Revista Colombiana de Química
ISSN: 0120-2804
Universidad Nacional de Colombia
Colombia
Kumar Kakarla, Ramana; Guru Prasad Aluru, Raghavendra; Vinnakota, Srilalitha; Swamy Golla,
Narayana; Rao Krishna Rao, Ravindranath Lakshmana
ELECTROCHEMICAL STUDIES OF CERTAIN 1-(TOLUENYL SULFONYL )-3- AMINO -4-(4’-
SUBSTITUTED ARYL HYDRAZONO )-2-PYRAZOLIN -5-ONES
Revista Colombiana de Química, vol. 40, núm. 2, 2011, pp. 165-184
Universidad Nacional de Colombia
Bogotá, Colombia
Available in: http://www.redalyc.org/articulo.oa?id=309026687009
How to cite
Complete issue
More information about this article
Journal's homepage in redalyc.org
Scientific Information System
Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal
Non-profit academic project, developed under the open access initiative
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
165
Org
ánic
a y
Bioq
uím
ica
Rev. Colomb. Quím., 2011, 40(2): 165-184
1 MallaReddyCollegeofEngineering,Hyderabad,A.P.,India,
2 ICFAIFoundationforHigherEducation,Hyderabad,A.P.,India
3 C.M.R.InstituteofTechnology,Hyderabad,A.P.,India,
4 SriKrishnadevarayaUniversity,Anantapur,A.P.,India.
ELECTROCHEMICAL STUDIES OF CERTAIN 1-(TOLUENYL SULFONYL)-3-AMINO-4-(4’-SUBSTITUTED ARYL HYDRAZONO)-2-PYRAZOLIN-5-ONES
ESTUDIO ELECTROQUÍMICO DE ALGUNOS 1-(TOLUENIL SULFONILO)-3-AMINO-4-(4’-HIDRAZINA FENIL SUSTITUIDAS)-2-PIRAZOLINA-5-ONAS
ESTUDO ELETROQUÍMICO DE ALGUNS 1-(TOLUENIL SULFONILA)-3-AMINA-4-(4’- HIDRAZINA FENIL SUBSTITUÍDAS)-2-PIRAZOLINA-5-ONAS
Ramana Kumar Kakarla1, Raghavendra Guru Prasad Aluru2,5, Srilalitha Vinnakota3, Narayana Swamy Golla4, Ravindranath Lakshmana Rao Krishna Rao4
Recibido: 29/07/11- Aceptado: 26/08/11
Resumen
El comportamiento electroquímico deciertos 1-(Toluenil sulfonil)3-amino-4-(aril hidrazonio)-2-pirazolin-5-onassustituidas fueron estudiados con unelectrododegotademercurioemplean-dopolarografíadecorrientedirecta.Lasvariables que influyen sobre el proceso enelelectrodofueronestudiadasamplia-mente.Todosloscompuestosestudiadospresentaron dos ondas polarográficas bien definidas. Se propone un mecanis-mo para las reacciones electroquímicasestudiadas tanto en medio ácido comobásico.
Palabras clave:Estudiospolarográf-icos,1-(Toluenilsulfonil)3-amino-4-(arilhidrazonio sustituidos)-2-pirazolin-5-
AbstRAct
The electrochemical behavior of certain1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazo-lin-5-ones were studied at the droppingmercuryelectrodebyemployingDCpo-larography. The variables that influence the electrode process were extensivelystudied.All compoundsunder investiga-tion gave two well-defined polarographic waves.Themechanismfortheelectrodeprocesswasproposedinacidaswellasinbasicmedia.
Key words: Polarographicstudies,1-(Toluenyl sulfonyl)-3-amino-4-(4’-sub-stituted aryl hydrazono)-2-pyrazolin-5-ones, influence of variables, mechanism ofelectrodereaction.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
166
onas, influencia de variables, mecanis-mosdereacciónenelelectrodo.
Resumo
Ocomportamentoeletroquímicodecer-tos 1-(Toluenil sulfonil)3-amino-4-(arilhidrazonio)-2-pirazolin-5-onassubstituí-dasforamestudadoscomumeletrododegotademercúrioempregandopolarogra-fia de corrente direta. As variáveis queinfluem sobre o processo no eletrodo foram estudadas amplamente. Todosos compostos estudados apresentaramduas ondas polarograficas bem defini-das. Propõe-se um mecanismo para asreações eletroquímicas estudadas tantoemmeioácidoquantoemmeiobásico.
Palavras chave: Estudos polarografi-cos,1-(Toluenil sulfonil)3-amino-4-(arilhidrazonio substituídos)-2-pirazolin-5-onas, influência de variáveis, mecanis-mosdereaçãonoeletrodo.
IntRoDuctIon
Pyrazole and its derivatives are impor-tant class of heterocyclic compoundsdue to their wide spread applications inmedicinal(1)andpesticidechemistry(2,3).Compounds containing pyrazole ringsystemareknowntodisplaydiversephar-macological activities such as antibacte-rial (4),antifungal(2),antiviral(5),anti-inflammatory(6, 7), analgesic(6, 7), and antipyretic(6). Some of them have been used as antihyperglycemic agents (8) orcardiovascular drugs (9), while some ofthemhavebeenusedasanxiolyticdrugs
(10).A systematic study of this class ofcompoundsreveledthattheirpharmaceu-ticalactivityresultsfromthepresenceof
pyrazolenucleus.Moreover, thebiologi-cal activities of pyrazol-5-ones dependonthenatureofthesubstituents.Varioustherapeutic aspects and numerous appli-cationsofabovesaidclassofcompoundshave inspired the authors to understandtheir reduction process at the droppingmercury electrode.However, theknowl-edgeofreductionisveryimportanttoun-derstandtheirbiologicalactivity.
Pyrazolin-5-onesarealsousedindyeindustry(11)andasindicators(12)incom-plexometric titrations. Many pyrazoleshavebeenfound to functionas lumines-cent and fluorescent(13,14)agents.
eXPeRImentAL
Allchemicalsandsolventsusedwereof analytical reagent grade procuredfromMerck,India.Doubledistilledwa-terwasusedforthepreparationofsolu-tions. Working solutions were preparedbyappropriatedilutionsof the standardsolution.
