Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 4(7), 61-65, July (2014) Res. J. Chem. Sci. International Science Congress Association 61 Kinetic study of Oxidation of some Monosaccharides by Chloramine-T induced by Visible light sourceWadhwani Meena and Jain Shubha, Advance College of Science & Commerce, Ujjain, MP, INDIA School of Studies in Chemistry & Biochemistry, Ujjain, MP, INDIAAvailable online at: www.isca.in, www.isca.me Received 11th June 2014, revised 10th July 2014, accepted 17th July 2014Abstract The kinetics of photochemical oxidation of glucose and fructose by chloramine-T in acidic medium has been studied. The reaction mixture including known quantity of substrate (glucose/fructose), acid and chloramine-T was taken in the vessel and irradiated in the visible light source. The course of the reaction was followed at definite interval by titrating the reaction mixture against standard hypo solution using starch as an indicator. The reaction has a first order dependence on chloramine-T. With excess concentration of other reactants , the reaction rate follows first order kinetics with respect to substrate. The reaction is catalysed by H ions as well. A small salt effect and increase in reaction rate with increasing the intensity of light source is also observed. Addition of p-toluene sulphonamide retards the reaction rate. On the basis of product analysis, a pertinent mechanism is proposed. Keywords: Kinetics, photochemical oxidation, glucose, fructose, chloramine-T. IntroductionCarbohydrates are the essential biomolecules and a chief source of energy for living system. The oxidation of carbohydrates and fats in living system is a free radical reaction and we get energy from these exothermic reactions. Thus the oxidation of carbohydrates is a basic source of life. Chloramine-T (p-Me-CSON-ClNa) generally written as CAT is a versatile oxidizing agent. The sodium derivative of N-chloro-p-toluene sulphonamide is generally known as the Chloramine-T and represented as follows O O H3C S N– Cl NaDuring last few years’ interest has been focused upon the studies in the mechanism of carbohydrates which led to the preparation of its degradation products or its complete breakdown. The oxidation of carbohydrates has been studied by various workers using a variety of oxidizing agents3-29 but the photochemical oxidation with chloramine-T as an oxidant has not been investigated. Therefore we have chosen CAT to study the oxidation of some carbohydrates in presence of light. The present work deals with the kinetics of photochemical oxidation of two monosaccharides i.e. glucose and fructose. Material and MethodsThe chemicals used were of analar grade and the reagent solutions were prepared in doubly distilled water. The required volumes of glucose/fructose, CAT, HCl and other reagents, where necessary, were mixed in a 250 ml beaker. The reaction vessel was kept under visible light source (tungsten lamp). The course of the reaction was followed by withdrawing 2 ml of reaction mixture at a definite time interval and adding it to a flask containing potassium iodide solution to quench the reaction. The unreacted chloramine-T quickly reacts with KI solution and liberates iodine which was titrated against standard sodium thio sulphate solution as titrant using starch as indicator. Analysis of reaction products: Glucose/fructose (9g/100ml), CAT (0.563 gm/100ml) and water were mixed in a flask and the flask was kept under tungsten lamp. After completion of the reaction (as indicated by TLC), the light source was removed. The spots obtained on the TLC plate were found to be of formaldehyde and formic acid by co-TLC with the authentic samples. The products were further confirmed by qualitative tests. The development of reddish brown color with Nessler’s reagent changing to yellow green confirms formaldehyde as one of the reaction product. The development of red color with ferric chloride solution and also the evolution of carbon monoxide with conc. HSO, which was confirmed by flame test, indicate the formation of formic acid as another product. Results and Discussion Chloramine-T is a strong electrolyte. It dissociates