Journal of ISSN: 2473-0831 JAPLR

Analytical & Pharmaceutical Research
Research Article
Volume 4 Issue 1 - 2017
The Inhibitive Action of Aniline on the Autoxidation of Sodium Sulfite in Acidic Medium
Arun Kumar Sharma1*, Parashar P1, Prasad DSN1 and Rashmi Sharma2
1Department of Chemistry, Govt P.G. College Jhalawar-326001, Rajasthan, India
2Department of Chemistry, S.P.C. Govt. College Ajmer-305001, Rajasthan, India
Received: December 05, 2016 | Published: January 19, 2017
*Corresponding author: Arun Kumar Sharma, Department of Chemistry, Govt. P.G. College , Jhalawar, 326001, Rajasthan, India, Email:
Citation: Sharma AK, Parashar P, Prasad DSN, Sharma R (2017) The Inhibitive Action of Aniline on the Autoxidation of Sodium Sulfite in Acidic Medium. J Anal Pharm Res 4(1): 00091. DOI: 10.15406/japlr.2017.04.00091

Abstract

The kinetics of atmospheric autoxidation of S (IV) by Ag(I) at pH 4.02-5.25 has been studied. The aqueous phase autoxidation of S (IV) is the major factor responsible for acidification of atmospheric aqueous system. The role of Aniline act as an inhibitor of Ag(I)  catalysed autoxidation of S(IV) in acidic medium has been identified, and based on the observed results following  rate law given and a free radical mechanism has been proposed.

d[ S( lV ) ]/dt =  ( k 1 +  k 2 [ Ag( I ) ] ) [ S( lV ) ]/1+B[ Aniline ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadsgajuaGpaWaamWaaOqaaKqzGeWdbiaadofajuaGpaWa aeWaaOqaaKqzGeWdbiaadYgacaWGwbaak8aacaGLOaGaayzkaaaaca GLBbGaayzxaaqcLbsapeGaai4laiaadsgacaWG0bGaaiiOaiabg2da 9iaacckacaGGGcqcfa4damaabmaakeaajugib8qacaWGRbWcpaWaaS baaeaajugWa8qacaaIXaaal8aabeaajugib8qacqGHRaWkcaqGGaGa am4AaKqba+aadaWgaaWcbaqcLbmapeGaaGOmaaWcpaqabaqcfa4aam WaaOqaaKqzGeWdbiaadgeacaWGNbqcfa4damaabmaakeaajugib8qa caWGjbaak8aacaGLOaGaayzkaaaacaGLBbGaayzxaaaacaGLOaGaay zkaaqcLbsapeGaaeiiaKqba+aadaWadaGcbaqcLbsapeGaam4uaKqb a+aadaqadaGcbaqcLbsapeGaamiBaiaadAfaaOWdaiaawIcacaGLPa aaaiaawUfacaGLDbaajugib8qacaGGVaGaaGymaiabgUcaRiaadkea juaGpaWaamWaaOqaaKqzGeWdbiaadgeacaWGUbGaamyAaiaadYgaca WGPbGaamOBaiaadwgaaOWdaiaawUfacaGLDbaaaaa@73F7@

Experiments were carried out at 30≤T°C≤40, 4.02≤pH≤5.25, 1×10−3mol/cm3≤ [S(IV)≤10×10−3 mol/cm3, 5×10−6mol/cm3≤[Ag(I)]≤2.5×10−5mol/cm3, 5×10−7mol/cm3≤[Aniline]≤8×10-3mol/cm3. Based on the experimental results, rate constants and orders of the reactions were determined. The reaction order in S(IV) were first order for both reactions in the presence and absence of Aniline. The effect of Ag(I) ion and Aniline concentrations as well as an initial pH of the solution on the S(IV) oxidation rate were discussed. It was found that the rate of the S(IV) oxidation depends on the initial pH of the solution but it is independent of the pH change during the reaction. Addition of Aniline leads to the introduction of an induction period and decrease in reaction rate, most likely due to SO4-1 radicals. The value of apparent energy and inhibition constant B were calculated in the presence of Aniline found as 26.43 KJ mol-1and 0.26x103mol dm-3 respectively.

Keywords: Kinetics; Autoxidation; S(IV); Ag(I); Catalysis; Inhibition; Aniline; Oxidation; Concentrations

Introduction

Although the SO2 oxidation by O2 has been the subject of many studies, the mechanism of the reaction is far for settled.  Both non radical and radical mechanism have been proposed. The atmospheric oxidation of S02 by 02 in aqueous media has been the subject of numerous studies, and the subject matter of several reviews, monographs and papers, notably by Kuo et al. [1-11]. It is interesting to point out that reaction is strongly inhibited by alcohol, benzene, and other compounds. Pointing to the participation of radical intermediates [12-17]. Bigelow [18] was the first to observe the inhibiting effect of alcohols such as methanol, ethanol, propanol, butanol on the rate of the reaction between sodium sulfite and oxygen. The inhibiting effect of alcohols was investigated subsequently by Alyea et al. [19]. The other Organics studied are phenols [20] organic acids [21-23], benzene [24], toluene, naphthalene, paraffin oil [25], alpha-pinene, cis – verbenol [26], sobrerol [27], myrtenol [28]. The effect of aromatic amines i.e. aniline in atmospheric water on the transition metal-catalysed oxidation of S(IV) is not fully known yet and more work in this area is needed to understand these processes better. The purpose of the present study was to study the kinetics of the Ag(I)catalysed S(IV) oxidation and to determine the inhibiting effect of aniline on this process under different experimental conditions.

Experimental

The experimental procedure was exactly the same as described earlier [29]. All the chemicals used were AR grade and their solutions were prepared in doubly distilled water.  The reaction were conducted in 0.15L Erlenmeyer flask, open to air and follow to passage of atmosphere oxygen. The flask was placed in a beaker which had an inlet at a lower part and an outlet at a outer part for circulating thermostatic water for maintaining the desired temperature 30+10C. The reaction was initiated by adding the desired volume of Na2S03 solution to the reaction mixture containing other additive such as buffer and catalyst. The reaction mixture was stirred continuously and magnetically at 1600+10 rpm to allow the passage of atmospheric oxygen and to save the reaction from becoming oxygen mass transfer controlled. The kinetics was studied in acetate buffered medium in which the pH remained fixed throughout the entire course of reaction.  For this purpose 10cm3 buffer made from sodium acetate (0.07mol L-1) and acetic acid (0.03mol L-1) for acidic medium were used (total volume 100cm3) for obtaining the desired pH. The kinetics were followed by withdrawing the aliquot samples periodically and titrating the unreacted S(IV) iodometrically. The reproducibility of replicate measurements was generally better than 10+1 %. All calculations were performed in MS Excel.