DC recordingpolarographmanufac-turedbyELICOPrivateLimited,Hyder-abad, India was used for polarographicstudies. The current voltage measure-ments were performed with three-elec-trode assembly, a dropping mercuryelectrodeasworkingelectrode,calomelasreferenceelectrodeandplatinumelec-trode as counter electrode. The currentresponses and applied potentials wererecordedat scan rate100mV/min.Thedroppingmercuryelectrodehadthecap-illarycharacteristics,m=2.422mg/s,t=2.5 s, h = 60 cm. pH measurements were madeusingpHmeterModelL1-10man-ufactured by ELICO Private Limited,Hyderabad,India.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
167
Org
ánic
a y
Bioq
uím
ica
synthesis pyrazolin-5-ones
Amixtureofappropriatediazoniumcy-anoesterandtoluenesulfonylhydrazidein ethanol was refluxed for six hours and cooled. The crystalline solid separatedwas filtered, washed with water, dried and
recrystallysed from dimethylformamide(1:1).Thephysicalcharacteristicsofthedifferentcompoundssynthesizedarepre-sentedinTable1.
table 1.Physicalcharacteristicsofpyrazolin-5-ones
S. No. Substituent (X) Compound colourCompound melting points
observed (°C)
A 4’-CH3 Yellow 120-122
B 4’-OCH3 Yellow 128-130
C 4’-OH Black 270-271
D 4’-Cl Yellow 150-152
General experimental procedure
10mLofbuffersolutionofrequiredpH,2.5 mL of pyrazolin-5-one (1×10-2 M)and10mLofdimethylformamideweretaken into the polarographic cell. Thesolutionwasmade toa totalvolumeof25mLwithdistilledwater.Polarogramswere recorded after deaeration with ni-trogengas.
ResuLts AnD DIscussIon
1-(Toluenyl sulfonyl)-3-amino-4-(4’-sub-stituted aryl hydrazono)-2-pyrazolin-5-ones(A-D)exhibit twowavesinthepHrange1.1-10.1.Adecreaseinwaveheight
withincreaseinpHwasobservedforallthe compounds. Among the three sitessusceptibleforreductionnamelytheexo-cyclic>C=N,cyclic>C=Nandcyclicam-ide,exocyclic>C=Nismoresusceptibleforreductionthancyclic>C=Nandcyclicamide as it was experimentally confirmed that 1-(Toluenyl sulfonyl)-3-amino- 2-pyrzolin-5-one does not undergo reduc-tion under the experimental conditions.Hence the polarographic reduction of1-(Toluenyl sulfonyl)-3-amino-4-(substi-tutedarylhydrazono)-2-pyrazolin-5-onesisduetothereductionofexocyclic>C=Ngroup.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
168
Half-wave potential- pH relation
Thecompounds(A-D)exhibit twowell-defined waves in the entire pH range 1.1-10.1ofstudy.Thehalf-wavepotentialsof
the first and second waves for all the com-poundsturnmorenegativewithincreaseinpHinthepHrange1.1-7.1andremainconstantinalkalinemedium(8.1-10.1).
Figure 1. (I), (II) & (III).EffectofpHonhalf-wavepotentialof1-(Toluenylsulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-one.[pyrazolin-5-one] = 1×10-3M;Medium=Dimethylformamide(40%byvolume)
0.8
0.6
0.4
0.2
0
E-2/1
ECS
svV
1
0 2 4 6 8 10
(I)A-I
B-II
C-I
X
pH
X
X
X
X
X
X
X
X X X 0.8
0.6
0.4
0.2
0
E-2/1
ECS
svV
1
0 2 4 6 8 10
(II)A-II
B-I
C-II
X
pH
X
X
X
X
X
X
X
X X X
0.8
0.6
0.4
0.2
0
E-2/1
ECS
svV
1
0 2 4 6 8 10
(III)D-IIX
pH
X
X
X
X
X
X
X
X XD-I
X
TheE1/2-pHplotsareshowninFigure1(I), (II)and(III).TheE1/2-pHrelation-ship for the first wave is represented by
a)-E1/2 = 0.05 + 0.08172 × pH V vs SCEb)-E1/2 = 0.03 + 0.08145 × pH V vs SCE
c)-E1/2 = 0.06 + 0.08372 × pH V vs SCEd)-E1/2 = 0.08 + 0.08546 × pH V vs SCE
The E1/2-pH relationship for the secondwaveisrepresentedby
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
169
Org
ánic
a y
Bioq
uím
ica
a)-E1/2 = 0.21 + 0.08172 × pH V vs SCE
b)-E1/2 = 0.15 + 0.08956 × pH V vs SCE
c)-E1/2 = 0.21 + 0.08372 × pH V vs SCE
d)-E1/2 = 0.24 + 0.08567 × pH V vs SCE
Thefactthatthehalf-wavepotentialvaluesdidnotvarywithpH inalkalinemedium suggests that the protons wereinvolved in the reduction process. Thenumberofprotons(P)involvedinthere-ductionprocesswascalculatedusingtheequation
Pn
05915.0
pH
E
a
2/1
α=
Δ
Δ
where α is transfer coefficient and na isnumberofelectrons involved.ThefractionalvalueofPpresented inTable2atdifferentpHvaluessuggeststhehet-erogeneousprotontransferinthereduc-tionprocess(15).
effect of mercury column height (h) on the wave height (H)
The wave height (H) linearly varieswithh1/2andtheplotofh1/2vsHpassesthroughtheorigin.Thissuggeststhedif-fusioncontrollednatureofthewave.
effect of concentration (c) of the depolariser on the wave height (H)
Theeffectofconcentrationofpyrazolin-5-ones(A-D)onthewaveheight in therange0.5-4.0mMinthetypicalpHme-dia 4.1 and 8.1 was studied.The linearwaveheight-concentrationplots (Figure2I,IIandIII)passingthroughtheoriginrevealed that the reduction process wasdiffusioncontrolledandthemethodcanbeappliedtodeterminethetraceamountsofpyrazolin-5-onesunderstudy.
