Water-DMSO Co–Solvent effect and kinetics of acid catalyzed Hydrolysis of butyl formate and Influence on Activation Parameters
A. K. Singh
Department of Chemistry, Teerthanker Mahaveer University, Moradabad, India.
*Corresponding Author E-mail: anilkumarsingh2009@gmail.com
ABSTRACT:
The acid catalyzed hydrolysis of butyl formate in presence of 0.1N-HCI in water and the presence of water-DMSO mixture containing up to 30-70% (v/v) was studied over the temperature ranging from 20-400C. The rate of reaction decreases with decrease of water content of the solvent mixture and reached minima at about 70% of organic solvent. The number of water molecule associated with activated complex was showing decreases in trend with increase of temperature, is an indication of change in mechanism from unimolecular to bimolecular in reaction media. The parameters of thermodynamic activation were also calculated and discussed in terms of solvent effect with help of plots of ΔH* versus ΔS*, the isokinetic temperature was calculated and found to be greater than 300.
Different models consider the solvent effect as continnum of dielectric effect, where as, some others treated it as bulk intraction which result due to particular molecular properties. For mechanistic evaluation of this type of reaction, some other thermodynamic parameters (∆G*,∆H* and ∆S*) are also used which depend upon type of solvents, nature of reaction and structure of substrate.
Hence, these thermodynamic parameters interpretate the mechanic path of reaction.All these activation parameters depend on the nature of solvent, nature of reaction and structure of substrate, hence it is often used for mechanistic interpretation. In the last decade various efforts have been made to explain the solvent effect1-5 which some time succeded, where as, some time it failed. In this project a great attention has been paied to an important ester (Butyl formate), which is used as solvent, a flavouring agent(food addative) and a fragrance.
2. EXPERİMENTAL:
Butyl formate (Pub Chem) was distilled. Standard solution of A R. Grade HCI (0.01) was prepared in solvent mixture of pure DMSO varying from 30-70% in double distilled water. The solution is now thermostated for 30 mints. After some time, 1mL butyl formate was added in above solution. 10mL of aliquot of the reaction mixture was removed at definite interval of time and added in ice cold water and titrated with standard Bayata solution using phenolphthlein as indicator. The rate constant has been determined using first order rate equation which is arranged in table-1.
3: RESULT AND DISCUSSION:
3.1 Reaction rate:
The acid catalyzed
hydrolysis of butyl formate has been carried out at
different temperature and different composition of organic solvent. The
specific rate has been determined using first order reaction. From the Table-1,
it has been found that the rate of reaction decreases with increasing proportion
of solvent in reaction mixture. With
reference to earlier report6-8 which account in the favour of more polarized transition state in the reaction
media with high dielectric constant C. K. Hughes9. The dielectric
values of the reaction media decreases with progressive increase of organic
solvent, which shows the similar trend of earlier finding of Ingold Laidler K.J and Landskroener P A 10.
Table: I Calculated values of rate constant [k x102(dm) 3/mole/mint] at different solvent composition.
|
Temp in OC |
% of DMSO |
||||
|
30% |
40% |
50% |
60% |
70% |
|
|
20OC |
74.98 |
64.56 |
53.70 |
41.68 |
32.35 |
|
25OC |
162.18 |
137.72 |
116.14 |
94.40 |
77.62 |
|
30OC |
330.36 |
316.22 |
242.66 |
206.53 |
175.79 |
|
35OC |
653.13 |
568.85 |
489.77 |
436.51 |
380.18 |
|
400C |
1318.25 |
114.15 |
1000.00 |
931.10 |
860.99 |
3.2 Water molecules involved in activated complex and mechanism of reaction:
The number of water molecules associated with activated complex also
affect the rate of reaction to a great extent. By the slope of the plots of
against different concentration of water in co-solvent mixture (Table-3,
Fig-1), the number of water molecule involved in transition state can be
calculated as suggested by Tommila11 and Lane12. The number of water molecule associated in
activated complex decreases from 1.071 to 0.634 with increase of temperature
which shows that the mechanism of the reaction changes from unimolecular to
bimolecular in presence of organic solvent with increase of temperature. This
is in accordance with earlier invention of Robertson et al.13. It is
obvious from the above observation that change in structure of water molecule
in presence of organic solvent at different temperature, the water component
changes its structure in reaction media from bulky to dense form.
[H2O] b ↔ [H2O]d
The past report of Robertson R. E., et al. 14, and some recent work of different authors 15, 16,17 also support this observation.
