Activation Parameter and Solvent effect on solvolysis of Ethyl benzoate in Aquo-organic Solvent System

 

A.K. Singh

Department of Chemistry (CCSIT), Teerthanker Mahaveer University, Moradabad, India

*Corresponding Author E-mail:

 

 

INTRODUCTION:

Solvent effect is most rationalized term of solvent polarity in different solvent media which attribute the sum of solvent- solute interaction, specific and non specific salvation and its dielectric behavior of different solvent system. Many workers [1-6] have published recently on the rationalized of solvent effect in different solvent system which some time fails and some time succeeds. To make for further research how for the thermodynamic properties of aqueous solvent binary system are reflected in the kinetic parameter and also understand the behavior of the activation parameter in terms of the physical properties of solvents, I report the outcome of hydrolysis of ethyl benzoate in water-methanol solvent system which acts an effective use in alcoholic beverage and that can be used as medicine for treatment of skin and eye problem

 

EXPERIMENTAL:

The base catalyzed hydrolysis of ethyl benzoate was estimated volumetrically in water-methanol solvent system at different degree of composition from 30 to 7 0% (v/v), ranging from 20^o C to 40 ^o at regular interval of 5^o C. Pure ethyl benzoate (Merck) was used for kinetics. Distilled water is used throughout and the experiment is carried out by keeping strength of solution 0.1M with respect to NaOH and 0.05M with respect to ester The detail of procedure was mention in my previous communication [7]. Using second order kinetics, specific rate constant was calculated and inserted in Table-1.

 

Enthalpy of Activation, Entropy of Activation and  Free energy Activation is calculated with Wynne-Jones and Eyring equation [8] and tabulated in Table-2

 

RESULT AND DISCUSSION:

(A)Effect of solvent composition on rate:

The kinetic result of hydrolysis of ethyl benzoate in water-methanol solvent system follow second order kinetic and calculated values is inserted in Table-1.The specific rate constant values decrease with increasing temperature may be attributed partly due to dielectric effect of reaction media and partly due to salvation taking place in media which is good agreement with Hughes and Ingold [9]. and recent publication of A K Singh[10]

 

Table – I Rate constant as function of solvent medium composition

Temp in OC	% of  Methanol
	30%	40%	50%	60%	70%
20OC	37.15	30.54	25.70	21.87	18.62
25OC	74.13	57.54	48.97	41.68	35.48
30OC	147.91	112.20	88.10	74.13	64.56
35OC	278.61	211.34	165.95	136.45	112.20
400C	543.25	316.22	301.99	245.47	199.52

k x10²(dm)3/mole/mint] values of hydrolysis of Ethyl benzoate in water-methanol media

 

(B) Observed values of Iso-composition Activation Energy (E_c) of the reaction in water-methanol media. The iso composition activation energy is calculated with Arrhenius plot which decreases with increasing solvent composition, inferred solvation in transition state and desolvation in initial state which is supported recently by Singh A K [11]

 

(C) Calculated values of Iso- Dielectric Activation Energy.The value ofIso-dielectric Activation energy(E_D) is calculated by plotting Arrhenius plot of logk_D values against 1/T. Iso-dielectric Activation energy (E_D) values goes on increasing from109.95 to120.12kj/mole with increasing dielectric value in reaction media. This is also supported by past view of Wolford [12] recently supported by Singh R T. et al. [13]

 

(D) Rate and thermodynamic activation Parameters of reaction:

The thermodynamic activation parameter plays an important role in determining properties of activated complex and solvating power of medium. The activation parameter (DG^*), DH^* and DS* is calculated with help of Wynne-jones and Eyring equation [14] and inserted in Table-2. The nonlinear increase in (DG^*) and decrease in (DH^*)  and (DS*)  with mole % fig-1,2 and 3 represent the specific solvation taking place in process of solvation already proposed by Saville andHudson[15].The nonlinearity in (DG^*) with mole % curve  in water-methanol media also indicate that random distribution of component is not acceptable.  The noted data in Table-2 it is observed that Free energy of activation (DG^*) increases with simultaneous decrease in enthalpy of activation (DH^*) and entropy of activation (DS*)   with mole%.

 

According to thermodynamic relation of free energy and entropy

DG^* =DH^* -DS* 

 

On the basis of above thermodynamic relation it is clear that increase in DG with simultaneous decrease in DH and DS possible only when extent of depletion in DS is greater than DH. The regular decrease in these activation parameter that is entropy of activation and enthalpy of activation also indicate that the reaction is enthalpy dominating and entropy control which also supported by recent communication of Singh A K[16]

Table-II Activation Parameters as a function of composition for reaction in Water- Methanol Media ∆H^*and ∆G^* in KJ/Mole, ∆S^*in J/K/Mole.

% of MEOH	Mole %	∆H* in Kj/Mole	200C		250C		300C		350C		400C
			∆G*	∆S*	∆G*	∆S*	∆G*	∆S*	∆G*	∆S*	∆G*	∆S*
30%	16.03	90.68	84.42	21.36	84.15	21.91	83.85	22.54	83.58	23.05	82.04	23.36
40%	22.90	89.65	84.83	16.45	84.76	16.48	84.55	16.83	84.32	17.30	84.55	17.57
50%	30.82	89.64	85.25	14.98	85.16	15.03	85.08	14.78	84.94	15.25	84.27	17.15
60%	40.06	89.06	85.65	11.63	85.56	11.74	85.60	11.41	85.44	11.75	84.82	13.54
70%	50.97	88.47	86.04	8.2	85.96	8.45	85.95	8.31	85.95	8.18	85.36	9.90

 

Fig (1)- Variation of ∆H^* with mole % at 25⁰c (water-methanol)