Figure 2 (I), (II) & (III).Effectofconcentra-tion of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substitutedarylhydrazono)-2-pyrazolin-5-oneonwaveheight.pH=4.1;Medium=Dimethylformamide(40%byvolume)
Wav
e he
ight
(m)
0.08
0.06
0.04
0.02
0
0 1 2 3 4
A-I,4.1
A-II,4.1
A-II,8.1
C-II,8.1
(I)
[Pyrazoline-5one] x 103
x
+
–
A-I, 8.1B-I, 4.1B-I, 8.1C-I, 4.1C-I, 8.1D-I, 4.1
D-I, 8.1
++
+
+
+
++
+
–––––––
Wav
e he
ight
(m)
0.08
0.06
0.04
0.02
0
0 1 2 3 4[Pyrazoline-5one] x 103
(II)W
ave
heig
ht(m
)
0.08
0.06
0.04
0.02
0
0 1 2 3 4[Pyrazoline-5one] x 103
x
B-II, 4.1B-II, 8.1C-II, 4.1D-II, 4.1D-II, 8.1
(III) x
x
x
x
x
x
x
x
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
170
Irreversible nature of the electrode process
Theirreversiblenatureofthewavesmaybeattributedtothebulkyarylhydrazonogroup at the end of >C=N linkage(16). SemilogplotsshowninFigure3(I)and(II) established the irreversiblenatureofthewave.Thefractionalvalueoftheslope0.049-0.051and0.048-0.053respectivelyfor first and second waves suggests that
Wav
e he
ight
(m)
X
A-IB-IC-ID-I
(I) 0.6
0.5
0.4
0.3
0.2-0.75 -0.25 0.25 0.75
log(i/id-i)
-Edm
e
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
the reduction process was irreversiblein nature. The irreversible nature of thewaveswasfurthersupportedbytheshiftofthehalf-wavepotentialvaluestowardsthe more negative values with increasein the concentration of the depolarizer (17), the decrease in heterogeneous rateconstant values K o
h,f and an increase inincreaseinactivationfreeenergychangevalues ∆G*withincreaseinthepHofthesolution(Table2).
Figure 3 (I) & (II). Semi log plot of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydra-zono)-2-pyrazolin-5-one.pH=4.1;Medium=Dimethylformamide(40%byvolume)
Wav
e he
ight
(m) X
A-IIB-IIC-IID-II
log(i/id-i)
-Edm
e
X0.7
0.6
0.5
0.4
X
X
X
X
X
X
X
X
X
X
X
X
X
X
-0.75 -0.25 0.25 0.75
(II)
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
171
Org
ánic
a y
Bioq
uím
ica
tabl
e 2.
Pol
arog
raph
ic c
hara
cter
istic
s an
d ki
netic
par
amet
ers
of 1
-(To
luen
yl s
ulfo
nyl)-
3-am
ino-
4-(4
’-su
bstit
uted
ary
l hyd
razo
no)-
2-py
razo
lin-5
-on
e (1
×10-3
M).
-XpH
-E1/
2
V v
s SC
EW
ave
heig
htH
(m
)∆
E1/
2/∆
pH (
mV
)α
n a
Num
ber
of
prot
ons
(P)
D ×
102
(m2 s
ec-1)
I ×
103
K° f,
h
(m s
ec-1)
∆G
*(K
J m
ole-1
)
I w
ave
IIw
ave
I w
ave
II w
ave
I w
ave
II w
ave
Iw
ave
II
wav
eI
wav
eII
w
ave
I w
ave
II
wav
eI
wav
eII
w
ave
I w
ave
II w
ave
Iw
ave
II
wav
e
-CH
3
2.1
0.24
0.40
0.05
0.05
30.
0956
0.08
873
0.63
0.52
1.01
80.
7800
5.23
55.
883
2.77
82.
944
1.74
×10
-57.
223×
10-7
19.5
923
.041
4.1
0.39
0.55
0.03
80.
041
0.63
0.52
1.01
80.
7800
3.02
43.
520
2.11
12.
278
3.35
3×10
-72.
682×
10-8
23.8
7426
.606
6.1
0.57
0.73
0.02
80.
027
0.57
0.45
0.92
120.
6750
1.64
21.
527
1.55
61.
500
6.44
4×10
-91.
751×
10-9
28.1
529
.564
8.1
0.77
0.95
0.01
50.
015
0.45
0.36
0.72
730.
5400
0.47
10.
471
0.83
30.
833
4.82
5×10
-10
2.46
9×10
-10
30.9
5731
.685
10.1
0.77
0.95
0.01
50.
015
0.45
0.36
0727
30.
5400
0.47
10.
471
0.83
30.
833
4.82
5×10
-10
2.46
9×10
-10
30.9
5731
.685
-OC
H3
2.1
0.25
0.41
0.05
20.
054
0.09
154
0.09
942
0.66
0.54
1.02
140.
9076
5.66
36.
107
2.88
93.
000
1.40
7×10
-55.
271×
10-7
19.8
2423
.38
4.1
0.40
0.56
0.04
0.04
20.
660.
541.
0214
0.90
763.
351
3.69
42.
222
2.33
32.
294×
10-7
1.75
1×10
-824
.284
27.0
7
6.1
0.58
0.74
0.03
0.02
80.
590.
480.
9131
0.80
681.
885
1.64
21.
667
1.55
64.
248×
10-9
8,51
0×10
-10
28.6
0230
.347
8.1
0.78
0.97
0.01
70.
016
0.48
0.38
0.74
300.
6387
0.60
50.
536
0.94
40.
889
2.44
6×10
-10
1.12
9×10
-10
31.6
9432
.535
10.1
0.78
0.97
0.01
70.
016
0.48
0.38
0.74
300.
6387
0.60
50.
536
0.94
40.
889
2.44
6×10
-10
1.12
9×10
-10
31.6
9432
.535
-OH
2.1
0.26
0.42
0.05
30.
055
0.09
541
0.09
395
0.68
0.57
1.09
680.
9053
5.88
36.
335
2.94
43.
056
1.09
3×10
-53.
