KINETICS AND MECHANISTIC OXIDATION OF 3-ETHOXY-4- HYDROXYBENZALDEHYDE USING POTASSIUM PERMANGANATE

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1 Estd Vol. 8 No January - March 2015 ISSN: e-issn: CDEN: RJCABP KINETICS AND MECHANISTIC XIDATIN F -ETHXY-4- HYDRXYBENZALDEHYDE USING PTASSIUM PERMANGANATE Siddharth B. Pakhare 1, Milind Ubale 2, Jaishree Gawai and Mazahar Farooqui 4, * 1 Post Graduate & Research Centre, Maulana Azad College, Aurangabad, India 2 Vasantrao Naik College, Aurangabad, India Jawaharlal Nehru Engineering College, Aurangabad, India 4 Dr. Rafiq Zakaria College for Women, Aurangabad, India * mazahar_64@rediffmail.com ABSTRACT Permagnetic oxidation of -Ethoxy-4-Hydroxybenzaldehyde has been studied at different temperatures using spectrophotometer under acidic conditions. The effect of variation of substrate (-E-4-HB), oxidant (KMn 4 ) and H 2 S 4 was studied under pseudo first order reaction conditions. The effect of different salts on oxidation of -E-4- HB was also studied. The reaction was found to be first order with respect to oxidant, substrate and H 2 S 4. A suitable mechanism is also suggested for the oxidation reaction. Keywords: -Ethoxy-4-Hydroxybenzaldehyde (-E-4-HB) 2015 RASĀYAN. All rights reserved INTRDUCTIN A survey of most recent literature on kinetic study reveals that there is a lots of scope for the study of oxidation process involving various oxidants. 1-4 There are different system reported in the literature such as oxidation of -E- 4HB by Mn(III): oxidation of aldehyde by Cr(VI), acid permanganate, N-Bromoacetamide, s(vii) pyridinium hydrobromide and bis 2,2 (bipyridyl), Cu(II) permanganate. 5-8 The Potassium Permagnate is used widely used as oxidizing agent The present investigation reports that the oxidation of -Ethoxy-4-Hydroxybenzaldehyde by KMn 4 under pseudo first order condition in acidic medium. The oxidation state of Mn in Mn - 4is (VII). Therefore it can be represented as Mn (VII) which is a powerful oxidizing agent and usually reduced to Mn (II). EXPERIMENTAL Material and Methods All the chemicals used for this kinetic study were of A.R. Grade. Kinetic investigations were performed under pseudo first order conditions with excess of -E-4HB over, the oxidant at 25 0 C to 45 0 C. Required amount of solution of substrate, H 2 S 4 were equilibrated. A measured amount of KMn 4 was added to the reaction mixture with constant stirring. The time of initiation of the reaction was recorded when half of the content of pipette were released. The solution was taken in a cuvette and absorbance was measured at 526nm using double beam spectrophotometer SL E-4HB (0.001M), KMn 4 (0.0002M) and H 2 S 4 (1M) and water volume 100ml kept a side for 24hrs. The unconsumed KMn 4 was determined spectrophotometrically and the product -Ethoxy-4-Hydroxybenzoic acid was verified by TLC. The stochiometry is determined to be 1:1. Product Analysis Product study was made under acidic condition in benzaldehyde. Keeping concentration of KMn 4 in excess over benzaldehyde. The two solutions were mixed and sulphuric acid was also added. The reaction mixture was set aside for about 24hr. to ensure completion of the reaction. The reaction mixture was then evaporated and extracted with ether. The ether layer was washed with water many times. The ether layer was than kept as a water bath for the XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE

2 evaporation of ether and cooled in ice-bath to obtain the product. The product was dissolved in benzene and a TLC analysis was done with substituted benzoic acid and respective benzaldehyde as references. nly one spot corresponding to respective benzoic acid was obtained. Formation of benzoic acid was further confirmed by mixing the product with pure benzoic acid and noting that there was no change in the melting point. RESULTS AND DISCUSSIN Effect of variation of potassium permanganate (KMn 4 ) concentration To study the effect of variation of KMn 4 concentration, the experimental sets were prepared in which concentration of KMn 4 was varied from 1 x10 - to 9 x 10 - M keeping constant concentration of -Ethoxy-4- Hydroxybenzaldehyde (-E-4-HB) and H 2 S 4 (Sulphuric acid). As the reaction has been studied under pseudo first order condition using equation a K = log t a x (1) Which was modified as-? 2.0 ( D) ( D) 0 k = log t ( D) ( D) t (2) Pseudo first order rate constants were calculated. When initial rate is plotted against concentration of KMn 4 the trend line has been found to be almost straight with negative slope indicating first order reaction at low concentration of KMn 4. This has been further confirmed when log [KMn 4 ] versus log [FR] is plotted. Hence the reaction under pseudo first order rate depends on the concentration of oxidant. Secondly, from the obtained results, it is clear that pseudo first order rate constant decrease with increase in concentration of potassium permanganate. Table-1: Effect of Variation of concentration of KMn 4 on initial rate and rate constant of -Ethoxy-4- Hydroxybenzaldehyde S. No. [KMn 4 ] (M) Initial Rate (10 4 x Rate constant (k) log (FR) mol/lit/sec) (sec 1 ) 1 1 x x x x x x x x x Table-2: Average rate determination of oxidation of -Ethoxy-4-Hydroxybenzaldehyde Time 10 5 Conc..D <c> 10 (s) (mole/lit) 10 8 <rate> Log c t log <c> mol/lit/sec <rate> XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 124

