Volumetric and Viscometric Studies of Copper Surfactant Derived from Karanj (Pongamia pinnata) Oil in Methanol-benzene Mixture at 298.15 K

The density, molar volume, apparent molar volume, viscosity and other parameters of Cu(II) surfactant derived from karanj oil in non-aqueous solvents of varying compositions have been determined at constant temperature 298.15 K. The results were used to determine the critical micelle concentration (CMC), soap-solvent interactions and the effect of chain length of the surface active molecule on various parameters. The CMC values of copper karanj soap solutions decreased with the increase in the concentration of polar solvent methanol in the solvent mixture. These studies were done to study the solution behaviour, micellar features and various interactions of the derived biologically active surfactant with polar and non-polar solvents to understand the applied part of the molecule. The apparent molar volume has been examined in terms of Masson equation, and the limiting apparent molar volume has been interpreted in terms of solute-solvent interaction. The detailed study of aforesaid compounds clearly indicates that the solutesolvent interaction decreases with the increase in ring strain and size of the synthesised complexes. The conclusions with regard to solute-solute and solute-solvent interaction have been discussed in terms of well-known Moulik’s and Jones-Dole equations. This vital information plays an important role in the selection of the synthesised molecule for various industrial and biological applications.


IntrODuCtIOn
Cu(II) surfactants have found various applications in many industrial uses and play an important role in the colloid chemical phenomena. The exact information on the nature and structure of these compounds are of great significance in explaining their characteristics under different conditions. Recently, work on polymetallic complexes and transition metal complexes of heterocyclic ligands has been done, and their structure and biological characteristics have also been discussed. 1,2 Additionally, researchers studied the molar volume and other parameters of various soaps. 3,4 Many nitrogen and sulphur containing compounds were synthesised and investigated for a wide range of pharmacological and biological activities. 5 They have been used as tranquilisers, sedatives, anti-inflammatory agents, antiviral, anti-malarial fungicide, bactericide, etc. 6 As apparent molar volume of a solute reflects the cumulative effects of solute-solute and solute-solvent interactions, such data are expected to highlight the role of the cation and anion of a weak electrolyte in influencing its apparent molar volumes at infinite dilution on mixed solvent systems. 7,8 The present work deals with the study of density, viscosity and other parameters derived from various equations of copper soap synthesised from (Pongamia pinnata) or karanj oil in a ternary system. The effect of soap concentration on viscosity of the solution in polar and non-polar solvent has been discussed in terms of Jones-Dole equations. 9 The density parameters are important to understand the colloidal behaviour, critical micelle concentration (CMC) characteristics and nature of the complexes. These studies indirectly help in identifying the structural insight, physical and biochemical properties of these class heterocyclic complexes. [10][11][12] The studies will definitely help future researchers to apply these novel binuclear complexes in multiple interlinked fields based on their widest applicability. 13,14 Overall, the present course of study helps us to understand the characteristic nature and application of biological active metal soaps. 15 The study definitely generates a new hope in biological, pharmacological and therapeutic testing. 16 It is anticipated that it will generate a new hope in various industrial and analytical applications. 17 This information is of fundamental importance for understanding solute-solute, solvent-solvent interactions in solutions below and above CMS. 18

ExpErIMEntAl
All the chemicals used were of LR/AR grade. Copper soap was prepared by refluxing the non-edible oil, i.e., karanj oil (extracted from kernels and purified) with ethyl alcohol and 2N KOH solutions for 3-4 h (Direct Metathesis). 19 The neutralisation of excess KOH present was done by slow addition of 0.5N HCl. 20 Saturated solution of copper sulphate was then added to it to convert neutralised potassium soap into their corresponding copper soap. Copper soap obtained was then washed with warm water and 10% alcohol at 50°C and recrystallised using hot benzene. Molecular weights of copper soaps were determined from saponification value. 21 The copper soap is abbreviated as copper-karanj (CK). The physical and analytical data given in Table 1.