Product Analysis

The qualitative test shows sulphate to be only oxidation product. For quantitative analysis, the reaction mixture containing catalyst and S(IV) in appropriate buffered solutions were constantly stirred for a sufficiently long time so as to ensure complete oxidation of S(IV). When the reaction was complete then S(VI) estimated gravimetrically by precipitating sulphate ions as BaSO4 using standard procedure.

The product analysis showed the recovery of sulphate to be 98+1%, in all cases in agreement with eq. (1)

S( IV )  + 0.5  O 2  S ( VI ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofajuaGpaWaaeWaaOqaaKqzGeWdbiaadMeacaWGwbaa k8aacaGLOaGaayzkaaqcLbsapeGaaiiOaiaacckacqGHRaWkcaGGGc GaaGimaiaac6cacaaI1aGaaeiiaiaad+eal8aadaWgaaqaaKqzadWd biaaikdaaSWdaeqaaKqzadGaeyOKH4AcLbsapeGaaiiOaiaadofaca qGGaqcfa4damaabmaakeaajugib8qacaWGwbGaamysaaGcpaGaayjk aiaawMcaaaaa@51D6@   (1)

Results

Preliminary investigation 

The kinetics of both uncatalysed and Ag(I) catalysed and aniline inhibited reaction were studied in acidic medium in pH 4.95 and temperature 30°C. In both the cases  the first order dependence of S(IV) was observed in the kinetics data treatment for the determination of first order rate constant k1 was carried out  from log [S(IV)] versus time, t. The plots were shown in Figure 1 It is obs. from Figure 1 that both the uncatalysed and Ag(I) catalysed autoxidation of S(IV) reaction are inhibited by aniline.

Figure 1: The disappearance of [S(IV)] with time in air saturated suspensions at [S(IV)] =2x 10-3 mol dm-3 at pH = 4.95, t = 30°C.
◊ Ag (I) = 1x 10-5mol dm-3, [Aniline] = 0.0 mol dm-3.
□ Uncatalysed without aniline.
△ Uncatalysed with [Aniline] = 3x10-3 mol dm-3.
x Ag (I) = 5x 10-6mol dm-3, [Aniline] = 3x 10-3mol dm-3.

Uncatalysed reaction

Uncatalysed reaction was studied in the absence of Ag(I) and all the solutions were prepared in doubly distilled water.

Dependence of S(IV)

The detail dependence of the reaction rate on [S(IV)] was studied by varying it is in the range 1x10-3mol dm-3 to 4x10-3mol dm-3 at pH = 4.95, t = 30°C in acetate buffered medium. The kinetics was found to be first order in [S(IV)] and values of K1 was calculated from  log [S(IV)] v/s time plots which was  linear. The values of first order rate constant K1 are given in Table 1. The dependence of reaction rate on [S(IV)] follows the rate law (2).

d [ S( IV ) ]/dt= k 1 [ S( IV ) ]      MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiabgkHiTiaadsgacaqGGaqcfa4damaadmaakeaajugib8qa caWGtbqcfa4damaabmaakeaajugib8qacaWGjbGaamOvaaGcpaGaay jkaiaawMcaaaGaay5waiaaw2faaKqzGeWdbiaac+cacaWGKbGaamiD aiabg2da9iaadUgajuaGpaWaaSbaaSqaaKqzadWdbiaaigdaaSWdae qaaKqbaoaadmaakeaajugib8qacaWGtbqcfa4damaabmaakeaajugi b8qacaWGjbGaamOvaaGcpaGaayjkaiaawMcaaaGaay5waiaaw2faaK qzGeWdbiaacckacaGGGcGaaiiOaiaacckacaGGGcaaaa@58AA@  (2)

[S(IV)] mol dm-3

(103) K1 s-1

0.001

1.04

0.002

1.06

0.003

1.09

0.004

1.09

Table 1: The values of K1 for uncatalysed reaction at different [S(IV)], pH = 4.95, t = 30°C, CH3COONa=7x10-2mol L-1, CH3COOH= 3x10-2mol L-1.

[Aniline] dependence

The major aim of this study was to examine the effect of aniline on the autoxidation of S(IV) in acetate buffer medium and varying the [aniline] from 5x10-7mol dm-3 to 8x10-3mol dm-3, we observed the rate of thereaction decreased by increasing [aniline] The results are given in Table 2 However the nature of the [S(IV)] dependence in presence of aniline did not change and remains first order. The first order rate constant Kinh in the presence of anilinewas defined by rate law (3).

d[ S( IV ) ] /dt =  k inh [ S( IV ) ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiabgkHiTiaadsgajuaGpaWaamWaaOqaaKqzGeWdbiaadofa juaGpaWaaeWaaOqaaKqzGeWdbiaadMeacaWGwbaak8aacaGLOaGaay zkaaaacaGLBbGaayzxaaqcLbsapeGaaeiiaiaac+cacaWGKbGaamiD aiaabccacqGH9aqpcaqGGaGaam4AaSWdamaaBaaabaqcLbmapeGaam yAaiaad6gacaWGObaal8aabeaajuaGdaWadaGcbaqcLbsapeGaam4u aKqba+aadaqadaGcbaqcLbsapeGaamysaiaadAfaaOWdaiaawIcaca GLPaaaaiaawUfacaGLDbaaaaa@5522@  (3)

The values of Kinh in the presence of aniline decreased with increasing [Aniline] are given in Table 2 which are in agreement with the rate law (4).

k inh =  k 1 / ( 1+B [ aniline ] ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadUgal8aadaWgaaqaaKqzadWdbiaadMgacaWGUbGaamiA aaWcpaqabaqcLbsapeGaeyypa0JaaeiiaiaadUgajuaGpaWaaSbaaS qaaKqzadWdbiaaigdaaSWdaeqaaKqzGeWdbiaac+cacaqGGaqcfa4d amaabmaakeaajugib8qacaaIXaGaey4kaSIaamOqaiaabccajuaGpa WaamWaaOqaaKqzGeWdbiaadggacaWGUbGaamyAaiaadYgacaWGPbGa amOBaiaadwgaaOWdaiaawUfacaGLDbaaaiaawIcacaGLPaaaaaa@53A9@   (4)

[Aniline] mol dm-3

103 Kinh s-1

1/Kinh s

5.0x10-7

0.94

1064

5.0x10-6

0.827

1209

8.0x10-6

0.707

1414

1.0x10-5

0.607

1647

5.0x10-5

0.513

1949

8.0x10-5

0.418

2392

1.0x10-4

0.36

2778

5.0x10-4

0.284

3521

8.0x10-4

0.189

5291

3.0x10-3

0.138

7246

5.0x10-3

0.075

13333

8.0x10-3

0.037

27027

Table 2: The values of Kinh at different [Aniline], pH = 4.95, t = 30°C CH3COONa =7x10-2mol L-1 CH3COOH= 3x10-2mol L-1.

