1. INTRODUCTION

With change of solvent composition in aqueous solvent system, the rate of reaction is changed which has very great importance in chemical industry as well in chemical laboratory. In this project we have discussed the acid hydrolysis of propyl methanoate which are used as food additive and flavoring agent and also as an adjuvant. In this study, an attempt has been made to observe the effect of solvent in water proplanol-2, solvent system in presence of acid. A number of reports have been found earlier^1-5 for the hydrolysis of different esters but there is not any s satisfactory report, published on acid catalyzed hydrolysis of methanote ester particularly in aqueous solvent system. The earlier report of Ingold⁶and Laidler⁷ showed that with increasing dielectric constant, the rate of reaction increases. However, Parker⁸ and Roberts¹⁰ found reverse order. That is rate decreases with increase of dielectric constant.

2. Material and method:

The conical flask contains the solution and small Stoppard bottle containing pure propyl Methanoate has been thermostaed for 30 minutes. Calculated amount of organic solvent (propanol-2) water and stock acid (HCI) have been mixed in 250 ml conical flask in such a ways that total volume of the solution was 50 mL and its strength became 0.5M. After then 0.60 ml of ester has been withdrawn and added quickly to the acidic solution of water-solvent mixture. Now, immediately, 2 mL of aliquot of the reaction mixture was withdrawn and allowed to run into a conical flask containing 25mL of ice cold water so that the reaction may be arrested quickly. The acid solution was titrated with standard baryitha solution using phenolphthalein indicator. The stop clock was started when half of aliquot was added into ice cold water. The time has been assuming as a starting time or zero time. Considering the zero time the rest of ester was estimated with definite interval of time.

3. RESULT AND DISCUSSION:

3.1 Solvent Effect Dependence and Rate Constant

The specific rate constant of propyl methanote has been measured in water-propanol-2 system. The rate constant is calculated with plots of logk against reciprocal of time. The calculated values are tabulated in Table-1.The retardation of rate with increasing proportion of organic solvent(Fig-1) may inferred that the polarisedtransition state is disfaviour with increasing proportion of solvent. The rate determines the step of solvolysis of ester is an addition of OH^- ion to the carbon of carbonyal group of and after which rapid reaction with water is followed. Hence, if the activity of hydroxyl ion decreases, the reaction-rate must be decreased Tommila et al.¹¹. The lower the rate in water-propanol system inferred that interaction between water and propanol increases with increase of concentration of free water available for salvation. The plots of logk against mole% represent the smooth decrease in rate[fig-2] which inferred that hydroxyl ion is stronger hence the rate is decreasing.^12,13

Table 1: Bimolecular rate constant k x10⁴(dm)³/mole/mint

Temp in ^OC	% of propanol-2
Temp in ^OC	30%	40%	50%	60%	70%
20^OC	53.08	44.15	36.30	30.19	21.87
25^OC	108.89	93.32	77.62	66.03	51.88
30^OC	201.83	177.82	154.88	133.35	108.39
35^OC	363.07	354.81	288.40	254.09	217.27
40⁰C	676.08	609.53	562.34	501.18	446.68

Table 2: log k values with different mole %

Percentage of propanol-2		3+ log k
Percentage of propanol-2	Mole%	20^OC	25^OC	30^OC	35^OC	40^OC
30	9.12	1.725	2.037	2.305	2.560	2.835
40	13.64	1.645	1.950	2.250	2.550	2.785
50	19.16	1.560	1.895	2.190	2.460	2.750
60	26.23	1.480	1.820	2.125	2.405	2.700
70	35.61	1.340	1.715	2.035	2.337	2.650

Fig. 1: Plots of log k with mole %

3.2 Activation Energy (Ec) and Rate of Reaction:

The values of activation energy (E_c) have been calculated with the help of Arrhenius plots and obtained value has been inserted in Table-4, By the observation of table-4, it has been found that activation energy increases from 93.46 to114.16 KJ/mole.