Characterisation of CK Soap
In order to study the structure of soap, the infrared absorption spectra of compound was obtained on a Fourier transform infrared (FTIR) spectrophotometer, Shimadzu 821PC (4000-400 cm -1 ) from analytical instrument facility, CDRI, Lucknow, India. Proton NMR spectra were also recorded at SAIF, CDRI, Lucknow, on NMR spectrometers, Bruker DRX-300 at 300 K using C 6 D 6 (deuterated benzene) as solvent for soap.

Ir spectral analysis
The absorption bands observed at 2927.6 cm -1 and 2855.7 cm -1 correspond to asymmetric and symmetric stretching of methylene (-CH 2 ) group in the IR spectra investigation of pure copper karanj soap, with the overlapping of CH 3 anti-symmetrical C-H (υ as ) at 2962 cm -1 and symmetrical C-H (υ s ) stretching at 2872 cm -1 , respectively. The presence of absorption band at 3018.4 cm -1 corresponds to olefinic =C-H stretch and the un-conjugated C=C stretching peaks are very much distinguished at 1655.8 cm -1 with two medium bands at 3018.4 cm -1 and 1655.8 cm -1 , and a strong band at 759.1 cm -1 confirms the cisnature of alkenes. This out of plane C-H bending vibration of alkene is the most characteristic vibrational mode of alkene. 22 It is clear from the spectra of CK soap that it usually is the strongest in the spectra of alkenes. The absorption peak at 1419.2 cm -1 is representative of symmetric C-H deformation bands of =C-H group.
The absorption band near 1377.3 cm -1 is very stable in position arising from the symmetric bending of the methyl C-H showing that the methyl group is attached to another carbon atom. The in-plane bending (δ s ) scissoring band of C-H of methylene group is positioned at 1462.8 cm -1 . This peak may also be assigned to C-H asymmetrical bending vibration of methyl group as it generally overlaps the scissoring vibrations of methylene group.
The peaks 1609.3 cm -1 and 1216.2 cm -1 may be assigned to carboxylate ion COO -, C−O anti-symmetric and symmetric stretching, respectively. Also, a very clear >C=O stretching is also observed at 1736 cm -1 , while a small peak at 1345 cm -1 corresponds to CH 2 twisting and wagging and 669.2 cm -1 to C-H rocking. 23 Copper-oxygen (Cu−O) stretching bands have been distinguished at 480 cm -1 (Table2).

nMr Spectral analysis
The CK showed signal as a triplet at 0.918δ, 0.969δ 0.987δ and 1.290δ representing the aliphatic -CH 3 proton and CH 2 proton attached to -CH 2 -R group. 24 While the peak at 2.093δ represents the proton of -CH 2 group attached to C=C group. Vinylic proton gave signal at 5.474δ. The peaks at 2.233δ and 1.590δ correspond to CH 2 proton on α and β carbon linked to (-COO) 2 Cu group. All the peaks are due to the long chain fatty acid content (R) of the soap molecule [(RCOO) 2 Cu], shown in Table 3.

Measurement of Density
Ostwald's modification of Sprengel pycnometer with a volume of about 10 ml was used for measuring the density of the soap solution in the thermo stated bath at 298.15 K. The density of the solutions was calculated by the following relationship. The measured values of density compared with literature values. 25 The possible error in the density was estimated to be less than. The density ρ was reproducible to within 0 kg m -3 : where w and w 0 are the weights (same volume) of solution and water, respectively.

Evaluation of Molar Volume
The molar volume of the complex solution V has been calculated by the following relationship: 26 where X 1 is the mole fraction of the soap of molecular weight M 1 whereas X 2 is the mole fraction of benzene of molecular weight M 2 , and X 3 is the mole fraction of methanol of molecular weight M 3 . On the other hand, ρ stands for density of the solution. The molar volume was reproducible to within 0 m 3 mol -1 .

Evaluation of Apparent Molar Volume
The apparent molar volume has been calculated from the density data using the following equation: 27 where 0 t represents the density of the solvent, t is the density of the soap solution, M is the molecular weight of the soap, and c is the concentration of solution in mol l -1 . The A.M.V. was reproducible to within 0 m 3 mol -1 .

