Kinetics Mechanism of Polarographic Reduction of Aromatic ...nopr.niscair.res.in/bitstream/123456789/49351/1/IJCA 22A...graphic behaviour of aromatic nitro compounds. comprehensive

Indian Journal of ChemistryVol. 22A, August 1983, pp. 664-670

Kinetics & Mechanism of Polarographic Reduction ofAromatic Nitro Compounds in Aqueous Alcoholic Medium

RAM RATAN. (Miss) RAMA RANI & MUKHTAR SINGH"

Department of Chemistry. Agra College. Agra 28~002

Recei •.ed 25 January 1983: r(,; isct! and accepted 14 April 1983

Polarographic reduction of nitrobenzene. ortho-; meta- and para- chioronitrobcnzenes. nirrotoluenes, nitro phenols andnitrobenzaldehydes has been studied in 25"" (v/v) aqueous ethanolic solutions. using Britton-Robinson (BR) butter or varyingpH values. KCI (0.1 M) has been used as the supporting electrolyte and Triton X-I 00 (0.001 ",,) as the maxima suppressor. Thepotential-dependent rate constant. kr.h has been calculated by Kouteck y's method at different pH values and the values orkinetic parameters ('1:11, and kr.hl have been calculated rromlogkr.h versus Ed., .. plots which arc linear thereby suggesting thatonly a single rate-deterrnimng step is involved in the electrode process or each dcpolarizcr. Based on the values or kineticparameter. (lna and the variation of E, 2 with pH. the stoichiometry or the rate-determining step has been established. This hasled to the postulation ofa tentative mechanism 1'01' the polarographic reduction or each dcpolarizcr. Besides. the effect or thenature and position of various substitucnts. viz. CI. CH.\. OH and CHO on the kinetics olthc polarographic reduction or NO 2

group has been investigated.

Though several workers! have studied the polaro-graphic behaviour of aromatic nitro compounds.comprehensive studies on the influence of varioussubstituents on the kinetics .and mechanism ofirreversible polarographic reduction of these com-pounds are still lacking. Therefore. a comprehensivestudy on the kinetics and mechanism of polarographicreduction of nitrobenzene. ortho-, II/('/{I- and PO/'([-

chloronitrobenzenes, nitrotoluenes, nitrophenols andnitrobenzaldehydes has been undertaken in aqueousalcoholic medium using Britton-Robinson (BR)buffers of different pH values.

Materials and MethodsNitrobenzene. «-nitrotoluene and III-nitrotoluene

(all BDH products) were dried over calcium chlorideand distilled under reduced pressure. The other solidaromatic nitro compounds. viz. 0-. 11/- and P:chloronitrobenzenes: p-nitrotoluene: 0-. 111- and P:nitrophenols: and 0-,11/- and p-nitrobenzaldehydes (all8DH products) were recrystallised from ethanolbefore use. Other chemicals used were of AR (BDH)grade.

The concentration of each depolarizer (in 25" o

ethanolic solution) was maintained at 1.0 x 10 -3 M.KCI (0.1 M) was used as the supporting electrolyte ineach case. Requisite amount of Triton X-IOO (1.0x 10 -30,,) was added to suppress the maxima. The pHvalues of the solutions were adjusted by adding BRbuffer and the pH values were measured by a PhilipsI'll-meter (PR 9404). A manual polarograph (Toshni-wal, type CL 02) in conjunction with a Scalamppolyflex galvanometer (Toshniwal. type PL 50) wasused to record the polarograms at 25 ± 0.1 C. The

664

(

d.m.e. had the following characteristics (in 0.1 M KCI.open circuit): 11/ = 2.80 mg see: t = 3.46sec: /1/1 -'1\ h

=2.44mg1 -'sec \ 1: h"",.=72.32cm.The number of electrons (II) involved in the electro-

reduction of each depolarizer was determined bymillicoulometric method of DeVries and Kroon",Knowing the value 01'11. the Ilkovic equation was used:'to calculate the value of D for the depolarizers atdifferent pH values. The current and potential werecorrected for residual current and iR-drop of the cellrespectively. The drop time (I) varied with the appliedpotentiaL but for the calculation of kinetic parameters.its value corresponding to the instant when the wave isjust levelling off has been used":". Throughout themeasurements the current at the end of the drop lifewas recorded instead of the average because thedetermination of kinetic parameters was based on theKouteckys":" calculations which are more accuratelyreproduced by measuring the maximum currents.

