Computational And Dielectric Studies On Binary Mixtures of Propan-2-Ol with N-Alkyl P-Hydroxy Benzoates

Computational And Dielectric Studies On Binary Mixtures of Propan-2-Ol with N-Alkyl P-Hydroxy Benzoates

T. Madhu Mohan

Department of Physics, Vasireddy Venkatadri Institute of Technology, Nambur, Andhra Pradesh

T. Vijaya Krishna

Department of Physics, Vasireddy Venkatadri Institute of Technology, Nambur, Andhra Pradesh

Ch. Ravishankar Kumar Department of Physics, GITAM University, Vishakapattanam, Andhra Pradesh

Abstract

The dielectric studies on the polar binary mixtures propan-2-ol with n-alkyl p-hydroxy benzoates (n=7 and

9) have been carried out at various mole and volume fractions. LF impedance analyzer, Microwave bench and Abbes refractometer are used respectively in radio, microwave (X-Band) and high frequency regions to determine the dielectric data. The experimental data is used to calculate the dielectric constant, dielectric loss, relaxation time, dipolemoment and excess dipolemoment. Hamiltonian quantum mechanical calculations are performed for both pure and equimolar binary systems with optimized converged geometry procedure using PC Spartan modeling software. Dipole moments of the pure and binary mixtures are calculated experimentally from the dielectric data using Higasis method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between propan-2-ol and n-alkyl p-hydroxy benzoates is supported by the FT-IR spectra.

1. Introduction

The aim of the dielectric relaxation study is to understand intermolecular and intramolecular interactions in a molecular system. Extensive studies have been done to understand these interactions on different types of binary polar mixtures. Many workers have reported dielectric relaxation studies of polar molecules and their binary mixtures in dilute solutions of nonpolar solvents [1-3] as well as in pure state [4-8]. Hydrogen bonding in liquid systems has been intensively studied for long and it is still subject to a lively scientific debate, because of its outstanding role

in chemistry and biology. Much attention has been also directed towards the physicochemical properties of alcohols not only due to their widespread use as solvents but also because of their fascinating features [9, 10]. As molecules with OH groups form associative liquid due to hydrogen bonding, the effect of the presence of molecules with other functional groups on these molecules is very important to understand the behavior of hydrogen bonding. Alkyl p – hydroxy benzoates are non-associated in solution, good hydrogen bonding acceptors and important industrial chemicals that are widely used in food and cosmetic preservatives. For the present study propan-2-ol is selected as an associative compound and Heptyl p- hydroxy benzoate, Nonyl p-hydroxy benzoate are selected as non associative compounds.

Dielectric dispersion studies like dipole moment and the relaxation behavior phenomena of polar liquids such as alcohols, benzoates and their binary mixtures were carried out to determine the nature of interaction existing between the molecules due to hydrogen bonding. Dipole moments are determined for the polar solute system diluted in non-polar solvent benzene to minimize the dipole-dipole interaction. The dielectric behavior of some hydrogen bonded polar liquid mixtures was studied by Vishwam et, al. [11]. The non associative compounds Heptyl p-hydroxy benzoate and nonyl p-hydroxy benzoate of the present study are useful for hydrogen bonding formation with liquid crystals [12] which eventually affect the dipole moment and relaxation time. The relaxation time studies have been carried out in the binary mixtures of propan-2-ol with methyl and ethyl benzoates [13].

The objective of the present work is to report the influence of non associative molecule on the associative

molecule in liquid state by studying the dielectric behaviour of the binary mixtures propan-2-ol with n- alkyl p-hydroxy benzoates (n=7 and 9) (solute system) in non-polar solvent medium (benzene) with different concentration. The average relaxation times are calculated from the respective Cole-Cole plots [14]. Dipole moment values are calculated using the Higasis

, ' and " are ± 0.002, ± 0.0002, ± 0.01 and ± 0.03 respectively. The FT-IR-spectra of pure and equimolar binary mixture systems are recorded in 400-4000 cm-1 region on Perkin-Elmer (spectrum bX) series.

3. Theory

method [15] and compared with the theoretical Hamiltonian quantum mechanical calculations.

