untitled Oxidative Spectrop Jayachamar a Department of C b Department of C *Corresponding a Tel.: +91.080.2843 ARTICLE INFO Received: 23 Sept Received in revis Accepted: 21 Nov Online: 31 March KEYWORDS Azo dye Carmosine Acid medium Chloramine‐T Decolorization Oxidation‐kinetic 1. Introductio Effluents c food processi problems. Min main issue in harmful dye e dye by simp method is mo one or more a and they form several monoa common food synthetic dye water bodies sunlight, whic water plants a the oxygenatio of water quali of unnatural c associated wit textile industr resistant to n containing az cause significa azo dye efflue main issue in commonly tre adsorption, p processes are e decolor photometr rajapura Pra Chemistry, Don Bosc Chemistry, Bangalor uthor at: Departme 37028; fax: +91.080 ORMATION tember 2011 ed form: 13 Novem vember 2011 h 2012 cs on containing azo d ing industries nimization of t waste water tr effluents from fo le, cost effect st required for azo groups (‐N m the largest c azo dyes which s and drugs [1 effluents can b , since these ch decreases th and phytoplank on of water res ty is greatly inf colors is esthet th contaminatio ry may be toxic natural biologi o dyes dischar ant environme ents generated n waste water eated using ph photodegradatio e very expensiv Eu ISSN 2153‐ Europ J rization of ric, kineti anesh Shubh co Institute of Tech re University, Centr ent of Chemistry, D 0.28437030. E‐mai mber 2011 dyes discharged cause signific toxicity caused reatment. Carm ood industries tive and envir r healthy societ =N‐) as the pri class of synthe h are widely u 1]. The discharg be very damag dyes in wate he intensity of kton, reducing ervoirs [2]. Als fluenced by its tically unpleasa on [3]. In additi c to aquatic org cal degradatio rged by food a ntal problems. d by food and r treatment. T hysico‐chemica on and coagul ve and not so uropean Journal Europe 2249 (Print) / IS DOI:10.5155 pean Jo Journal home f carmosi ic and me haa,* and Pu nology, Kumbalago ral College Campus Don Bosco Institute il address: shubhap ABSTRACT Carmosine is m dye is of greate reactions is im exploited as ox toxic, water to carmosine with out in order spectrophotom decolorization reaction rate ex unit order dep toluenesulfonam solvent isotope parameters hav was found to b complete agree d by dye, textile cant environm by these dyes mosine is one o and removal o ronmentally be ty. Azo dyes co imary chromop etic dyes. There used as coloran ge of highly co ing to the rece er strongly ab f light absorbe photosynthesis o, public percep color. The pres ant and tends t ion, dyes used i ganisms and ca on [2,4,5]. Efflu and dye indus . Hence, remov dye industries These effluents al methods suc lation. All of t simple. There of Chemistry 3 ( ean Journal of Ch SSN 2153‐2257 5/eurjchem.3.1. ournal o epage: www.e ne with a echanistic uttaswamy P odu, Bangalore, 56 s, Bangalore, 56000 of Technology, Kum pranesh@gmail.com mainly used as a r significance an mportant. Chlor xidant for a varie olerant and eas h acidic chloram to explore th metry is used to of carmosine wi xhibits a first‐or pendence on [H mide, (b) halide e. The reaction ve been deduced be negative. Th ement with the o e and mental s is a of the f this enign ntain phore e are nts in lored eiving bsorb ed by s and ption sence to be in the an be uents stries, val of s is a s are ch as these efore, ther harm attra C The sign mec liter oxid mec desi dete T deco halo effec abili The this proc T cons catio elect oxid func wide mole unde elect (1) (2012) 112‐1 hemistry (Online)  2012 112‐118.532 of Chem eurjchem.com acidic chlo c chemistr Puttaswamy 0060, India 01, India mbalagodu, Bangal m (J.P. Shubha). colorant in food nd understandin ramine‐T bears ety of substrates y to handle. A mine‐T (CAT: TsN he mechanistic monitor