Effect of mixed methyl ketones on the catalyzed resorcinol based oscillatory reaction at different temperatures

Journal of Industrial and Engineering Chemistry 16 (2010) 634–639

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Effect of mixed methyl ketones on the catalyzed resorcinol based oscillatory reaction at different temperatures Nadeem B. Ganaie *, Masood A. Nath, G.M. Peerzada Post Graduate Department of Chemistry, University of Kashmir, Srinagar 190006 (J&K), India

A R T I C L E I N F O

A B S T R A C T

Article history: Received 24 June 2009 Accepted 3 February 2010

The present investigation establishes a comparative trend on the single, binary and ternary reaction systems having resorcinol as main substrate, inorganic bromate as oxidant and different metal ions as catalysts. However, in binary system, acetone has been added (v/v) to the skeletal (single) reaction system as co-substrate and in the ternary system, acetone with butanone, pentanone; hexanone and acetylacetone have been added (v/v) to the skeletal system in order to monitor the oscillatory parameters in presence of mixed methyl ketones at different temperatures. It is found that the temperature; the enolization constant and the hydrophobic interactions influence the oscillatory behavior as well as the formation of the end products in both binary and ternary reaction systems under investigation. The interpretation of the kinetic data revealed that the rate of bromination reaction increases with a decrease in the enolization constants of methyl ketones leading to a decrease in the time period of the oscillations. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Keywords: BZ reaction Methyl ketone Enolization Catalyst Bromate Ternary system

1. Introduction In an oscillatory chemical reaction [1], the concentrations of the catalyst and intermediate species undergo oscillations in time. This behavior is driven by the Gibb’s free energy decrease of an overall chemical reaction occurring far from the thermodynamic equilibrium. The diffusion of the species may couple with chemical reactions under some circumstances and leads to traveling waves of the chemical activity in which their concentrations are far above or below those in the bulk of the reacting mixture. These waves often propagate in a manner reminiscent of nerve pulse transmission [2– 5]. It is therefore, an important reason to study oscillating chemical reactions with lucid mechanism and kinetics in order to develop examples of what is possible under far from equilibrium circumstances. According to Belousov-Zhabotinsky [6], the pioneers of this field, such reactions being the complex ones involve a large number of species, categorized as reactants, products and the intermediates. It is the concentration of intermediate species that undergo oscillations in time as a result of chemical kinetics [7,8]. These reactions have been described fully by FKN [9] and GTF [10,11] mechanisms and are generalized by the following core reactions: BrO3  þ HBrO2 þ Hþ $ 2BrO2  þ H2 O

(1)

BrO2  þ Mred þ Hþ ! HBrO2 þ Mox

(2)

* Corresponding author. E-mail address: [email protected] (N.B. Ganaie).

Here Mred and Mox are the metal ions such as cerium, iron or manganese in their reduced and the oxidized forms respectively. A detailed study of the BZ reaction with aliphatic compounds like oxalic acid [12], malonic acid [13], citric acid [1], glucose [14] and ketones viz. cyclohexanone [15] and acetone [16] in wide range of concentrations of the substrates have been reported, but the effect of binary mixtures of ketones (mixed ketones) on BZ system containing aromatic compounds as the main substrate has not been studied till date. Although, it is reported that oscillations exhibit remarkable change with ketones, e.g., increasing or decreasing the concentration of acetone causes the concentration of Br2 to be either very low or else high [17]. Removal of Br2 by reaction with acetone is competitive with its formation, very little BrO3 was present after the formation of Br2. Enolization of acetone is the rate determining step for its bromination [18]. The varying concentration of acetone affects the induction period [19] (tin), time period (tp) as well as the rate of reaction. As temperature is one of the environmental factors that has a pronounced effect on bromate driven oscillators, temperature dependence for a variety of catalyzed and uncatalyzed bromate driven oscillators have been characterized [20–26]. The present investigation has been made to explore the effect of mixed methyl ketones like acetone with butanone, pentanone and hexanone as ternary reaction systems comprising of resorcinol as main organic substrate and different metal ions as catalysts in 1.3 mol L1 sulfuric acid. Resorcinol was chosen because of its sufficient solubility in aqueous acid medium. Thus, in order to evolve a comparative trend of three reactions systems viz. single