The dielectric data obtained i.e.,

static ,

Minimum energy structures of the polar systems propan-2-ol, n- alkyl p-hydroxy benzoates and their equimolar binary system are determined with optimized converged geometry optimization procedure using PC Spartan modeling software [16]. Conformational analysis of the formation of hydrogen bond between the mixture systems is carried out from FT-IR spectra in 400-4000 cm -1 region.

2. Experimental

Propan-2-ol (IPA) and benzene are Qualigen chemicals of Analar grade and double distilled before use. Heptyl p-hydroxy benzoate (7HB) and Nonyl p- hydroxy benzoate (9HB) are purchased from M/s Frinton Laboratories, USA. In the preparation of

* ' j " , and the data from LF-impedance

analyzer is used to fit in an Argand diagram to calculate the relaxation time ( ). The distribution of relaxation

time is witnessed from Cole-Cole arc plot. In Cole-Cole method, the semicircle corresponding to one relaxation time is generally replaced by the arc of a circle in which the center lies below the actual axis. The diameter of this circle cuts the axis of abscissas at the point

corresponding to the value of and forms an angle

2

with the axis of abscissa. By plotting through

the experimental points, determined for various frequencies, an arc is obtained whose center lies below

solution the binary mixtures propan-2-ol + Heptyl p-

the ' axis. It is possible to find the value of relaxation

hydroxy benzoate (system 1) or propan-2-ol + Nonyl p- hydroxy benzoate (system 2) is used as solute and benzene is used as solvent. First n- alkyl p-hydroxy benzoates are dissolved in propan-2-ol at various mole

time by the equation,

1

v 1

u

(1)

fractions (MF) i.e., 0.01%, 0.02%, 0.03%, 0.04% and then each concentration of solute is diluted with solvent in different volume fractions (10%, 20%, 30% and 40%) of the solution . The mass measurements are performed on a digital electronic balance (Mettler Toledo AB 135, Switzerland) with an uncertainty of ±

0.00001 g.

where (distribution u v values are determined from their respective Cole-Cole plots. A typical Cole-Cole plot is shown in the results and discussion part.

The dipole moments of dilute systems were calculated from Higasis method.

The permittivity values at spot frequencies 1 kHz (

2 27kTM2 a0 – a

=

(2)

static ), 10 kHz, 100 kHz, 1 MHz and 10 MHz for the above systems are measured using HP-LF impedance

4Nd + 22

1 1

where M2 is molecular weight of solute, a and a are

analyzer (Model No: 4192 A). The real ( ' ) and 0

imaginary ( " ) parts of the complex dielectric

respectively the slopes of

static

and with

permittivity ( * ' j " ) are determined in X- Band (8.60 GHz) using microwave bench with plunger technique [17]. The high frequency dielectric

permittivity ( n2 ) is obained from the

respect to the weight fraction of the solute, d1 is density of solvent, 1 is the static dielectric permittivity of

solvent (benzene). The average uncertainty in the measurement of dipole moment is ± 0.02 Debye.

The excess dipole moments ( ) of the binary

refractometer measurements using M/s ASCO make Abbes refractometer with sodium D light as source. The average uncertainties in the measurement of static ,

systems are determined [11] by the equation,

= 12 – 1 – 2

(3)

where 1 is the dipole moment of propan-2-ol, 2 is the dipole moment of either heptyl p-hydroxy benzoate or nonyl p-hydroxy benzoate and 12 is the dipole

Table 1: Dielectric constant data from static, microwave, optic and relaxation time for various concentrations of (IPA+7HB)

moment of the equimolar solute mixture propan-2-ol + Heptyl p- hydroxy benzoate (system 1) or propan-2-ol

+ Nonyl p- hydroxy benzoate (system 2).

Minimum energy structures of the pure monomers of propan-2-ol, Heptyl p- hydroxy benzoate, Nonyl p- hydroxy benzoate and the equimolar hydrogen bonded complexes are obtained from semi-empirical calculations such as Austin Model 1 (AM1), Parameterized Model number 3 (PM3) and Modified Neglect of Differential Overlap (MNDO) Hamiltonian quantum mechanical calculations with optimized converged geometry optimization procedure using PC Spartan modeling software.