the re ith CAT were es der dependence +]. The reaction e ions, (c) ioni n was studied a d. Oxidation pro he derived rate observed kinetic re is a need for mful dyes in acted much atte Carmosine is m oxidative de ificance and hanistic aspec ature review s dative decolori hanistic view p gned through ermine the mech The main aim olorization of oamine, which h ctiveness of th ity to decrease high efficiency economic, ea cess could also b The diverse na sequence of th ons, hypohalite trophiles and n dants and are s ctional groups. e variety of ecular transfo ergo a two‐ele tron oxidants [1 118 2 EURJCHEM mistry m oramine‐T ry yb lore, 560060, India d industries. The ng of its kinetic a diverse chem s. It is commerci systematic kin NClNa here Ts = aspects of th eaction. Optimu stablished. The k e each on [CAT]o n rate was exam c strength, (d) at different tem ducts were char law based on t data. inexpensive an effluents. The ention in recent mainly used as ecolorization o the understa cts in redox r shows that the zation of this point. Conseque oxidative deco hanism of this r m of this w carmosine by has a low energ he proposed p e in color and t y observed with asily operated be employed in ature of the c heir ability to e species and nucleophiles [1 suitable for the Consequently, functional gro ormations. Ge ectron change w 10]. T: a. oxidative decol nd mechanistic a ical properties ially available, in netic study of t = CH3C6H4SO2‐) h his redox syst m conditions fo kinetic results re o and [carmosine mined for the e dielectric perm mperatures and racterized. Test the proposed m nd simple meth oxidation of t years [6‐9]. a colorant in f of this dye anding of its reactions is im ere is no infor s dye from it ently, this resea olorization kin reaction. work was to environmental gy cost and is in rocess was ev total organic c h the dye mod and maintain n the remediatio hemistry of N act as source N‐anions whic 10‐14]. They b e limited oxida these reagent oups affecting enerally, thes while dihaloam lorization of this aspects in redox and has been nexpensive, non he oxidation of has been carried tem. UV‐Visible or the oxidative evealed that the e]o and less than effects of (a) p‐ mittivity and (e) d the activation for free radicals mechanism is in hods to abolish azo dyes has food industries. is of greater s kinetic and mportant. The rmation on the ts kinetic and arch program is etic studies to promote the lly friendly N‐ nexpensive. The valuated by its carbon content. el showed that ned treatment on of effluents. N‐haloamines is es of halonium ch act both as behave as mild ation of several ts react with a an array of e haloamines mines are four‐ s x n n f d e e e n ‐ ) n s n h s . r d e e d s o e ‐ e s . t t s m s d l a f s ‐ Shubha and Puttaswamy / European Journal of Chemistry 3 (1) (2012) 112‐118 113 Scheme 1 The reduction products are the respective sulfonamide and NaCl or HCl. The prominent member of this class of compounds, sodium N‐chloro‐4‐methylbenzenesulfonamide, commonly known as chloramine‐T (CAT; p‐CH3C6H4SO2NClNa.3H2O) is a by‐product of saccharin manufacture. The redox potential of chloramine‐T/p‐toluenesulfonamide is pH dependent [11] and decreases with increase in pH of the medium (1.139 V at pH = 0.65, 1.778 V at pH = 7.0 and 0.614 V at pH = 9.7). The nature of active oxidizing species of CAT depends on the pH of the medium and the reaction condition. Chloramine‐T is a source of positive halogen and this reagent has been exploited as oxidant for a variety of substrates in both acidic and alkaline media [10,11,14‐20]. Although a large numbers of various substrates have been oxidized by CAT, very few oxidation kinetic investigations of dyes have been carried out with CAT. Preliminary experimental results revealed that the oxidation of carmosine by