Results and DiscussionNitrobenzene. 0-. 11/- and p-nitrotoluenes

These nitro compounds give two waves at pH:::;3.85. At higher pH (~5.65) a single wave is obtained.At all pH values the waves are well-defined.Millicoulometric studies indicate that the first wavecorresponds to a four-electron reduction process whilethe second one corresponds to two-electron reductionprocess. At pH ~ 5.65 four electrons are involved in thereduction process.

[J. , m- and p-chloronitrobenzenesUnlike nitrobenzene .. 0-. /11- and p-chloronitro-

benzenes give a single well-defined wave in the pH

RAM RATAN et al: POLAROGRAPHIC REDUCTION OF AROMATIC NITRO COMPOUNDS

range 1.81-11.00. Millicoulometric studies indicatethat four electrons are involved in the reductionprocess.

0-, 111- and p-nitrophenolsLike nitrobenzene the reduction of 0-, /11-and p-

nitrophenols occurs in two steps at pH < 5.65 involvingfour-electron and two-electron reduction processes. Inall six electrons are involved in the overall reductionprocess at lower pH values. At pH?- 5,65 111-

nitrophenol behaves like nitrobenzene giving a singlewave involving four electrons. However. 0- and P:nitrophenols are reduced in a six-electron reductionprocess. The para-isomer differs from the ortho-isomerin that it gives two steps at these pH values involvingfour and two electrons respectively.

0-, /11-and p-nitrobencaldehydesThe first step in all the three isomers is a four-

electron reduction process, representing the reductionof the nitro group to the hydroxylamine derivativesince the half-wave potentials are of the samemagnitude as those obtained with nitrobenzene. Thesecond step obtained in the case of Or/I/O-isomer at pH~ 3.85 and that in the case ofp({/'{/-isol1ler at pH ~ 6.90,represent a combination of the reduction ofphenylhydroxylamine to the amine and the reductionof the aldehyde group apparently to the carbinol sincea total of four electrons are involved in each case asrevealed by millicoulornctric study, The behaviour ofl11-isomer differs from that of Ii- and p-isomers in thatat pH ~ 2.21 three steps are obtained. The first one is afour-electron reduction process corresponding to thereduction of nitro group. The second step is a two-electron reduction process representing the. reductionof the phenylhydroxylarnine to the amine. This isfurther supported by the fact that the half-wavepotential of this step is almost similar to the half-wavepotential of the second step of nitrobenzene. The thirdmore negative step corresponds to the two-electronreduction process of aldehyde group to the carbinol.At pH?- 3.85 the second step which is a two-electronreduction process represents the reduction of thealdehyde group to the carbinol. Same is the case withthe ortho-isomer at pH ?- 5.65. In the case of p-isomerthree steps are obtained atpH ?-9.35. The first step is afour-electron reduction process corresponding to thereduction of nitro group to phenylhydroxylamine. Thesecond step which is a two-electron reduction processcorresponds to the reduction of aldehyde group tocarbinol. The third step which is also a two-electronreduction process may be attributed I to some sort ofsecondary reactions between the groups within themolecule, after the second step and reduction of theresulting products.

(

Diffusion-controlled nature of' the polarographic 1t'Gi'esThe wave-heights of all the steps are diffusion-

controlled for all aromatic nitro compounds atdifferent pH values. This is supported by the fact that idversus h~o;r and i" versus C plots are linear and passthrough the origin.

Nature of' the polarographic reduction of thedepolarizers at different p H rclues

The various criteria IV I J of irreversibility indicatethat the polarographic reduction of aromatic nitrocompounds under study is irreversible.

