research article kinetics and mechanism of the oxidation

Research ArticleKinetics and Mechanism of the Oxidation of NaphtholGreen B by Peroxydisulphate Ion in Aqueous Acidic Medium

B Myek1 S O Idris2 and J F Iyun2

1 Department of Basic Research National Research Institute for Chemical Technology PMB 1052 Zaria Kaduna State Nigeria2 Department of Chemistry Ahmadu Bello University Zaria Nigeria

Correspondence should be addressed to B Myek myekbbyahoocom

Received 21 October 2013 Revised 21 February 2014 Accepted 24 February 2014 Published 25 March 2014

Academic Editor Alfonso Castineiras

Copyright copy 2014 B Myek et al This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Thekinetics of the oxidation of naphthol greenB (NGB3minus) by peroxydisulphate ion has been carried out in aqueous acidicmediumat120582max of 700 nm119879 = 23plusmn1∘C and 119868 = 050mol dmminus3 (NaCl)The reaction shows a first-order dependence on oxidant and reductantconcentration respectively The stoichiometry of the NGBmdashS

2O8

2minus reaction is 1 2 Change in hydrogen ions concentration of thereaction medium has no effect on the rate of the reaction Added cations and anions decreased the rate of the reaction The resultsof spectroscopic and kinetic investigation indicate that no intermediate complex is probably formed in the course of this reaction

1 Introduction

Naphthol green B is used in histology to stain collagen Thedye is a lake in which the mordant metal is ferric ironHowever the iron appears to play no part in its staining ability[1] Naphthol green B is very soluble in water and has anabsorptionmaximumof 714 nmAs an anion it acts as an aciddye [2] Kinetic spectrophotometric method for the determi-nation of cerium (IV) with naphthol green B has been studied[3] The reaction was monitored spectrophotometrically bymeasuring the decrease in absorbance of naphthol green B at710 nm It was found that the reaction rate is very slow whenthe temperature is below 60∘C but the rate of the catalyzedreaction increases rapidly when the reaction temperatures areabove 70∘C

Peroxydisulphate ion is one of the powerful oxidizingagents known [4 5] A large number of investigations havebeen carried out in the oxidation of metal ions [6 7] metalcomplex [8 9] and various organic compounds [10] byS2O8

2minus Most electron transfer reactions of S2O8

2minus occur bythe outer-spheremechanism [11ndash13] However reactions withsome positively charged metal complexes such as Fe(bpy)

3

2+Fe(Phen)

3

2+ and Os(bpy)3

2+ occur by both the outer-sphereand the inner-sphere mechanisms [5 9] Except when thereducing agent can be protonated the redox reaction of

S2O8

2minus was found to be independent of hydrogen ion concen-tration [14] Despite its reactions with other compounds theredox reaction of this oxidant with naphthol green B is scanty

It is our hope that this investigation will help to gainmore insight into the redox reaction of naphthol green B withperoxydisulphate ion

2 Materials and Methods

The chemicals used were of analytical grade and were usedwithout further purification Standard solution of NGB3minus wasprepared by dissolving 0088 g in 100 cm3 volumetric flaskusing distilled water Sodium peroxydisulphate solution wasprepared by dissolving knownquantities in distilledwater Allother reagents used were of analytical grade

The stoichiometry of the reaction was determined spec-trophotometrically using the mole ratio method by keepingthe concentration of the dye constant at 40 times 10minus5mol dmminus3[H+] = 10 times 10minus4mol dmminus3 119868 = 050 120582max = 700 nm119879 = 23 plusmn 1

∘C and [S2O8

2minus] = (008ndash14) times 10minus4mol dmminus3

The stoichiometry was evaluated from the plot of absorbanceversus [reductant][oxidant] after the reaction had reachedcompletion by the observation of a steady zero absorbancevalue over a period of two days

Hindawi Publishing CorporationInternational Journal of Inorganic ChemistryVolume 2014 Article ID 768575 4 pageshttpdxdoiorg1011552014768575

2 International Journal of Inorganic Chemistry

Table 1 Pseudo-first-order and second-order rate constants for the reaction of naphthol green B and S2O82minus at [NGB3minus] = 40times10minus5mol dmminus3

120582 = 700 nm and 119879 = 23 plusmn 1∘C

103[S2O82minus] mol dmminus3 104[H+

] mol dmminus3 101 119868 mol dmminus3 1031198961 sminus1 119896

2 dm3 molminus1 sminus1

48 10 50 730 15252 10 50 822 15856 10 50 850 15260 10 50 939 15764 10 50 979 15368 10 50 1070 15756 01 50 839 15056 05 50 850 15256 10 50 859 15356 15 50 882 15856 20 50 864 15456 40 50 817 14656 100 50 864 15456 10 05 177 31656 10 10 154 27456 10 20 1010 18056 10 50 858 15356 10 60 691 12356 10 70 614 110