Table 2: Variation of logk values with log [H2O] at different temperature
|
% of DMSO |
% of H2O |
log [H2O] |
4 + log k |
||||
|
200C |
250c |
300c |
350c |
400c |
|||
|
30% |
70% |
1.569 |
1.875 |
2.210 |
2.519 |
2.815 |
3.12 |
|
40% |
60% |
1.522 |
1.810 |
2.139 |
2.500 |
2.755 |
3.060 |
|
50% |
50% |
1.4437 |
1.730 |
2.065 |
2.385 |
2.690 |
3.000 |
|
60% |
40% |
1.346 |
1.620 |
1.975 |
2.315 |
2.640 |
2.969 |
|
70% |
30% |
1.221 |
1.510 |
1.890 |
2.245 |
2.580 |
2.935 |
Fig. 1: Plot of log [H2O] with log k
Table 3: Different values Slopes of log k against log [H2O] Water-DMSO media.
|
Temp0C |
Slope |
|
200c |
1.071 |
|
250c |
1.048 |
|
300c |
0.814 |
|
350c |
0.799 |
|
400c |
0.634 |
3.3 Calculated values of activation parameters and effect on reaction rate:
Since the three activation parameters (enthalpy of activation, entropy of activation and Gibb’s free energy of activation) play an important role in determination of solvent effect in aqueous solvent system. All these activation parameters are calculated using Wynne-jones and Eyring equation18 and it is tabulated in Table-4. By the observation of different data of activation parameters from the Table-4, it has been found that all these values are increase with increase of solvent composition. From the table-4, it is observed that the numerical value of ∆G*, increases with increase of solvent composition at all different value temperature. Although this is not large variation yet it can be considerable. The simultaneous increase of all these parameters with increase mole% of the reaction media is possible only when there is degree of enhancement in entropy of activation ∆S* is less than that of in enthalpy of activation H*. The non-linear variation of ∆H* and ∆S* (figure-3and4) with increasing mole % of DMSO indicate that there is specific solvation taking place in the process of activation as already reported by Salive and Hudson19 and Tomilla et al.20. The simultaneous increase in enthalpy of activation, entropy of activation and entropy of activation are only possible when degree of enhancement in entropy of activation is less than that of enthalpy of activation and this observation also supports that the presence of DMSO in reaction media is entropy control and enthalpy dominating. Such observation has been also found in my previous communication21,22.
3.4. Barclay-Butlar rule(Iso-kinetic Temperature):
This reaction follows Barclay-Butlar rule23 as a straight line is obtained when ∆H* values are plotted against ∆S*(fig-5) at 200C. From the value of slope of the plot, the iso-kinetic temperature is calculated which is found to be 512.05. On the basis of earlier report of Leffler24 and recent report in my communication25 the high values (greater than 300) indicate that there is strong-solvent interaction in presence of dimethyle sufoxide in reaction media.
Table 4: Consolidated values of thermodynamics Activation Parameters ∆H*and ∆G* in KJ/Mole, ∆S*in J/K/Mole
|
% of DMSO |
Mole % |
∆H* in KJ/Mole |
200C |
250C |
300C |
350C |
400C |
|||||
|
∆G* |
∆S* |
∆G* |
∆S* |
∆G* |
∆S* |
∆G* |
∆S* |
∆G* |
∆S* |
|||
|
30% |
9.77 |
97.99 |
93.90 |
13.85 |
93.64 |
14.59 |
93.47 |
14.91 |
93.26 |
15.35 |
93.00 |
15.94 |
|
40% |
14.40 |
107.07 |
94.26 |
43.72 |
94.04 |
43.724 |
93.58 |
44.52 |
93.61 |
43.70 |
93.36 |
43.80 |
|
50% |
20.17 |
110.00 |
94.71 |
52.18 |
94.47 |
52.11 |
94.25 |
51.98 |
94.00 |
91.94 |
93.72 |
52.01 |
|
60% |
27.49 |
118.85 |
95.33 |
80.27 |
94.98 |
80.10 |
94.66 |
79.83 |
94.29 |
79.74 |
93.91 |
79.68 |
|
70% |
37.09 |
123.12 |
95.95 |
92.73 |
95.47 |
92.78 |
95.06 |
92.60 |
94.65 |
92.43 |
94.11 |
92.68 |
Fig (2)- Variation of ∆G* against mole % at 200c
Fig (3)- plot of ∆H* against mole %
Fig (4)- Variation of ΔSˣ versus mole % at 200
Fig. 5: Variation of ∆ H* with ∆S* at 200C water-DMSO media
4. CONCLUSION:
In this report, the hydrolysis of butyl formate has been described on the basis of solvent- solute interaction and also with interaction with transition state. The reaction rate has been found to be decreasing with increase proportion of solvent composition. The number of water molecule associated with transition state that has been calculated with the help of Robertson relation. Small change in free energy of activation and large change in enthalpy and entropy of activation, shows the entropy-enthalpy compensation effect. The high values of slope (greater than 300) of the linear plots of ∆H* and ∆S* indicate strong solvent solute interaction in presence of organic solvent in reaction media.
REFERENCES:
1. Sharma Sangita et al. Kinetic study of specific base catalyzed hydrolysis of Ethyl Acrylate in water-Ethanol binary system. Russian Journal of Physical Chemistry A. Vol. 87, No. 5, Pp730-736. (2013)
2. Nisha Chhetri., S. A. Bhoite. Study of Solvent Effects on Hydrolysis of Mono-m-toluidine Phosphate. International Journal of Chem Tech Research, Vol.9, No.02 pp 106-109, (2016)
3. DK Varma, Prahalad Kumar, RK Lal, Study of solvent effect on kinetics of alkaline hydrolysis of ethyl picolinate in water acetone medium. International Journal of Advance Engineering and Managements. (IJAEM),Vol-2 Issue-9 pp5-6, 2020.