The cause of enhancement in (E_c), in this binary solvent is due to solvation in initial state and desolvation in transition state. ^13,14

Table 3: Different log k values as a function of temperature

Temp in ^OC		3+ Logk
Temp in ^OC	10³/T	30%	40%	50%	60%	70%
20^OC	3.412	1.725	1.645	1.560	1.480	1.340
25^OC	3.355	2.037	1.950	1.895	1.820	1.715
30^OC	3.300	2.305	2.250	2.190	2.125	2.035
35^OC	3.247	2.560	2.550	2.460	2.405	2.337
40⁰C	3.195	2.830	2.785	2.750	2.700	2.650

Fig- 2. Plots of log k with 10³/T

Table 4: Iso- Composition activation energy at different solvent fraction

% of E_c	30%	40%	50%	60%	70%
E_exp in KJ/mole	93.46	99.01	103.60	104.83	114.16

Table 5: The values logk_Dat different D

Temp in ^OC	10³/T	D=35	D=40	D=45	D=50	D=55
20^OC	3.413	1.330	1.420	1.515	1.610	1.700
25^OC	3.356	1.655	1.749	1.840	1.935	2.030
30^OC	3.300	2.010	2.090	2.178	2.260	2.340
35^OC	3.247	2.340	2.415	2.480	2.545	2.615
40⁰C	3.195	2.630	2.690	2.760	2.820	2.880

Fig. 3. Variation of log k_d with 10³/T

3.3 Dielectric Effect on reaction rate:

The solvent effect on reaction rate may also by observe the effect on dielectric constant on reaction rate. An increse in rate normaly increase the rate. For ion-dipole reaction the a linear plots are obtained by ploting the logk against D or 1/D. With the slopes of curve at constant D, the values of iso-dielectric composition energy were calculated and tabulated in Table-6. By the observation of above table-6 and fig-3, it has been found that, decrease in iso-comosition dielectric energy (E_D) values are similar as iso-composition activation energy which was recently supported by different authors.^15,16,17

Table 6: Calculated values of (E_D) at constsnt D

Dielectric constant(D)	D=35	D=40	D=45	D=50	D=55
E_D in KJ/mole	118.70	116.79	115.00	111.27	93.83

4. CONCLUSION:

By the observation and analysis of above project, it has been found that the rate of reaction decreases gradually addition of solvent to reaction media. Iso-composition energy and iso- dielectric activation energy has been calculated with the help of Arrhenius plots which explain the effect of solvent on reaction media.

References:

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11. Singh AK. 2019 Solvent effect and kinetics on ethyl benzoate in aqueous solvent system. International Journal of Chemical Science. Vol-3, Issue-5, pp26-28

12. Harimohan kumar,Sunita kumara, Surjeet kumar singh.2019. Kinetic Studies on the of Solvolysis Reaction of Aromatic Esters Which have Medicinal Properties. International Journal of Creative Research Thought. Vol-7, issue -1,pp295-303

13. Singh A K. 2023 Kinetics and Binary-Solvent Effect on Acid Catalysed Hydrolysis of Butyl Formate. TMU Journal of Basic & Applied Chemistry Vol.3, pp28-23.

14. Singh Lallan, AK Gupta, Singh R T, Varma DK, R C Jha. 1984 Effect o DMSO on the kinetic behavior of alkali catalysed hydrolysis of methyl salicylate. Reac. Kinet. Catal. Letters, vol-24,1-2., pp 161-65.

15. Arjuman Bano, Singh AK. A kinetics study of dipolar protic solvent in alkaline hydrolysis of ethyl Nicotinate in water-ethanol media- A Solvent effect. Journal of Ultra Chemistry. Vol. 13(6), 145-150 (2017).

Received on 29.05.2023 Modified on 08.06.2023

Asian J. Research Chem. 2023; 16(3):246-248.

DOI: 10.52711/0974-4150.2023.00041