Kinetics and mechanism ofpolarographic reduction0/ aromatic nitro compounds

It is well known I that the aromatic nitro compoundsare reduced at d.rn.e. in a four-electron step to affordphenylhydroxylamine. In an acid medium thephenylhydroxylarnine is reduced further to anilinegiving a second wave. In the alkaline medium,depending upon the strength of the base, thephenylhydroxylarnine docs not undergo furtherreduction but may. under the influence of the alkali,form condensation products which are electro-reducible. Exceptionl.l+ to this generalization are (1-,

and p-nitrophenols. which form phenyl hydroxylaminethat can be converted into reducible quinonoid forms,which are reduced to the substituted anilines in neutraland alkaline media.

Based on these observa tions a nd a lso on the valuesof the kinetic parameters of the irreversible electrodereactions of the above mentioned nitro compounds, atentative mechanism can be put forward for thepolarographic reduction of these compounds.

Nitrobenzene, 0-. /1/-. p-nitrotoluenes. nitrophenolsand chloronitrobcnzenes

Kinetics of electrode reactions of the abovedepolarizers has been studied as a function of pH. Theplots of log kr.h versus Ed." at different pH values arelinear. This showsl5.

16 that there is only one rate-determining step involved in the electrode reaction.The values of kinetic parameters ('l.na and kuJ for boththe reduction steps are listed in Tables I and 2. Anattempt to estimate l1a (the number of electronsinvolved in the rate-determining step) apparently leadsto a conclusion L5.17 that lIa is equal to 2 because fortotally irreversible systems. as the present ones are, 'l.

should be less than 0.5. However. according toMeites 10 only a single electron can be transferred at atime during the course of an electrode reaction.Therefore, a value of lIa exceeding I implies thatsuccessive steps are too nearly simultaneous to bedistinguished on the time scale implicit in thepolarographic measurements. Similarly, a perusal of

665

INDIAN J. CHEM .. VOL. 22A. AUGUST 1983

Table I-Kinetic Parameters (~na and k?.J for theElectrode Reaction of Nitrobenzene in

25% (v/v) Ethanolic SolutionspH 7:na k?h (em/see)

1 step ll step 1 step Il step1.81 0.71 0.52 1.4 x 10-5 3.2 X 10-5

2.21 0.72 0.60 5.2 x 10-5 3.1 x 10-63.85 0.70 0.66 3.6 x 10-5 8.9xI0-9

5.65 0.66 1.2 x 10-6

6.90 0.77 5.8 x 10-69.35 0.64 1.8 x 10 7

10.10 0.53 8.7 x 10-7

11.00 0.48 l.4xlO-7

ana values for the second step shows that l1a can betaken as equal to 2. A perusal of £1 2values shows that£1/2 of both the reduction steps get shifted to morenegative potentials. The £1 2 versus pH plots for boththe steps are linear. The value of p. i.e. the number ofH + ions involved in the rate-determining step. can beobtained from the relation (I)

d£1/2= _0.059J.2p(at 25 C)(~H) alia

Thus. from the slope of £1 2 versus pH plots thevalue ofp can be determined provided that the value ofana is constant throughout the pH range studied.According to Meites 1 M. for the elucidation of thestoichiometry of the rate-determining step associatedwith a totally irreversible wave. xn, must be constantand independent of the experimental conditions. As 11"is equal to 2 in the entire pH range. the change in thevalue of product :Xlla with pH shows that it is "1.. thetransfer coefficient. which is changing with the changein the pH. Thus. it follows that the change in £11 maynot be entirely due to the change in pH of the mediumbUI may also be due to a change in transfer coefficient(a) of the electrode reaction of the depolarizer.Therefore. a correction for the variation in transfercoefficient is necessary. This can be done by

... (1)

considering!" the variation of:xE 1 2 with pH. With thismodification Eq. (I) takes up the form:

d("1.EI22=_0.05915 ( ?5C)d(pH) II. P at z ... (2)

From this equation it follows that a plot of 'loE 1 2 versus

H h Id b I·' . h 1 0.05915 Thi hp s ou e inear wit a s ope. - p. IS aslIa

been actually observed. In this way the value of p canbe obtained since n, is equal to 2. This has been foundto be I in each case except for p-nitrophenol where it isequal to 2 for the second step at pH ~ 5.65.