CAT in alkaline medium is too slow to be measured but the reaction is facile in the presence of an acid. Hence, the present kinetic investigations have been carried out in acid medium. In the light of available information and in continuation of our research interest in the kinetic and mechanistic investigations of oxidation of various substrates in general and dyes in particular by CAT, the title reaction was undertaken. Consequently, in this communication we report on the detailed kinetics of carmosine oxidation by CAT in HClO4 medium at 297 K in order to (i) elucidate a plausible mechanism, (ii) design appropriate kinetic model, (iii) ascertain the reactive species, (iv) characterize the oxidation products and (v) develop an optimum condition for the facile oxidation of the substrate. 2. Experimental 2.1. Materials CAT (Merck) was purified by the method of Morris et al. [21]. An aqueous solution of CAT was prepared, standardized iodometrically and stored in amber colored stoppered bottles until further use. The concentrations of stock solutions were periodically determined. Carmosine (S.D. Fine‐Chem Ltd.) was of acceptable grade of purity and was used as received. An aqueous solution of carmosine was freshly prepared whenever required. Solvent isotope studies were made in D2O (99.24% purity) medium supplied by Bhabha Atomic Research Centre, Mumbai, India. Reagent grade chemicals and doubly distilled water were used throughout. 2.2. Kinetic measurements The kinetic runs were performed under pseudo first‐order conditions with a known excess of the [CAT]o over [carmosine]o at 303 K using a UV–visible spectrophotometer (Digital Spectrophotometer 166, Systronics, India). In the present study, the kinetic experiments were carried out between 288 and 313 K. For this purpose, a Raaga Ultra Cold Chamber with digital temperature control (India) was used. A constant temperature was maintained with an accuracy of ± 0.1 oC. Reactions were carried out in glass stoppered Pyrex boiling tubes whose outer surfaces were coated black to eliminate any photochemical effects. The oxidant as well as requisite amounts of dye and HClO4 solutions and water (to keep the total volume constant for all runs) taken in separate tubes were thermostatted for 30 min at 297 K. The reaction was initiated by the rapid addition of a measured amount of oxidant to the stirred reaction mixture. Immediately, the solution was pipetted into a cuvette placed in the spectrophotometer. Absorbance measurements were made at λmax of carmosine 518 nm for nearly three half lives. The absorbance readings at t = 0 and t = t are D0 and Dt. Plots log D0/Dt versus time were made to evaluate the pseudo‐first‐order rate constants (k/) which found reproducible within ±4‐5%. Regression analysis of the experimental data was carried out on an fx‐100W scientific calculator to evaluate the regression coefficient, r. 2.3. Reaction stoichiometry Reaction mixtures containing different ratios of CAT to carmosine were equilibrated at 297 K in 1.00 x 10‐4 mol/dm3 HClO4 for 48 h. Iodometric titrations of unreacted CAT showed that one mole of carmosine consumed one mole of CAT confirming the stoichiometry given in Scheme 1. 2.4. Product analysis The reaction mixture in 1:1 ratio under stirred condition was allowed to progress for 48 h at 297 K. After the reaction, solution was neutralized with NaOH and the products were extracted with ether. The organic products were subjected to spot tests and chromatographic analysis (Thin layer chromatography (TLC) technique), which revealed the formation of oxidation products, namely naphthalene and 1,2‐ naphthoquinone. These oxidation products were separated by column chromatography and identified from their melting points: 80 oC (Lit. melting point (M.p.): 78‐80 oC [8]) and 125 oC (Lit. M.p.: 