530×
10-7
20.0
9623
.815
4.1
0.41
0.57
0.04
10.
043
0.68
0.57
1.09
680.
9053
3.52
03.
872
2.27
82.
389
1.59
5×10
-79.
436×
10-9
24.6
7727
.74
6.1
0.59
0.75
0.03
10.
029
0.61
0.50
0.98
390.
7942
2.01
21.
761
1.72
21.
611
2.65
9×10
-94.
919×
10-1
029
.112
30.9
36
8.1
0.79
0.96
0.01
80.
017
0.50
0.41
0.80
600.
6512
0.67
80.
605
1.00
00.
944
1.40
1×10
-10
6.00
5×10
-11
32.3
33.2
17
10.1
0.79
0.96
0.01
80.
017
0.50
0.41
0.80
600.
6512
0.67
80.
605
1.00
00.
944
1.40
1×10
-10
6.00
5×10
-11
32.3
33.2
17
-Cl
2.1
0.19
0.35
0.04
40.
047
0.09
657
0.09
135
0.54
0.43
0.88
160.
6640
4.05
44.
626
2.44
42.
611
4.37
9×10
-52.
580×
10-6
18.5
9421
.661
4.1
0.34
0.50
0.03
20.
035
0.54
0.43
0.88
160.
6640
2.14
42.
565
1.77
81.
944
1.36
0×10
-61.
560×
10-7
22.3
5524
.702
6.1
0.52
0.68
0.02
20.
021
0.48
0.36
0.78
30.
5560
1.01
30.
923
1.22
21.
167
4.07
7×10
-81.
520×
10-8
26.1
5427
.221
8.1
0.72
0.92
0.00
90.
009
0.36
0.27
0.58
770.
4170
0.17
00.
170
0.50
00.
500
3.72
5×10
-92.
436×
10-9
28.7
4429
.204
10.1
0.72
0.92
0.00
90.
009
0.36
0.27
0.58
770.
4170
0.17
00.
170
0.50
00.
500
3.72
5×10
-92.
436×
10-9
28.7
4429
.204
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
172
effect of pH on wave height
TheeffectofpHonwaveheightispre-sentedinFigure4(I)and(II).Theplotsfor the first and second waves for all the
compounds(A-D)assumedtheshapeofdissociationcurve.Thistypeofbehaviorisexpectedif thedepolarizerundergoeschemicalcleavageintheacidicoralka-linemedium.
Figure 4 (I) & (II). Effect of pH on wave height of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substi-tutedarylhydrazono)-2-pyrazolin-5-one.[pyrazolin-5-one] = 1×10-3M;Medium=Dimethylformamide(40%byvolume)
0.055
0.045
0.035
0.025
0.015
0.0050 2 4 6 8 10
Wav
e he
ight
(m)
pH
(I)
A-I
B-I
C-I
D-Ix
X
X
XX
X
X
X
XX
X
X
X
XXX
X
X
X
X
0.055
0.045
0.035
0.025
0.015
0.0050 2 4 6 8 10
Wav
e he
ight
(m)
pH
(II)
A-II
B-II
C-II
D-IIx
X
X
X
XX
X
X
X
XX
XX
XXX
X
X
X
X
X
XX
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
173
Org
ánic
a y
Bioq
uím
ica
Kinetic parameters of electrode reaction
The heterogeneous rate constant, K oh,f
and activation free energy change, ∆G*indifferentpHmedia(1.1-10.1)for thecompoundsunderstudyarepresentedinTable 2.As reveled from the table, thedecrease in K o
h,f and the increase in∆G*valuewithincreaseinpHareindica-tive of the enhanced irreversible natureofthereductionprocesswiththeincreaseinpH.
effect of temperature
Thepolarogramsofpyrazolin-5-onesinamediaofpH4.1wererecordedat303K,313K,323Kand333K, tostudy theef-fectoftemperatureonthehalf-wavepo-tentialandwaveheight.The resultsarepresentedinTable3.Thecompoundsun-der study exhibit two well-defined waves atalltemperaturesstudied(303-333K)atpH4.1.Thewaveheightincreaseswithincrease in temperature. The tempera-ture coefficient values were in the range 0.734-1.495% deg-1 and were in goodagreement with the values reported intheliterature(18)forothersimilarcom-pounds.
The table reveals that theαna valuesdecrease as the temperature increasesfrom303Kto333K.Thedecreaseinαnavalues with increase in temperature wasduetodecreaseinαvalue.Thedecreaseinα values indicates that the transferofelectrons was made increasingly difficult with the increase in temperature.Hence,thesystemtendstobecomemoreirrevers-ible(19)withtheincreaseintemperature.This fact was further supported by theshiftofhalf-wavepotentialstowardsmorenegativevalueswithraiseintemperature.Literaturesurvey(20)reveals thesimilarobservationsforsimilarcompounds.
Theformalrateconstant(K oh,f )cal-
culatedatdifferenttemperaturesisshownin Table 4. Stoke-Einstein equation wasused to calculate diffusion coefficient necessaryforthecalculationoftheformalrate constant at different temperatures.Table 4 shows that the formal rate con-stantdecreaseswithincreaseintempera-ture.ThedecreaseinK o
h,f withincreaseintemperaturesuggeststhattheelectrodereaction was becoming increasingly ir-reversible with the raise in temperature.Thisobservationwasinaccordancewiththeconclusionarrivedonthebasisofαnavalues.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
174
tabl
e 3.
Effe
ct o
f tem
pera
ture
on
the
pola
rogr
aphi
c ch
arac
teris
tics o
f 1-(
Tolu
enyl
sulfo
nyl)-
3-am
ino-
4-(4
’-su
bstit
uted
ary
l hyd
razo
no)-
2-p
yraz
o-lin
-5-o
ne (1
×10-3
M);
pH:4
.1;M
ediu
m:A
queo
usd
imet
hylfo
rmam
ide
(40%
v/v
).