Evaluation of Viscosity
The viscosity of the soap solutions was calculated by the following relationship. 28 .
. t where η 0 , η, ρ 0 , ρ, t 0 and t are the viscosity, density and time of flow for the known and unknown solutions, respectively. The viscosity η was reproducible to within mPa s -1 .

Density
The effect of varying soap concentrations on the density of Cu (II) karanj soap solution in 100% benzene, 80% benzene-methanol and 60% benzene-methanol in methanol benzene solvent were studied and the solutions were abbreviated as CK 100 , CK 80 and CK 60 , respectively. The density of CK soap solutions initially increases and then decreases and shows a sudden increase again. The plot of density t against concentration c (mol l -1 ) is characterised by an intersection of two convex curves with reference to X-axis. The point of intersection of possible two straight lines at a definite concentration corresponds to the CMC (Figure 1) suggests the sudden change in density, i.e., behaviour of the solution. 29 The CMC values of copper karanj soap solutions decreases with the increase in methanol the polar solvent. The CMC of the CK soap solution: CK 100 > CK 80 > CK 60 This difference clearly demonstrates that agglomeration of soap molecules initiates at a slightly lower soap concentration with the increase of methanol the polar solvent in benzene. This fact suggests that micellar entities are formed a little more easily and efficiently at a much lower soap concentration in the system with higher percentage of polar solvent. It is known that the CMC decreases by about one third per methylene group in aqueous solutions because the energy required to transfer a methylene group from micelle to bulk in small as intermolecular forces are stronger in polar solvents like water and methanol, whereas in non-polar solvents like benzene, these intermolecular forces are weaker.

Molar Volume
The effect of varying soap concentrations on the molar volume of CK soap solution in benzene, 80% benzene-methanol and 60% benzene-methanol is observed and mentioned below: The molar volume of CK soap solutions also initially decreases and then increases and shows a sudden decrease again. The plot of molar volume`V against concentration is characterised by an intersection of two concave curves ( Figure 2).

Apparent Molar Volume
The effect of varying soap concentrations on the apparent molar volume of CK soap solution in 100% benzene, 80% benzene-methanol and 60% benzene-methanol is observed and mentioned herewith: The plot of molar volume`V against concentration is characterised by an intersection of two concave curves, shown in Figure 3.
Here, v z represents apparent molar volume, whereas v 0 z and S v represent limiting apparent molar volume and limiting apparent slope, respectively. v 0 z and S v have been regarded as the measure of solute-solvent interactions and solute-solute interactions, respectively.
According to our observation of v z volume for CK soap, their some negative volume could be ascribed to the earlier study done on the basis of group additively. 16 Some trends that are observed can be explained, at least partially, in terms of structural ion-ion interactions, i.e., hydrophilic-hydrophilic, hydrophilic-hydrophobicand and hydrophobic-hydrophobic interactions. The solute which is studied is CK soap with both hydrophilic and hydrophobic features, i.e., COOof fatty acid chain is hydrophilic in nature and long alkyl chain is hydrophobic in nature. On the other hand, the solvents, i.e., non-polar solvent, benzene is hydrophobic and polar solvent methanol is hydrophilicin nature. Thus, the various interactions occurring between solute and solvent have been analysed. 30 The plot of v z against √c is characterised by an intersection of two convex curves with reference to X-axis ( Figure 4). The point of intersection of possible two straight lines in the curves at a definite concentration corresponds to the critical micelle concentration. Of course, this is the maximum concentration of molecular dispersion at which there is balancing of internal forces causing the formation of micelles. The value of apparent molar volume v z shows a sharp decrease below CMC and increases above CMC in CK soap solution in pure benzene, 80% benzene-methanol and 60% benzene-methanol system.
The CMC obtained from plot of v z against √c has also been confirmed by the density and molar volume measurements. The CMC obtained in this study, is in good agreement with the physical properties like viscosity and various ultrasonic parameters. It is obvious from Table 4 that v v 1 0 2 0 2 z z for CK soap solutions. Thus, for CK soap solute-solvent interaction is more pronounced below CMC as compared to above. This may be ascribed to the favourable interactions between soap-solvent molecules before formation of the micelles. Similarly, the parameter S v in Masson's equation represents the limiting apparent slope and is indicative of solute-solute interactions. A greater magnitude of S v shall be referred to as greater solute-solute (i.e., soap-soap) interactions. It is reasonable to determine two values of parameters S v , i.e., below and above CMC designated as S v1 and S v2 , respectively. It is evident from Table 4 that values of S v parameters follow the order S v1 < S v2 . Therefore, it can be concluded that solutesolute interactions become more pronounced above CMC with respect to solvents the observed order for v2 0 z and S v2 , i.e., above CMC: φ v2 0 (CK 60 ) >φ v2 0 (CK 80 ) >φ v2 0 (CK 100 ) S v2 (CK 100 ) >S v2 (CK 80 ) >S v2 (CK 60 ) Thus, it is obvious that above CMC, the soap-solvent interaction becomes more pronounced with more percent of polar-solvent methanol while the soap-soap interaction decreases, shown in Table 5.

