Co-Solvent effect and Kinetics of Alkaline Hydrolysis of Butyle Salicylate

 

A. K. Singh

Department of Chemistry, Teerthanker Mahaveer University, Moradabad, Uttar Pradesh, India.

*Corresponding Author E-mail: dr.anilkumarsingh2009@gmail.com

 

ABSTRACT:

The base catalised hydrolysis of buyl salicylate has been carred out in water-DMF binary solvent mixture covering range of 30 to 70% (v/v) of solvent composition at different Temperature (20 to 400 C). The reaction followed second order rate constant which decreases with increase of solvent composition. The salvation and desolvation concept are used to explain the solvent influence on rate and mechanism is the reaction. The relation between changes in dielectric constant due to variation of reaction mixture and change in specific rate constant has been explained on the basis of electrostatic and non-electrostatic contribution of solvent mixture. Calculated value of Iso-composition activation energy is found to be increases with increase of solvent composition. The thermodynamic parameters (ΔG*, ΔH* & ΔS*) has been determined with help of Wynne Jone and Eyring equation which show the great dependency on solvent composition.

 

KEYWORDS: Butyl Salicylate, Water-DMF, Hydrolysis, kinetic solvent effect,. Iso-composition activation energy. Dielectic activation energy.

 

INTRODUCTION:

The rate of chemical reaction is changed with the change of solvent composition of reaction mixture which has great importance in laboratory as well as in chemical industry. Some time it is found that rate is increased by a factor109 with change of solvent.1 The solvent affect the reaction rate in two ways. One through static or equilibrium solvent effect and another through dynamic or fractional solvent effect.2-5 The static solvent effect on reaction rate can be understood in term of Transition state theory. The second method are influence the rate of fast reaction. The solvent effect is also closely related to nature and extent of solvent-solute interaction. Solvent- solute interaction are very much complex in mixture of the solvent than pure solvent due to possibility of specific solvation of any of solvent present in the mixture. In this investigation studies of solvent effect in hydrolysis of which has greater use as food addative for flavor enhancer, flavorıng agent or adjuvant.

 

MATERIAL AND METHOD:

The reactions kinetics has been studied under second-order which has greater use as solvent for the antimony reduction of aluminium chloride phosphorus, trichloride alkyl complex to form the corresponding alkyl phosphorus dichloride. conditions The chemicals used are Merck grade or BDH (Analar). Known procedure is followed for purifying the DMF. The salicylate ester containing in a conical flask has been thermo- stated for half an hour. Immediately after then 0.4 mI of Salicylate ester was withdrawn quickly and added to organic co-solvent mixture with help of pipette. Again 10mI of aliquot has been withdrawn and allowed to pour into conical flask in which N/10 HCL solution was already present.. Phenolphthalein indicator has been used to titrate the excess of alkali with standard solution.When half of aliquot into the cold 0.1N HCI solution the stop clock was started. Rest of ester has been estimated after quenching the 10ml of aliquot in 10 ml of 0.1N HCl in a fixed interval of time. Evaluated value rate constant of the reaction has been recorted in Table 1. The numerical value of logkwith mole persent has been in Table-2 and its variation  shown in Fig.1

 

 

 

Table 1: Bimolecular rate constant k x103(dm)3/mole/mint

Temp in OC

% of DMF

30%

40%

50%

60%

70%

20OC

60.53

44.66

37.58

36.72

22.38

25OC

118.85

95.27

82.79

66.07

53.70

30OC

231.73

192.75

171.79

144.54

122.74

35OC

428.54

380.18

350.75

307.60

269.15

400C

829.85

776.24

707.94

656.14

602.55

 

Table 2: Log k values with different mole %

Temp in OC

 

3 + Log k

Mole%

20OC

25OC

30OC

35OC

40OC

30 OC

9.12

1.782

2.075

2.365

2.632

2.919

40 OC

13.58

1.650

1.979

2.285

2.580

2.890

50 OC

18.96

1.575

1.918

2.235

2.545

2.850

60 OC

25.98

1.565

1.820

2.160

2.488

2.817

70 OC

35.27

1.350

1.730

2.089

2.430

2.780

 

Fig. 1: plots of log k with mole %.