3 Initial rate 0.70 log [FR] Initial rate mole/lit/sec Conc. of KMn 4 Fig.-1: Variation of Conc. of KMn 4 Vs Initial rate at constant [-E-4-HB] = 1x10 - log[fr] Log [KMn 4 ] Fig.-2: Variation of conc. of KMn 4 Vs log [FR] at constant [-E-4-HB] Effect of variation of -Ethoxy-4-Hydroxybenzaldehyde concentration To study the effect of variation of concentration of substrate, the sets were prepared in which the concentration of -E- 4-HB was varied from 1 x 10 - to 9 x 10 - M, keeping constant concentration of [KMn 4 ] = 7 x10-4 M, [H 2 S 4 ] = 2 x10-1 M. As the reaction has been studied under pseudo first order condition pseudo first order rate constants were calculated. It is clear that pseudo first order rate constants were found decrease with increases with concentration of [- E-4-HB] in irregular way. When initial rate is plotted against concentration of -E-4-HB, the trend line is linear with positive slope. When log [FR] versus log [-E-4-HB] is plotted it confirms the fractional order of reaction. Hence the reaction under pseudo first order rate depends on the concentration of substrate. Table-: Effect of Variation in concentration of -Ethoxy-4-Hydroxybenzaldehyde on initial rate and rate constant S. No. [-E-4-HB] (M) Initial Rate (10 4 x Rate constant (k) log (FR) mol/lit/sec) (sec 1 ) 1 1 x x x x x x x x x Effect of variation of H 2 S 4 concentration To study the effect of variation of concentration of sulphuric acid (H 2 S 4 ), in the experimental sets the concentration of H 2 S 4 is varied from 2 x 10-2 to 9 x 10-2 M, keeping constant concentration i.e. [-E-4-HB]= 1 x 10-4 and [KMn 4 ] = 1 x 10-4 M. As the reaction has been studied under pseudo first order condition for varying [H 2 S 4 ] was made and pseudo first order rate constants were calculated. It is clear from that pseudo first order rate constants decreases with XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 125

4 change in concentration of H 2 S 4 confirming the first order dependence with respect to acid. Hence the reaction under pseudo order rate depends on the concentration of acid. The average rate determination data confirm that the order with respect to acid concentration is unity. 5 Initial rate 0.70 log [FR] Initial rate 4 log [FR] Conc. of [-E-4-HB] Fig.-: Variation of Conc. of -E-4-HB Vs initial rate log [-E-4-HB] Fig.-4: Variation of Conc. of -E-4-HB Vs log [FR] Table-4: Effect of Variation in concentration of H 2 S 4 on initial rate and rate constant of [-E-4-HB] oxidation [KMn 4 ]=1 x 10-4 [-E-4-HB] = 1 x 10 4 [H 2 S 4 ] = 1 M S. No. [H 2 S 4 ] (M) Initial Rate Rate constant (k) (10 4 log (FR) x mol/lit/sec) (sec 1 ) Time (s) Table-5: Average rate determination of oxidation of -Ethoxy-4-Hydroxybenzaldehyde [-E-4-HB] = 5 x 10 [KMn 4 ] = 7 x 10 4 M [H 2 S 4 ] = 1M 10-5 Conc..D < c > 10 (mole/lit) <rate> c log <c > t mole/lit/sec log <rate> XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 126