1. Results and discussion

   The Dielectric data static , * ' j " , and

   relaxation times for the systems IPA+7HB (system 1) and IPA+9HB (system 2) with various volume fractions in the solution are given in Tables 1 and 2 respectively. The relaxation times are found to increase in magnitude for a given mole fraction of n-alkyl p-hydroxy benzoate in propan-2-ol with the increase of solute volume fraction which shows that the molecules are unable to rotate freely as benzene concentration decreases in the solution. In general, the magnitude of average relaxation time is increasing with the increase of MF of n-alkyl p-hydroxy benzoate in system 1 and also in system 2, which may be attributed to the formation of hydrogen bonding between the compounds of solute systems. A representative Cole-Cole plot for 0.01% MF of 7HB in propan-2-ol with 40% volume fraction is shown in Figure 1.

   The dipole moment ( ) values for pure and equimolar mixture systems are determined

   experimentally with Higasis method and are given in Table 3. The theoretical dipole moment ( ) values

   (pure and equimolar systems) are determined with Hamiltonian quantum mechanical semi-empirical calculations AM1, PM3, MNDO and the corresponding values are given in Table 4.

   MF of 9HB in IPA	Volume fraction of solute (IPA+9HB ) in solvent (benzene)	static	* ' j"		(pico sec)
   0.01%	10	2.76	2.68-j0.29	2.229	06.85
   	20	3.07	2.98-j0.62	2.190	12.14
   	30	4.30	3.12-j0.87	2.150	30.15
   	40	5.35	2.61-j1.07	2.114	44.11
   0.02%	10	2.64	2.61-j0.17	2.229	08.46
   	20	3.42	3.09-j0.39	2.193	20.21
   	30	4.92	2.95-j0.43	2.157	48.07
   	40	5.00	2.74-j0.62	2.122	55.12
   0.03%	10	2.71	2.68-j0.21	2.232	10.26
   	20	3.42	2.82-j0.49	2.190	32.46
   	30	4.91	2.89-j0.59	2.175	67.96
   	40	5.28	2.78-j0.48	2.128	79.76
   0.04%	10	2.77	2.69-j0.12	2.229	14.57
   	20	3.23	2.83-j0.43	2.187	44.12
   	30	4.23	2.99-j0.48	2.166	78.92
   	40	5.30	3.12-j0.87	2.134	95.23

   Table 2: Dielectric constant data from static, microwave, optic and relaxation time for various concentrations of (IPA+9HB)

   Table 3: Experimental dipole moment values for various mole fractions of

   7HB and 9HB in IPA

   MF of n-alkyl p- hydroxy benzoate in propa-2-nol	IPA+7HB	IPA+7H B
   0.01%	5.228	5.39
   0.02%	5.279	5.19
   0.03%	5.095	5.10
   0.04%	5.052	5.08

   Figure 1. Cole Cole plot for 0.01% MF of 7HB in propan-2-ol with 40% volume fraction

   It is very clear from Table 4, the theoretical dipole moment values, that there is an increase in the dipole momet of equimolar binary mixture compared to that of the pure compounds.

   This may be due to the formation of hydrogen bonding between the compounds of the mixture systems [11].

   Compo und	Theoretical (PC Spartan )
   	AM1		PM3		MNDO
   IPA	1.62	—	1.53	—	1.44	—
   7HB	1.22	—	1.42	—	1.61	—
   9HB	1.25	—	1.46	—	1.64	—
   IPA+ 7HB	3.17	0.33	3.90	0.95	2.55	-0.50
   IPA+ 9HB	3.23	0.36	3.89	0.95	2.62	-0.46

   Table 4: Theoretical dipole moment ( ) and excess dipole moment ( ) values in Debye for pure IPA, 7HB, 9HB and equimolar systems (IPA+7HB, IPA+9HB)

   Table 5: Experimental and theoretical FT-IR analysis for the pure and binary mixtures of propan-2-ol (IPA) with Heptyl p-hydroxy benzoate (7HB) and Nonyl p-hydroxy benzoate (9HB).