A Corning Colorimeter Model 252 spectrophotometerwas used to follow the decrease in absorbance of the dye at700 nm 119879 = 23 plusmn 1∘C 119868 = 05mol dmminus3 (NaCl) and [H+] =10 times 10

minus4mol dmminus3 (HCl) The kinetic runs were conductedunder pseudo-first-order conditions with [S

2O8

2minus] in at least120-fold excess over [NGB3minus]The pseudo-first-order plots oflog (119860

119905minus 119860infin) versus time were made (where 119860

119905and 119860

infin

are the absorbance at time 119905 and at the end of the reactionresp) From the slope of the plots the pseudo-first-order rateconstant (119896

1) was determined [15]

The effect of acid on the rate of reaction was studied byvarying [H+] in the range (01ndash100) times 10minus4mol dmminus3 while[NGB3minus] and [S

2O8

2minus] were kept constant at 23 plusmn 1∘C and119868 = 05mol dmminus3 (NaCl)The range was narrow because acidwas stable at such range

The effect of ionic strength on the rate of the reaction wasinvestigated in the range of 005ndash07mol dmminus3 (NaCl) whilethe concentrations of other reagentswere kept constant at 23plusmn1∘C

3 Results and Discussion

The result of stoichiometric studies reveals that one moleof NGB3minus reacted quantitatively with two moles of S

2O8

2minusHence the overall equation for the reaction is

NGB3minus + 2S2O8

2minus997888rarr SO

4

2minus+ other products (1)

The presence of SO4

2minus was confirmed qualitatively by theaddition of BaCl

2followed byHClwhich formed an insoluble

white precipitate in excess HCl Kinetic studies indicated

06

05

04

03

02

01

0

0 02 04 06 08 1

logk2

I12

Figure 1 Plot of log 1198962versus 11986812 for the redox reaction between

naphthol green B and S2O8

2minus at [NGB3minus] = 40 times 10minus5mol dmminus3[S2O8

2minus] = 56 times 10

minus3mol dmminus3 [H+] = 10 times 10minus4mol dmminus3 119868 =005ndash07mol dmminus3 120582 = 700 nm and 119879 = 23 plusmn 1∘C

first-order dependence of rate of reaction on [NGB3minus] and[S2O8

2minus] Under the experimental conditions employed 1198962

was found to be 155 plusmn 022 dm3molminus1 sminus1

International Journal of Inorganic Chemistry 3

250

200

150

100

50

0

0 20 40 60 80 100 120 140 160

1k1

(s)

1[S2O8

2minus] (mol dmminus3)

Figure 2TheMichaelis-Menten plot for the redox reaction betweennaphthol green B and S

2O8

2minus at [NGB] = 40 times 10minus5mol dmminus3[S2O8

2minus] = (48ndash68) times 10minus3mol dmminus3 [H+] = 10 times 10minus4mol dmminus3

119868 = 050mol dmminus3 120582 = 700 nm and 119879 = 23 plusmn 1∘C

The rate equation for the reaction is

minus119889 [NGB]119889119905= 1198962[NGB3minus] [S

2O8

2minus] (2)

Effect of changes in ionic strength of the reactionmediumindicated that the rate constant decreases with increase inionic strength This obeyed a negative Bronsted-Debye salteffect [16] Plot of log 119896

2against 11986812 (Figure 1) gave a slope

of minus071 (1198772 = 096)The reaction was found to be independent of [H+] in the

range of (01ndash10) times 10minus4mol dmminus3 investigated indicatingthat the reaction occurs through an acid-independent path-way (Table 1) Similar results have been reported for the redoxreaction of S

2O8

2minus [17ndash19] Added cation and anion inhibitedthe rate of the reaction (Tables 2 and 3) This inhibited effectby the ions suggested that the reactionmight be operating viathe outersphere mechanism [20]

Spectroscopic evidence and the Michaelis-Menten plotof 11198961versus 1S

2O8

2minus (Figure 2) suggest that intermediatesmay be unimportant in the rate determining step Free radicaltest did not yield gel formation or if present it might betransient

On the basis of the above findings the mechanism belowis proposed for this reaction