5 D M 0.002M 0.00M 0.004M 0.005M 0.006M 0.007M 0.008M 0.009M Time (Sec.) Fig.-5: Effect of variation of [H 2 S 4 ] Effect of variation of temperature The effect of temperature was studied keeping constant concentration of all reactants such as [KMn 4 ] = 7 x 10-4 M, [-E-4-HB] = 5 x 10 - M and [H 2 S 4 ] = 8 x 10-2 M. The temperature variation was done in the range of 25 to 45 C. The energy of activation was calculated by plotting graph between log k verses 1/T, a straight line was obtained. The temperature dependence on a number of reactions can be depicted by an equation. The modest enthalpy of activation and higher rate constant of slow step indicate that the oxidation presumably occurs by an inner sphere mechanism. The free energy change ( G) enthalpy changes ( H) and entropy change ( S) was determined. The energy of activation was found to be J/mole. This activation energy was used to calculate the enthalpy of activation ( H) using equation- H = E RT D Time (sec) Fig.-6: Effect of temperature XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 127

6 log k H log k H / T Fig.-7: log K Vs 1 / T S Fig.-8: S Vs H Table-6: Effect of Temperature on Kinetics of permanganate xidation of -Ethoxy-4-Hydroxybenzaldehyde in acidic media Rate k t 0 C T K 1 / T logk Table-7: Effect of Temperature on Kinetics of permanganate xidation of -Ethoxy-4-Hydroxybenzaldehyde in acidic media [KMn 4 ]=7x10-4 M [-E-4-HB]= 5x10 - M [H 2 S 4 ]=8x10-2 M Activation Energy = J/mole The value of ( H) decreases with increase in temperature; which is obvious. The average ( H) was found to be J/mole with a range to J/mole. From this, we calculated entropy of activation using formula- K K = T B e # Ea RT S. No. temp K H (J/mole) S (J/mole) G (J/mole) e # S R Where k= pseudo first order rate constant k B = Boltzmann constant T = Temperature Average There was no regular trend of entropy change it varies from to J/mole. The average entropy of activation was found to be J/mole which is negative and indicates that the transition state is highly organized () XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 128

7 due to loss of number of degrees of freedom. The average free energy ( G) was then calculated using ( H) and ( S) as per the equation- G = H T S (4) It was observed that ( G) increases with increase in temperature. The average ( G) was found to be J/mole, and changes from to J/mole. A plot of ( H) verses ( S) is linear which is followed by this equation- ( H) = β S (5) Where β is called isokinetic temperature, for -E-4-HB it was K Effect of variation of salts To study the effect of variation of salts, the concentration of salts was varied from1 x 10-2 to 9 x 10-2 M, keeping constant concentration of reactants such as [KMn 4 ] = 7 x 10-4 M, [-E-4-HB] = 5 x 10 - M, [H 2 S 4 ] = 8 x 10-2 M. These results are given in the table From the obtained results, it is clear that pseudo first order rate constant k obs increases with the increase in concentration of salts. A plot of log k obs vs µ, according to extended Bronsted Debye- Huckel equation was found to be linear with positive slopes (MgCl 2 and Ca(N ) 2 ) indicating positive salt effect. n the other hand pseudo first order rate constant decreased with increase in concentration of salts. A plot of log k obs versus µ was found to be linear with negative slopes (KBr, KI, KCl, K 2 S 4, CaCl 2, AlCl and MnS 4 ) indicating negative salt effect. K obs KCl KBr KI µ Fig.-9: Effect of Salt AlCl K obs K 2 S 4 MgCl Ca(N ) CaCl µ Fig.-10: Effect of Salt MnS K obs K obs µ Fig.-11: Effect of Salt µ Fig.-12: Effect of Salt Kinetic expression: n the basis of above discussion following kinetic schemes have been suggested- K Mn H HMn 4 Fast Step-1 4 HMn 4 S k 2 X Fast Step-2 k -2 XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 129

8 X k X' Slow and RDS Step- k 4 X' H 2 Product Fast Step-4 Where S is a substrate X, X are intermediate species since third step is rate determining step. Rate =k [X] (6) Applying steady state approximation to X, K 2 [HMn 4 ] [S] - k -2 [X]-k [X] =0 K -2 [X] k [X] = k 2 [HMn 4 ] [S] (7) Applying Law of mass action to first step, K [ HMn ] 4 = [ Mn4 ][ H ] [ ] = k[ Mn ][ H ] HMn4 4 (8) Substituting equation-8 in 7, X k k Kk Mn H S [ ]( ) [ ][ ][ ] 2 = 2 4 Kk 2 [ ] [ Mn4 ][ H ][ S] X = k 2 K Substituting equation-9 in equation-6, Kk Rate = k 2 [ Mn ] [ S][ H ] k 2 4 k If the concentration of acid and substrate is kept constant than- Rate = kobs Mn 4 Where Kk k 2 k obs = k 2 [ H ][ S] k Hence the graph of k obs against concentration of acid [H ] is a straight line which confirms that the present model is for kinetics. The reaction rates observed allows us to assume that protonated Mn 4 i.e. HMn 4 as a active oxidising species involved. 15 Table-8: Effect of added Salt on first order rate constant Conc. f salts (M) [KMn 4 ]=7x10-4 M [-E-4-HB]= 5x10 - M [H 2 S 4 ]=8x10-2 M Rate constant (k), S 1 KCl KBr KI K 2 S 4 MgCl 2 Ca(N ) 2 CaCl 2 AlCl MnS KMn 4 is selected as an oxidizing agent for this study because it is an economically low cost material. It has high oxidation potential (E 0 = 1.7V). It can oxidize wide variety of substances and it is effective over wide range of ph. There are various oxidation states of Mn like (=II, III, IV, V, VI and VII). Hence it is complicated to find out the exact species 16 involved in it. In acidic media Mn 4-4 H 2 2H 2 4Mn 2 even Mn 4-2 is converted to Mn 2. (9) (10) (11) XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 10