Having thus established the stoichiometry of therate-determining step. i.e. II" = 2 and H + = I (for P:nitrophenol, P = 2 for second step at pH ~ 5.65).mechanisms can be suggested for the polarographicreduction of the aromatic nitro compounds underin vestiga lion.

0-. 11/-. p-JlirfOf.O/II£'II£'S. nt-nitrophenol and 0-. P:nitropheuols at pH < 5.65 follow a mechanism similarto that of nitrobenzene. shown in Scheme I. Themechanism of reduction of o-nitrophenol at pH ~ 5.65is shown in Scheme 2 and that of p-nitrophenol at pH~ 5.65 is shown in Scheme 3.

M cchau ism o! rcduct ion o]' 0-. /1/- andp-chloron i r ro/J£'II ::£'11£'.1

Unlike nitrobenzene. isomeric chloronitrobenzenesgive only one wave in the entire pH range (1.81-11.00).This type of behaviour may be attributed to thepresence of chloro group which shows '" a ( + 7) and (-!) effect. Since chloro group has three unshared pairsof electrons it is most likely that ( + 7) effect wouldoverweigh the (-!) effect thereby resulting into anincrease of electron density around the nitrogen ofnitro group. Consequently the reduction of nitrogroup into - NHOH group becomes difficult. Sincethe nitrogen in - NHOH group has still high electrondensity its further reduction to corresponding anilinedoes not take place and thus the reduction stops at- NHOH. Therefore, only one reduction step appears

SECOND STEP

N=O NHOH

,.,6"" 2e,2H+ ,.,6""§ Fast h

NHDH ~H20H NH2

~----~F:-:-t--~"'~--~~~::-:-+----~"'~666

/

Scheme 1

RAM RATAN et al.: POLAROGRAPHIC REDUCTION OF AROMATIC NITRO COMPOUNDS

Scheme 2

FIRST STEP

SECOND STEP

---::R-"-Q-~-:-':g,-o••-m-••-n-I---' ¢-u

aScheme 3

2".21-1+----_.Slow ~Q

01-1

Table 2 Kinetic Parameters (:XIIa and k:\) for Electrode Reactions of (/-. 11/- and p-Chloronitrobcnzencs. Nitrotolucncs,Nitrophcnols and Nitrobenzaldchydes in 25"" (v v) Ethanolic Solutions

pH 'or/I/O-Isomer III.'ICI-isomer Illlfa-lsomer

':1.11 •• k:·'.l1 1..11 •• /.;:.I.h 1..1I;t ,,"Lh(em see) (em see) (em see)

Chloronurobcn/cnc1.81 0.63 2.2 x 10 "

O.N( ~.h x 10 '" O.M '.1.'.1x 10 "2.21 0.65 2.5 x 10 " 0.70 '.1.4 x III " 0.67 70xl()

"US 0.56 5.1 x 10 I! 0.65 I.X x I() '0 0.60 7.7xlO I'5.65 0.5'.1 4.0 x 10 '0 O.M 8.7 x 10 '0 0.61 4.'.1 x 10 '06.'.10 0.52 t« x 10 " 0.65 '.1.'.1x 10 '" 0.57 5.8 x 10 ,09 ..15 0.47 UxlO " 0.60 7.7xlll "

0.4'.1 4.5 x III "10.10 0.44 LX x 10 '0 0.51 1.'.1x 10 " 0.48 2.6 x 10 ,011.00 0.41 1.6 x 10 4 0.46 h.1 x 10 '. 0.43- 1.8 x 10 '.