4 Reaction Scheme

The reaction scheme is as follows

NGB3minus + S2O8

2minus1198961

997888997888997888rarr NGBminus + 2SO4

2minus slow (3)

Table 2 Rate data for the effect of added cations (Ca2+ and Mg2+)on the rate of reaction of naphthol green B with S2O8

2minus at [NGB3minus]= 40 times 10minus5mol dmminus3 [S2O8

2minus] = 56 times 10minus3mol dmminus3 [H+] = 10 times10minus4mol dmminus3 119868 = 050mol dmminus3 120582 = 700 nm and 119879 = 23 plusmn 1∘C

Ion 103[ion] mol dmminus3 1031198961 sminus1 119896


Ca2+

10 825 147100 784 140200 730 130600 705 126800 691 1232000 557 099

Mg2+

10 742 13350 559 100100 448 080200 411 073800 365 0652000 265 047

Table 3 Rate data for the effect of added anions (SO42minus and

CH3COOminus) on the rate of reaction of naphthol green B with S2O82minus

at [NGB3minus] = 40 times 10minus5mol dmminus3 [S2O82minus] = 56 times 10minus3mol dmminus3

[H+] = 10 times 10minus4mol dmminus3 119868 = 050mol dmminus3 120582 = 700 nm and 119879= 23 plusmn 1∘C



SO42minus

10 726 13050 660 118100 560 100200 532 095800 326 058

CH3COOminus

10 645 11520 419 07530 288 05140 269 04850 177 032

NGBminus + S2O8

2minus1198962

997888997888997888rarr NGB + S2O8

3minus (4)

S2O8

3minus1198963

997888997888997888rarr SO4

2minus+ SO4

∙minus (5)

SO4

∙minus+H2O1198964

997888997888997888rarr SO4

2minus+OH∙ +H+ (6)

H+ +OH∙ + SO4

∙minus1198965

997888997888997888rarr H2SO5

(7)

Rate = 1198961[NGB3minus] [S

2O8

2minus] (8)

Equation (8) is analogous to (2) where 1198962= 1198961

5 Conclusion

The redox reaction of naphthol green ldquoBrdquo and peroxydisul-phate ions in aqueous acidicmedium showed a stoichiometryof 1 2 a first order was observed for NGB3minus and S

2O8

2minus

ions respectivelyThe rate constant decreases with increase in


ionic strength and the reaction was found to be independentof [H+] Spectroscopic evidence and the Michaelis-Mentenplot of 1119896

1versus 1S

2O8

2minus suggest that intermediates maybe unimportant in the rate determining step Polymerizationtest suggests the absence of free radicals in the reactionmedium Based on the above results it is proposed that thereaction most probably operates through the outer-spheremechanism

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] G Edward Synthesis Dyes in Biology Medicine and ChemistryAcademic Press London UK 1971

[2] B Myek S O Idris and J F Iyun ldquoKinetics of the oxidation ofnaphthol green B by periodate ion in aqueous hydrochloric acidmediumrdquo International Journal of Modern Chemistry vol 5 no2 pp 127ndash135 2013

[3] Y Liu and P Wang ldquoKinetic spectrophotometric method forthe determination of cerium(IV) with naphthol green Brdquo RareMetals vol 28 no 1 pp 5ndash8 2009

[4] J W L Fordham and H Leverne Williams ldquoThe persulfate-iron(II) initiator system for free radical polymerizationsrdquo Jour-nal of The American Chemical Society vol 73 no 10 pp 4855ndash4859 1951

[5] D H Irvine ldquo441The oxidation of the trisdipyridylosmium(II)ion by the peroxydisulphate ion in aqueous solutionrdquo Journal ofthe Chemical Society (Resumed) pp 2166ndash2170 1958

[6] D M Yost and H H Clausen ldquoReduction of peroxysulfate byvanadyl ion with silver ion as catalystrdquo Journal of the AmericanChemical Society vol 53 no 9 pp 3349ndash3354 1931

[7] K Y Gupta and D D Misra ldquoThe silver ion catalyses oxidationof arsenous acid by S

2O2minus8rdquo Bulletin of the Chemical Society of

Japan vol 32 pp 1306ndash1309 1959[8] RW Chlebeck andNW Lister ldquoReaction between alkali metal

ferrocyanides and peroxydisulphate in aqueousrdquo CanadianJournal of Chemistry vol 45 pp 2411ndash2418 1967

[9] S Raman and JH C Brubakar ldquoThe kinetics of the oxidation ofsubstituted 2 21015840-bipyridine and 1 10-phenanthroline complexesof iron (II) with S