Where B is inhibition parameter for rate inhibition by aniline. The equation (4) on rearrangement becomes

1/ k inh =1/ k 1 + B [ aniline ]/ k 1   MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaaigdacaGGVaGaam4AaKqba+aadaWgaaWcbaqcLbmapeGa amyAaiaad6gacaWGObaal8aabeaajugib8qacqGH9aqpcaaIXaGaai 4laiaadUgal8aadaWgaaqaaKqzadWdbiaaigdaaSWdaeqaaKqzGeWd biabgUcaRiaabccacaWGcbGaaeiiaKqba+aadaWadaGcbaqcLbsape Gaamyyaiaad6gacaWGPbGaamiBaiaadMgacaWGUbGaamyzaaGcpaGa ay5waiaaw2faaKqzGeWdbiaac+cacaWGRbqcfa4damaaBaaaleaaju gWa8qacaaIXaaal8aabeaajugib8qacaGGGcaaaa@5886@  (5)

In accordance with the equation (5) the plot of 1/ Kinh v/s [aniline] was found to be linear with non- zero intercept. The values of intercept (1/ K1) and slope (B/ K1) were found to be 1.53 x 103s and 2.86 x 106 mol dm-3s at  pH = 4.95, t = 30°C From these values the value of inhibition parameter B was found to be 1.86x 103mol dm-3.

Ag(I) catalysed reaction

At first the kinetics of Ag(I) Catalysed reaction in the absence of inhibitor was studied.

[S(IV)] variation

The dependence of S (IV) on reaction rate was studied by varying  [S(IV)] from 1x10-3mol dm-3 to 10x10-3mol dm-3 at two different but fixed Ag(I) of 5x10-6mol dm-3and 1x10-5mol dm-3 at  pH = 4.95, t = 30°C The kinetics was found to be first order in [S(IV)] v/s time were linear as shown in Figure 1.

Ag(I) variations

The dependence of Ag(I) on the reaction rate was studied by varying Ag (I) from 5x10-6mol dm-3 to 2.5x10-5moldm-3at S(IV) = 2x10-3mol dm-3 pH= 4.95, t= 30°C in acetate buffer medium. The values of First order rate constant kcat for S(IV) oxidation was determine are shown in Figure 2. The nature of dependence of kcat on Ag (I) was indicated as two term rate law (6).

d [ S( IV ) ]/dt=  k cat [ S( IV ) ] = ( k 1 + k 2 [ Ag( I ) ] [ S( IV ) ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiabgkHiTiaadsgacaqGGaqcfa4damaadmaakeaajugib8qa caWGtbqcfa4damaabmaakeaajugib8qacaWGjbGaamOvaaGcpaGaay jkaiaawMcaaaGaay5waiaaw2faaKqzGeWdbiaac+cacaWGKbGaamiD aiabg2da9iaabccacaWGRbWcpaWaaSbaaeaajugWa8qacaWGJbGaam yyaiaadshaaSWdaeqaaKqbaoaadmaakeaajugib8qacaWGtbqcfa4d amaabmaakeaajugib8qacaWGjbGaamOvaaGcpaGaayjkaiaawMcaaa Gaay5waiaaw2faaKqzGeWdbiaacckacqGH9aqpcaqGGaWdaiaacIca peGaam4AaSWdamaaBaaabaqcLbmapeGaaGymaaWcpaqabaqcLbsape Gaey4kaSIaam4AaSWdamaaBaaabaqcLbmapeGaaGOmaaWcpaqabaqc fa4aamWaaOqaaKqzGeWdbiaadgeacaWGNbqcfa4damaabmaakeaaju gib8qacaWGjbaak8aacaGLOaGaayzkaaaacaGLBbGaayzxaaqcLbsa peGaaeiiaKqba+aadaWadaGcbaqcLbsapeGaam4uaKqba+aadaqada GcbaqcLbsapeGaamysaiaadAfaaOWdaiaawIcacaGLPaaaaiaawUfa caGLDbaaaaa@7321@ (6)
Or  k cat =   k 1 +k[ Ag( I ) ]  MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadUgal8aadaWgaaqaaKqzadWdbiaadogacaWGHbGaamiD aaWcpaqabaqcLbsapeGaeyypa0JaaiiOaiaacckacaWGRbqcfa4dam aaBaaaleaajugWa8qacaaIXaaal8aabeaajugib8qacqGHRaWkcaWG Rbqcfa4damaadmaakeaajugib8qacaWGbbGaam4zaKqba+aadaqada GcbaqcLbsapeGaamysaaGcpaGaayjkaiaawMcaaaGaay5waiaaw2fa aKqzGeWdbiaacckaaaa@507C@   (7)

Figure 2: The dependence of catalyst concentration at [S(IV)] = 2x10-3 mol dm-3, pH = 4.95, t = 30°C in acetate buffered medium.

From the plot in Figure 2 the values of intercept is equal to K1 and slope is equal to k2 were found to be 0.72x 101 s and 8.6 x 10-3 mol dm-3 s respectively at pH = 4.95, t = 30°C  in acetate buffered medium.

Variation of pH

Variation of pH was carried out from 4.02- 5.25 at different [S (IV), Ag (I), [Aniline] and temperatures. The rate decreases slightly by varying pH is inverse H+ ion dependence was observed. From the plot of log K1 v/s log (H+) the order with respect to H+ is 0.16 which is a fractional order and can be neglected as shown in Figure 3 (Table 3 & 4).