Nitrotoluenc1.81 I 0.65 1.2 x 10 " 0.69 6.9 x 10 " 0.67 4.2 x 10 h

II 0.42 4.2 x 10 " 0.4t< 8.~ x 10 " 0.44 6.1 x 10 "2.21 I (l.67 4.7 x 10 " 0.70 7.8 x 10 h 0.68 6.7 x 10 (,

II 0.51 6.3- x 10 0.56 1.1 x 10 " 0.54 10.0 x 10,

U5 I 0.6.1 5.6 x 10-h 0.69 9.2 x 10 " 0.66 7.1 x 10 "II 0.54 1.7 x 10 " 0.62 7.6 x 10 4 0.59 5.4 x 10 "

5.65 I 0.52 4.1 x 10 0.59 8.9 x 10 0.56 R.7xlO- -

6.'.10 0.56 8.2 x 10 " 0.65 9.6xI0- - 0.60 ~.I x 10 "9.35 0.53- 8.0 x 10-" 0.61 0.8 x 10-- 0.57 9.4 x 10 "

10.10 0.~9 7.2 x 10-8 0.52 I.lxiO-' 0.50 9.0 x 10 "11.00 0.42 9.1 x 10 ~ 0.47 4.4xI0-8 0.44 1.1 x 10 "

Nitrophenol1.81 I 0.72 3-.7x 10-; 0.61 U x 10-5 0.46 1.0 x 10 5

II 0.65 5.2xI0-5

2.21 I 0.75 8.1 x 10-; 0.52 4.2 x 10-5 0.50 3.0 x 10II 0.61 6.1 x IO-h

3-.85 I 0.77 7.4xI0·5 0.43 2.3 x 10-5 0.33 1.1 x 10 5

II 0.68 9.3xI0-"5.65 I 0.72 4.Jx 10 h 0.41 1.0 x 10-· 0.39 6.8 x 10

II 0.64 8.0 x 10 q

C(III/(/

667

(

INDIAN J. CHEM .. VOL. 22A. AUGUST 1983

Table 2-Kinetic Parameters (':1.11. and k?J for Electrode Reactions of 0-.1/1- and p-Chloronitrobenzenes. Nitrotoluenes.Nitrophenols and Nitrobenzaldehydes in 250

0(v v) Ethanolic Solutions-Collid.

pH ortho-Isomer meta-Isomer para-Isomer

':1.11, kO 111• kO 111• kP.hr.h f.h

(em/see) (em see) (em see)

Nitrophenol6.90 0.80 9.2 x IO-6 0.49 8.1 x 10 - O.-D 7.0 x 10 s

9.35 I 0.68 4.7 x 10,

0.63 3.7xIO-" 0.61 2.5 x 10 II

II 0.49 8.8 x IO -1.\

10.10 I 0.64 9.8xI0-' 0.52 9.2xI0-" 0.50 3.7 x 10 I'

II 0.47 1.0 x 10 I'

11.00 I 0.50 6.1 x 10 7 0.47 2.2 x 10 I' 0.44 1.6 x 10 I.'

II 0.67 1.5 x 10 I:;

Nitrobenzaldehyde1.8 I I 0.76 6.3 x 10 • 0.73 1.1 x 10 . 0.75 2.3 x 10 •

II 0.61 9.1 x 10 5 0.49 5.9 x 10 ; 0.50 7.R x 10 ;

III 0.74 1.1 x 10 IJ

2.21 I 0.78 10.0 x 10 .• 0.74 1.2 x 10 • 0.76 9.7 x 10 4

II 0.69 9.2 x 10 h 0.62 7.1 x 10 h 0.64 8.2 x 10 ,.III 0.69 1.0 x 10 14

3.S5 I 0.77 5.6 x 10 • 0.72 3.8 x 10 on 5.2 x 10 4

II 0.84 1.3 x 10 ,0.73 5.1 x 10 x 0.76 7.~ x 10 "

5.65 I 0.78 9.5 x 10 5 0.6X I.X x 10 h 0.70 6.7 x 10II 0.81 6.3 x 10 If) 0.76 ~.I x 10 10 O.XO 3.2 x 10 1(1

6.90 I 0.83 7.2 x 10,

0.7X 6.2 x 10 h 0.81 5.2 x 10,

II 0.88 7.2 x 10 II 080 1.6 x 10 " 0.81 1.8 x 10 "9.35 I 0.80 X.Xx 10 h 0.65 6.7 x 10 h 0.76 X.6 x 10 h

