for cyclohexanone + 1-butanol (dotted lines) at 293.15 K. molar volumes.In other words,    arises due to the result of physical, chemical, and structural contributions.Physical interactions involving mainly nonspecific interactions such as dispersion or weak forces (breaking of the liquid order on mixing, i.e., loss of dipolar association between the molecules) contribute to positive    .The chemical or specific interactions such as complex formation and hydrogen bond formation between constituent molecules contribute to negative    .The structural effects arise from interstitial accommodation due to the difference in the molar volumes and free volumes between the liquid components on mixing contributing to negative    [17].The variation of    is found to be positive over the entire composition range in the present investigation which indicates that weak forces exist.Sri Lakshmi et al. [11] reported similar results in CH with -heptanol, -octanol, and iso-octanol at temperatures of 303.15, 308.15, 313.15, and 318.15 K.The    data obtained by Tsierkezos et al. [10] for CH + 1-butanol binary system are negative at 293.15 K whereas in our investigations they are found to be positive when performed at 308.15 K.Such behaviour may arise due to the fact that as temperature increases the effective collision between the component molecules increases.Thus larger number of free dipoles of component molecules may be available due to declusttering of molecules in the pure state.
The nature of interaction in binary liquids can be analysed by knowing their chemical and physical properties (physicochemical properties).Generally, butanols are associated through the hydrogen bonding as shown below and in the pure state, they exhibit equilibrium between the monomer and multimer species.Also, they can be associated with any other groups having some degree of polar attractions.As discussed earlier, butanol exhibits strong intermolecular interactions (H-bond).Alcohol size, chain length, and physical properties (boiling point, density, hydrophobic property, viscosity, insolubility, and refractive index) are important parameters that must be taken into account to explain the behaviour of the interactions (Scheme 2).
CH is a polar molecule because of the presence of carbonyl group (C=O); this is due to the fact that oxygen is more electronegative (O − ) than carbon (C + ).Thus they Resonance structure cause strong dipole-dipole interactions in chemical reactions.Moreover CH lacks hydroxyl groups, so it is incapable of creating intermolecular hydrogen bonds.In CH + isomers of butanol binary systems, the negatively charged oxygen (O − ) in CH tries to drag the positively charged H + which were bounded in very strong intermolecular interactions of butanol (Scheme 3).An equilibrium stage is reached where rupturing of hydrogen bond or reduction in H-bond strength of butanol or breaking of the structure of one or both of the components in a solution, that is, the loss of dipolar association between the molecules (dispersion forces) [18], will be favourable leading to weak interactions.This causes increase in volume of binary liquid and explains the observed positive values    in the systems.Kiyohara and Benson [19]  The variations of excess acoustic impedance (  ) and deviation in ultrasonic speed (Δ) have been presented in Figures 4 and 5, respectively.From Figure 4, it has been observed that the values of   are negative over the entire mole fraction range indicating the decreasing strength of interactions between component molecules of the mixture.According to Gowrisankar et al. [22], the negative values for Δ indicate the decrease in the strength of interaction between the molecules and the negative deviations in Δ from linear dependence suggest the presence of weak interaction between the component molecules.These deviation/ excess properties further support the conclusions drawn from    ,    , and Δ  .The existing molecular interactions in the systems are well reflected in the properties of partial molar volumes.The partial molar volumes  ,1 of component 1 (CH) and  ,2 of component 2 (isomers of butanol) in the mixtures over the entire composition range have been calculated by using the following relations: where  * 1 and  * 2 are the molar volumes of the pure components of CH and butanols, respectively.The derivates in the above equations are obtained by differentiating Redlich-Kister equation ( 7) which leads to the following equations for  ,1 and  ,2 : using the above equations   ,1 ,   ,2 have been calculated using The pertinent values of  ,1 and  ,2 are furnished in Table 4. From this table, the values of  ,1 and  ,2 for both the components in the mixtures are greater than their respective molar volumes in the pure state; that is, an expansion of volume takes place on mixing alcohols with ketone.These results also support the observed positive values of    in all the binary systems.Figures 6 and 7 represent the variation of excess partial molar volumes of  (isomers of butanol) in the binary mixtures.Examination of these figures reveals that dispersion forces exist between the unlike molecules.These figures support the conclusions drawn from    .The partial molar volumes and excess partial  ,2 , respectively, were obtained by putting  = 0 in (10) and  = 1 in (11).Consider The pertinent values of ,1 , and  ,∞ ,2 are reported in Table 5.From this table it is seen that these values are positive, from which we conclude that weak interactions exist among the unlike molecules of the liquid mixtures.
FT-IR spectra of pure CH, butanols, and binary mixtures of CH with butanols at equal concentrations are depicted in Figures 8, 9, and 10.According to Karunakar and Srinivas [23], the intensity of an absorption in the IR spectrum is related to the change in dipole moment that occurs during the vibration.Consequently, vibrations that produce a large change in dipole moment (e.g., C=O stretch) result in a more intense absorption than those that result in a relatively modest change in dipole (e.g., C=C).Vibrations that do not result in a change in dipole moment (e.g., a symmetrical alkyne C≡C stretch) will show little or no absorption for this vibration.In the present FT-IR spectra liquid mixture shows very small variations in the intensity of the respective bonds, that is, dipole moment, and hence it supports that weak interactions take place between the components of liquid molecules.Theoretical evaluation of ultrasonic speed in binary liquid mixtures and its correlation to study molecular interaction has been successfully done in recent years.Ultrasonic speeds in liquid mixtures have been calculated and compared with experimental values using various theories.Such an evaluation offers a simple method to investigate molecular interactions besides verifying the applicability of various theories to liquid mixtures.Nomoto [24] established the following relation for sound speed (  ) based on the assumption of the linearity of the molecular sound speed and the additivity of molar volume: where   is molar sound speed and   is molar volume.van Dael and Vangeel [25] obtained the ideal mixture relation Baluja and Parsania [26] have given impedance relation on the basis of force of resistance for sound speed by the interacting molecules Rao's (specific sound speed) [27] relation is given by where   =  1/3  /  is Rao's specific sound speed of th component of the mixture.
Percentage deviation in ultrasonic speed is given by Table 6 shows the values of ultrasonic speed computed by various theories along with their percentage error for all the systems.The variations between the evaluated and experimental values may be due to interactions occurring between the hetero molecules of the binaries.From the observed values of all three systems, there is a good agreement between theoretical and experimental values through van Deal and Vangeel relation.It can be seen from Table 6 that the theoretical values of ultrasonic speed calculated by using various theories show deviation from experimental values.The limitations and approximation incorporated in these theories are responsible for the deviations of theoretical values from experimental values.Nomoto's theory proposes that the volume does not change upon mixing.Therefore, no interaction between the components of liquid mixtures has been taken into account.Similarly, the assumption for the formation of ideal mixing relation is that the ratios of specific heats of ideal mixtures and the volumes are also equal.Again no molecular interactions are taken into account.But upon mixing, interactions between the molecules occur because of the presence of various types of forces such as dispersion forces, charge transfer, and hydrogen bonding dipole-dipole and dipoleinduced dipole interactions.Thus, the observed deviation of theoretical values of speed from the experimental values shows that the molecular interactions are taking place between the CH and isomers of butanol molecules.The deviations of experimental values and values calculated from impedance relation and Rao's relation imply nonadditivity of acoustic impedance and Rao's speed in the liquid mixtures.Among all the empirical theories van Dael and Vangeels relation gives better estimate of experimental values of sound speed in all the systems.In the present binary systems, the difference between experimental and theoretical speeds is greater where the mole fraction of CH varies in the region 0.3 to 0.6.Hence it can be qualitatively inferred that the strength of interaction in the binary mixtures is more in this range of composition of CH with isomers of butanol liquid system.

