Ultrasonic and Viscous Behaviour of Hydroquinone in Alcohols

Introduction

Knowledge of densities, viscosities and ultrasonic velocity of liquid mixture is important to understand the solute-solvent interactions between Hydroquinone in n-propanol and iso-propanol to develop new theoretical models and also for engineering applications.^1-5 Hydroquinone, also benzene – 1,4 – diol or quinol was first obtained in 1820 by the French chemist Pelletier and Caventou⁶ via the dry distillation of quinic acid which obtained by the bark of cinchona trees. Hydroquinone is a skin-bleaching agent that is used to lighten the dark patches of skin caused by pregnancy, birth control pills, hormone medicine, or injury to the skin. Hydroquinone most common use is it ability to act as a reducing agent that is water soluble.

In view of growing interest, in this paper, the results of an ultrasonic velocity, density and viscosity to study the related acoustical parameters, for the binary systems of hydroquinone + n-propanol and hydroquinone + iso-propanol at 27°C + 0.05°C have been reported. The results are discussed in terms of solute-solvent interactions.

Experimental

All the chemicals used in the present work were analytical reagent (AR) grade. The liquid mixtures of various concentration (mole/L) of hydroquinone + n-propanol and hydroquinone + iso-propanol were prepared by mass in a 25cm³ flask using a analytical balance. The speed of sound waves were obtained by using ultrasonic interferometer (Model F-81, Mittal Enterprises, New Delhi) at a fixed frequency of 2Mhz with an accuracy of + 2ms^–1 and a constant temperature 27°C + 0.05°C. An electronically digital operated constant temperature bath (RAAGA industries, Madras) has been used to circulate water through the double walled inter-ferometric cell made up of steel containing the experimental solution at the desired temperature. The density of pure solvents and solutions were determined using a specific gravity bottle of 10ml. capacity. An Ostwald’s viscometer which is 10ml capacity was used for the viscosity measurement. The viscometer was calibrated with fresh conductivity water immersed in the water bath which was kept at the experimental temperature. The time flow of water (t_w) and the time flow of solution (t_s) was measured with digital stop watch having an accuracy + 3 x 10^–6 Nm^–2S. The temperature around the viscometer was maintained in an electronically controlled thermostatic water bath. The purity of chemicals was checked by comparing with their densities with literature values.

Using the measured data, some acoustical parameters have been calculated using the standard relations,

Isentropic compressibility (β_s)⁷ is given by

Intermolecular free length (L_f)⁸ is calculated by

where K is the temp. dependent Jacobason constant.

Specific acoustic impedance (Z)⁹ is calculated by

Z = V. ρ             ….3

Molar sound velocity (R) is obtained by

and

where  n₁, n₂ and m₁, m₂ are the number of moles and molecular weight of the solvent and solute respectively.

Relative association (R_A)¹⁰ is given by

where  V₀, V,  and r are the ultrasonic velocity and density of the solvent and solution respectively.

Solvation number (S_n)¹¹ is calculated by

Apparent molal adiabatic compressibility

is given by—

Where

are isentropic compressibility and density of solvent and solution respectively. C is the concentration in mole/l. M is the molecular weight of the solute.

is the function of C as obtained by Gocker from Debye-Huckel theory.¹²

Specific viscosity (η_sp), Reduced viscosity (η) and relative viscosity (η_r) are calculated by the following well known relationship—

Where η, η₀  & C  are the viscosity of solution, solvent and concentration of solution in mole/L respectively.

Results and Discussion

Ultrasonic velocity (V) in the solution of hydroquinone in n-propanol and iso-propanol increases with increasing concentration of hydroquinone. The variation of velocity with concentration (C) of hydroquinone solution in n-propanol and iso-propanol can be expressed by the following relation—

The result shows that while the density increases, the isentropic compressibility decreasing with increasing concentration of solute¹³ and the quantity (dρ/dc) is positive while (dβ_s/dc) is negative. Since the value of [1/β_s (dβ_s/dc)] are greater than the values of [1/ρ (dρ/dc)] for hydroquinone solution in n-propanol and iso-propanol. The concentration derivative of velocity (dv/dc) is positive^14-16 i.e. the ultrasonic velocity increases with increasing the concentration of hydroquinone in solution.

System : Hydroquinone  +  iso-propanol  at 27°C + 0.05°C

Concentration       (C) mol/li.	Density                  (r) gm/ml	Ultrasonic Velocity (V)	Isentropic Compressibility (bs) Cm2/dyne.1012	Apparent molal Adiabatic Compressibility (fK) cm2/dyne 109	Specific Acoustic Impedance               (Z) 2×10-5 (C.G.S.)	Intermolecular free length (Lf) A°
0.0909	0.7905	1124.0	100.13	-29.619	0.8885	0.6274
0.1000	0.7915	1124.5	99.91	-30.423	0.8900	0.6267
0.1111	0.7927	1124.5	99.76	-30.137	0.8913	0.6262
0.1250	0.7942	1125.0	99.48	-30.585	0.8934	0.6253
0.1428	0.7962	1125.5	99.14	-31.148	0.8961	0.6242
0.1666	0.7988	1126.5	98.65	-31.518	0.8998	0.6227
0.2000	0.8025	1127.5	98.02	-31.808	0.9048	0.6207
0.2500	0.8080	1129.5	97.00	-32.385	0.9126	0.6175
0.3333	0.8171	1132.0	95.50	-32.339	0.9249	0.6127
Molar Sound Velocity (R)	Solvation          Number (Sn)	Relative Association                  (RA)	Viscosity (Cantipoise)                   (h)	Specific                     Viscosity              (hsp)	Reduced                Viscosity (h) Centipulse	Relative               Viscosity (hr)
795.05	1.94	1.0127	2.1916	0.1714	1.8857	1.1714
795.05	2.04	1.0139	2.2083	0.1803	1.8034	1.1803
793.97	2.01	1.0154	2.2167	0.1848	1.6636	1.1848
793.28	2.07	1.0172	2.2250	0.1892	1.5141	1.1892
792.28	2.12	1.0196	2.2417	0.1981	1.3879	1.1981
791.10	2.19	1.0226	2.2752	0.2160	1.2971	1.2160
788.43	2.23	1.2071	2.3087	0.2340	1.1700	1.2340
786.79	2.30	1.0335	2.3756	0.2697	1.0790	1.2697
782.52	2.30	1.0443	2.4952	0.3144	1.0943	1.3144