Viscosity
Flow characterisation of soap solutions in terms of viscometric measurements has been employed as a tool for finding out the CMC of copper soaps in benzene and two compositions of benzene-methanol systems.
The plot of viscosity h against concentration c is shown in Figure 5 for CK soap solution in benzene-methanol mixture. The intersection of the two possible straight lines corresponds to the CMC of the CK soap. Before CMC, the plot is of the curve nature and after CMC, the viscosity value increases almost linearly. Interestingly, Moulik's equation also fits equally well to our referred systems: 32

M Kc
where M and K are constants. Thus, the values of M and K could be evaluated both below and above CMC and are designated as M 1 , M 2 , K 1 and K 2 , respectively.
For convenience, the equation may be expressed as: where the coefficient A and B refer to the solute-solute and solute-solvent interactions, respectively. The values of A and B are evaluated from the plot of (ψ/√c) vs. √c, which is characterised by an intersection of two straight lines. Thus, Jones-Dole equations fit well both below and above CMC. The value of CMC obtained is in close agreement with the CMC obtained from η vs. c, η sp vs. c, and φ v vs. c plots, shown in Figure 6. The values of A and B evaluated are recorded in Table 6. Literature survey reveals that positive value of A suggests a strong solute-solute interaction. This contributes negatively to the B-coefficient. Thus, B coefficient is the resultant of these two opposite forces. Therefore, the systems/molecules exhibiting negative B-coefficient have been assumed to exert a structure breaking effect by the solute on the solvent molecules. 34 It is suggested that solute-solute interaction is greater below CMC as compared to above CMC for our referred CK 100 , CK 80 and CK 60 systems as A 1 > A 2 , and A 1 is positive while A 2 is negative for all the systems. Literature survey also reveals that B-coefficient measures the structural modification induced by solute-solvent interaction, and the molecules exhibiting negative B-coefficient have been assumed to exert a structure-breaking effect by the solute on the solvent molecules and it has been observed for our CK 100 , CK 80 and CK 60 systems that the B-coefficient below CMC, i.e., B 1 is negative. This suggests that structure-breaking effect is more below CMC as B 1 < B 2 . It can be suggested that the structure breaking effect by the solute on the solvent molecules is more prominent below CMC as compared to above CMC, i.e., after the formation of the micelles. 35

COnCluSIOn
The present research work attempts to prepare surface active organic compounds from natural non-edible oil and to study their solution behaviour, micellar features and various interactions with polar and non-polar solvents to understand the applied part of the solute. The beneficial effects of the synthesised pharmaceuticals and their biological applications may be explored in the further researches. The current topic will not only strengthen relation between industries, private sectors and research laboratories on the focal theme of biology, physics and environment, but also will also play a significant role in forth coming scientific development through the information related to micellar behaviour of surfactants.

ACKnOwlEDgEMEntS
The authors pay their sincere gratitude to University Grants Commission