[Aniline], mol dm-3

Ag (I) =5x10-6 mol dm-3

Ag (I) =1 x 10-5mol dm-3

Ag (I) =1.5 x 10-5

pH = 4.02

5.0 x 10-4

0.470 x 10-3

0.564 x 10-3

0.717 x 10-3

8.0x 10-4

0.400 x 10-3

_

_

3.0 x 10-3

0.319 x 10-3

_

_

pH = 4.50

5.0 x 10-4

0.499 x 10-3

0.590 x 10-3

0.788 x 10-3

8.0 x 10-4

0.471 x 10-3

_

_

3.0 x 10-3

0.402 x 10-3

_

_

pH = 5.25

5.0 x 10-4

0.586 x 10-3

0.718 x 10-3

0.942 x 10-3

8.0 x 10-4

0.577 x 10-3

_

_

3.0 x 10-3

0.516 x 10-3

_

_

Table 3: Rate of Ag (I) catalysed autoxidation in the presence of Aniline.

[Aniline] 5.0 x 10-4 mol dm-3

Ag (I) =5x10-6 mol dm-3

Ag (I) =1 x 10-5 mol dm-3

Ag (I) =1.5 x 10-5 mol dm-3

pH = 4.50

3.02

3.82

3.54

Table 4: Ratio of rates for Ag (I) catalysed oxidation in the absence and in the presence of Aniline.

Figure 3: Effect of pH at [S(IV)] = 2x10-3 mol dm-3 ,Ag (I) = 5x10-6 mol dm-3, [Aniline]= 5.0x10-4 mol dm-3, t= 30°C in acetate buffered medium.

[Aniline] dependence

To know the effect of aniline on Ag(I) catalysed autoxidation of S(IV) aniline variation was carried out from 5x10-7mol dm-3 to 3 x 10-3 mol dm-3 at two different Ag (I) that is 5x10-6mol dm-3 to 1 x 10-5mol dm-3 but fixed S(IV) = 2x10-3mol dm-3, pH= 4.95, t= 30°C The results indicated that by increasing aniline the rate becomes decelerates (Figure 4 & 5).

d [ S( IV ) ] /dt = ( k 1 + k 2 [ Ag( I ) ] [ S( IV ) ] /1+B [ Aniline ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiabgkHiTiaadsgacaqGGaqcfa4damaadmaakeaajugib8qa caWGtbqcfa4damaabmaakeaajugib8qacaWGjbGaamOvaaGcpaGaay jkaiaawMcaaaGaay5waiaaw2faaKqzGeWdbiaabccacaGGVaGaamiz aiaadshacaqGGaGaeyypa0Jaaeiia8aacaGGOaWdbiaadUgajuaGpa WaaSbaaSqaaKqzadWdbiaaigdaaSWdaeqaaKqzGeWdbiabgUcaRiaa dUgajuaGpaWaaSbaaSqaaKqzadWdbiaaikdaaSWdaeqaaKqbaoaadm aakeaajugib8qacaWGbbGaam4zaKqba+aadaqadaGcbaqcLbsapeGa amysaaGcpaGaayjkaiaawMcaaaGaay5waiaaw2faaKqzGeWdbiaabc cajuaGpaWaamWaaOqaaKqzGeWdbiaadofajuaGpaWaaeWaaOqaaKqz GeWdbiaadMeacaWGwbaak8aacaGLOaGaayzkaaaacaGLBbGaayzxaa qcLbsapeGaaeiiaiaac+cacaaIXaGaey4kaSIaamOqaiaabccajuaG paWaamWaaOqaaKqzGeWdbiaadgeacaWGUbGaamyAaiaadYgacaWGPb GaamOBaiaadwgaaOWdaiaawUfacaGLDbaaaaa@72EB@        (8)
Where

k inh =  ( k 1 + k 2 [ Ag( I ) ] / 1 + B [ Aniline ] =  k cat /1+B[ Aniline ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadUgal8aadaWgaaqaaKqzadWdbiaadMgacaWGUbGaamiA aaWcpaqabaqcLbsapeGaeyypa0JaaiiOaiaacckapaGaaiika8qaca WGRbWcpaWaaSbaaeaajugWa8qacaaIXaaal8aabeaajugib8qacqGH RaWkcaWGRbWcpaWaaSbaaeaajugWa8qacaaIYaaal8aabeaajuaGda WadaGcbaqcLbsapeGaamyqaiaadEgajuaGpaWaaeWaaOqaaKqzGeWd biaadMeaaOWdaiaawIcacaGLPaaaaiaawUfacaGLDbaajugib8qaca qGGaGaai4laiaabccacaaIXaGaaeiiaiabgUcaRiaabccacaWGcbGa aeiiaKqba+aadaWadaGcbaqcLbsapeGaamyqaiaad6gacaWGPbGaam iBaiaadMgacaWGUbGaamyzaaGcpaGaay5waiaaw2faaKqzGeWdbiaa cckacqGH9aqpcaGGGcGaam4AaSWdamaaBaaabaqcLbmapeGaam4yai aadggacaWG0baal8aabeaajugib8qacaGGVaGaaGymaiabgUcaRiaa dkeajuaGpaWaamWaaOqaaKqzGeWdbiaadgeacaWGUbGaamyAaiaadY gacaWGPbGaamOBaiaadwgaaOWdaiaawUfacaGLDbaaaaa@7877@    (9)
1/ k inh =1+B [ Aniline ]/ k cat MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaaigdacaGGVaGaam4AaKqba+aadaWgaaWcbaqcLbmapeGa amyAaiaad6gacaWGObaal8aabeaajuaGcqGH9aqpjugib8qacaaIXa Gaey4kaSIaamOqaiaabccajuaGpaWaamWaaOqaaKqzGeWdbiaadgea caWGUbGaamyAaiaadYgacaWGPbGaamOBaiaadwgaaOWdaiaawUfaca GLDbaajugib8qacaGGVaGaam4AaSWdamaaBaaabaqcLbmapeGaam4y aiaadggacaWG0baal8aabeaaaaa@537C@ (10)
1/  k inh =1/  k cat + B [ Aniline ]/ k cat MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaaigdacaGGVaGaaeiiaiaadUgajuaGpaWaaSbaaSqaaKqz adWdbiaadMgacaWGUbGaamiAaaWcpaqabaqcfaOaeyypa0tcLbsape GaaGymaiaac+cacaqGGaGaam4AaKqba+aadaWgaaWcbaqcLbmapeGa am4yaiaadggacaWG0bqcLbsacaqGGaGaey4kaScal8aabeaajugib8 qacaWGcbGaaeiiaKqba+aadaWadaGcbaqcLbsapeGaamyqaiaad6ga caWGPbGaamiBaiaadMgacaWGUbGaamyzaaGcpaGaay5waiaaw2faaK qzGeWdbiaac+cacaWGRbWcpaWaaSbaaeaajugWa8qacaWGJbGaamyy aiaadshaaSWdaeqaaaaa@5D1E@  (11)

Figure 4: Effect of catalyst at [S(IV)] = 2x10-3mol dm-3, [Aniline]= 5.0x10-4mol dm-3, t= 30°C in acetate buffered medium. The value of intercept and slope are 4.8 x 10-4 s and 2.7x101 mol dm-3 s respectively. Depending on the observed results the reaction follows the following rate law (8).