1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2010.03.002

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(without ketone), binary (with acetone) and ternary (with mixed ketones) and to derive the kinetic parameters, detailed studies of these systems have been carried out at different temperatures. Moreover, owing to the fact that better oscillations appeared in presence of Mn(II) ion as catalyst, the comparative trend of all the three reaction systems was explored in presence of Mn(II) ion as the effective catalyst. 2. Experimental 2.1. Reagents All reagents used were either analytical grade chemicals or else of high purity. These reagents were resorcinol (Himedia, AR), potassium bromate (Merck), acetone (Ranbaxy), butanone (Qualigens), pentanone (Himedia), hexanone (Himedia), acetyl acetone (Himedia), manganese(II) sulfate monohydrate (s.d.fine), ferroin (s.d.fine), cerium(III) nitrate tetrahydrate (s.d.fine) and cerium sulfate (Merck). All desired solutions of these reagents were prepared in 1.3 mol L1 sulfuric acid (Merck LR). 2.2. Methodology The ion analyzer (ELICO LI-126) having pH as well as mV option was calibrated in ORP (Oxidation Reduction Potential) mode with the standard solutions, using Platinum electrode as the indicator and Calomel (SCE) as the reference electrodes. The equipment was hooked to two half cells, one containing any of the reaction systems under investigation into which Platinum electrode was dipped as indicator electrode. The another half cell was filled with 2.5  104 mol L1 solution of potassium chloride and the calomel electrode was dipped into it as reference electrode. The two half cells were connected through salt bridge and thermostated to a range of temperatures from 25  0.1 8C to 45  0.1 8C in a Siskin Julabo water bath. All the solutions used in the reaction systems were first kept under thermostatic conditions at desired temperatures for about ten minutes in order to attain the temperature of the bath. In all the three reaction systems, the reaction was initiated by adding 2 mL of potassium bromate solution to the premixed solutions of organic substrate (single or mixed) and metal ion. 3. Results and discussion 3.1. Influence of catalysts Initially the experiments were performed for the single substrate system (without ketones) with different metal ions in order to choose the efficient catalyst for the detailed study of single, binary and ternary reaction systems. The data obtained to this effect is reported in Table 1 and the potential (mV) versus time (s) plot is depicted in Fig. 1. The tin and tp values of the metal ions indicate that Mn(II) ion reacts faster to form HBrO2 and Mn(III) as the oxidized species as compared to Fe(II) ion, which reacts very

Table 1 Effects of metal ions on the oscillatory parameters of the systems containing [Metal] = 4  103 mol L1, [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, Temperature = 30  0.1 8C. Catalyst

Mn2+ Ce3+ Ce4+ Fe2+

Induction period

Time period

Frequency

Amplitude

tin/s

tp/s

n/s1

mV

130 350 170 600

67.5 460.0 95.5 470.5

0.0148 0.0022 0.0105 0.0021

65 40 46 20

No. of oscillations

>40 >10 >25 >7

Fig. 1. Potential versus time plots for the [Ce(III)] = [Ce(IV)] = [Mn(II)] = [Fe(II)] = 4  103 mol L1, [Resorcinol] = 0.0225 mol L1 at 30  0.1 8C.

systems containing [BrO3] = 0.1 mol L1,

slowly in the given system to yield HBrO2 and Fe(III) as its oxidized form. Thus, the order of reactivity of these metal ions is as under: MnðIIÞ > CeðIVÞ > CeðIIIÞ > FeðIIÞ The other oscillatory parameters like frequency and amplitude are in good agreement with this order. Thus, we have chosen Mn(II) ion as the catalyst for studying the effect of mixed methyl ketones on the oscillatory parameters of resorcinol based BZ oscillator at varying temperatures. 3.2. Influence of temperature Fig. 2 represents the nature of oscillations observed with bromine controlled [27] BZ reaction with resorcinol as the main (single) substrate, potassium bromate as the oxidizer and manganese(II) sulfate as catalyst in 1.3 mol L1 sulfuric acid. Although, oscillations have been reported for this system [28], but effect of catalysts, temperature and mixed methyl ketones is studied in detail in the present investigation. Oscillations start after an induction period as is evident in Fig. 2. It is found that with increase in temperature, both induction period and time period of the oscillations decreases. It is noteworthy to mention that the oscillations were observed in a batch reactor and results have been repeated a number of times to check the reproducibility of the data, owing to the fact that such reactions are quite complex in nature. Thus, the time period is obtained from the average between second and sixth oscillations [29]. However, the amplitude and frequency of oscillations give better results at 30  0.1 8C. Amplitude of the oscillations gives the change in the [Mn(III)]/[Mn(II)] ratio during each cycle. 3.3. Effect of acetone Fig. 3 reveals the effect of varying concentration of acetone (binary system) on the oscillatory parameters of the single substrate (resorcinol) system. It is found that in a binary reaction system with 10% (v/v) concentration of acetone (Fig. 3b), the

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Fig. 2. Potential versus time plots showing dependence of oscillatory characteristics on temperature variations. System: [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1. (a) 25  0.1 8C, (b) 30  0.1 8C, (c) 35  0.1 8C, and (d) 40  0.1 8C.