9 Mn 4-2 8H 6e Mn 2 4H 2 The Mn 2 may react with Mn 4-2 and the product is Mn 2. 2 Mn 4-2 Mn 2 2H 2 5Mn 2 4H Vol. 8 No January - March 2015 It is assumed that during oxidation of aldehyde positively change species attack a lone pair of electron of the reductant at centre of high electron density. 17 The formation of oxo-bridge in intermediate compound indicates the oxygen passage of one electron from the substrate bonded to Mn 7. This bridge due to protonation, rupture and give Mn species. Since the solution dies not indicate any presence of Mn(III) is precipitated Mn 2 it is quite logical to state that Mn(III) react or its disproportionated product Mn(IV) instantaneously react with substrate giving final product Mn Mn (III) Mn (II) Mn (IV) Mn (IV) substrate Mn (II) product Considering the following step in the reaction is as- C H [] C H H H And the mechanism can be depicted as- H H H Substrate H 2 H H H H H H - Mn - H Mn - H H H H H H H H Mn - Product H Mn(III) 2H Scheme-1 REFERENCES 1. Sayyed Hussain S., Mazhar Farooqui, Gaikwad Digambar, Int. J. Chem. Tech. Res., 2(1), 242(2010). 2. Sayyed Hussain, B.R. Agrawal, S.B. Pakhare, Mazahar Farooqui, Int. J. Chem. Res., 2, (2011).. I.A. Zaafarany, K.S. Khairou, R.M. Hassan, J. Mol. Catal. A: Chem., 02, 112(2009). 4. Bhagwansing Dobhal, Mazahar Farooqui and Milind Ubale, Int. J Chem. Tech. Res., 2(1), 44(2010). XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 11

10 5. Abdo Taher, Mazahar Farooqui and Maqdoom Farooqui, Int. J. of Green and Herbal Chem., 1(2), 20 (2012) 6. Vimal Soni, R.S. Sindal, Raj N. Mehrotra, Chimica Acta, 60, 141(2007). 7. Ibrahim A. Darwish, Analytica Chimica Acta, 551, 222(2005). 8. Virender K. Sharma, Coordination Chemistry Reviews, 257, 495(201). 9. Alsediq A. beid, Rasayan Journal of Chemistry, 2(4), 786(2009). 10. Syed Asif ', Syed Sultan, Syed Abed and Mazahar Farooqui, Rasayan J. Chem., (2), 22 (2010). 11. M. Komal Reddy, Narmeta Bhasker and K. Raghava Raju, Rasayan J. Chem., 2(1), 108(2009). 12. G. Sailaja and R. Ramachandra Murthy, Rasayan J. Chem., (2), 21(2010). 1. Goutam K. Ghosh and Sankar Chandra Moi, Rasayan J. Chem., 2(4), 924(2009). 14. Brijesh Pare, Anjali Soni and V.W. Bhagwat, Rasayan J. Chem., 1(2), 41(2008) 15. H.V. Rajeshwari, K.S. Byadagi, S.T. Nandibewoor and S.A. Chimatadar, J. Chem. Eng. & Mat. Sci., (5), 65(2012). 16. Alexandra Csavdari and Ioan Baldea, Studia Universitatis Babes-Bolyai, Chemia, LII, 1, (2007). 17. A.A. sunlaja, S.. Idris and J.F. Iyun, Arch. Appl. Sci. Res., 4(2), 772(2012). 18. S.P. Deraniyagala and T.N.T. Premasiri, Vidyodaya J. of Sci., 159, 8149(1999). 19. S. Udhayavani and K. Surbamani, Acta Chim. Pharm. Indica: 2(4), 21(2012). [RJC-12/2015] XIDATIN F -ETHXY-4-HYDRXYBENZALDEHYDE 12