Advances in Consumer Research
The solvent effect of aquo-dipolar aprotic solvent system for the base catalyzed propyl caprate has been studied in water-acetone of various compassion at different temperature range (20 to 400 C). With gradual Addition of organic co-solvent the rate has been decreasing which have been explain in term of initial and transition state. Salvation and desolvation are explained in term of iso activation energy and iso- dielectric activation energy. The influence of solvents on rate as well as on mechanism has been studies in relation to the idea of salvation. Wynne-jones and Eyring equation has been used to calculate the thermodynamic activation parameter. Iso- kinetic temperature has also been calculated.
The rate of a chemical reaction is significantly influenced not only by the nature of the reactants and products but also by the solvent medium in which the reaction takes place. This phenomenon is known as the kinetic solvent effect. Solvents affect reaction kinetics through several factors such as polarity, dielectric constant, solvation ability, hydrogen bonding, and viscosity. These interactions can stabilize or destabilize the transition state relative to the reactants, thereby either accelerating or retarding the reaction. In many studies(Alaa.omer,2025),( Reichardt C,2003),( Seliverstove T. S.,2020),( Magda F Fathalla,2019),( Bano Arjuman,2017),( Younes Ghalandarzehi,2023),( Shashibata Kundo,2022) has been published in field of kinetics reaction of ester hydrolysis for the calculation of specific rate, mechanism and other physical properties but no satisfactory result has been found particularly propyl caprate ester in aqueous mixture of acetone. The solvent effect has been very closely related to solvent solute interaction which is become more complex when it is mixed with water in compare to pure solvent. Binary solvents are used because they allow fine-tuning of physicochemical properties like polarity, dielectric constant, and hydrogen-bonding ability. Such mixtures often exhibit non-ideal behavior, leading to unique solvent–solute interactions that cannot be explained simply as the sum of the properties of the two pure solvents. In this report the solvent effect for the hydrolysis of propyl caprate has been noticed. The molecular formula of propyl caprate is C13H16O2.Its structure is linear as CH3-(CH2)8-C(=O)-O-CH2-CH3. Acetone itself does not readily react with ester under neutral aqueous condition but in water, ester linkage in propyl caprate can undergoes hydrolysis. In basic medium(specification) , giving deconate salt and propanol. Propyl caprate has unique properties hence it is used for various applications. This compound is used in cosmetics and personal care industry as emollient which help to soften and moisture the skin. It is also used in pharmaceutical, serving as recipient to improve the stability and bioavability of active ingredients.
EXPERIMENITAL
Material and Methods:
The chemical used are Merck grade and acetone are purified by standard procedure. The ester has been taken and thermo stated for 30 minutes in a conical flask. In a few minutes, 0.5 mI of ester that had been withdrawn and added to organic solvent Now 10 mI of aliquot was withdrawn and put into a flask in which N/10 HCI has been placed already. Now titrate the solution by adding N/10 NaOH from the burette using phenolphthalein as indicator. Similarly again pipette out 5mI of reaction mixture after 5 minutes and repeated the procedure. Repeat the above procedure by withdrawing 5mI of reaction mixture after 15,30,45,60 minute. This give the values of different timing (Vt) The V reading indicate the complition of of hydrolysis calculated after 24 hours in same procedure. Specific rate has been calculated which is keeped in Table-1
Rate constant:
The solvent effect plays a important role in controlling the rate of a chemical reaction. The medium in which a reaction takes place can stabilize or destabilize reactants, transition states, or intermediates, and this directly influences the rate constant. According to the calculated rate constant result shown in Table 1, the rate constant values in the solvolysis reaction of propyl caprate decrease as the amount of acetone in the reaction media increases. The degree of rate depletion with mole%, as depicted in fig. 1, is slower as the temperature rises, according to a plot of the logk values against the mole% of organic co-solvent. However, the depletion of rate is possibly due to decrease in dielectric constant values of the reaction media or polarity of less polar solvent
The two depletion factors mentioned above are both oppressive and in good agreement with Hughes and Ingold's(Hughes E.D.,2035) idea. This theory states that when there is concentration or contraction of charges on the transition state, an increase in the dielectric constant values of the reaction medium causes the rate to increase; when there is diffusion or destruction of charges on the transition state, the rate decreases. In this report the rate of reaction has been found to be decreases with increase proportion of solvent (acetone) which is good agreement with earlier report of Elsemongy(Elsemongy M. M.,2025), Singh&Jha(Singh. Lallan,1981) and most recent report of Kumar(Kumar,2025) However, the partial dielectric constant effect and the salvation change occurring in the reaction media are the causes of the decrease in the rate constant values.