II O.XO 6.6 x 10 " 07X 1.lxlO-" 0.79 4.7 x 10 "III 0.84 5.1 x 10 It,

10.10 I 0.79 9.7 x 10 -, 0.65 9.0 x 10- 0.68 9.1 x 10II 094 3.7xlO-" 0.X4 2.6xIO-'J O.R6 5.6 x 10 IJ

III 0.90 7.3 x 10 '"11.00 I 0.75 5.8xIO-' 0.60 ~.O x 10- O.M 3.1 x 10

II 0'>0 1.5 x 10-" 0.81 3.6 x 10 -1.\ (UD 5.9 x 10 1.\

III " " 1.19 1.3 x 10- 1'1" "

in the entire pH range. Thus the reduction of all thethree isomers is analogous to the first step reduction ofnitrobenzene (see Scheme I).

0-. 11/- and p-nitrobcnzaldehvdesFrom the values of 7.11, (Table 2) in respect of

different reduction steps of 0-. 111- and 1'-nitrobenzaldehydes it may be concluded that II, isequal to 2 in each case. From the plots of 'Y.El 2 versuspH it is inferred that P is equal to I in each case. Havingthus established the stoichiometry of rate-determiningstep vis-a-vis the nature of reduction steps of isomericnitrobenzaldehydes in different pH range. mechanismscan be suggested for the polarographic reduction ofnitrobenzaldehydes. o-Nitrobenzaldehyde undergoesreduction by the mechanism shown in Scheme 4. Thefirst step polarographic reduction of III-nitrobenzalde-hyde is like that ofo-nitrobenzaldehyde. The reductionof second step at pH ~ 2.21 is similar to that ofnitrobenzene. while at pH ?-:3.85 it is similar to that ofsecond step of o-nitrobenzaldehyde at pH?-: 5.65. Thethird step reduction is similar to that of the second

668

!

reduction step of II-nitro benzaldehyde at pH ~ 3.85after the uptake of two electrons i.e. beyond theformation of amino derivative. The first steppolarographic reduction of p-nitrobenzaldehyde is thesame as that of the first step of «-nitrobenzaldehyde.The second step reduction at pH ~ 6.90 is similar tothat of second reduction step of o-nitrobenzaldehydeat pH ~ 3.85 while at pH ?-:9.35 it is similarto that of 0-

nitrobenzaldehyde at pH ?-:5.65.

Effect or nature and POSiliOIl or carioussubstituents Oil the kinetics ofthe polarographicreduction ofnitro group

(i) CI group-From Table 2 it is clear that the valueof ki.h for the first reduction step of ortho-, meta- andpara-chloronitrobenzenes is less than that ofnitrobenzene (Table I) in the entire pH range studied.From this it is inferred that the reduction of nitrogroup becomes difficult as a result of the introductionof the CI group at ortho, meta and para positions. Thisconclusion is in agreement with the theoreticalpredictions made on the basis of( + nand ( -I) effects.

RAM RATAN et al.: POLAROGRAPHIC REDUCTION OF AROMATIC NITRO COMPOUNDS

NHOH

~/CHO

OJ

SECOND STEP I pH:::] ~S;

~ECONO STEP I pH ~ S 6S1

NHOH10/<: z. H'~;r - Slow

A comparison or kl,h values for the first reduction stepor the three isomeric chloronitrobcnzencs shows thatthe ease of reduction at the d.m.e. is in the followingorder: meta >para> ortho.

(ii) C H 3 grollp - Methyl group only exhibits a ( + I)effect which again is most pronounced ifpresent in theortho and para positions to the nitro group. Inagreement with this. the meta isomer should be theeasiest to reduce ". This theoretical prediction isconfirmed by the value of f.;I.hcalculated for the firstreduction step of the isomeric nitrotoluenes. The orderof f.;r.hvalues for the three isomers is in the order: nteta>para >ortho, The value off.;I.h for the first reductionstep of nitrobenzene is less than those for thenitrotoluenes at different pH values, This shows thatthe reduction of nitro group at d.m.e becomesditficuhif CHJ group is present alongwith.