 

DISCUSSION:

Solvent Effect dependence and Rate constant:

The rate of hydrolysis of Butyl Salicylate has been measured in water-DMF medium by the slope of logk against time (Logk against 1/T. Table-3)The plot of logk againt receprocal of time has been found has been found to be linear.The retardation of rate with increase solvent composition my be explain on the basis of the fact that formation of polarised transition state is disfavoured with increase proportion of DMF. This fact is also supported by Hugh and Ingold6 qualitative theory. The rate determine step of hydrolysis of ester is addition of hydroxyl ion to the carbon of carbnoyl group of and after which rapid reaction with water is followed. Hence if the activity of hydroxyl ion decreases, the reaction rate must be decreasesTommila et al.7 The lower the rate in water-DMF mixture suggested that interaction between water and DMF increases with increase concentration of free water available for salvation of hydroxyl ion. The curve logk against mole fraction of representing smooth decrease (fig. 1), which implies that salvation of hydroxyl ion is stronger and hence the values of rate constant is decreases.8,9

 

Table 3: different logk values as a function of temperature

Temp in OC

 

3 + Logk

103/T

30%

40%

50%

60%

70%

20OC

3.413

1.782

1.650

1.575

1.565

1.350

25OC

3.356

2.075

1.979

1.918

1.820

1.730

30OC

3.300

2.365

2.285

2.235

2.160

2.089

35OC

3.247

2.632

2.580

2.545

2.488

2.430

400C

3.195

2.919

2.890

2.850

2.817

2.780

 

Fig. 2: plots of log k with 103/T

 

Activation Energy (Ec) and rate of reaction: Arrhenius plots (Logk against 1/T) has been used to calculate value of activation energy (Ec). Table 4 collects the obtained values of activation energies under different solvent composition. The increase in (Ec) values with increase in solvent composition has been noticeable because it will only happened when there is salvation change take place either in initial level or transition level or both.

 

Table 4: Iso-composition activation energy at different solvent fraction.

% of Ec

30%

40%

50%

60%

70%

Eexp in KJ/mole

98.92

107.74

113.69

117.96

124.75

 

The increasing value of (Ec) as a function of solvent composition indicates that there is salvation taking place at initial level where as desolvation takes place at transition level.10-12

 

Table 5: The values log kD at different D

Temp in OC

103/T

D=60

D=62

D=64

D=66

D=68

20OC

3.412

1.415

1.465

1.515

1.568

1.620

25OC

3.355

1.770

1.820

1.865

1.915

1.965

30OC

3.300

2.115

2.170

2.230

2.275

2.330

35OC

3.247

2.480

2.520

2.565

2.605

2.650

400C

3.195

2.829

2.850

2.875

2.900

2.920

 

Fig. 3: variation of log kd with 103/T

 

Dielectric Effect on reaction rate:

The another aspect of effect solvent may also be considered by observing the effect of dielctric constant D on reaction rate. There is an increase in rate is found to increase in D where as the rate is decreses with decrease in D. The dielectric constant values are obtained by by interpolation of Akerlof data11. Linear relationships are obtained between logk and D-1/2D+1 for dipole-dipole interaction Lanndskroner12. However for ion-dipole linear relation are obtained by plotting Logk and LogD or Logk against1/D. With help of slope of plots of LogkD against receprocal of absolute temperature, the iso-dielectric values has been calculated [Table-5,] with help of slopes(Fig-3) with help of slope of different linear line. The depletion in (ED) with decreasing D [Table 6], showed that depletion in(ED) values followed similar trend as (Ec) vales with increasing proportion of solvent composition.13,14,15.

 

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

Dielectric constant(D)

D=40

D=45

D=50

D=55

D=60

ED in KJ/mole

83.76

80.62

79.64

78.84

77.31

 

CONCLUSION:

The gradual decrease of rate is constantly found with increase proportion of solvent composition due to increase concentration of free water available for salvation of hydroxyl ion. The increase of activation energy with increasing composition of solvent indicates desolvation in Fig. 2. plots of log k with 103/T transition state and salvation in initial state. Dielectric value follows similar trend as iso-composition activation energy.

 

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Received on 19.07.2024                    Modified on 03.08.2024

Accepted on 17.08.2024                   ©AJRC All right reserved

Asian J. Research Chem. 2024; 17(3):156-158.

DOI: 10.52711/0974-4150.2024.00029