Figure 5: Effect of aniline at [S(IV)] = 2x10-3 mol dm-3, Ag (I) = 5x10-6 mol dm-3, pH = 4.95, t = 30°C in acetate buffered medium. The plot of 1/ Kinh v/s [Aniline] is linear with intercept 1.21 x 103s and slope 3.25x105 mol dm-3 s from which the value of B = 0.26 x103 mol dm-3.

Effect of temperature

The values of kobs were determined at three different temperatures in the range of 30°C to 40°C. The results are given in Table 5.  By plotting a graph between log k v/s 1/T yield us an apparent empirical energy of activation 26.43 KJ moL-1.

toC

103 kobs S-1

30

0.686

35

0.781

40

0.915

Table 5: Effect of temperature kobs air saturated suspensions at [S(IV)] = 2x10-3mol dm-3, Ag (I) = 5 x10-6mol dm-3, [Aniline] = 5.0 x 10-4mol dm-3, pH = 4.95.

Discussion

In aqueous solutions S02 is present in four forms S02.H2O, HS03-1, S03-2, S203-2 In the experimental range of pH the following equilibrium operates

HS O 3 1 H + +  S O 3 2    MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadIeacaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaG4m aaWcpaqabaWaaWbaaeqabaqcLbmapeGaeyOeI0IaaGymaaaajugibi aadIealmaaCaaabeqaaKqzadGaey4kaScaaKqzGeGaeSiZHmOaey4k aSIaaiiOaiaacckacaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaG 4maaWcpaqabaWaaWbaaeqabaqcLbmapeGaeyOeI0IaaGOmaiaaccka caGGGcGaaiiOaaaaaaa@523A@ (12)

The equilibrium constant is 5.07x 10-7In the experimental range of pH both species HS03-1, S03-2 are present but former one present predominantly. During the course of reaction fraction order obtain is 0.18 indicates that it is almost independent of pH which is co-relate with the work of Irena [30]. Prasad et al. [31] studied the inhibiting effect of formic acid [31], isopropyl alcohol [32], isoamyl alcohol [33] in the presence of Ag(I) catalysed autoxidation of S(IV) and reported the they all are influence the S(IV) oxidation in atmosphere with moderate rate. Gupta et al. [34] studied the role of some organic organics on the oxidation of dissolved sulfur dioxide by oxygen in rain water medium and found it follows radical mechanism so free radical scavengers such as VOCs decelerate the S(IV) oxidation and control the rain water acidity [35].  Bigelow et al. [18] studied the effect of alcohols on the reactions between sodium sulphite and 02 and found that the alcohols inhibited the reaction rate. Alyea et al. [19] studied the inhibiting effect of aliphatic alcohols on sodium sulphite in alkaline medium. Gupta et al. [34] studied the kinetics of environmentally important oxidation of S(IV) in acetate buffered medium in presence of Iron (III) in pH range 5.27- 5.70 and reported that addition of ethanol leads to decrease in reaction rate. Grgic et al. [36] studied about scavenging of SO4- radical anions by mono and dicarboxylic acids in the Mn(II) catalysed oxidation in aqueous solutions and reported that low molecular weight carboxylic acids have low reactivity towards sulphate radical anion. Backstrom [19] proposed a radical chain mechanism for alcohol inhibited oxidation reaction between sodium sulphite and 02. Gupta et al studied the influence of hydroxyl VOCs on the oxidation of S(IV) by oxygen and found VOCs inhibited the S(IV) oxidation. Grgic et al. [36] studied the inhibition effect of acetate, oxlate, format on Fe- catalysed autoxidation of S(IV) at pH 2.8, 3.7,4.5 and found that oxlate has strong inhibiting effect on reaction rate due to the decrease  amount of catalytic activity of Fe+3 due to formation of complexion with oxlate. Bostjan et al. [32] studied the effect of carboxylic acid on Mn(II) catalysed oxidation of S(IV) and found that monocarboxylic acid exhibit strong inhibition and out of which acetic acid shows strong inhibition. The rate of uncatalysed and Ag(I) catalysed reaction is decelerated by the addition of aniline in the present study. Gupta et al. [37] reported that radical mechanism operate in those reaction in which the inhibition parameters lies 103-104 In the present study the value of inhibition parameter for uncatalysed and Ag(I) catalysed autoxidation of S(IV) by anilineare found to be in the range 103-104 These values are in the same range as reported by Gupta et al. [37] This is strongly support the radical mechanism in the present case too based on the observed results. The free radical mechanism is very complex, the present work close to the experimental condition of Connick et al. [38].