Fig (2)- Variation of ∆G^* with mole % at 25⁰c (water-methanol)

 

Fig (3)- The enhancement in the value of and G^*with Variation of ∆S with mole % at 25⁰c (water-methanol)

 

Fig. 4: Variation of ∆H* with ∆S* at 25⁰C (water-methanol) system

 

 

 

Solvent-Solute Interaction and Iso-kinetic Temperature:

The Iso kinetic temperature is calculated by plotting DH^* against DS^* [fig-4] and its slope of straight line which come to less than 300(265 K/Mole²) conclude that there is weak interaction between solvent and solute present in reaction mixture and no any considerable change take place in structure of reactant or solvent or both. Which is earlier supported by Lefler [17] The above conclusion arebased on Barclay [18] and Butler relationship between Enthalpy and Entropy of Activation,

 

CONCLUSION:

By comparing the result of above project hydrolysis of ethyl benzoate in water-methanol media, following conclusion are found as:

1.    The specific rate constant is decreases with increases temperature.

2.    The iso composition energy and iso-dielectric activation energy are on opposite trend that one (E_c) is depleting where another(E_D) is enhancing.

3.    Simultaneous decrease in DH^*and ∆S^* with values with increase in DG^*with for the hydrolysis ethyl benzoate in water- methanol is enthalpy stimulator and entropy inhibitor solvent.

4.    The value of iso kinetic temperature is less than 300 indicatethat reaction is not ion-dipole but ion-molecule type.

 

REFERENCE:

1.     Bano Arjuman and Singh A K., “A Kinetic study of dipolar protic solvent in alkaline hydrolysis of ethyl nicotinate in water-ethanol media-A Solvent effect, “Journal of Ultra Chemistry, Volume-13(6) Nov,2017, pp-145-150.

2.     Singh A K., “Studies of Solvent Effect of Aquo-Methanol Solvent System on Kinetics and Activation Parameters of Base Catalyzed Hydrolysis of Ethyl Cinnamate”. Journal of Physical chemistry and Biophysis Volume: 02, Issue: 03, August 2017.pp-1000251

3.     Bano Arjuman and Singh A K., “A kinetic studies of solvent effect of aquo-ethanol solvent system on thermodynamic activation parameter of canalised solvolysis of ethyl nicotinate,” Journal of Ultra Chemistry, Vol-13(5).2017 pp121-124

4.     Singh A K., “Solvent effect on Enthalpy and Entropy of activation for the Hydrolysis of Ethyl Cinnamate in mixed solvent system.” Journal of Phy. Chem. Biophys. Volume-7, Issue-7, March, 2017

5.     Singh A K., “The influence of solvent on solvolysis of ethyl cinnamate in water-acetone mixed solvent system”.  Chemical Science Journal, Vol-8 Issue-1, March, 2017 pp 1-4

6.     Magda F Fathalla., Kinetics of reaction of 2-chloro-quinosalin with Hydroxide ion in CAN- H₂O and DMSO- H₂O binary solvent mixture,” Journal of Solution Chemistry, 40, 1258-70, 2011

7.     Singh A K., “Solvolysis Rate and Activation Parameter of Ethyl Acetate in mixed Dipolar Organic Solvent Systems– A Solvent Effect.” International Journal for Research in Applied Science and Engineering Technology X, October 2016 (IJRASET) Volume 4 Issue 16 PP704-710

8.     Wynne-Jones W. F. K, and Eyring, H,:“ The Absolute Rate of Reaction in condense Phase”. J. chem. phys. 3, 492-502, 1935.

9.     Hughes E.D. and Ingold C.K, ^” Mechanism of substitution at saturated carbon atom part IV, A discussion of constitution  and solvent effect on mechanism, kinetics, velocity, and orientation of substitution^”. J Chem. Soc 1935, 244- 255

10.   Bano Arjuman and Singh A K., “A Kinetic study of dipolar protic solvent in alkaline hydrolysis of ethyl nicotinate in water-ethanol media- A Solvent effect, “Journal of Ultra Chemistry, volume-13(6) Nov,2017, pp-145-150.

11.   Singh R T et. al. “A Kinetic study of solvent effect aquo-polyhydric alcohol solvent system on biochemical behavior of ethyl cinnamate” Napie Ind. Advance Journal of Science. Vol-16 pp15-24

12.   Wolford R K,: “ Kinetics of acid catalised hydrolysis of Acetal in dimethylsulfoxide-water solvent system at 15,25 and 35⁰c.” Phys Chem, 68,3392 1964

13.   Singh A K., “Solvolysis Rate and Activation Parameter of Ethyl Acetate in mixed Dipolar Organic Solvent Systems– A Solvent Effect.”International Journal for Research in Applied Science and Engineering Technology X, October 20(IJRASET) Volume 4 Issue 16 PP704-710

14.   Ibid Wynne-jones W F K and Eyring H., The Absolute rate of reaction in condense phases” Journal of  Chemical Physics 3; 492-502.

15.   Saville B.J. and Hudson, R.E.: J. chem. soc. 4114, 1955.

16.   Singh R T et. al. “A Kinetic study of solvent effect aquo-polyhydric alcohol solvent system on biochemical behavior of ethyl cinnamate” Napier Ind. Advance Journal of Science. Vol-16 pp15-24

17.   Lefler J.E. “Entropy relationship and implication for organic chemistry.”J. Org. Chem., 20, 1201, 1955

18.   Barclay L. and Butler, J.A.V. “The Entropy of solution.”J. Am. Chem. Soc. 34, 1445, 1938

 

 

 

 

 

 

Received on 21.02.2019                    Modified on 25.03.2019

Accepted on 10.04.2019                   ©AJRC All right reserved