Research Journal of Chemical Sciences ______ ______________________________ ______ ____ ISSN 2231 - 606X Vol. 2 ( 8 ), 26 - 30 , August (201 2 ) Res.J.Chem.Sci. International Science Congress Association 26 Kinetics of Oxidation of Vitamin - B 3 (Niacin) by Sodium N - bromo benzenesulphonamide (Bromamine - B) in HCl Medium and Catalysis by Ru(III) ion Chandrashekar 1 , Venkatesha B.M . 1 * and Ananda S . 2 1 epartment of Chemistry, Yuvaraj’s college, University of Mysore, Mysore - 570005, INDIA 2 Department of studies in Chemistry, Manasagangothri, University of Mysore, Mysore , INDIA Available online at: www.isca.in Received 1 8 th April 201 2 , revised 30 th April 201 2 , accepted 3 rd May 201 2 Abstract Kinetics of uncatalyzed and Ru(III) catalyzed oxidation of vitamin - B 3 (niacin) by the titled compound (bromamine - B) in HCl medium has been studied at 303K. The uncatalyzed reaction shows a first order dependence of the rate on ( BAB ) and ( vitamin - B 3 ) , inverse fractional order in ( acid ) . The Ru(III) Catalyzed reaction on the other hand shows a first order behavior on each of ( BAB ) and ( vitaminB 3 ) , fractional order dependence on Ru(III) and inverse fractional order in ( acid ) . The reaction rate shows inverse fractional order ( benzenesulphonamide ) in both uncatalyzed and Ru(III) ion catalyzed reactions. Addition of halide ions, variation of ionic strength and dielectric constant of the medium had no effect on the reaction rate. Activat ion parameters have been evaluated from the arrhenius plots, mechanisms consistent with the above kinetic data have been proposed . Keyword s : Vitamin - B 3 , bromamine - B, oxidation, Ru (III), catalysis. Introduction Aromatic N - halo sulphonamides are mild oxidants containing a strongly polarized N - linked halogen in its +1 oxidation state. The prominent member of this group, chlroamine - T (CAT) is a well known analytical reagent and the mechanistic aspects of many of its reaction have been documented 1,2,3,4 . Bromamine - B (BAB) (p - C 6 H 5 SO 2 NBrNa.3H 2 O) is a halo - amine containing a positive bromine has been recently introduced as an oxidimetric titrant in aqueous medium. Nicotinic acid (niacin) is also known as pellagra - preventive factor (p - p factor) or vitamin - B 3 . Niacin is one of the most important vitamin, it plays a vital role in cell respiration, release carbohydrates, fat and proteins, and normal secretion of bile. Deficiency of nicotinic acid in human leads to the condition pellagra followed by malfunction of digestive and nervous system. The literature survey provides information regarding the determination of nicotinic aci d and metabolic effects of nicotinic acids 5 - 8 . The reports on kinetic study of reactions of nicotinic acid are scanty 9 - 11 . Kinetic and mechanistic study of chromium (VI) catalyzed oxidation, bioremediation of hydrocarbon, hydrogenation of cyclopentene with out catalyst and in the presence of molybdenum disulfide 12 - 14 . Hence we are reporting a kinetic investigation of vitamin - B 3 with bromamine - B in presence of hydrochloric acid at 303K. Material and Methods Experimental: Bromamine - B (BAB) was prepared using a standard method and its purity checked iodometrically and through IR and NMR spectral data 15 . An aqueous solution of BAB was prepared, standardized by iodometric method and preserved in amber colored bottle until use, to prevent its photochemical deteri oration. Analar grade niacin (E - Merck) was used and aqueous solution of the substrate was prepared. A solution of RuCl 3 .3H 2 O (Arora Matthey) in 0.5 M HCl was prepared and used as the stock catalyst solution. Allowance was made for the amount of HCl presen t in the catalyst solution while preparing reaction mixtures for kinetic runs. All other chemicals used were of accepted grades of purity. The ionic strength of reaction mixture was kept at a high value by adding required amount of concentrated NaClO 4 solu tion. Triply distilled water was employed for preparing aqueous solutions. Kinetic Measurements: Kinetic runs were performed under pseudo - first order condition of ( niacin ) �� ( BAB ) 0. Mixture containg requisite amount of solutions of the niacin, NaClO 4, Ru(III) (in case of catalyzed reaction only) and HCl were taken in a stopperd pyrex