124‐126 oC [8]) for naphthalene and 1,2‐ naphthoquinone, respectively. These two products were further confirmed by GC‐MS data obtained on a 17A Shimadzu gas chromatograph with a QP‐5050A Shimadzu mass spectrometer. The mass spectrum was obtained using the electron impact ionization technique. The mass spectra showed parent molecular ion peaks at 128 and 158 amu, confirming naphthalene and 1,2‐naphthaquinone, respectively (Figure 1 114 and 2). Furth reaction betw CAT under the Figure 1. GC‐Ma 128 amu. Figure 2. GC‐Mas at 158 amu. p‐Toluene detected by saturated wit vanillin in 1% 0.905). Furthe (Figure 3) co observed in G with the obser Figure 3. GC‐M molecular ion pea her, it was no ween naphthale e present set of ass spectrum of na ss spectrum of nap esulfonamide w paper chrom th water was % HCl solution er the parent onfirms p‐tolu GC‐Mass spectra rved structure. Mass spectrum of ak at 171 amu. Shubha an oticed that the ene and 1,2‐na experimental c aphthalene with it phthaquinone with as extracted wi matography [18 used as the s in ethanol as molecular ion enesulfonamid a can be interp f p‐toluenesulfona nd Puttaswamy / ere was no fu aphthoquinone conditions. ts molecular ion p h its molecular ion ith ethyl acetate 8]. Benzyl alc solvent with 0 spray reagent n peak of 171 e. All other p reted in accord amide with its p / European Journ rther with eak at n peak e and cohol .5 % (Rf = amu peaks dance parent 3. Re 3.1. T inve in H of [c temp (r > [carm liste varia denc U [CAT [CAT indic [CAT 0.99 depe temp [HCl with on [H Table the re 104 [ (mol 0.40 0.80 1.60 2.00 3.20 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 3.2. on th A redu the indic limit TsNC TsNH X 3.3. A sodi pron ions reac NaC cons negl invo nal of Chemistry esults and disc Effect of reacta The oxidation estigated at diff ClO4 medium a carmosine]o << perature, plots 0.9901), indic mosine]o. The ed in Table 1. Fu ation in [carm ce of the rate on Under the sam T]o increased t T]o was linear cating a first‐o T]o. Further, a 983) passing th endence on [CA perature, the ra lO4] (Table 1). A h a slope of 0.6 HClO4]. e 1. Effect of varia eaction rate at 297 CAT]o dm‐3) 104 (mo 0.80 0.80 0.80 0.80 0.80 0.40 0.80 1.60 2.00 3.20 0.80 0.80 0.80 0.80 0.80 Effects of halid he rate Addition of uction product reaction mixtu cates that PTS ting step in Sch Cl- + H+ HCl + Carmosine Products K1 H2O Effect of ionic s Addition of ha um salts (1.0 nounced effect play no role ction medium w lO4 solution stant. It was ligible effect olvement of non 3 (1) (2012) 112 cussion ant concentrat n of carmosin ferent initial co at 297 K. Under [CAT]o at const of log (absorba cating a first‐o pseudo first‐o urther, the valu mosine]o, confir n [carmosine]o. me experimenta the rate (Table (r = 0.9976) h order depende plot of kˊ ve hrough the orig AT]o. At consta ate of the reacti A plot of log kˊ 60, indicating a ation of CAT, carm 7 K. [carmosine]o ol dm‐3) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 de and benzen p‐toluenesulfo of CAT (1.0 x ure did not af is not involved eme 2 propose (Com k2 TsNHCl X Scheme strength of the alide ions, Cl‐ x 10‐3 ‐ 8.0 x on the rate. T in the reactio was varied fro keeping othe found that a on the rea nionic species in 2‐118 tion on the rate ne by CAT w oncentrations o pseudo first‐or tant [carmosine ance) versus tim order dependen order rate cons es of kˊ remain rming the first al conditions, e 1). A plot of having a slope ence of the rea rsus [CAT]o w gin, confirming ant [CAT]o, [ca ion increased w versus log [HC a fractional‐ord mosine and HClO4 103 [HClO4] (mol dm‐3) 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.20 0.40 0.80 1.60 3.20 nesulfonamide onamide (PTS 10‐3 ‐ 8.0 x 10‐ ffect the rate s d in any step pr d. (i) Fast mplex) (ii) Slow (iii) Fast e 2 e medium