Tem
pera
ture
Hal
f-w
ave
pote
ntia
l,-E
1/2 V
vs
SCE
Wav
e he
ight
H (
m)
Tem
pera
ture
C
oeff
icie
nt,
% d
eg-1
αn a
D x
102
m2 s
ec-1
I w
ave
II w
ave
I w
ave
II w
ave
I w
ave
II w
ave
I w
ave
II w
ave
I w
ave
II w
ave
4’-m
ethy
l
303
0.36
0.52
0.03
30.
036
--
0.69
0.55
2.28
2.71
313
0.39
0.55
0.03
80.
041
1.41
1.30
0.63
0.52
3.02
3.52
323
0.43
0.59
0.04
30.
046
1.24
1.15
0.58
0.48
3.87
4.43
333
0.50
0.65
0.04
90.
052
1.31
1.23
0.54
0.43
5.03
5.66
4’-m
etho
xy
303
0.37
0.53
0.03
50.
037
--
0.72
0.57
2.56
2.87
313
0.40
0.56
0.04
0.04
21.
341.
270.
660.
543.
353.
69
323
0.45
0.60
0.04
50.
047
1.18
1.12
0.61
0.50
4.24
4.63
333
0.51
0.66
0.05
10.
053
1.25
1.20
0.57
0.45
5.45
5.88
4’-h
ydro
xy
303
0.37
0.54
0.03
60.
038
--
0.74
0.60
2.71
3.02
313
0.41
0.57
0.04
10.
043
1.30
1.24
0.68
0.57
3.52
3.87
323
0.45
0.61
0.04
60.
048
1.15
1.10
0.63
0.53
0.43
0.82
333
0.51
0.66
0.05
20.
054
1.23
1.18
0.59
0.48
5.66
6.11
4’-c
hlor
o
303
0.31
0.47
0.02
80.
031
--
0.60
0.46
1.64
2.01
313
0.34
0.50
0.03
20.
035
1.34
1.21
0.54
0.43
2.14
2.56
323
0.38
0.55
0.03
70.
041.
45
1.34
0.49
0.39
2.87
3.35
333
0.44
0.62
0.04
30.
046
1.50
1.40
0.45
0.34
3.87
4.43
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
175
Org
ánic
a y
Bioq
uím
ica
table 4.Effectoftemperatureontheformalrateconstantforthepolarographicreductionof1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-one (1×10-3M);pH=4.1;Medium:Aqueousdimethylformamide(40%v/v).
X / Kºf,h in m sec-1
I wave X / Kºf,h in m sec-1
II wave
303 K 313 K 323 K 333 K 303 313 323 333
4’-methylKºf,h×108
2.645 1.894 1.143 0.3954’-methyl
Kºf,h × 109 1.792 1.516 1.282 1.031
4’-methoxyKºf,h×108
1.843 1.297 0.597 0.2434’-methoxy Kºf,h×109
1.189 0.989 0.823 0.642
4’-hydroxyKºf,h×108
1.716 0.901 0.518 0.2014’-hydroxy Kºf,h ×109 6.892 5.592 4.491 4.011
4’-chloroKºf,h×107
1.093 0.768 0.495 0.2454’-chloro Kºf,h×108
1.004 0.881 0.695 0.568
millicoulometry
The number of electrons involvedin the reduction of pyrazolin-5-oneswas evaluated in Britton-Robinson buf-fers containing 40% (v/v) dimethylfor-
mamide.ThemillicoulometerofDeVr-ies and Kroon (21) with mercury poolcathodewasemployedtodetermine thevalue of ‘n’. The results are presented in Table5.
table 5. Millicoulometric data of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazo-no)-2-pyrazolin-5-one (1×10-3M);Medium:Aqueousdimethylformamide(40%v/v).
pH Time (sec) 4’-CH3 4’-OCH3 4’-OH 4’-Cl
Iwave
II wave
Iwave
IIwave
Iwave
II wave
Iwave
II wave
4.1 0 - - - - - - - -
7200 2.0 1.9 2.2 2.0 1.9 2.1 1.8 1.7
10800 1.8 1.9 2.0 1.9 1.8 2.0 1.7 1.8
8.1 0 - - - - - -
7200 1.6 1.6 2.1 1.9 2.3 2.1
10800 2.2 2.2 1.7 2.3 1.7 1.6
Reduction mechanism
AninspectionoftheresultspresentedinTable 2 reveal that the compoundsA-Dexhibit two 2-electron reductive wavesinthepHrange1.1-10.1.Itwasevidentfromthepolarographicreductionofsemi-
carbazonesandhydrazones(22)thatN-Nbond in hydrazono group (>C=N-NH-)wasreducedmoreeasilythantheazome-thine(>C=N-)group.
In acidic medium, the first step in-volves the two-electron reductivecleav-
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
176
ageofN-Nbondleadingtotheformationof 1-(Toluenyl sulfonyl)-3-amino-4-im-ino-2-pyrazolin-5-ones (23, 24) (II) andsubstituted aniline. The second step in-volves two-electron reduction of keti-mine (II) to the corresponding diamine(III).Thewaveheightofboththesestepswas affected by acid-base equilibrium.The variation of wave height with pHwassimilartothetrendreportedinthelit-erature(25).Therefore,reductionmecha-nismshowninFigure5(I)wasproposedinacidicmedium.
In alkaline medium, the azomethinegroup (>C=N-NH-) of the compoundsexist in the azomethine anionic form
(>C=N- N ) (26). The first wave wasat-tributed to the two-electron reductivecleavage of N-N bond in azomethineanionicform(IV)whichwassusceptibleforcleavagetothecorrespondinghetero-cyclic carbonyl compound. The secondwavewasduetothetwo-electronreduc-tionofheterocycliccarbonylcompoundtothecorrespondingalcohol.Therefore,reductionmechanismshowninFigure5(II)wasproposedinalkalinemedium.
Figure 5 (I).Reductionmechanisminacidicmedium
NH2
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
177
Org
ánic
a y
Bioq
uím
ica
Figure 5(II).Reductionmechanisminalkalinemedium
tionsareusuallydonewithσpvaluesforthecompoundsinanaromaticseries.E1/2 - σpplotsforthecompoundsunderinves-tigation are presented in Figure 6 (I) and (II). The values of specific reaction con-stant(ρ)calculatedfromtheslopesofE1/2 - σp plots are presented in Table 6.