HS O 3 1 k d H + + S O 3 2 K d =5.01 x  10 7,18 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadIeacaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaG4m aaWcpaqabaWaaWbaaeqabaqcLbmapeGaeyOeI0IaaGymaaaajuaGpa Waa4GbaSqaaKqzGeGaam4AaKqbaoaaBaaameaajugWaiaadsgaaWqa baaaleqakiaawcCicaGL9gcajugib8qacaWGibqcfa4damaaCaaale qabaqcLbmapeGaey4kaScaaKqzGeGaey4kaSIaaeiiaiaadofacaWG pbWcpaWaaSbaaeaajugWa8qacaaIZaaal8aabeaadaahaaqabeaaju gWa8qacqGHsislcaaIYaaaaKqzGeGaam4saKqba+aadaWgaaWcbaqc LbmapeGaamizaaWcpaqabaqcLbsapeGaeyypa0JaaGynaiaac6caca aIWaGaaGymaiaabccacaWG4bGaaeiiaiaaigdacaaIWaWcpaWaaWba aeqabaqcLbmapeGaeyOeI0IaaG4naiaacYcacaaIXaGaaGioaaaaaa a@6609@ (13)
A g + + O 2 CC H 3 KoAc Ag O 2 CC H 3 K oAc =  2.29 33   MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadgeacaWGNbqcfa4damaaCaaaleqabaqcLbmapeGaey4k aScaaKqzGeGaey4kaSYcpaWaaWbaaeqabaqcLbmapeGaeyOeI0caaK qzGeGaam4taSWdamaaBaaabaqcLbmapeGaaGOmaaWcpaqabaqcLbsa peGaam4qaiaadoeacaWGibWcpaWaaSbaaeaajugWa8qacaaIZaaal8 aabeaajuaGdaGdgaWcbaqcLbsacaWGlbqcLbmacaWGVbGaamyqaiaa dogaaSqabOGaayjWHiaaw2BiaKqzGeWdbiaadgeacaWGNbGaam4taK qba+aadaWgaaWcbaqcLbmapeGaaGOmaaWcpaqabaqcLbsapeGaam4q aiaadoeacaWGibWcpaWaaSbaaeaajugWa8qacaaIZaaal8aabeaaju gib8qacaWGlbWcpaWaaSbaaeaajugWa8qacaWGVbGaamyqaiaadoga aSWdaeqaaKqzGeWdbiabg2da9iaabccacaaIYaGaaiOlaiaaikdaca aI5aWcpaWaaWbaaeqabaqcLbmapeGaaG4maiaaiodaaaqcLbsacaGG Gcaaaa@6BCB@ (14)
A g + + S O 3 2 K 1 AgOS O 2 K 1 = 2.51x  10 5 ,29    MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiqaaW0cjugiba baaaaaaaaapeGaamyqaiaadEgal8aadaahaaqabeaajugWa8qacqGH RaWkaaqcLbsacqGHRaWkcaqGGaGaam4uaiaad+eal8aadaWgaaqaaK qzadWdbiaaiodaaSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaa ikdaaaqcfa4damaaoyaaleaajugibiaadUeajuaGdaWgaaadbaqcLb macaaIXaaameqaaaWcbeGccaGLahIaayzVHaqcLbsapeGaamyqaiaa dEgacaWGpbGaam4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaikdaaS WdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTaaajugibiaadUeal8aa daWgaaqaaKqzadWdbiaaigdaaSWdaeqaaKqzGeWdbiabg2da9iaabc cacaaIYaGaaiOlaiaaiwdacaaIXaGaamiEaiaabccacaaIXaGaaGim aSWdamaaCaaabeqaaKqzadWdbiaaiwdaaaqcfa4damaaCaaaleqaba qcLbmapeGaaiilaiaaikdacaaI5aaaaKqzGeGaaiiOaiaacckaaaa@6AA1@   (15)
A g + + HS O 3 1 K 2 AgHS O 3 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiqaaW0cjugiba baaaaaaaaapeGaamyqaiaadEgal8aadaahaaqabeaajugWa8qacqGH RaWkaaqcLbsacqGHRaWkcaqGGaGaamisaiaadofacaWGpbWcpaWaaS baaeaajugWa8qacaaIZaaal8aabeaadaahaaqabeaajugWa8qacqGH sislcaaIXaaaaKqba+aadaGdgaWcbaqcLbsacaWGlbqcfa4aaSbaaW qaaKqzadGaaGOmaaadbeaaaSqabOGaayjWHiaaw2BiaKqzGeWdbiaa dgeacaWGNbGaamisaiaadofacaWGpbWcpaWaaSbaaeaajugWa8qaca aIZaaal8aabeaaaaa@53E2@  (16)
AgOS O 2 +  O 2 K 3 AgOS O 2 1 . O 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiqaaW0cjugiba baaaaaaaaapeGaamyqaiaadEgacaWGpbGaam4uaiaad+eal8aadaWg aaqaaKqzadWdbiaaikdaaSWdaeqaamaaCaaabeqaaKqzadWdbiabgk HiTaaajugibiabgUcaRiaabccacaWGpbWcpaWaaSbaaeaajugWa8qa caaIYaaal8aabeaadaGdgaadbaqcLbsacaWGlbaddaWgaaqaaKqzad GaaG4maaadbeaaaeqaliaawcCicaGL9gcajugib8qacaWGbbGaam4z aiaad+eacaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaGOmaaWcpa qabaWaaWbaaeqabaqcLbmapeGaeyOeI0IaaGymaaaajugibiaac6ca caWGpbWcpaWaaSbaaeaajugWa8qacaaIYaaal8aabeaaaaa@5A33@ (17)
AgHS O 3 + O 2 K 4 AgHS O 3. O 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiqaaW0cjugiba baaaaaaaaapeGaamyqaiaadEgacaWGibGaam4uaiaad+eajuaGpaWa aSbaaSqaaKqzadWdbiaaiodaaSWdaeqaaKqzGeWdbiabgUcaRiaad+ eal8aadaWgaaqaaKqzadWdbiaaikdaaSWdaeqaaOWaa4GbaSqaaKqz GeGaam4saSWaaSbaaWqaaiaaisdaaeqaaaWcbeGccaGLahIaayzVHa qcLbsapeGaamyqaiaadEgacaWGibGaam4uaiaad+eajuaGpaWaaSba aSqaaKqzadWdbiaaiodajugibiaac6caaSWdaeqaaKqzGeWdbiaad+ eal8aadaWgaaqaaKqzadWdbiaaikdaaSWdaeqaaaaa@54DF@ (18)
AgHS O 3. O 2 k 1 A g + + HS O 5 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiqaaW0cjugiba baaaaaaaaapeGaamyqaiaadEgacaWGibGaam4uaiaad+eajuaGpaWa aSbaaSqaaKqzadWdbiaaiodajugibiaac6caaSWdaeqaaKqzGeWdbi aad+eal8aadaWgaaqaaKqzadWdbiaaikdaaSWdaeqaamaaoqcameaa jugibiaadUgammaaBaaabaqcLbmacaaIXaaameqaaaqabSGaayPKHa qcLbsapeGaamyqaiaadEgal8aadaahaaqabeaajugWa8qacqGHRaWk aaqcLbsacqGHRaWkcaqGGaGaamisaiaadofacaWGpbWcpaWaaSbaae aajugWa8qacaaI1aaal8aabeaadaahaaqabeaajugWa8qacaGGtaca aaaa@55E9@  (19)
HS O 5 + HS O 3 1 k 2 S O 4 +  S O 3 +  H 2 O MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadIeacaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaGyn aaWcpaqabaWaaWbaaeqabaqcLbmapeGaai4eGaaajugibiabgUcaRi aabccacaWGibGaam4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaioda aSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaaigdaaaqcfa4dam aaoqcaleaajugibiaadUgalmaaBaaameaajugWaiaaikdaaWqabaaa leqakiaawkziaKqba+qadaWfGaGcbaqcLbsacaWGtbGaam4taKqba+ aadaWgaaWcbaqcLbmapeGaaGinaaWcpaqabaaapeqabeaajugibiab gkHiTiabgkci3caacqGHRaWkcaqGGaqcfa4aaCbiaOqaaKqzGeGaam 4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaiodaaSWdaeqaaaWdbeqa baqcLbsacqGHsislcqGHIaYTaaGaey4kaSIaaeiiaiaadIeal8aada WgaaqaaKqzadWdbiaaikdaaSWdaeqaaKqzGeWdbiaad+eaaaa@6675@ (20)