   Compound	Band	Experimental		Theoretical ( PC Spartan )
   		(cm-1)	(cm-1)	AM1		PM3		MNDO
   				(cm-1)	(cm-1)	(cm-1)	(cm-1)	(cm-1)	(cm-1)
   IPA	OH	3550	—	3503	—	3903	—	4006	—
   7HB	OH	3432	—	3449	—	3864	—	3980	—
   9HB	OH	3433	—	3451	—	3873	—	3985	—
   IPA+7HB	OHOH	3541 3384	09–(IPA) 48–(7HB)	3495 3399	08–(IPA) 50–(7HB)	3884 3839	19–(IPA) 25–(7HB)	3935 3934	71–(IPA) 46–(7HB)
   IPA+9HB	OHOH	3538 3401	12–(IPA) 32–(9HB)	3492 3397	11–(IPA) 54–(9HB)	3878 3811	25–(IPA) 62–(9HB)	4098 4066	92–(IPA) 81–(9HB)

   Fig. 2 Optimized geometrical structure of hydrogen bonded propan-2-ol and Heptyl p-hydroxy benzoate.

   The excess dipole moment ( ) values, obtained

   theoretically, are given in Table IV. It is observed that the values of are low and even negative which indicates the

   absence of any contribution from ionic structure of the binary mixture system to the total dipole moment because, the formation of ionic structure involves very high positive value of [18]. The excess dipole moment value is a

   qualitative index for the presence of hydrogen bonding in both the mixture systems (system1 and system 2).

   Observing the experimental FT-IR spectra for the solute mixture of system 1(IPA+7HB), there is a shift of 09 cm-1 wave number for the mixture compared with the pure spectrum of IPA and a shift of 48 cm-1 wave number in the position of OH for the mixture compared with the pure spectrum of 7HB. Similarly the FT-IR spectra for the solute mixture of system 2 (IPA+9HB), there is a shift of 12 cm-1 wave number for the mixture compared with the pure spectrum of IPA and a shift of 32 cm-1 wave number in the position of OH for the mixture compared with the pure spectrum of 9HB. This shift is caused by the strong interaction between the high electro-negative charge of oxygen in the benzoate group and the hydrogen of IPA [19]. Thus the IR analysis convinces intermolecular hydrogen bonding between the compounds of the binary mixtures in system 1 and system2 effectively with proportionate variations in stretching frequencies of OH compared to their respective pure spectrums. The experimental and theoretical FT-IR values, which are in good agreement, for OH group of pure compounds IPA, 7HB, 9HB and solute mixture systems (system 1 and system 2) are shown in Table V. The optimized geometrical structure representing the formation of hydrogen bonding between propan-2-ol and 7HB (system 1), which is obtained from Hamiltonian quantum mechanical calculation [20], is shown in Figure 2.

2. Conclusions

In this paper, the dielectric properties of hydrogen bonded complexes formed by n- alkyl p-hydroxy benzoates (n=7 and 9) with propan-2-ol have been studied by computing experimental, theoretical dipole moments and relaxation times for various mole fractions. The formation of hydrogen bond between n- alkyl p-hydroxy benzoates (n=7 and 9) and propan-2-ol, which causes an increase in dipole moment values when compared to that of individual compounds and also considerable changes in relaxation times is confirmed through FT-IR spectra. The absence of ionic contribution to the structure is confirmed by the excess dipole moment values.

Acknowledgement

We are greatly indebted to Prof. S. Sreehari Sastry, Department of Physics, ANU and Prof. V. R. K. Murthy, Department of Physics, IIT, Chennai for their detailed and helpful discussions.

References

1. S. I. Abd – El Messieh, Dielectric relaxation of binary systems of some disubstituted fumarates with acrylonitrile and vinylacetate in CCl4 solutions, J. Mol. Liq., vol. 95, pp. 167- 182, 2002.

2. D. G. Trivedi, V.A. Rana, S. P. Bhatanagar and A.D. Vyas, Dielectric relaxation study of 1-propanol, benzonitrile and their mixtures at microwave frequency, J. Mol. Liq., vol.129, pp. 173-175, 2006.

3. K. Kasthury, S. Mayilavelan and R. Balakrishanan, Dielectric relaxation and structural studies of binary mixture of benzonitrile and o-nitrophenol in benzene at different temperatures, J. Mol. Liq., vol. 129, pp. 125-128, 2006.

4. A. C. Kumbharkhane, S. N. Helambe, S. Doraiswamy and S.C. Mehrotra, Dielectric relaxation studies of Hexamethyl phosphoramidewater mixtures using time-domain Refractometry, J. Chem. Phys., vol. 99, pp. 2405- 2409, 1993.