NX N C C
C N
N
SO2
CH3
NH 2
H
O
OH- (-)
NX N C C
C N
N
SO2
CH3
NH2
O
-H2O
Chemicalcleavage
(I) (IV)
H2O
2 e-
+C C
C N
N
SO 2
CH3
NH2
O
O
(V)
C C
C N
N
SO2
CH3
NH2
O
HO
H
(VI)
X NH2NH
effect of substituents on the polarographic reduction
Heyrovsky(27) was the first man to cor-relate the polarographic behaviour of arepresentative number of compoundswith their structure. Structural correla-
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
178
Figure 6 (I) & (II). –E1/2 –σp plot of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydra-zono)-2-pyrazolin-5-one;(I):Firstwave;(II):Secondwave;Medium=Dimethylformamide(40%byvolume)
σP
-E1/
2V v
s SC
E
-0.4 -0.2 0 0.2
pH6.1
pH7.1
pH 1.1
pH5.1
X
pH3.1
pH2.1
X
pH4.1
pH8.1
(I)
X X X XX
X XX
XX
0.8
0.6
0.4
0.2
0
-E1/
2V v
s SC
E
-0.4 -0.2 0 0.2
1
0.8
0.6
0.4
0.2
pH6.1
pH7.1
pH 1.1
pH5.1
X
pH3.1
pH2.1
X
pH4.1
pH8.1
X X X XX
X X X XX
σP
(II)
table 6. Effect of pH on the reaction constant for the reduction of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-ones. Medium:Aqueous dimethylfor-mamide(40%v/v)
pH ρ value
I wave II wave
2.1 0.113 0.113
4.1 0.105 0.112
6.1 0.113 0.105
8.1 0.099 0.103
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
179
Org
ánic
a y
Bioq
uím
ica
Thediscussionoftheeffectofsubstit-uentsintermsoftheHammettequationwas possible because ∆E1/2/∆pH, 〈naandI(diffusioncurrentconstant)values(Ta-ble2)werepracticallyinthesamerangefor the entire reaction series. The val-uesoftheHammettsubstituentconstantwere taken from the literature(28).Thevaluesofρwerefoundtobeintherangeof 0.10-0.30. Positive and low values
(29)ofρindicatethatthepolarographicreduction involves a nucleophilic addi-tionofelectrontothesubstrate.Thisfactconfirms that the electron uptake process wasthepotentialratedeterminingstepinallthereductionprocessesstudied.
effect of cation on the polarographic reduction of 1-(toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-ones
Not much work is reported (30) on theeffect of cation on ρ values of the po-larographic reduction. Few studies werereportedon the reductionofbenzylidineacetone(31)andnitrobenzene(32).TheρvaluespresentedinTable7increaseswithincreaseinthesizeofcation.Thisimpliesthatthesusceptibilityfornucleophilicad-ditiondiminisheswithincreaseinthesizeofthecation.Similarresultswerereportedforbenzylidineacetones(31) and N’-Ben-zylsulfonylarylazopyrazoles(33).
table 7. Effectofcationsonthereactionconstantforthereductionof1-(Toluenylsulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-ones; pH 4.1; Medium:Aqueous dimeth-ylformamide(40%v/v)
Cation (0.1 M)
ρ value
I wave II wave
LiCl 0.212 0.231
NaCl 0.250 0.280
KCl 0.316 0.331
N (CH3)4Br- 0.403 0.387
effect of organic co-solvent on the polarographic behaviour of 1-(toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-ones
Thepolarogramsof the1-(Toluenyl sul-fonyl)-3-amino-4-(4’-substituted aryl hy-drazono)-2-pyrazolin-5-oneswererecord-edatpH4.1in50and75%v/vaqueoussolutions of dimethylformamide (DMF),dimethylsulfoxide (DMSO), acetonitrile
(CH3CN) and methyl alcohol (CH3OH).The results are presented in Table 8.These results indicate that thechange incompositionofthesolventdoesnotbringanychange in thenumberofwavesandthe shape of the polarograms. However,a change in thepositionof thewaveonthepotentialaxisandamarkeddecreaseinthediffusioncurrentwasobserved.Thedecrease in thediffusioncurrentmaybeattributedtothedecreaseintheeffectivediffusion coefficient value. This may be
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
180
duetotheincreaseintheviscosityofthesolutionor the change in the sizeof thesolvated species(34). In the presence oforganic solvents, thehalf-wavepotentialvalueswereshiftedtovaluesthataremorenegative and the magnitude of the shiftdependsonthenatureofthesolvent.Theshiftwas in theorder,DMSO<DMF<CH3CN<CH3OH,andparallelsthetrendin dielectric constant of solvents. TheobservedshiftinE1/2canbeattributedtoseveralfactorssuchasdielectricconstant,solvationofionsandadsorptionoforgan-icsolventontheelectrodesurface.
Thediffusion-controllednatureofthepolarographicwaveinthepresenceofor-ganicsolventwasevidentfromthelinearplotofHversush1/2passing throughthe
origin.The semi log plots (-EdmeVs log
ii
i
d –)werelinearandtheirslopeswere
morethanthetheoreticallyexpectedval-ues for reversible waves. This indicatestheirreversiblenatureoftheelectrodere-actioninthepresenceoforganicsolvent.This shows that the mechanism of theelectrochemicalreactionissimilareveninthepresenceoforganicsolventsalthoughamarkedshiftinthediffusioncurrentandthehalf-wavepotentialswereobserved.
effect of surfactants on the polarographic behaviour of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-one
Pyrazoles have immense medicinal andbiologicalimportanceandhenceknowl-edgeoftheeffectofsurfactantsontheirredoxbehaviouratthesolutionmercury
interfacemayproveveryusefulfromthephysiologicalpointofview(35).Theef-fectofsurfactantsonredoxbehaviourofthese compounds is of immense impor-tance since the surfactants are used asemulsifiers in drugs. Malik and Rajeev Jain1982 (36) reported that the addition of surfactants beyond the concentrationjust sufficient to eliminate the maximum hasaffectedthereversibilityoftheelec-trodereaction.