AgOS O 2 1 . O 2  k3 A g + +  S O 3 + O 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadgeacaWGNbGaam4taiaadofacaWGpbWcpaWaaSbaaeaa jugWa8qacaaIYaaal8aabeaadaahaaqabeaajugWa8qacqGHsislca aIXaaaaKqzGeGaaiOlaiaad+eal8aadaWgaaqaaKqzadWdbiaaikda caGGGcaal8aabeaajuaGdaGdKaWcbaqcLbsacaWGRbqcLbmacaaIZa aaleqakiaawkziaKqzGeWdbiaadgeacaWGNbqcfa4damaaCaaaleqa baqcLbmapeGaey4kaScaaKqzGeGaey4kaSIaaeiiaKqba+aadaWfGa GcbaqcLbsapeGaam4uaiaad+eajuaGpaWaaSbaaSqaaKqzadWdbiaa iodaaSWdaeqaaaqabeaajugibiabgkHiTiabgkci3caajuaGdaWgaa WcbaqcLbsapeGaey4kaScal8aabeaajugib8qacaWGpbWcpaWaaSba aeaajugWa8qacaaIYaaal8aabeaaaaa@61C6@ (21)
S O 3 + O 2 k 4 S O 5 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbqcfa4damaaBaaaleaajugWa8qacaaIZaaa l8aabeaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacq GHsislcqGHIaYTaaGaam4taKqba+aadaWgaaWcbaqcLbmapeGaaGOm aaWcpaqabaqcfa4aa4ajaSqaaKqzGeGaam4AaKqbaoaaBaaameaaju gWaiaaisdaaWqabaaaleqakiaawkziaKqzGeWdbiaadofacaWGpbWc paWaaSbaaeaajugWa8qacaaI1aaal8aabeaaaaa@4F43@ (22)
S O 5 + S O 3 2 k 5 S O 3 +S O 5 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbqcfa4damaaBaaaleaajugWa8qacaaI1aaa l8aabeaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacq GHsislcqGHIaYTaaGaam4uaiaad+eajuaGpaWaaSbaaSqaaKqzGeWd biaaiodaaSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaaikdaaa qcfa4damaaoqcaleaajugibiaadUgalmaaBaaameaajugWaiaaiwda aWqabaaaleqakiaawkziaKqbaoaaxacakeaajugib8qacaWGtbGaam 4taKqba+aadaWgaaWcbaqcLbmapeGaaG4maaWcpaqabaaabeqaaKqz GeWdbiabgkHiTiabgkci3caacqGHRaWkcaWGtbGaam4taSWdamaaBa aabaqcLbmapeGaaGynaaWcpaqabaGcdaahaaWcbeqaaKqzadWdbiab gkHiTiaaikdaaaaaaa@5E86@   (23)
S O 5 + S O 3 2 k 6 S O 4 +S O 4 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbWcpaWaaSbaaeaajugWa8qacaaI1aaal8aa beaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacqGHsi slcqGHIaYTaaGaam4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaioda aSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaaikdaaaqcfa4dam aaoqcaleaajugibiaadUgajuaGdaWgaaqaaKqzadGaaGOnaaqcfaya baaaleqakiaawkziaKqzGeWdbiaadofacaWGpbqcfa4damaaBaaale aajugWa8qacaaI0aaal8aabeaajugib8qacqGHRaWkcaWGtbGaam4t aSWdamaaBaaabaqcLbmapeGaaGinaaWcpaqabaWaaWbaaeqabaqcLb mapeGaeyOeI0IaaGOmaaaaaaa@5BA6@   (24)
S O 5 2 +S O 3 2 k 7 2S O 4 2 +S O 4 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbWcpaWaaSbaaeaajugWa8qacaaI1aaal8aa beaadaahaaqabeaajugWa8qacqGHsislcaaIYaaaaKqzGeGaey4kaS Iaam4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaiodaaSWdaeqaamaa CaaabeqaaKqzadWdbiabgkHiTiaaikdaaaqcfa4damaaoqcaleaaju gibiaadUgajuaGdaWgaaadbaqcLbmacaaI3aaameqaaaWcbeGccaGL sgcajugib8qacaaIYaGaam4uaiaad+eal8aadaWgaaqaaKqzadWdbi aaisdaaSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaaikdaaaqc LbsacqGHRaWkcaWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaGinaa WcpaqabaWaaWbaaeqabaqcLbmapeGaeyOeI0IaaGOmaaaaaaa@5D6F@   (25)
S O 4 + S O 3 2 k 8 S O 3 +S O 4 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbWcpaWaaSbaaeaajugWa8qacaaI0aaal8aa beaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacqGHsi slcqGHIaYTaaGaam4uaiaad+eal8aadaWgaaqaaKqzadWdbiaaioda aSWdaeqaamaaCaaabeqaaKqzadWdbiabgkHiTiaaikdaaaqcfa4dam aaoqcaleaajugibiaadUgajuaGdaWgaaqaaKqzadGaaGioaaqcfaya baaaleqakiaawkziaKqzGeWdbiaadofacaWGpbWcpaWaaSbaaeaaju gWa8qacaaIZaaal8aabeaajugib8qacqGHRaWkcaWGtbGaam4taSWd amaaBaaabaqcLbmapeGaaGinaaWcpaqabaWaaWbaaeqabaqcLbmape GaeyOeI0IaaGOmaaaaaaa@5B18@ (26)
S O 4 + x k 9 Non Chain product MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbqcfa4damaaBaaaleaajugWa8qacaaI0aaa l8aabeaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacq GHsislcqGHIaYTaaGaamiEaKqbaoaaoqcaleaajugibiaadUgajuaG daWgaaadbaqcLbmacaaI5aaameqaaaWcbeGccaGLsgcajugibiaad6 eacaWGVbGaamOBaiaabccacaWGdbGaamiAaiaadggacaWGPbGaamOB aiaabccacaWGWbGaamOCaiaad+gacaWGKbGaamyDaiaadogacaWG0b aaaa@57A7@ (27)
S O 4 + sodium benzoate k 10 Non Chain product MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadofacaWGpbqcfa4damaaBaaaleaajugWa8qacaaI0aaa l8aabeaajuaGpeWaaCbiaOqaaKqzGeGaey4kaScaleqabaqcLbsacq GHsislcqGHIaYTaaGaam4Caiaad+gacaWGKbGaamyAaiaadwhacaWG TbGaaeiiaiaadkgacaWGLbGaamOBaiaadQhacaWGVbGaamyyaiaads hacaWGLbqcfa4aa4ajaSqaaKqzGeGaam4AaKqbaoaaBaaabaqcLbma caaIXaGaaGimaaqcfayabaaaleqakiaawkziaKqzGeGaamOtaiaad+ gacaWGUbGaaeiiaiaadoeacaWGObGaamyyaiaadMgacaWGUbGaaeii aiaadchacaWGYbGaam4BaiaadsgacaWG1bGaam4yaiaadshaaaa@65A4@  (28)