on th or Br‐, in the x 10‐3 mol/dm This indicates t on. The ionic s om 0.1 to 0.3 er experiment addition of N ction rate, i n the rate‐limit e was kinetically of the reactants rder conditions e]o, [HClO4] and me were linear nce of rate on stants (kˊ) are unaltered with t‐order depen‐ an increase in f log kˊ versus equal to unity, action rate on was linear (r = the first‐order rmosine]o, and with increase in ClO4] was linear er dependence concentrations on 104 kˊ x (s‐1) 1.74 4.81 9.30 11.5 18.6 4.78 4.85 4.89 4.73 4.88 2.88 4.81 7.17 10.2 18.3 concentration S or TsNH2), ‐3 mol/dm3), to significantly. It rior to the rate‐ / rate determining he rate form of their m3) showed no that the halide strength of the mol dm‐3 with tal conditions aClO4 showed indicating the ing step. Hence y s s d r n e h ‐ n s , n = r d n r e n n , o t ‐ r o e e h s d e e Shubha and Puttaswamy / European Journal of Chemistry 3 (1) (2012) 112‐118 115 no attempts were made to keep the ionic strength of the medium constant for kinetic runs. 3.4. Effect of dielectric constant of the medium on the rate The dielectric constant (D) of the medium was varied by adding MeOH (0‐30 %; v/v) to the reaction mixture with all other experimental conditions being held constant. The rate decreased with increase in MeOH content (Table 2, Figure 4). A plot of log kˊ versus 1/D was linear (r = 0.9978) with a negative slope. It was further noticed that no reaction of the dielectric with the oxidant under the experimental conditions employed. The values of the dielectric constant of CH3OH ‐ H2O mixtures reported in the literature [22] were employed. Table 2. Effect of varying dielectric constant (D) of medium on the rate of reaction at 297 K*. % MeOH (v/v) D kˊ x 104 (s‐1) 0 76.7 4.81 5 74.5 2.15 10 72.3 1.04 15 69.7 0.36 20 67.5 0.13 * [CAT]o = 8.00 x 10‐4 mol dm‐3, [carmosine]o = 8.00 x 10‐5 mol dm‐3, [HClO4] = 4.00 x 10‐4 mol dm‐3. Figure 4. A plot of log kˊ versus 1/D. 3.5. Effect of solvent isotope on the rate As the oxidation of carmosine by CAT was accelerated by [H+], the solvent isotope effect was studied in D2O as the solvent medium, with carmosine as a probe. Values of kˊ (H2O) and kˊ (D2O) were 4.81 x 10‐4 s‐1 and 4.96 x 10‐4 s‐1, giving a solvent isotope effect kˊ (H2O) / kˊ (D2O) = 0.96. 3.6. Effect of temperature on the rate The effect of temperature on the reaction rate was studied by performing the kinetic runs in the range of 288‐313 K, keeping other experimental conditions constant. From the linear Arrhenius plot of log kˊ versus 1/T (r = 0.9930, Figure 5), values of activation parameters (Ea, ∆H≠, ∆G≠, ∆S≠ and log A) for the overall reaction were evaluated. These data are presented in Table 3. 3.7. Test for free radicals Addition of the reaction mixture to the acrylamide monomer did not initiate polymerization, indicating the absence of free radicals in the reaction mixture. Control experiments performed with solutions containing all the components of the reaction mixture except the oxidant and with the individual oxidant solutions were found to be negative. Table 3. Temperature dependence on the reaction rate and activation parameters for the oxidation of carmosine by CAT acid medium. Temperature (K) kˊ x 104 (s‐1) 288 1.84 293 3.16 297 4.81 307 12.6 313 23.4 Ea (kJ mol‐1) 71.7 ΔH≠ (kJ mol‐1) 69.2 ΔG≠ (kJ mol‐1) 91.8 ΔS≠ (JK‐1 mol‐1) ‐75.4 [CAT]o = 8.00 x 10‐4 mol dm‐3; [carmosine]o = 8.00 x 10‐5 mol dm‐3; [HClO4] = 4.00 x 10‐4 mol dm‐3. Figure 5. Arrhenius plot of log kˊ versus 1/T. 3.8. Reactive species of Chloramine‐T Chloramine‐T (TsNClNa) behaves as a strong electrolyte [21] in aqueous solutions, and depending upon the pH of the medium, it furnishes the following types of reactive species in solutions (Equilibrium 1‐7). Chloramine‐T dissociates according to Equilibrium 1 in aqueous solution. The anion picks up a proton in acid (Equilibrium 2) to give the free acid TsNHCl. It undergoes disproportionation [23‐25] via Equilibrium 3 giving rise to dichloramine‐T and the parent amide. The free acid and dichloramine‐T undergo hydrolysis (Equilibrium 4 and 5). Finally the hypohalous acid undergoes ionization according to Equilibrium 6. Possibly the hypohalous acid with a proton gives H2OCl+ species (Equilibrium 7 and 8). Consequently, the possible oxidizing species in acidified CAT solutions are TsNHCl, TsNCl2, HOCl and perhaps H2OCl+. 