glass tubes whose outer surfaces were coated black to eliminate photochemical effects. A required amount of water was added to maintain constant total volume for all run s. The reaction vessel was thermostated in a water bath set at a temperature 303K. To this solution a measured amount of pre - equilibrated BAB solution was added to give a known concentration. The progress of the reaction was Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 8 ), 26 - 30 , August (201 2 ) Res.J.Chem.Sci International Science Congress Association 27 monitored iodometrically for tw o half - lives by withdrawing aliquots of the reaction mixture at regular time intervals. Under pseudo - first order conditions, rate constants k′ were reproducible with in 3%. The regression analysis of experimental data was carried out on an origin 5.0 by HP 7540 computer. Stoichiometry and Product Analysis: Investigations under the conditions [BAB] �� [vitamin - B 3 ] revealed that two moles of BAB were consumed by one mole of substrate. The stoichiometry of oxidation is illustrated by following equation. The reaction product of BAB, benzenesulphonamide was identified by TLC using petroleum ether - chloroform - 1 - butanol (2:2:1 v/v) solvent system for ascending irrigation and iodine as developing reagent (Rf = 0.88).The 2,5, - dihydroxy pyr idine present in the reaction mixture was identified with authenticated sample by TLC method. Further it was confirmed by conventional ferric chloride test 16 . The evolved CO 2 was detected by the conventional lime water test. Attempts to quantitative measur e of the CO 2 evolved were unsuccessful. Results and Discussion Uncatalyzed Reaction : The reactions were performed in the presence of HCl under pseudo - first order condition of ( niacin ) �� ( BAB ) 0 , gave a linear plots of log ( BAB ) verses time. The linearity of these plots, together with the constancy of the slope for various ( BAB ) 0 indicates a first order dependence of the reaction rate on ( BAB ) . The pseudo - first order rate constants k′ obtained at 303K are listed in table 1. Under the same experimental conditions an increase in [niacin] 0 increased the rate were given in table 1. The plots of log k′ verses log [niacin] were linear with slope ≈1.0 thus indicating a first order dependence on ( niacin ) . Table - 1 Effects of varying react ant concentrations on the reaction rate [Ru (III)] = 6.215 x 10 - 6 mol dm - 3 ; [HCl] = 2.5 x 10 - 4 mol dm - 3 ;Temp = 303 K ; = 0.2 mol dm - 3 [BAB] x 10 4 mol dm - 3 [NA] x 10 2 mol dm - 3 k′ x 10 4 Sec - 1 1.26 2.0 6.14 (0.541) 1.73 2.0 6.52 (0.560) 2.00 2.0 6.06 (0.558) 2.43 2.0 6.65 (0.574) 2.86 2.0 6.39 (0.531) 2.00 0.5 1.58 (0.142) 2.00 1.0 3.16 (0.310) 2.00 1.5 4.89 (0.446) 2.00 2.0 6.06 (0.558) 2.00 2.5 7.80 (0.758) 2.00 3.0 9.77 (0.851) * The values in the parenthesis are for the uncatalyzed oxidation of niacin by BAB in HCl medium. The addition of Cl - or Br - ions in the form of NaCl or NaBr at constant [H + ] did not affect the rate. Hence the dependence of the rate on [HCl] reflected the effect of [H + ] only on the reaction. Addition of reaction product benzenesulphonamide (5.0 x10 - 5 - 30.0 x10 - 5 mol dm - 3 ) to the reaction mixture retarded the reaction rate. Further the plots of log k′ vs log ( BSA ) were linear (r � 0.9907) with negative fract ional slope (≈  0.62). The variation of ionic strength of the medium had no effect on the reaction rate. Addition of reaction mixture to aqueous acrylamide did not initiate the polymerization, showing the absence of free radical species. The reactions wer e studied at varying temperatures from 298K to 313K, from the linear plots the activation parameter were computed are given in table 3. Ru(III) Catalyzed Reaction: The reaction performed in the presence of Ru(III), under pseudo - first order condition of ( vitamin - B 3 ) �� ( BAB ) 0 gave a linear plots of log ( BAB ) vs time (r � 0.9988), indicating a first order dependence of the reaction rate on ( BAB ) , as in the uncatalyzed reaction. The values of k′ were given in table 1. When the variables kept constant, the rate increased with increase in ( vitamin - B 3 ) (r � 0.9989) and obtained a unit slope indicates a first order rate dependence on the substrate conce ntration. At constant ( vitamin - B 3 ) 0 , ( BAB ) and [Ru(III)], the reaction was studied with varying concentration of HCl at 303K, the plots of log k′ vs. log [HCl] were linear (r � 0.9924) with negative fractional slope indicating inverse fractional order (≈  0.51) dependence of rate H + ion concentration and shown in table 2. Table - 2 Effects of varying [HCl] on the reaction rate [NA] = 2.0 x 10 - 2 mol dm - 3 ; [BAB] 0 = 2.010 - 4 mol dm - 3 ; [Ru (III)] = 6.215 x 10 - 6 mol dm - 3 ; Temp = 303K ; = 0.2 mol dm - 3 [HCl]x10 4 mol dm - 3 k ′ x 10 4 sec - 1 1.0 9.40 (0.871) 1.5 7.61 (0.725) 2.0 6.70 (0.635) 2.5 6.06 (0.558) 3.5 5.10 (0.478) 4.5 4.30 (0.381) * The values in the parenthesis are for the uncatalyzed oxidation of niacin by BAB in HCl medium. Runs performed with increasing [Ru(III)], keeping other conditions constant, showed an increase in the rate. The slopes of the linear plots of log k′ vs l og [Ru(III)] indicates fractional order (≈ 0.6) dependence of the rate on Ru(III) concentration as shown in figure 1. Addition of reaction product benzenesulphonamide (5.0 x10 - 5 - 30.0 x10 - 5 mol dm - 3 ) to the reaction mixture retarded the reaction rate. Further, the plot of log k′ vs log ( BSA ) was linear (r > 0.9958) with negative fractional slope (≈  0.62). Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 8 ), 26 - 30 , August (201 2 ) Res.J.Chem.Sci International Science Congress Association 28 Figure - 1 Plot of log k′ vs log [Ru(III)]. [NA] = 2.0 x 10 - 2 mol dm - 3 ;[BAB] 0 = 2.0 10 - 4 mol dm - 3 ; [HCl] = 2.5 10 - 4 mol dm - 3 ;= 0.2 mol dm - 3 ; Temp = 303K Figure - 2 Plot of log k′ vs log [BSA]. [NA] = 2.0 x 10 - 2 mol dm - 3 ; [BAB] 0 = 2.0 10 - 4 mol dm - 3 ; Ru(III) = 6.21510 - 6 mol dm - 3 ; [HCl] = 2.5 10 - 4 mol dm - 3 ; = 0.2 mol dm - 3 ; Temp = 303K Addition of Cl - or Br - ions in the form of NaCl and NaBr and variation of ionic strength by adding NaClO 4 had no influence on the reaction rate in the presence of Ru (III) as catalyst. Test performed using aqueousacryl amide monomer for the presence of free radicals in the reaction mixture was found to be negative. Mechanism: Bromamine - B (PhSO 2 NBrNa) like its chlorine analog chlroamine - B and chlroamine - T behaves as a strong electrolyte in aqueous solutions forming different species as shown in Equation2 - 6 17,18,19 . In acid solutions, the probable oxidizing species are the free acid PhSO 2 NHBr, PhSO 2 NHBr 2 , HOBr and H 2 O + Br. The involvement of PhSO 2 NBr 2 in mechanism leads to a second - order rate law according to equation (5), which is contrary to the experimental observations. The monohaloamines can be further protonated at pH 2 as in equation (7) and (8) for chlroamine - T and chlroamine - B res pectively 20,21 . Therefore in acidic conditions, for bromamine - B, PhSO 2 NHBr is expected to protonate as follows. Uncatalyzed Reaction : In the present study of oxidation of vitamin - B 3 in the absence of Ru(III) catalyst, the inverse fractional order in [H + ] suggests that the deprotonation of PhSO 2 N + H 2 Br results in formation of PhSO 2 NHBr, as shown in step (i) and in step (ii) the PhSO 2 NHBr undergo hydrolysis with the formation of active oxidizing species HOBr with the elimination of PhSO 2 NH 2 , as the inverse fractional order with [PhSO 2 NH 2 ] was observed. Further the reaction rate shows dependence of first order on [vitamin - B 3 ], indicating HOBr is reacting with the substrate with slow step and gives products on the subsequent steps. Based on the preceding discussion a mechanism scheme 1 is proposed to account for the experimental observations. K 3 HOBr + S X Slow (iii) Scheme - 1 From the slow step of the preceding sheme1 Total effective concentration of BAB for scheme 1 given by equation (11) and solving for [HOBr] gives equation (12) K 1 fast K 1 K 2 fast K 1 k 4 Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 8 ), 26 - 30 , August (201 2 ) Res.J.Chem.Sci International Science Congress Association 29 Substitution for [HOBr] in equation (11) we get the rate law equation (13) The rate law is consistent with the experimental observation of first order in ( BAB ) and ( vitamin - B 3 ) , and fractional order in [H + ]. Ru(III) catalyzed reaction: Electronic spectral studies have shown that coordination species such as [RuCl 5 (H 2 O)] - 2 , [RuCl 4 (H 2 O) 2 ] - , [RuCl 3 (H 2 O) 3 ], [RuCl 2 (H 2 O) 4 ] + and [RuCl 5 (H 2 O) 5 ] 2+ do not exist in the aqueous solution of RuCl 3 . Ruthenium (III) however exists in the following ligand substitution equilibrium in acid medium 22 - 26 . The above equilibrium was used in ruthenium (III) chloride catalyzed oxidation of primary alcohols by BAB and ethylene glycols by N - bromoacetamide in HClO 4 medium 27,28 . In the present study however, the chloride ion has no effect on the rate which indicates t hat the complex ion [RuCl 3 ] 3 - is the reactive catalyst species, simillar results were observed in the Ru(III) catalyzed oxidation of chloroacctic acids by bromamine - T (BAT) 29 and bromamine - B. In the present study the oxidation of vitamin - B 3 in the presence of Ru(III) as catalyst, the inverse fractional order in [H + ] suggest that, the deprotonation of PhSO 2 N + H 2 Br in step(i) results in the formation of regeneration of PhSO 2 NHBr. A retardation by the added benzene sulphonamides (PhSO 2 NH 2 ) i.e.an inverse fract ional order on [PhSO 2 NH 2 ] indicates hydrolysis of monobromamine [PhSO 2 NHBr] to form HOBr in step (ii) which act as the active species in fast pre - equilibrium step. The reaction rate shows fractional order in Ru(III) concentration and first order on [vitam in - B 3 ]. Based on the preceding discussion a mechanism scheme 2 is proposed to account for the experimental observation . Scheme - 2 Scheme 2 leads to the rate law as follows: Total effective concentration of BAB for scheme 2 was given by the equation (16) From equilibria (i), (ii), and (iii) in scheme 2 By solving for [BAB] t of equation (15) and equations (16), (17), (18) and (19) one gets , Substituting [X] in the rate equation (15) leads to the rate law equation This rate law equation (22) is in agreement with the experimental observations, including a first - order in [BAB], an inverse fractional order in [H + ] , and [BSA] and a fractional order in [Ru(III)]. The energy of activation for ruthenium catalyzed reactions is less than uncatalyzed reaction indicating the rate of reaction for ruthenium catalyzed reaction is faster than uncatalyzed reactions. The thermodynam ic parameters Ea, ∆H ≠ , ∆S ≠ , and ∆G ≠ were calculated as shown in table 3. The moderate value of enthalpy of activation (  H ≠ ) is supportive of the proposed mechanism in scheme 1 and scheme 2. The high negative value of entropy of activation (  S ≠ ) indicates t he formation of a rigid transition state by associative process . K 2 ′ K 3 ′ k 4 ′ k 5 ′ K 1 ′ Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 8 ), 26 - 30 , August (201 2 ) Res.J.Chem.Sci International Science Congress Association 30 Table - 3 Temperature dependence and activation parameters for the reaction of Niacin with Bromamine - B [NA] = 2.010 - 2 mol dm - 3 ;[BAB] = 2.010 - 4 mol dm - 3 ; [Ru (III)] = 6.215 x 10 - 6 mol dm - 3 ; [HCl] =2.510 - 4 mol dm - 3 ;Temp = 303 K; = 0.2 mol dm - 3 Temparature in K k′ x 10 4 sec - 1 Thermodynamic parameters 298 4.60 (0.354) Ea = 46. 424 (48 .053) kJ mol - 1 303 6.06 (0.558)  S ≠ =  161. 87 (  177. 21) JK - 1 mol - 1 308 8.70 ( 0.725)  H ≠ = 43. 862 (45. 49) kJ mol - 1 313 11.51(0.932)  G ≠ = 94. 560 (100. 07) kJ mol - 1 318 14.50 ( 1.258) --- * The values in the parenthesis are for the uncatalyzed oxidation of niacin by BAB in HCl medium . Conclusion The oxidation of vitamin - B 3 was carried out by bromamine - B as oxidant. The ruthenium catalyzed reaction is very much faster than uncatalyzed reaction. The kinetic study of these reactions helpful for understanding mechanistic reactions of vitamin - B 3 in biochemical reactions. Acknow ledgement One of the authors Chandrashekar acknowledges the Management of PES college of Engineering Mandya, for permission and encouragement. References 1 . Mahadevappa D.S., Ananda S., Murthy A . S . A. and Rangappa K.S., Tetrahedron , 10, 1673 ( 1984 ) 2 . Rao P.V.S., Subbaiah K.V. and Murthy P . S . N., React Kinet , Catol, Lett. , 10, 79, ( 1979 ) 11, 287 ( 1979) 3 . Venkatesha B.M., Ananda S. and Mahadevappa D.S., Indian J. Chem . , 30A , 789 - 792 ( 1991 ) 4 . Ananda S., Venkatesha B.M., Mahadevappa D.S. and Madegowda N.M. , Int J . Chem Kinet . , 25, 755 - 770 ( 1993 ) 5 . 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