By assuming long chain hypothesis and steady state approximation d[S03]/dt, d[SO4]/dt, d[SO5]/dt, to zero. It can be shown that rate of initiation is equal to rate of termination (eq. 29).

k 1 [ Ag( I )( S O 3 2 )( O 2 ) ]   = { k 7 [ X ] +  k 8 [ Aniline ] } [ S O 4 1 ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadUgal8aadaWgaaqaaKqzadWdbiaaigdaaSWdaeqaaKqb aoaadmaakeaajugib8qacaWGbbGaam4zaKqba+aadaqadaGcbaqcLb sapeGaamysaaGcpaGaayjkaiaawMcaaKqbaoaabmaakeaajugib8qa caWGtbGaam4taSWdamaaBaaabaqcLbmapeGaaG4maaWcpaqabaWaaW baaeqabaqcLbmapeGaeyOeI0IaaGOmaaaaaOWdaiaawIcacaGLPaaa juaGdaqadaGcbaqcLbsapeGaam4taKqba+aadaWgaaWcbaqcLbmape GaaGOmaaWcpaqabaaakiaawIcacaGLPaaaaiaawUfacaGLDbaajugi b8qacaGGGcGaaiiOaiaacckacqGH9aqpcaGGGcqcfa4damaacmaake aajugib8qacaWGRbWcpaWaaSbaaeaajugWa8qacaaI3aaal8aabeaa juaGdaWadaGcbaqcLbsapeGaamiwaaGcpaGaay5waiaaw2faaKqzGe WdbiaabccacqGHRaWkcaqGGaGaam4AaSWdamaaBaaabaqcLbmapeGa aGioaaWcpaqabaqcfa4aamWaaOqaaKqzGeWdbiaadgeacaWGUbGaam yAaiaadYgacaWGPbGaamOBaiaadwgaaOWdaiaawUfacaGLDbaaaiaa wUhacaGL9baajugib8qacaqGGaqcfa4damaadmaakeaajugib8qaca WGtbGaam4taSWdamaaBaaabaqcLbmapeGaaGinaaWcpaqabaWaaWba aeqabaqcLbmapeGaeyOeI0IaaGymaaaaaOWdaiaawUfacaGLDbaaaa a@7F25@  (29)

Since the reaction is completely stopped in the presence of [Aniline] = 2x10-4mol dm-3, so the step (22) and (25) appear to be unimportant. The step (24) is ignored because the reaction is completely seized in the presence of higher concentration of Aniline by omission and substitution from the above mechanism the following rate law can be obtain (30).

R cat  =  k 1 [ Ag( I ) ] [ S( IV ) ] /  { k 9 [ x ] +  k 10 [ Aniline ] }  MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcLbsaqaaaaa aaaaWdbiaadkfal8aadaWgaaqaaKqzadWdbiaadogacaWGHbGaamiD aaWcpaqabaqcLbsapeGaaiiOaiabg2da9iaabccacaWGRbWcpaWaaS baaeaajugWa8qacaaIXaaal8aabeaajuaGdaWadaGcbaqcLbsapeGa amyqaiaadEgajuaGpaWaaeWaaOqaaKqzGeWdbiaadMeaaOWdaiaawI cacaGLPaaaaiaawUfacaGLDbaajugib8qacaqGGaqcfa4damaadmaa keaajugib8qacaWGtbqcfa4damaabmaakeaajugib8qacaWGjbGaam OvaaGcpaGaayjkaiaawMcaaaGaay5waiaaw2faaKqzGeWdbiaabcca caGGVaGaaiiOaiaacckajuaGpaWaaiWaaOqaaKqzGeWdbiaadUgaju aGpaWaaSbaaSqaaKqzadWdbiaaiMdaaSWdaeqaaKqbaoaadmaakeaa jugib8qacaWG4baak8aacaGLBbGaayzxaaqcLbsapeGaaeiiaiabgU caRiaabccacaWGRbqcfa4damaaBaaaleaajugWa8qacaaIXaGaaGim aaWcpaqabaqcfa4aamWaaOqaaKqzGeWdbiaadgeacaWGUbGaamyAai aadYgacaWGPbGaamOBaiaadwgaaOWdaiaawUfacaGLDbaaaiaawUha caGL9baajugib8qacaGGGcaaaa@7770@  (30)

Prasad & Gupta et al. [11,37] proposed a similar mechanism for the C0203 and CoO catalysed autoxidation of S02 inhibited by formic acid and ethanol  respectively, which lead to the same rate law. By comparing derived rate law with the experimental rate law we observe the similarity in these two. The calculated value of inhibition constant B is 1.86x103mol dm-3 which is in the range of 103-104 and also coincide with the reported value of B of C0203 catalysed autoxidation of S(IV) by formic  acid is 3.58 x 103 mol dm-3.  So on the basis of calculated value of B we concluded that Aniline act as an free radical scavenger in Ag(I) catalysed autoxidation of aqueous S02 in acidic medium and a free radical mechanism can operate in this system.

Conclusion

The following conclusions are deduced from the results of the Aniline inhibited Ag(I) catalysed autoxidation of S(IV) was that inhibit the oxidation with the fast influence. The value of inhibition factor of both uncatalysed and Ag(I) catalysed autoxidation of S(IV) in the present study are in the range of 103-104  which shows that free radical mechanism is operative.    

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