116 Shubha and Puttaswamy / European Journal of Chemistry 3 (1) (2012) 112‐118 Absence of a retardation effect by the p‐toluenesulfonamide rules out the involvement of HOCl in the reaction sequence. Bishop and Jennings [23] have shown in aqueous solutions of CAT, at pH > 3, the concentration of anion TsNCl‐ is greater than that of the free acid. Hence the protonation Equilibrium 2 involving the anion can be assumed in aqueous acidic solution. 3.9. Reaction scheme In the present investigations, the conjugate free acid TsNHCl is assumed to be most active oxidizing species. Based on the preceding discussion and experimental facts, Scheme 2 is proposed to explain the reaction mechanism for the oxidation of carmosine by CAT in HClO4 medium. Dyes such as carmosine containing hydroxyl groups conjugated to azo group exhibit azo‐hydrazone tautomerism as shown in Scheme 3. Scheme 3 In the present case, the azo form of the dye reacts with the conjugate acid of the oxidant to form a substrate‐CAT complex (X) with the elimination of TsNH2. The complex in acid medium undergoes protodesulfonation followed by hydrolysis and cleavage of azo bond to yield the ultimate products naphthalein and 1,2‐naphthaquinone as shown in Scheme 4. 3.10. Kinetic rate law A detailed mode of oxidation of carmosine by CAT in acid medium is depicted in Scheme 4, where the structure of the intermediate complex X is shown. In a fast initial equilibrium (step (i) of Scheme 2), the anion TsNCl‐, in acid accelerating step generates the active oxidizing species TsNHCl. In a slow / rate limiting step (step (ii)), the lone pair of electrons on oxygen of carmosine attacks the positive chlorine of TsNHCl forming an intermediate species X. This intermediate complex X (step (iii)) undergoes hydrolysis followed by several fast steps leading to the formation of naphthaquinone and naphthalene as end products. If [CAT]t represents the total concentration of the oxidant, then from steps (i) and (ii) of Scheme 2, [CAT]t =[TsN‐Cl] + [TsNHCl] (8) By substituting [TsN‐Cl] from step (i) of Scheme 2, into Equation 8 and solving for [TsNHCl], one gets, TsNHCl K1 CAT t H 1 K1 H (9) From the slow and rate determining step (step (ii) of Scheme 2), Rate = k2 [TsNHCl] [carmosine] (10) By substituting for [TsNHCl] from Equation 9 into Equation 10, the following rate law is obtained: Rate K1k2 CAT t Carmosine H 1 K1 H (11) The derived rate law (Equation 11) is in good agreement with the experimental results, wherein a first order dependence of rate on each [CAT]o and [carmosine]o and a fractional order dependence on [H+]. Since rate = [CAT]t, Equation 11 can be transformed into Equation 12. ˊ K1k2 Carmosine H k2 Carmosine (12) A plot of 1/kˊ versus 1/[carmosine] passes through the origin confirming observed kinetics. Further from the slope and intercept of the linear plot of 1/kˊ versus 1/[H+], values of protonation constant (K1) and dissociation constant (k2) were found to be 2.612 x 105 dm3/mol and 208.3 dm3/mol.s, respectively. 