So,inthepresentstudiestheeffectofdifferentsurfactantsonthepolarographicreductionof1-(Toluenylsulfonyl)-3-ami-no-4-(4’-substituted aryl hydrazono)-2-pyrazolin-5-oneshasbeeninvestigatedinsolutionsofpH4.1.Theresultsshowthatthe reduction becomes increasingly diffi-cult and the wave height decreases withincreaseintheconcentrationofthesurfac-tants.Thehalfwavepotentialsshifttoval-uesthataremorenegativeandwasduetothepreferential adsorptionof the surfac-tant atdroppingmercuryelectrode.Thisresulted in the partial desorption of thedepolariserfromtheelectrodesurfaceandthusloweringthesurfaceconcentrationofthedepolarizer(37).Similarobservationswerereportedintheliterature(38).
concLusIon
The reduction of 1-(Toluenyl sulfonyl)-3-amino-4-(4’-substituted aryl hydra-zono)-2-pyrazolin-5-ones leads to twoirreversible and diffusion-controlled po-larographicwaves.Thekineticparametersof the electrode process were evaluatedandpresented.Theeffectofsubstituents,cations, solvents and surfactants on thereduction process were detailed. Basedontheresultsobtained,aplausiblereduc-tionmechanismwasproposed.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
181
Org
ánic
a y
Bioq
uím
ica
tabl
e 8.
Effe
cto
forg
anic
co-
solv
ento
nha
lf-w
ave
pote
ntia
l(-E
1/2 V
vs S
CE)
of 1
-(To
luen
yl su
lfony
l)-3-
amin
o-4-
(4’-
subs
titut
ed a
ryl h
ydra
zono
)-2-
pyra
zolin
-5-o
nes(
1 ×10
-3M
)atp
H4
.1.
-XD
mso
(50%
)D
mso
(75%
)D
mF
(50%
)D
mF
(75%
)c
H3c
n (5
0%)
cH
3cn
(75%
)
Iw
ave
II
wav
eI
wav
eII
w
ave
Iw
ave
II
wav
eI
wav
eII
w
ave
Iw
ave
II
wav
eI
wav
eII
w
ave
-H0.
420.
530.
620.
730.
480.
590.
680.
790.
540.
650.
750.
86
4’-C
H3
0.34
0.52
0.44
0.63
0.39
0.57
0.59
0.77
0.44
0.63
0.65
0.83
4’-O
CH
30.
350.
530.
500.
590.
400.
580.
630.
720.
460.
640.
670.
76
4’-O
H0.
350.
550.
470.
680.
410.
590.
600.
810.
470.
660.
660.
87
4’-C
l0.
270.
450.
410.
580.
330.
510.
540.
7103
90.
570.
600.
77
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
182
ReFeRences
1. Haddad,N.;Salvango,A.;Busacca,C.ApplicationofthePalladium-Cat-alyzed N-Arylation of HydrazonestoDeactivatedHeteroarylHalidesintheSynthesisofPyrazoles.Tetrahe-dron Lett.2004.45:5935-5937.
2. Bosum-Dybus,A.;Neh,H.Prepara-tion of enantiomerically pure pyr-azolines by an enantioconvergentprocess. Ann. Chem. 1991. 8: 823–825.
3. Jelich, K.; Brandes, W.; Hanssler,G.;Reinecke,P.Substitutedpyrazo-lin-5-ones, composition containing,andmethodofusingthemtocombatfungi. 1988. 06/925184.
4. Tanitame, A.; Oyamada, Y.; Ofugi,K.;Fujimoto,M.;Iwai,N.;Hiyama,Y.;Suzuki,K.;Ito,H.;Terauchi,H.;Kawasaki, M.; Nagai, K.; Wachi,M.; Yamagishi, Jun-ichi. SynthesisandantibacterialactivityofanovelseriesofpotentDNAgyraseinhibi-tors. Pyrazole derivatives. J. Med. Chem.2004.47: 3693-3696.
5. Kedar,R.M.;Vidhale,N.N.;Chin-cholkar, M. M. Synthesis of newheterocyclicsandtheirantimicrobialstudies. Orient J Chem. 1997. 13:143-148.
6. Tsurumi, K.; Abe, A.; Fujimura, H.; Asai,H.;Nagasaka,M.Generalphar-macological actions of l-(m-chloro-phenyl)-3-N,N-dimethylcarbamoyl-5-methoxypyrazole (PZ-177), Folia Pharmacol. Jpn. 1976. 72:41-52.
7. Mariappan, G.; Saha, B.P.; Suthat-son, L.; Haladar, L. Synthesys and
biological evaluation of pyrazolonederivatives.Indian Journal of Chem-istry.2010.49b: 1671-1674.
8. Kees,K.L.;Fitzgerald,J.J.;Steiner,K.E.; Mattes, J.F.; Mihan, B.;Tosi,T.J. New potent antihyperglycemicagentsindb/dbmice: Synthesisandstructure−activity relationship stud-ies of (4-Substituted benzyl)(trifluoromethyl)pyrazolesand-pyrazolones.Med. Chem. 1996. 39: 3920-3926.
9. Yukihito, H.; Daisuke, J.; Kazuaki,C.;Masao,Y.Edaravone(3-methyl-1-phenyl-2-pyrazolin-5-one),anovelfreeradicalscavenger,fortreatmentof cardiovascular diseases. Recent Patent Cardiovasc. Drug Discov.2006. 1:85-93.
10. Athina,G.;Babaev,E.;Dearden,J.;Dehaen,W.;Filimonov,D.;Galaeva,I.; Krajneva, V.; Lagunin, A.; Ma-caev,F.;Molodavkin,G.;Poroikov,V.;Pogrebnoi,S.;Saloutin,V.;Ste-panchikova,A.;Stingaci,E.;Tkach,N.; Vlad, L.; Voronina, T. Design,synthesis,computationalandbiolog-ical evaluation of new anxiolytics.Bioorg. Med. Chem.2004.12: 6559-6568.