Conclusion
(i) Ultrasonic speeds, , and densities, , of mixtures of cyclohexanone with -butanol or sec-butanol or tertbutanol over the entire composition range have been measured at  = 308.15K.
(ii) The values of    , Δ  ,    ,   , and Δ are calculated from experimental data of density and ultrasonic speed.The excess and deviation properties have been fitted to Redlich-Kister type polynomial and corresponding standard deviations have been evaluated.The observed positive values of    , Δ  , and    and negative values of   , Δ for all the liquid mixtures studied clearly indicate the presence of weak interactions such as rupturing of hydrogen bond or reduction in H-bond strength of butanol or breaking of the structure of one or both of the components in a solution.
(iii) The deviation/excess properties have been fitted to Redlich-Kister type polynomial and the corresponding standard deviations have been calculated.
(iv) The calculated values of partial molar volumes have also been examined.The observed higher partial molar volumes in the liquid mixture when compared to the respective molar volumes of pure components indicate weak interactions present in the systems.
(v) The strength of interaction in the mixtures follows the order CH +, tert-butanol > sec-butanol > -butanol.
(vi) FT-IR spectra for the present binary mixture also support the conclusions drawn from the    ,    , Δ  , Δ, and   .
(vii) Further theoretical values of sound speed in the mixtures have been evaluated using various theories and have been compared with experimental sound speeds to verify the applicability of such theories to the systems studied.

Table 1 :
Comparison of experimental values of density, , and ultrasonic speed, , of pure liquids with the corresponding literature values at 308.15 K.

Table 3 :
(7)fficients   of Redlich-Kister type polynomial equation(7)and the corresponding standard deviations, , of all the systems at 308.15 K.
[21] suggested that Δ  is the resultant of several opposing effects.Negative values of Δ  contribute to charge transfer, dipole-induced dipole and -dipole interactions, interstitial accommodation, and breaking up of the alcohol structures leads to positive values of Δ  .From Figure2, the observed positive values of Δ  for binary mixtures of CH with -butanol, -butanol, and butanol are due to declustering of alcohols in the presence of CH.The positive deviation in Δ  for the binary systems follows the order CH +, -butanol > -butanol > -butanol.Figure3represents the variation of    with mole fraction ( 1 ) of CH.The observed values of    are positive.According to Fort and Moore[20], positive    should be attributed to the dispersive forces.As mentioned earlier, positive values of Δ  and    are mainly attributed to weak forces between the component molecules in the mixture[21].

Table 5 :
Partial molar volumes ( ) of the components at infinite dilution for all the systems at 308.15 K.

Table 6 :
Theoretical values of ultrasonic speed from various equations and percentage error with mole fraction  1 of CH for all binary systems at 308.15 K.