in aqueous solution as follows Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 61-65, July (2014) Res. J. Chem. Sci. International Science Congress Association 62 ArSONClNa ArSONCl + NaThe anion picks up a proton in acidic medium to give free acid ArSONCl- + H ArSONHCl 2ArSONHCl ArSONH2 + ArSONClArSONHCl + HO ArSONH2 + HOCl ArSONCl2 + HO ArSONHCl + HOCl The CAT generates HOCl, which is the oxidizing species of the reaction. The reaction was carried out by varying the concentration of all the reactants and the following results have been obtained: Reaction order with respect to chloramine-T: In a typical kinetic run, a straight line was obtained by plotting log (a-x) versus time, indicating that the reaction under the chosen conditions follows pseudo first order kinetics. The order with respect to oxidant is unity table 1. Effect of variation of oxidant (chloramine-T) concentration: By keeping the concentration of other reactants constant, only the concentration of oxidant is varied from 3.7 x 10-3 to 10.0 x 10-3. The rate constants were calculated at definite time intervals. The results obtained are summarized in table-1. Table-1 Effect of variation of oxidant (chloramine-T) concentration S.No. [CAT]x10M k x 10 4 sec - 1 (For Glucose) k x 10 4 sec-1 (For Fructose) 1 3.7 2.06 2.34 2 5.0 2.36 2.77 3 6.2 2.78 3.27 4 7.5 3.31 3.80 5 8.8 3.89 4.30 6 10.0 4.60 4.58 [Glucose/Fructose] = 5.0 x10-3 M [HCl] = 1.0 x 10-3 M The results reveal that the value of rate constant increases as the concentration of CAT increases. It is because the increase in [CAT] generates more HOCl which acts as an oxidizing species. Reaction order with respect to substrate: On varying the concentration of glucose/fructose from 1.2x10-3 to 7.5x10-3 , an increase in reaction rate was observed. The plot of log k versus [substrate] gave a straight line with a slope suggesting that the order with respect to substrate is one table 2. Effect of variation of substrate concentration: The concentrations of other reactants were kept constant and only the concentration of substrate (glucose/fructose) was varied from 1.2 x 10-3 to 7.5 x 10-3. The rate constants were calculated at definite time intervals. The results obtained are summarized in table 2. Table-2 Effect of variation of substrate concentration S.No. [Glucose/ Fructose] 10 M k x 10 sec-1(For Glucose) k x 10 4 sec-1(For Fructose) 1 1.2 3.39 3.31 2 2.5 3.72 3.63 3 3.7 4.02 4.25 4 5.0 4.60 4.58 5 6.2 5.08 5.10 6 7.5 5.70 5.59 [CAT]=10.0x10-3 M [HCl] = 1.0 x 10-3 M Reaction order with respect to acid: On varying the hydrochloric acid concentration from 1x10-3 to 5.0x10-3 , an increase in reaction rate was observed. The plot of log k versus [H] gave a straight line suggesting that the reaction is catalyzed by acid table 3. Effect of variation of acid concentration: The kinetics of reaction was also studied by varying the concentration of acid and keeping that of oxidant and substrate constant. The rate constants were calculated at definite time intervals. The results obtained are summarized in table 3. Table-3 Effect of variation of acid concentration S.No. [HCl]x10 M k x 10 sec-1(For glucose) k x 10 4 sec - 1 (For Fructose) 1 0.2 2.40 2.55 2 0.4 2.80 2.97 3 0.6 3.35 3.39 4 0.8 3.96 3.88 5 1.0 4.60 4.58 [CAT]=10.0x10-3 M [Glucose/Fructose] = 5.0x10-3 M Effect of variation of Cl ion concentration: The role of chloride ion in the kinetics of the oxidation reaction by CAT is very crucial. The straight lne obtained in the plot of log k versus [Cl] indicates an increase in reaction rate with increase in Clion concentration. The cause of speeding up in reaction rate is the generation of HOCl due to the interaction between a chloride ion and a chloronium ion produced by the hydrolysis of N-Cl bond table 4. Salt Effect - Effect of variation of concentration of KCl: The concentrations of other reactants were kept constant and only the concentration of KCl was varied from 0.4 x 10-3 to 1.0x 10-3. The rate constants were calculated at definite time intervals. The results obtained are summarized in table 4. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(7), 61-65, July (2014) Res. J. Chem. Sci. International Science Congress Association 63 Table-4 Salt Effect - Effect of variation of concentration of KCl S.No. [KCl]x 10M k x 10 4 sec - 1 (For Glucose) k x 10 4 sec - 1 (For Fructose) 1 0.4 3.86 3.10 2 0.6 4.25 3.43 3 0.8 4.65 3.76 4 1.0 5.00 4.42 [CAT]=10.0x10-3 M [Glucose/Fructose] = 5.0x10-3 M [HCl]= 1.0x 10-3 M Effect of addition of p-toluene sulphonamide (PTS): The addition of PTS, one of the reaction products, from 1.0x10-3 to 4.0x10-3 at constant CAT and substrate concentration, decreases the reaction rate. This decrease is the result of mass-law effect according to which the addition of product causes the reversal of reaction and hence the reaction proceeds in backward direction30. This further confirms the hypochlorous acid (HOCl) as being the main oxidizing species during the phototchemical oxidation by chloramines-T in acidic medium table 5. Kinetics and activation parameters: The values of enthalpy of activation, entropy of activation and free energy of activation give an idea about the progress of reaction. It has been observed that if H* is positive, S* is negative and G* is positive then the reaction is non spontaneous31. This fact has been confirmed by carrying out the reaction without heat and light and no reaction was observed in that condition which shows that the reaction needs some initiation which can be provided by means of light or heat table 6. Effect of variation of product concentration: p-Toluene sulphonamide (PTS) is considered as a major product during the oxidation reactions by chloramine-T. Therefore the addition of PTS also affects the reaction rate. The reaction was studied by keeping the concentrations of other reactants constant and only the concentration of PTS was varied from 0.4 x 10-3 to 1.0x 10-3. The rate constants were calculated at definite time intervals. The results obtained are summarized as follows. Table-5 Effect of variation of product concentration [CAT]=10.0x10-3 M [Glucose/Fructose] = 5.0x10-3 M [HCl]= 1.0x 10-3 M S.No. [PTS]x 10M k x 10 4 sec - 1 (For Glucose) k x 10 4 sec - 1 (For Fructose) 1 0.4 3.44 3.29 2 0.6 3.17 2.98 3 0.8 2.88 2.69 4 1.0 2.56 2.42 Activation Parameters: Different kinetics and activation parameters were calculated using the experimental findings and their values are given in table below for glucose and fructose both. Table-6 Activation Parameters Activation Parameter Glucose Fructose Energy of activation (Ea) 20.046 KJ mol-113.783 KJ mol-1 Frequency factor (log PZ) 3.986 2.909 Enthalpy of activation (H*) 17.48 KJ mol-111.22 KJ mol-1 Entropy of activation (S*) -172.5 JK - 1 mol-1-193 JK - 1 mol-1 Free energy of activation (G*) 70.61KJ mol-170.66 KJ mol-1 Mechanism: On the basis of experimental findings and results a tentative mechanism has been proposed for the photochemical oxidation of some carbohydrates by chloramine-T. The mechanism for the dissociation of CAt giving HOCl has already been given. The HOCl dissociates photochemically into free radicals as follows: HOCl OH + ClThese OH radicals bring about the oxidation of carbohydrates. The Cl radicals combine with the H radicals produced during oxidation to give HCl which has been detected by bringing the rod dipped in NHOH on the flask. The evolution of CO has been confirmed by lime water test. The overall reaction for the oxidation is: CAT ArSONH + ArSONHCl + HOCl 12 + 6HOCl HCHO + 4HCOOH + CO + HO + 6HCl ConclusionThe kinetic study of photochemical oxidation of monosaccharides by CAT in visible light confirms that the reaction order with respect to oxidant as well as the substrate is one. The reaction rate shows enhancement with the increase in concentration of acid. Further, due to photochemical condition, the reaction follows radical mechanism. The reaction velocity accelerated with increase in the intensity of light source. The values of different activation parameters viz. enthalpy of activation, entropy of activation and free energy of activation give an idea about the progress of reaction. It has been reported that when H* is positive, S* is negative and G* is positive then the reaction is non spontaneous. 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