3.11. Effect of dielectric constant Several approaches have been put forward to explain quantitatively the effect of the dielectric constant of the medium on the rates of reactions in solutions. For the limiting case of zero angle of approach between two dipoles or an ion‐ dipole system, Amis [26] has shown that a plot of log kˊ against 1/D gives a straight line with a negative slope (Figure 4; r > 0.9943) for the reaction between a negative ion and a dipole or between two dipoles, while a positive slope indicates a reaction between a positive ion and a dipole. The negative dielectric effect in the present studies is in agreement with dipole‐dipole nature of the rate‐limiting step in the proposed Scheme 4 and the reaction pathways are suggested to explain the kinetic results. 3.12. Solvent isotope studies Reactions in aqueous medium that are susceptible to acid‐ base catalysis have been studied in heavy water (D2O) after equilibrium. Since most oxidation reactions of organic compounds involve the cleavage of C‐H bond, deuterium isotope effect on such reactions gives information regarding the nature of the rate limiting step. In the present investigations, solvent isotope studies have shown that the rate of reaction is higher in D2O medium. For a reaction involving a fast equilibrium with H+ or OH‐ ion transfer, the rate increases in D2O medium since D3O+ and OD‐ are a stronger acid and a stronger base respectively, than H3O+ and OH‐ ions [27‐28]. The observed solvent isotope effect of kˊ (H2O) / kˊ (D2O) < 1 is due to the greater acidity of D3O+ compared to H3O+. However, the magnitude of increase in rate in D2O is small as compared to the expected value which is 2‐3 times greater. This may be due to the fractional order dependence of the rate on [H+]. Hence, this observation supports the proposed mechanism. The negligible influence of variation of ionic strength and addition of p‐toluenesulfonamide and halide ions are in agreement with the proposed mechanism. The proposed mechanism is also supported by the moderate value of energy of activation and other thermodynamic parameters (Table 3). The fairly high positive values of ΔG≠ and ΔH≠ indicate that the transition state is highly solvated while the negative entropy of activation reflects the formation of a compact and ordered transition state. Further, the experimental observation shows that there is no effect of p‐toluenesulfonamide, halide ions and ionic strength on the reaction rate which also substantiates the proposed mechanism. In the present redox system the optimum conditions for the controlled oxidation of carmosine by CAT to naphthalene and 1,2‐naphthaquinone were established in acid medium. These products are largely used in the syntheses of naphthalene analogues such as naphthols and naphthalene sulfonic acid, which are widely used in dyestuff industries. Consequently, this redox system can be scaled up to industrial operation. Shubha and Puttaswamy / European Journal of Chemistry 3 (1) (2012) 112‐118 117 Scheme 4 Furthermore, carmosine is one of the chief components in the effluents of various industries and is environmentally hazardous and also carcinogenic compound. Hence, the present simple method developed can be adopted for treating the carmosine dye present in industrial effluents to reduce toxicity caused by this dye. Also, this method offers several advantages including short reaction time, ease of isolation of products, cost effective and relatively non‐toxic reagents which make the reaction process simple, elegant and environmentally benign. 4. Conclusions The kinetics of oxidation of carmosine by chloramine‐T in acid medium obeys the rate law –d[CAT] / dt = k [CAT]o [Carmosine]o [acid]0.60. Oxidation products were identified by GC‐MS analysis. The present method developed for the oxidative decolorization of carmosine with CAT offers several advantages including cost effective and relatively non‐toxic reagents, which make the reaction process simple, smooth and environmentally benign. 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