5. S. Mashimo, S. Kuwabara, S. Yagihara and K. Higasi, The dielectric relaxation of mixtures of water and primary Alcohol, J. Chem. Phys., vol. 90, pp. 3292-3294, 1989.

6. P. Sivagurunathan, K. Dharmalingam, K. Ramachandran, B. Prabhakar Undre, P. W. Khirade and S. C. Mehrotra, Dielectric studies on binary mixtures of ester with alcohol using time domain reflectometry, J. Mol. Liq., vol. 133, pp. 139-145, 2007.

7. S. K. Garg and C. P. Smyth, Microwave absorption and molecular structure in liquids. LXII. The three dielectric dispersion regions of the normal primary alcohols, J. Phys. Chem., vol. 69, pp. 1294- 1301, 1965.

8. A. D. Vyas, V. A. Rana, S. P. Bhatanagar and V. M. Vashith, Dielectric dispersion and relaxation of mixtures o 1- propanol and phenol at lower microwave frequencies, Indian J. Pure and Appl. Phys., vol. 46, pp. 521- 525, 2008.

9. J. George, N. V. Sastry, S. R. Patel and M. K. Valand, Densities, Viscosities, Speeds of Sound, and Relative Permittivities for Methyl Acrylate + 1-Alcohols (C1C6) at T = (308.15 and 318.15) K, J. Chem. Eng. Data., vol. 47, pp. 262- 269, 2002.

10. K. Ramachandran, K. Dharmalingam, P. Sivagurunathan, B. Prabhakar Undre, P.W. Khirade and S.C. Mehrotra, Dielectric relaxation studies of formamide-alcohol mixtures using time domain reflectometry, Main Group Chemistry, vol. 4 (4), pp.303-308, 2005.

11. T. Vishwam, V. Subramanian, D. V. Subbaiah and V. R. K. Murthy, Conformational and microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of propionaldehyde with isopropyl amine, Mol. Phys., vol. 106, pp. 95-101, 2008.

12. Ch. Ravi Shankar Kumar, T. Madhu Mohan and S. Sreehari Sastry, Smectic G Phase of Liquid Crystalline Mesogen by Intermolecular hydrogen bonding, Bulletin of Pure and Applied Sciences, vol. 27D (2), pp. 217-224, 2008.

13. T. Madhu Mohan, S. Sreehari Sastry, and V. R. K. Murthy, Conformational and dielectric relaxation studies on hydrogen bonded binary mixture of isopropyl alcohol in methyl benzoate and ethyl benzoate, J. Mol. Struc., vol. 973, pp. 157-162, 2010.

14. K. S. Cole and R. H. Cole, Dispersion and Absorption in Dielectrics 1. Alternating Current Characteristics, J. Chem. Phys., vol. 9, pp. 341- 351, 1941.

15. K. Higasi, Y. Koga and M. Nakamura, Dielectric relaxation and molecular structure. V. Application of the single frequency method to systems with two Debye dispersions, Bull. Chem. Soc. Japan., vol. 44, pp. 988-992, 1971.

16. Spartan version 5.1.1., Wave function Inc., 18401 Von Kaman Ave., Suite 370, Irvine, CA, USA, 1999.

17. N. E. Hill, W. E. Vaughan, A. H. Price, M. Davies, Dielectric properties and molecular behavior. Van Nostard- Reinhold, London, 1969.

18. J. Sobhanadri, V. Satheesh and M. Jayaraj, Dielectric studies of allyl alcohol with (i) Pyridine, (ii) 1, 4-Dioxane and (iii)Phenol hydrogen bonded complexes, J. Mol. Liq., vol. 64, pp. 247- 261, 1995.

19. T. Madhu Mohan, S. Sreehari Sastry, and V. R. K. Murthy, Microwave dielectric relaxation, thermodynamic and conformational studies of hydrogen bonded binary mixtures of propan-1-ol with methyl benzoate and ethyl benzoate, Indian

    J. of Pure and Appl. Physics., vol. 48, pp. 668, 2010.

20. T. Vijaya Krishna, S. Sreehari Sastry, and V. R. K. Murthy, Dielectric and thermodynamic studies on hydrogen bonded binary system of isopropyl alcohol and aniline, J. Sol. Chem. vol. 39, pp. 1377-1393, 2010.