 

The isentropic compressibility (β_s) of hydroquinone solutions decreases with increase in the molar concentration of solute. The results of isentropic compressibility have been explained in terms of Bechem’s equation.¹⁷

where

is the isentropic compressibility of the solvent, C is the molar concentration and A & B are constant [A (-14.50 and -15.60) and B(6.868 and 1.389)].

System : Hydroquinone  +  n-propanol  at 27°C + 0.05°C

Concentration       (C) mol/li.	Density                  (r) gm/ml	Ultrasonic Velocity (V)	Isentropic Compressibility (bs) Cm2/dyne.1012	Apparent molal Adiabatic Compressibility (fK) cm2/dyne 109	Specific Acoustic Impedance               (Z) 2×10-5 (C.G.S.)	Intermolecular free length (Lf) A°
0.0909	0.8047	1216.5	83.97	-24.199	0.9789	0.5745
0.1	0.8057	1217	83.8	-24.722	0.9805	0.5739
0.1111	0.8069	1217.5	83.6	-25.247	0.9824	0.5732
0.125	0.8084	1218	83.38	-25.484	0.9846	0.5725
0.1428	0.8104	1218.5	83.1	-25.766	0.9874	0.5715
0.1666	0.813	1219.5	82.7	-26.155	0.9914	0.5701
0.2	0.8167	1220.5	82.19	-26.316	0.9967	0.5684
0.25	0.8222	1221.5	81.51	-26.149	1.0043	0.566
0.3333	0.8314	1224	80.28	-26.974	1.0176	0.5617
Molar Sound Velocity (R)	Solvation          Number (Sn)	Relative Association                  (RA)	Viscosity (Cantipoise)                   (h)	Specific                     Viscosity              (hsp)	Reduced                Viscosity (h) Centipulse	Relative               Viscosity (hr)
801.87	1.93	1.0123	1.9686	0.0232	0.261	1.0232
801.42	2.01	1.0134	1.9837	0.0311	0.3113	1.0311
800.87	2.09	1.0147	1.9913	0.035	0.3158	1.035
800.16	2.13	1.0167	1.9989	0.039	0.3122	1.039
799.15	2.17	1.019	2.014	0.0469	0.3283	1.0468
798.14	2.23	1.022	2.0443	0.0626	0.3759	1.0626
798.34	2.26	1.0263	2.0746	0.0783	0.3919	1.0783
763.61	2.23	1.033	2.1742	0.1098	0.4395	1.1098
789.24	2.24	1.0438	2.2109	0.1492	0.4477	1.1492

 

The value of constants (A & B) were obtained from the intercept and slope of plots

The complementary use of isentropic compressibility data can provide interesting information about solute–solvent interaction. Apparent molar adiabatic compressibility

varies linearly as the square root of concentration

.The values of apparent molal adiabatic compressbilities are negative with the increase in molar concentration of hydroquinone in n-propanol and iso propanol.¹⁸ The values of

[–24.30 and   –28.10cm²/dyne.10⁹] for the solution of hydroquinone in n-propanol and iso- propanol respectively. The values of

were evaluated by extra plotting. The graph of

Vs

(shown in fig 1).

Figure 1: Apparent Modal Adiabatic Compressibility Click here to View figure

 

The intermolecular free length (L_f) decreases while the specific acoustic impedance (Z) increases with an increase in the concentration of hydroquinone in solutions which can be explained on the basis of lyophobic interaction between solute and solvent molecules which increase the intermolecular distance making relatively under gaps between the molecules and becoming the main cause of impedance in the propagation of ultrasound waves. These results are in agreement with results reported by Bhandakkar¹⁹ for methylmethacrylate with methanol, p-dioxane and cyclohexane.  The molar sound velocity (R) has been found to varied linearly with the molar concentration of hydroquinone in solutions. Linear decrease of molar sound velocity with molar concentration has been also reported for cerous nitrate salt by Singh²⁰.The relative association (R_A) and solvation number (S_n) increases with molar concentration has been also reported by Diwidi et.al²¹ in complex formation between KCl, CaCl₂ and HgCl₂.

Figure 2: ViscosityVs Concentration   Click here to View figure

 

The increase in viscosity may be due to the increasing tendency of hydroquinone molecules to form aggregates with the increase in the hydroquinone concentration in solution. The plots of viscosity Vs molar concentration are shown in figure 2. The slops of lines is found to be positive in each case. Linear increase of the viscosity results has been also reported for some ternary electrolytes in dioxane water mixture by Das²². These results of viscosity indicates that there is a significant interaction between the solute and solvent molecules.^23-25

Conclusion

The solute-solvent interaction present in hydroquinone with n-propanol & iso-propanol have been studied by ultrasonic velocity, density and viscosity study. On the basis of the results obtained from the study, it is concluded that the solute-solvent interaction in the solution of hydroquinone with n-propanol and iso-propanol is significant and the computed acoustical parameters and their values indicates to the presence of solute-solvent interaction in the solutions.

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