(iii) OH grollp- A comparison of kl.h values for thefirst reduction step or the three isomeric nitrophenolsshows that the order of ease of reduction of threeisomers is: 01'///0>meta >para. This is in accord withthe theoretical consideration. From Table 2 it isevident that the values of f.;f.h for the first reductionstep of 11/- and p-nitrophenols are smaller than that ofnitrobenzene in the entire pH range (1,81-11.00) whilethat of o-nitrophenol is greater than that ofnitrobenzene. This shows that the reduction of nitrogroup becomes difficult due to the presence of OHgroup in mew and para positions while it is facile whenOH group is present in the ortho position.

(iv) CHO grollp -A perusal of Table 2 shows thatthe values of k I.h for first reduction step of the isomeric

(

NHOH

&CHZOH

I"-0

',c·rn.- I.

nitrcbcnzuldehydc , are greater than that ofnitrobenzene in the entire pH range (1,81-11.00). Thisshows tha t the reduction of nitro group becomes easierdue to the presence of -CHO group in differentpositions with respect to nitro group. Further, acomparison of "r.h values for the first reduction step ofthe isomeric nitrobcnzaldehydcs shows that the orderof ease of reduction at d.m.e. is: ortho >para> meta, inaccord with the theoretical consideration.

ReferencesI KohhofT I M & Linganc J J. PIJ/Clmgral'itr. Vol. II Ilntcrscicncc.

New York) 1905. 74X,

~ DeVries T & Kroon J L J Alii chcm Soc. 75 (1'i53) 24X4,

.< Delahay P. ,V<'II' instrumcntol nrc! hods ill electrochemistrv(Intcrscicnce. New York) 1954. gl.

4 Jha S K. Jha S & Srivastava S N. Z N{/wr/i)l'Sch.30b(I975)X59,

5 Jha S K.lha S. Khatri J C & Singh M.lndi{/nJ Chem, ISA (1974)IR4,

6 Koutecky J. Chern Listv. 47 (1953) 323: Colin Czech ChemCOIIIIIIIII/. 18 (1953) 597,

7 Kouteck y J & Cizek J. Col/II Czech Chern Commun, 21 (1956) 836,

8 Meites L. Polarographic techniques (I nterscience, New York)1965. 241.

9 KolthotT I M & Lingane J J. Polarographv Vo!.11 (Interscience.New York) .1965.756,

10 Meites L. Polarographic techniques (Interscience. New York)1965. 246,

II Goto R & Tachi I. Pror lnt ernl Polarogr Congr, Prague. Vo!.1.(1951) 69.

12 Delahay P. J Alii chem Soc. 73 (1951) 4944: 5219,13 Kivalo P. Oldham K B & Laitinen H A, J Alii chem 50('. 7S( 1953)

4148,

J 4 Astle M 1 & Cropper W P. J Alii CIIl'1II Soc. 65 (1943) 2395,15 Vijaylaksharnma S K & Subrahmanya R S. J electroanat Chenr.

23 (1969) 99.

669

INDIAN J. CHEM .. YOL. 22A. AUGUST 1983

16 Gupta S L & Kishore N. Indian J Ch(!lII. 9 (1971) 236.

17 Krishna. Varshney A. Dubey M C & Jha S K. J Indian ch(,111SOl'.57 (1980) 658.

18 Meites L. Polarographic techniques (Interscience. New York)1965.248.

19 Vlcek A A. Progress ill inorganic chemistrv. Vo15. edited by FAlbert Colton (Interscience, New York) 1963. 241.

670

I

20 Kolthoff I M & Lingane J J. Polarographv. YollI (Interscicncc.New York) 1965.632.

21 Kolthoff I M & Lingane j J. Polarography. v-in (Intcrscience.New York) 1965. 63 I.

22 Jayadevappa E S. Indian J Ch(,lII. 7 (1969) 1146.23 Prakash R. Kalia R K & Verma R S. Proc Indian Acad Sci. 84A

(1976) 64.24 Semerano G & Capitanio V. Gaz: Chilli iial. 70 (1940) 490.