TABLE 1. Specific rate constant k x103(dm)3/mole/mint]
|
Temp in OC |
% of Acetone |
||||
|
30% |
40% |
50% |
60% |
70% |
|
|
20OC |
48.30 |
44.05 |
40.08 |
36.30 |
33.26 |
|
25OC |
102.56 |
89.12 |
87.29 |
68.70 |
60.25 |
|
30OC |
218.27 |
191.42 |
159.58 |
126.18 |
112.20 |
|
35OC |
440.55 |
363.91 |
294.44 |
239.88 |
184.92 |
|
400C |
889.20 |
706.31 |
571.47 |
423.64 |
337.28 |
Table 2. Log k values with different mole %
|
Temp in OC |
|
3 + Log k |
||||
|
Mole% |
20OC |
25OC |
30OC |
35OC |
40OC |
|
|
30% |
9.56 |
1.684 |
2.011 |
2.339 |
2.644 |
2.949 |
|
40% |
14.11 |
1.644 |
1.950 |
2.282 |
2.561 |
2.849 |
|
50% |
19.77 |
1.603 |
1.941 |
2.203 |
2.469 |
2.757 |
|
60% |
26.99 |
1.560 |
1.837 |
2.101 |
2.380 |
2.627 |
|
70% |
36.45 |
1.522 |
1.780 |
2.050 |
2.267 |
2.528 |
Fig. 1. plots of logk with mole %.
Effect of solvent on activation Energy (Ec) and rate of reaction:
Water is a highly polar protic solvent (D ≈ 80 at 25 °C). It stabilizes charged or polar transition states more than non polar solvents. As a result, the activation energy (Ec) decreases if the reaction involves formation of polar/ionic intermediates or transition states. By the observation of data mention in Table-4 (which has been calculated with plots of logk against 103/T), it has been found that the iso composition activation energy goes on decreasing from 113.25 to 92.95 kJ/mole with increasing proportion of acetone from 30 to 70% (v/v) The depletion of activation energy infer that transition state is solvated and initial state is desolvated. This fact is also supported because the values of enthalpy of activation (H*) and entropy of activation (S*) also decreases with increasing proportion of acetone (Elsemongy M. M,1975)( Singh Lallan,1984)( Sharma Sangita,2013)
Table 3. Values logk at different temperature
|
Temperature in OC |
|
3 + Logk |
||||
|
103/T |
30% |
40% |
50% |
60% |
70% |
|
|
20OC |
3.413 |
1.684 |
2.011 |
2.339 |
2.644 |
2.949 |
|
25OC |
3.356 |
1.644 |
1.950 |
2.282 |
2.561 |
2.849 |
|
30OC |
3.300 |
1.603 |
1.941 |
2.203 |
2.469 |
2.757 |
|
35OC |
3.247 |
1.560 |
1.837 |
2.101 |
2.380 |
2.627 |
|
400C |
3.195 |
1.522 |
1.780 |
2.050 |
2.267 |
2.528 |
Fig. 2. plots of log k with 103/T
Table 4. Values of Energy of activation at different solvent composition.
|
% of Ec |
30% |
40% |
50% |
60% |
70% |
|
Eexp in KJ/mole |
113.25 |
110.88 |
102.77 |
99.44 |
92.95 |
Table 5. the values logkD at Constant D
|
Temperature in OC |
103/T |
D=40 |
D=45 |
D=50 |
D=55 |
D=60 |
|
20OC |
3.412 |
1.531 |
1.560 |
1.590 |
1.635 |
1.660 |
|
25OC |
3.355 |
1.815 |
1.860 |
1.905 |
1.950 |
1.990 |
|
30OC |
3.300 |
2.055 |
2.120 |
2.180 |
2.245 |
2.310 |
|
35OC |
3.247 |
2.319 |
2.400 |
2.480 |
2.570 |
2.660 |
|
400C |
3.195 |
2.575 |
2.675 |
2.775 |
2.875 |
2.970 |
Fig 3. Plot of log kd with 103/T
Rate of reaction and dielectric Effect:
The reaction rate of many reactions is strongly influenced by the dielectric constant (D) of the solvent. The dielectric constant is a measure of how well a solvent can stabilize charges or dipoles. Its effect on rate depends on the nature of the reaction—particularly the type of transition state formed. With view of minimise the dielectric effect, the iso-dielectric constant energy has been evaluated with the slope of Arrhenious plot logkD against D and summerised in Table-6, it has been observed that there is enhancement of( ED) values with increasing D which good agreemet of earlier views of ( Elsemongy M. M,2075) and Wolfoard(Wolfod . R.K, 1964),(AKLOF G, 1932). A group of researchers. (Elsemongy M. M,2075),( Varma. D. K,2023),( Namaishanker Sudhansu,2020), also support this view.( Singh Anil Kr,2021),( Rai H. C,2018)
Table: 6. Dielectrric activation energy(ed) at constsnt d
|
Dielectric constant(D) |
D=40 |
D=45 |
D=50 |
D=55 |
D=60 |
|
ED in kJ/mole |
93.31 |
94.86 |
101.83 |
104.97 |
111.17 |
The hydrolysis of the propyl caprate in water- acetone has been carried out at different composition and different temperature. With increase of solvent fraction, the rate has been found to be decrease which is posssibly due to dielectric values and also due to polarity of less polar solvent of the reaction media.The isocomposition activation energy and dielectric activation energy has been calculated by Arrhenious plots which shows solvetion and desolvation effect of initial and transition state Thermo dynamic activation parameter has been also been calculated to undesand the clear mechanism of the reaction.
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