2O2minus8

ionrdquo Journal of Inorganic and NuclearChemistry vol 31 pp 1091ndash1201 1969

[10] S S Gupta and Y K Gupta ldquoKinetics and mechanism of theiron(III)-catalyzed oxidation of hydrazine with peroxydisulfatein acid mediumrdquo Inorganic Chemistry vol 20 no 6 pp 1748ndash1751 1981

[11] D E Pennington and A Haim ldquoKinetics and mechanism ofthe chromium(II)-catalyzed substitution of iodide ion in theiodopentaaquochromium(III) ion by water and by fluoridechloride and bromide ionsrdquo Inorganic Chemistry vol 6 no 12pp 2138ndash2146 1967

[12] K Ohashi H E Matsuzama and Yamamato ldquoThe kineticsstudy of the oxidation reaction of tris-(2 21015840-bypyridine)Cobalt(II) ion and ethylenediamine-N N N1015840 Nrsquotetraacetate(II) ion byS2O2minus8rdquo Bulletin of the Chemical Society of Japan vol 49 no 9

pp 2440ndash2442 1976[13] G A Ayoko J F Iyun and I F El-Idris ldquoElectron transfer

at tetrahedral cobalt(II) part III kinetics of copper(II) ion

catalysed reduction of periodaterdquo Transition Metal Chemistryvol 17 no 5 pp 423ndash425 1992

[14] K Y Gupta and S Ghosh ldquoHydrogen ion dependence of theoxidation of iron(II) with peroxydisulphate in acidic perchlo-rate solutionsrdquo Inorganic Chemistry vol 20 pp 434ndash439 1959

[15] Y Mohammed J F Iyun and S O Idris ldquoKinetic approach tothe mechanism of the redox reaction of malachite green andpermanganate ion in aqueous acidic mediumrdquo African Journalof Pure and Applied Chemistry vol 3 no 12 pp 269ndash274 2009

[16] G Adefikayo Ayoko J Femi Iyun and I Faskari El-IdrisldquoElectron transfer at tetrahedral cobalt(II) part II Kinetics ofsilver(I) ion catalyzed reduction of peroxydisulphaterdquo Transi-tion Metal Chemistry vol 17 pp 46ndash49 1992

[17] S S Gupta and Y K Gupta ldquoHydrogen ion dependenceof the oxidation of iron(II) with peroxydisulphate in acidicperchlorate solutionsrdquo Inorganic Chemistry vol 20 pp 434ndash439 1981

[18] P Banerjee and P M Pujara ldquoThe kinetics of oxidation of N(2-hydroxyl)ethylenediamminetetraacetatecobaltate(II) by S

2O2minus8

in aqueous acidic solutionrdquo Transition Metal Chemistry vol 6pp 47ndash54 1981

[19] P S V Rao P S N Murty and L A N Murty ldquoKinetic andmechanism of indigo carmine with peroxydisulphaterdquo Journalof the Chemical Society vol 60 p 1180 1978

[20] T J Mayer and H Taube Comprehensive Coordination Chem-istry The Synthesis Reaction Properties and Application ofCoordination Compounds Pergamon Press London UK 1987

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


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Applied ChemistryJournal of



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Spectroscopy

Analytical ChemistryInternational Journal of


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Quantum Chemistry


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ElectrochemistryInternational Journal of



CatalystsJournal of


Table 1 Pseudo-first-order and second-order rate constants for the reaction of naphthol green B and S2O82minus at [NGB3minus] = 40times10minus5mol dmminus3

120582 = 700 nm and 119879 = 23 plusmn 1∘C

103[S2O82minus] mol dmminus3 104[H+

] mol dmminus3 101 119868 mol dmminus3 1031198961 sminus1 119896


48 10 50 730 15252 10 50 822 15856 10 50 850 15260 10 50 939 15764 10 50 979 15368 10 50 1070 15756 01 50 839 15056 05 50 850 15256 10 50 859 15356 15 50 882 15856 20 50 864 15456 40 50 817 14656 100 50 864 15456 10 05 177 31656 10 10 154 27456 10 20 1010 18056 10 50 858 15356 10 60 691 12356 10 70 614 110

A Corning Colorimeter Model 252 spectrophotometerwas used to follow the decrease in absorbance of the dye at700 nm 119879 = 23 plusmn 1∘C 119868 = 05mol dmminus3 (NaCl) and [H+] =10 times 10

minus4mol dmminus3 (HCl) The kinetic runs were conductedunder pseudo-first-order conditions with [S