4. F. Y. Khalil and M.T. Hanna, kinetic, activation parameters and mechanism of acid hydrolysis of ter-Butyl acetate in aqueous DMSO. Croatica Chemica Acta, vol-52(4)pp329-338,(1979).
5. Metwally M. S.: Kinetic study of resin catalised hydrolysis of Ethyl Propinoate in aqueous solvent system. Reaction kinetic catalysis and Letters vol-47. No-2 pp319-336. (1992)
6. Singh AK. A kinetics study of solvent effect on alkali catalysed solvolysis of methyl salicylate in water-DMF media. İnternational journal of advance research and innovation. Vol-3(3);547-549. 6.F. Y. Khalil and M.T. Hanna, kinetic, activation parameters and mechanism of acid hydrolysis of ter-Butyl acetete in aqueous DMSO. Croatica Chemica Acta, vol-52(4)pp329-338,(1979).
7. Metwally M. S.: Kinetic study of resin catalyzed hydrolysis of Ethyl Propinoate in aqueous solvent system. Reaction kinetic catalysis and Letters vol-47. No-2 pp319-336. (1992)
8. AK. Singh, Activation parameters and solvent effect on solvolysis of ethyl benzoate in aqueous organic solvent system. Asian J. of Research in Chemistry, Vol-12(2),pp99-102, 2019.
9. Ingold C K. Structure and mechanism of organic chemistry. Cornell University press Ithyca (1967
10. Laidler K.J and Landskroener P A,: Trans Faraday Soc. 52, 200( 1956)
11. E. Tommilla, M Tiilikainen, A. Viapio, Effect of solvent on reaction velocity(X). Solvolysis of alkyl halide in acetone-water mixture. Ann. Acta Sci. Fenn. A2, 91. 1959.
12. C. A. Lane, The possibility of cyclic mechanism for thr acid catalysed ester hydrolysis. J. Amm. Chem. Soc. 86,12,pp2521-2523, 1964.
13. R.E. Robertson,: A survey of thermodynamic parameter for solvolysis in water”, Prog. Phy.Org. chem. 4, pp213 (1967)
14. Robertson. R E., Heppolitite. R L, Scott J.M.W.: A survey of thermodynamic parameter for the solvolysis of water. Canad. Journal of Chemistry. 37(4) pp803-824.(1959)
15. AK. Singh, Activation parameters and solvent effect on solvolysis of ethyl benzoate in aqueous organic solvent system. Asian J. of Research in Chemistry, Vol-12(2),pp99-102, 2019
16. Arjuman Bano, AK. Singh, A kinetics study of dipolar protic solvent in alkaline hydrolysis of ethyl nicotinate in water-ethanol media-A solvent effect. J. of Ultra Chemistry, Vol-13(6)pp145-150,2017.
17. AK. Singh, Solven effect and kinetics on solvolysis of propyl formate in water propanol solvent mixture. International J. of Chemical Science, Vol-3,Issue-4, pp82-84, 2019.
18. Wynne-jones W F K and Eyring H.: The Absolute rate of reaction in condense phases” Journal of Chemical Physics 3; 492-502 (1953).
19. RF Hund and Salive B. Solvent participation in nucleophilic displacement reaction part-II. The reaction between ethanol and acid chloride. Journal of Chem. Soc.1955,pp41-4129.
20. E Tommila, E Mirikallo. Effect of solvent on reaction velocity(VI). Hydrolysis of alkyl ester of benzenesolfonic acid in dioxane-water mixture. Suom. Kemistil. 26B: 1953. Pp79-80.
21. AK Singh, kinetic and solvent effect on activation parameter of aquo-propanol solvent for acid catalyzed solvolysis of propyl format. International J. of Chemical Science, Vol-3, Issue-4,pp85-88, 2019.
22. AK Singhand LK. Tiwari, Study of solvent effect of protic solvent on solvolysis of Hexanoate ester and activation parameter, Asian J. of Research in Chemistry, Vol-13(3),pp216-218, 2020.
23. Barclay I M. and Butlar IAV. The Entropy of solution. Trans Farad Soc. 1938. 34. Pp1445-1454.
24. Laffler J E. The enthalpy entropy relationship and its implication for organic chemistry. The Journal of Organic Chemistry. 20(9):1955. pp1220-1231
25. AK. Singh. Solvent effect and Activation Parameters: A Kinetic Reaction of Ethyl Caprylate in Water-Acetone Media. Asian J. of Research in Chemistry, Vol-14(6),pp441-446, 2021.
Received on 17.01.2023 Modified on 23.02.2023
Accepted on 21.03.2023 ©AJRC All right reserved