Fig. 3. Potential versus time plots showing variation of oscillatory characteristics for the system containing [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1, [H2SO4] = 1.3 mol L1. [Acetone]: (a) 5%, (b) 10%, (c) 15%, and (d) 20%. Temperature = 30  0.1 8C.

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Fig. 4. Potential versus time plots showing variation of oscillatory parameters with change in temperature for the system containing 10% acetone (v/v), [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1. (a) 25  0.1 8C, (b) 30  0.1 8C, (c) 35  0.1 8C, and (d) 40  0.1 8C.

number as well as the amplitude of oscillations was found greater as compared to the other sets of binary reaction systems with varying concentrations of acetone. However, with increase in temperature there is gradual decrease in average amplitude of oscillations and hence low amplitude oscillations are observed (Fig. 4). The data obtained with respect to oscillatory parameters without and with acetone (i.e., single and binary systems) is recorded as Table 2. 3.4. Effect of mixed methyl ketones The effect of mixed methyl ketones (ternary system) on the oscillatory behavior of resorcinol was studied by adding 1:1 binary mixture (v/v) of methyl ketones like acetone + butanone, acetone + pentanone, acetone + hexanone and acetone + acetylacetone to the single substrate system and the data obtained to this effect is reported as Table 3. The apparent rate constants were derived from the reciprocal of average oscillatory period [30]. It is observed that

the apparent rate constant is due to the reaction of Mn(III) with bromo-substrate derivative involving Mn(II)/Mn(III) redox couple. Needless to mention that BZ reaction being a set of complex reactions, it is not possible to have the rate constant for the overall reaction under the prevalent experimental conditions. However, the apparent rate constant is used to calculate the activation parameters like enthalpy of activation (DH#) and entropy of activation (DS#) from the Eyring-Polanyi equation (Eq. (3)): ! !   kB T DSz DH z exp exp  (3) k¼ h R RT Rearranging and taking logarithm, we have: ln

k DHz 1 kB DSz ¼  þ ln þ T T R h R

(4)

From Eq. (4) the linear form of Eyring-Polanyi equation, ln(k/T) versus 1/T gives (DH#) from the slope and (DS#) from intercept

Table 2 Effect of temperature on the oscillatory parameters and rate constants for the systems without ketone and with 10% (v/v) acetone; [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1, [H2SO4] = 1.3 mol L1. Temperature

Induction period

Time period

Rate constanta

(0.1 8C)

tin/s

tp/s

k/s1(103)

25 30 35 40 a

Without ketone

Acetone

Without ketone

Acetone

Without ketone

Acetone

250 130 90 70

320 190 120 100

140 110 85 65

95.0 65.0 45.0 37.5

7.14 9.09 11.76 15.38

10.5 15.4 22.2 26.6

Derived as reciprocal of average oscillatory period. Ref. [30].

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Table 3 Effect of temperature on the oscillatory parameters and rate constants for the systems containing 1: 1 solutions (v/v) of acetone with butanone, pentanone, hexanone each separately added to system: [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1 and [H2SO4] = 1.3 mol L1. Temperature

Induction period

Time period

Rate constanta

(0.1 8C)

tin/s

tp/s

k/s1

25 30 35 40 a

Butanone

Pentanone

Hexanone

Butanone

Pentanone

Hexanone

Butanone

Pentanone

Hexanone

290 210 160 100

280 200 140 90

275 170 155 100

62.5 50.0 40.0 30.0

58.75 42.50 35.00 27.25

55.5 40.0 30.0 26.0

0.016 0.020 0.025 0.033

0.017 0.024 0.029 0.037

0.018 0.025 0.033 0.038

Derived as reciprocal of average oscillatory period. Ref. [30].

This trend is justified on the basis of rate of the enolization constant, which is higher for acetone and lower for hexanone and of course highest for acetyl acetone (Fig. 6) owing to which no oscillation was observed in this system due to the considerable stability of the bromoderivative. In case of acetone, the enolization can be shown as:

Fig. 5. ln k/T versus 1/T plots for the systems containing [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1, 1 [H2SO4] = 1.3 mol L (a) without ketone, (b) acetone, (c) acetone/butanone, (d) acetone/pentanone, and (e) acetone/hexanone.