2O8

2minus] in at least120-fold excess over [NGB3minus]The pseudo-first-order plots oflog (119860

119905minus 119860infin) versus time were made (where 119860

119905and 119860

infin

are the absorbance at time 119905 and at the end of the reactionresp) From the slope of the plots the pseudo-first-order rateconstant (119896

1) was determined [15]

The effect of acid on the rate of reaction was studied byvarying [H+] in the range (01ndash100) times 10minus4mol dmminus3 while[NGB3minus] and [S

2O8

2minus] were kept constant at 23 plusmn 1∘C and119868 = 05mol dmminus3 (NaCl)The range was narrow because acidwas stable at such range

The effect of ionic strength on the rate of the reaction wasinvestigated in the range of 005ndash07mol dmminus3 (NaCl) whilethe concentrations of other reagentswere kept constant at 23plusmn1∘C

3 Results and Discussion

The result of stoichiometric studies reveals that one moleof NGB3minus reacted quantitatively with two moles of S

2O8

2minusHence the overall equation for the reaction is

NGB3minus + 2S2O8

2minus997888rarr SO

4

2minus+ other products (1)

The presence of SO4

2minus was confirmed qualitatively by theaddition of BaCl

2followed byHClwhich formed an insoluble

white precipitate in excess HCl Kinetic studies indicated

06

05

04

03

02

01

0

0 02 04 06 08 1

logk2

I12

Figure 1 Plot of log 1198962versus 11986812 for the redox reaction between

naphthol green B and S2O8

2minus at [NGB3minus] = 40 times 10minus5mol dmminus3[S2O8

2minus] = 56 times 10

minus3mol dmminus3 [H+] = 10 times 10minus4mol dmminus3 119868 =005ndash07mol dmminus3 120582 = 700 nm and 119879 = 23 plusmn 1∘C

first-order dependence of rate of reaction on [NGB3minus] and[S2O8

2minus] Under the experimental conditions employed 1198962

was found to be 155 plusmn 022 dm3molminus1 sminus1


250

200

150

100

50

0

0 20 40 60 80 100 120 140 160

1k1

(s)

1[S2O8



2O8






2O8

2minus] (2)





2O8



2O8



4 Reaction Scheme


NGB3minus + S2O8

2minus1198961

997888997888997888rarr NGBminus + 2SO4

2minus slow (3)






Ca2+

10 825 147100 784 140200 730 130600 705 126800 691 1232000 557 099

Mg2+

10 742 13350 559 100100 448 080200 411 073800 365 0652000 265 047







SO42minus

10 726 13050 660 118100 560 100200 532 095800 326 058

CH3COOminus

10 645 11520 419 07530 288 05140 269 04850 177 032

NGBminus + S2O8

2minus1198962

997888997888997888rarr NGB + S2O8

3minus (4)

S2O8

3minus1198963

997888997888997888rarr SO4

2minus+ SO4

∙minus (5)

SO4

∙minus+H2O1198964

997888997888997888rarr SO4


H+ +OH∙ + SO4

∙minus1198965

997888997888997888rarr H2SO5

(7)


2O8

2minus] (8)


5 Conclusion


2O8

2minus




1versus 1S

2O8




References












2O2minus8













2O2minus8













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


250

200

150

100

50

0

0 20 40 60 80 100 120 140 160

1k1

(s)

1[S2O8



2O8






2O8

2minus] (2)





2O8



2O8



4 Reaction Scheme


NGB3minus + S2O8

2minus1198961

997888997888997888rarr NGBminus + 2SO4

2minus slow (3)






Ca2+

10 825 147100 784 140200 730 130600 705 126800 691 1232000 557 099

Mg2+

10 742 13350 559 100100 448 080200 411 073800 365 0652000 265 047







SO42minus

10 726 13050 660 118100 560 100200 532 095800 326 058

CH3COOminus

10 645 11520 419 07530 288 05140 269 04850 177 032

NGBminus + S2O8

2minus1198962

997888997888997888rarr NGB + S2O8

3minus (4)

S2O8

3minus1198963

997888997888997888rarr SO4

2minus+ SO4

∙minus (5)

SO4

∙minus+H2O1198964

997888997888997888rarr SO4


H+ +OH∙ + SO4

∙minus1198965

997888997888997888rarr H2SO5

(7)


2O8

2minus] (8)


5 Conclusion


2O8

2minus




1versus 1S

2O8




References












2O2minus8













2O2minus8













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



1versus 1S

2O8




References












2O2minus8













2O2minus8













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article kinetics and mechanism of the oxidation

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