11. Metwally, M.A.; Khalifa, M.E.;Amer, f.a. New azodisperse dyeswith 4-hydroxymethyl-2-pyrazolin-5-oneringfordyeingpolyesterfab-rics. Dyes and Pigments. 2008. 76:379-385.
12. Luminiţa, V.; Lerch-Gurguţa, R.; Badea,I;Marinescu,V.Spectralbe-haviorofanazopyrazolonicderiva-tive and its use as a new metal in-
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
183
Org
ánic
a y
Bioq
uím
ica
dicator forTi(IV).Acta Chim. Slov. 2002.49: 623-629.
13. Yang, J.G.; Ge, H. M.; Jie, N. Q.;Ren,X.Z.;Wang,N.X.;Zou,H.B.Study on the co-luminescence sys-tem of terbium - gadolinium - 4,4’-(1,6-dioxohexamethylene)bis-(3-methyl-1-phenyl-2-pyrazolin-5-one)hexcadecyltrimethylammoniumbro-mideanditsanalyticalapplications,Spectrochim. Acta, Part A. 1995.51A:185-195.
14. Zheng,Z.;Yu,Z.;Luo,N.;Han,X.Tautomerism-dependent ring con-struction of N-heterocyclic com-pounds from the reactions of 1-al-kynyl Fischer carbene complexesandsubstitutedpyrazolinones.J Org Chem. 2006. 71: 9695-9700.
15. Ravindranath,L.K.;RamaDas,S.R.;BrahmajiRao,S.Polarographicbe-haviourofarylazopyrazoles.Electo-chimica Acta.1983.28: 601-603.
16. Malik, W.V.; Goyal, R.N.; Jain, R. Polarographic reduction of somearylazopyrazoles in N,N’-dimethyl-formamide. J. Electroanal. Chem.1978.87:129-135.
17. Meites,L.PolarographicTechniques,2nd ed. New York: Interscience.1967. p. 234.
18. Meites,L.PolarographicTechniques.2nd ed. New York: Interscience. 1967. p.139.
19. Sharma, S.S.; Singh, M. Polaro-graphic studies on the influence of concentrationandnatureofdifferentsupportingelectrolytesonthekinet-
ics of irreversible electrode processofNi(II)andCo(II).J. Indian Chem. Soc.1979.56:183-191.
20. Ram, R.; Singh, M. Polarographicreduction of nitrobenzene at differ-ent temperatures. Indian J. Chem.1979.18A: 69-71.
21. DeVries,T.;Kroon,J.L.Amillicou-lometermethodforthedeterminationof polarographic n-values. J. Am. Chem. Soc.1953.75: 2484-2486.
22. Kitayev, Y.P.; Budnkov, G.K.; Nal-sora,L.I.Studyofthestructureandreactivity of nitrogen-containingderivativesofcarbonylcompounds.Izv. Akad. Nauk. SSSR, Serv. Khiw. 1967. 9:1911-1917.
23. Millefiori, S.; Campo, G. Polaro-graphicreductionofazocompounds.I. 1-phenylazo-2-naphthols. Ann. Chim., (Rome). 1969. 59:128-137.
24. Millefiori, S. Polarographic reduction ofazocompounds. II.4-phenylazo-2-naphthols., Ann. Chim., (Rome).1969. 59:138-154.
25. Cordes, B.H.; Jemcks, W.P. Themechanism of hydrolysis of schiffbasesderivedfromaliphaticamines. J. Am. Chem. Soc. 1963. 85: 2843-2848.
26. Prasad, A.R.G.; Seshagiri, V.; Ravin-dranath, L.K. Polarographic inves-tigations of certain propiophenonebenzoic acid hydrazones. Jordan Journal of Chemistry. 2011. 6: 51-64.
27. Heyrovsky, J. Polarography. Wien:SpringerVerlag.1941.p.185.
REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 40, nro. 2 DE 2011
184
28. Jaffe, H.H. A reexamination of theHammettequation.Chem. Rev.1953.53: 191-261.
29. Hammett, L.B. Physical OrganicChemistry. New York: McGraw-Hill.1940.p.184.
30. Mairanovskii, S.G. Effect of thedoublelayerstructureandofthead-sorptionofelectrodereactionpartic-ipantsuponpolarographicwavesinthereductionoforganicsubstances.J. Electroanal. Chem. 1962. 4: 161-181.
31. Sato,Polarographyofnitroandhy-drazine compounds. H. Bull. Natl. Hyg. Lab.1957.75: 58-65.
32. Holleck, L.; Becher, D. Influence of ionsof supportingelectrolyteonpolarographicreductionofaromaticnitrocompounds inacetonitrileandDMF,J. Electroanal. Chem. 1962. 4:321-331.
33. Jain,R.;Sudha,R.;Goyal,R.N.Po-larographic behaviour of some po-tentialantidiabeticbenzylsulphonyl-arylazopyrazoles,Electrochim. Acta.1981.26:1519-1523.
34. Patai, S. The Chemistry of the hy-drazo,azoandazoxygroups.London:Interscience, Part I. 1964. p. 479.
35. Pillman, B.; Pullman, A. QuantumBiochemistry.NewYork:JohnWileyand Sons. 1963. p. 202.
36. Malik, W.U.; Rajeev, J. Polarograph-icstudiesoneffectofsomeionicandnonionic surfactants on the kineticsof irreversible electrode process ofarylazopyrimidine and arylazopyr-azole. J. Indian Chem. Soc. 1982.LIX: 962-964.
37. Kastening, B.; Cartmann, H.; Hol-leck,L.Überdiewirkungsweisevoninhibitoren bei elektrochemischerreduktion organischer verbindun-gen—III. Faraday-Admittanz-mes-sungen zur ermittlung der adsorp-tionsverdrängung. Electrochemica Acta. 1864. 9:741-755.
38. Parsons,R.The effect of specific ad-sorptionon the rateof an electrodeprocess.J. Electroanal. Chem. 1969. 21:35-43.
AcRonYms
The short form ‘A-I, 4.1’ indicated in the figures, stands for ‘compound-nthwave,pH’ i.e. A represents the compound, I represents first wave and 4.1 represents thepH.