The enol form acts as a nucleophilic site for bromo attack to form bromo-acetone as intermediate product. The bromo-acetone or the bromoketone derivative is responsible for the decrease in induction period. According to FKN mechanism, the bromoderivative acts as positive feedback for the bromination of resorcinol. With increase in the rate of enolization, there is increase in the formation of bromoketone derivative and thus the stability order of this derivative is: acetylacetone  acetone > butanone > pentanone > hexanone

(Fig. 5). The values pertaining to the enthalpies and the entropies of activation of the systems under investigation as reported in Table 4 are apparent or experimental values which do not respond to any reaction step rather provide us information about the extent to which the temperature, the catalyst and the substrate influence the oscillations. From the data reported in Tables 2 and 3, it is concluded that with an increase in temperature the rate of reaction also increases as is apparent from the decrease in the time period of oscillations for both the binary and the ternary systems under investigation. The maximum number of oscillations was observed at 35  0.1 8C and at lower temperatures, oscillations occur for a longer period of time as compared to the higher temperatures where oscillations stop after some time owing to the increase in the rate of reaction. The rate constant values and the oscillatory parameters as reported in Tables 2 and 3 for the binary and ternary systems establish the following order with respect to both tin and tp values: resorcinol þ acetone > resorcinol þ acetone þ butanone > resorcinol þ acetone þ pentanone > resorcinol þ acetone þ hexanone

The trend clearly shows that stability of bromoderivative of the ketone is directly proportional to the induction period (tin) and time period (tp) of the oscillators. It is reported in literature [31] that acetyl acetone is scavenger for HOBr and Br2 and the small amplitude oscillations shown here are purely radical controlled at higher concentrations of ketone, which is also true in our system. The BZ oscillator studied here is having an aromatic substrate (resorcinol) and in such substrates, the bromoderivative precipitates out at the end of the reaction. The use of co-substrates, like ketones, increases the solubility of the end product and is showing more oscillations. Further, the increase in chain length of the ketones goes on increasing the non-polar character (hydrophobic nature) of the reaction mixture. In our reactions systems, the precipitate particles were observed to be smaller for the lower ketones as compared to that for the 1:1 binary mixture of acetone and hexanone, though in small quantity. The known values of dielectric constants [32] for acetone, butanone, pentanone, hexanone and acetyl acetone are 20.7 (25 8C), 18.5 (20 8C), 15.4 (20 8C), 14.6 (15 8C) and 23.1 (20 8C). Hence the higher hydrophobic nature of hexanone (lower dielectric constant of the reaction medium) provides the energy for the larger particles to form and lower hydrophobic character (higher dielectric constant)

Table 4 Values of enthalpy and entropy of activation for the BZ systems containing [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1, [H2SO4] = 1.3 mol L1, with and without ketones. Activation parameter #

*

DH [kJ/mol] DS# [J/mol K]* *

Without ketone

Acetone

Acetone/Butanone

Acetone/Pentanone

Acetone/Hexanone

46.51 135.2

37.54 168.89

35.51 169.05

36.50 164.87

37.25 161.76

Values derived from Eyring-Polanyi equation (Eq. (4)).

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4.4. Hydrophobic interactions These interactions affect the mode of product formation, e.g., in higher ketones larger crystals are formed due to the increase in non-polar (increase in chain length of ketone) character of the reaction mixture. The formation of large crystals in BZ reaction owing to decrease in dielectric constant can help in studying various other phenomena in oscillatory chemical reactions. Acknowledgements The authors are thankful to CSIR, New Delhi for providing financial support. The authors also thank Head, Department of Chemistry, University of Kashmir, Srinagar for providing infrastructure to undertake the investigation. References

Fig. 6. Potential versus time plot for the system containing 1:1 solution (v/v) of acetone and acetyl acetone at 30  0.1 8C. System: [Resorcinol] = 0.0225 mol L1, [BrO3] = 0.1 mol L1, [Mn2+] = 4  103 mol L1, [H2SO4] = 1.3 mol L1.

gives rise to smaller particles. This observation needs further investigation with other similar systems. 4. Conclusions 4.1. Catalyst effect Resorcinol shows the dynamic behavior with respect to different metal ions as catalysts. It is observed that the reactivity with respect to Fe(II) is the lowest, compared to Ce(III), Ce(IV) and Mn(II). However, it is observed that oxidized form of the metal ion Ce(IV) used initially is more reactive than its reduced form Ce(III). 4.2. Temperature effect There is a decrease in the induction period and in the average oscillatory period of oscillations with an increase in temperature. At higher temperatures, the life time of the oscillators can be deduced. The amplitudes of the oscillations show a gradual change with an increase in temperature. 4.3. Enolization effect The rate of formation of enols by the ketones and the stability of the bromo ketone derivatives also influence the induction period and the time period of oscillations. Higher is the stability of the bromo ketone, larger will be the induction period and the time period.

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