Indian Journal of ChemistryVIII. 18A, November 1979, pp. 408·411

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Studies on Polarographic Maxima of 0-, m & p-Nitrotoluenes &Their Suppression by Some Ionic & Non-ionic Surfactants

GITA RAM & MuKHTAR SINGH.Chemistry Department, Agra College, Agra

Received 15 July 1978; revised 23 November 1978; accepted 17 April 1979

The role of some ionic and non-ionic surfactants in the suppression of polarographic maxima of 0-, m- andp-nitrotoluenes has been studied. It has been observed that all types of surfactants (anionic, cationic and non-ionic)suppress these negative maxima, the cationic surfactants being the most effective. Their characteristic properties,viz., maximum suppression point (m.s.p.), specific suppression coefficient (s.s.e.j and critical micelle concentration(e.m.c.j have been determined. On the basis of (m.s.p.) values, the order of the relative efficacies of cationic, anionic andnon-ionic surfactants has been established.

NITRO compounds exhibit maxima in theirreduction waves'. However, data on the. effect of ionic and non-ionic surfactants onthe maxima of aromatic nitro compounds are sparse.Lal and Srivastava 2 have studied the effect of someionic and non-ionic surfactants on the maximum ofnitrobenzene but no work seems to have been doneon nitrotoluenes. A polarographic study on the0-, m- and p-nitrotoluenes (in 25 % ethanol in finalsolution) has been undertaken and the results arepresented in this paper. Since all organic reductionprocesses at d.m.e. involve the participation of H+ions, it is essential to work in solutions which arewell buffered. Therefore, the present study has beendone in the presence of Britton-Robinson buffer(BR buffer). Effect of increasing concentrations ofionic and non-ionic surfactants on Emax, imax,E1/2 and id has been studied. The characteristicproperties, viz. maximum suppression point" (m.s.p.),specific suppression coefficient! (s.s.c.) and criticalmicelle concentration" (c.m.c.) of the surfactantshave been determined and their correlation with therelative efficacies of the surfactants in the suppressionof the maxima has been studied. Effect of hydro-carbon chain length (polar head remaining the same)of cationic and anionic surfactants in the suppressionof the maxima has also been studied.

Materials and MethodsThe following surfactants have been usedCationic: Lauryl pyridinium chloride (LPC),

cetyl pyridinium chloride (CPC) , cetyl dimethylbenzyl ammonium chloride (CDBAC), lauryl pyridi-mum bromide (LPB), tetradecyl pyridinium bromide(TDPB), cetyl pyridinium bromide) (CPB) and cetyltetramethyl ammonium bromide (CTAB).

Anionic: Manoxol-IB, Manoxol-O'I', sodiumlauryl sulphate (SLS), dodecyl benzene SUlphonate(DBS), Tergitol-7, XL-Anionic and methyl red{sodium salt).

Non-ionic: Gelatin, Triton X-lOO, 2-ethyoxye-thanol; ethyldigol and Decon-90.

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0-, m- and p-Nitrotoluenes were BDH products ofhigh purity and were recrystallised before use. Thesurfactants used were also of high purity. Theconcentration of each of the depolarizers was main-tained at 1.0 x 10-3 M in 25 % ethanol solutioncontaining the appropriate amounts of the consti-tuents of BR buffer of pH 7. All the solutions wereprepared in doubly distilled water. A manual polaro-graph (Worseley Lane's) in conjunction with a Pyegalvanometer was used for recording the potentialand current values. Deoxygenation of the sampleswas done by a continuous flow of purified hydrogen".The polarograms of the solutions were taken at 25±0.10 in the presence of varying amounts of surfac-tants. The dropping mercury electrode (d.m.e.)had the following characteristics (in 0.1 M KCI,open circuit) : m= 1.892 mg/sec; t=3.08 see; m2/3r1/6= 1.845 mg2/3 sec.-1/2; hcorr = 72.0 em.

The number of electrons (n) involved in the electro-reduction of each depolarizer was found to be 4 atpH 7 as determined by the millicoulometric methods,Knowing the value of n, Ilkovic equation was used tocalculate the value of D in each case. The relativevalues of imax (in p.A) for the maxima of 0-, m- andp-nitrotoluenes in BR buffer of pH 7 are 28.70, 40.18and 44.69 respectively. The corresponding valuesof -Emax (in V versus S.C.E.) are 0.74, 0.76 and0.76 respectively. The other experimental data havebeen presented in Tables 1 and 2.

Results and DiscussionUnder the chosen experimental conditions 0-, m-

and p-nitrotoluenes yield sharp maxima which lieat -0.74 V, -0.76 V and -0.76 V (vs. S.C.E.)respectively from the potential of the electrocapillaryzero, which is -0.40 V (S.C.E.). These maximaare of negative polarity". Under the same experi-mental conditions the relative heights of the maximaare in the following order: p-Nitrotoluene>m-Nitro-toluene> 0-Nitrotoluene.

Effect of the concentration of surfactants onEmax, imax, E1/2 and id - The effect of increasing

GITA RAM & MUKHTAR SINGH: POLAROGRAPHY OF 0-, m & p-NITROTOLUENES

TABLE1 - EFFECTOFIONICANDNON-IoNIC SURFACTANTSONTHEMAXIMAOF0-, m- ANDp-NITROTOLUENESINBR BUFFEROR pH 7

o-Nitrotoluene m-Nitrotoluene p-Nitrotoluene

[Surf] -Emax imax [Surf] -Emax imax [Surf.] -Emax imax

(M) (V) (IL A) (M) (V) ( ILA) (M) (V) (IL A)(SC.E.) (S.CE) (S.C.E)

Cationic[LPC] x 10·

0.4 0.74 26.65 0.2 0:711 36.08 . 0.4 0.74 38.955.0 0.63t 13.53* 6.0 0.555t 13.94* 10.0 0.635t 14.76*

[CPC] X 10'0.4 0.74 25.83 0.2 0.74 33.21 0.2 0.73 40.183.0 0.630t 13.53* 4.0 0.55ot 13.53* 6.4 0.635t 15.17*

[CDBAC] X 10'0.2 0.74 25.42 0.2 0.73 32.80 0.2 0.72 38.132.6 0.623t 13.94* 3.2 0.550t 13.94* 4.8 0.640t 14.76*

[LPB] X 10'0.4 0.74 27.06 0.2 0.74 36.49 0.4 0.75 42.235.8 0.624t 13.53* 6.4 0.556t 14.35* 12.0 0.645t 15.48'"

[TDPB] X 10'0.4 0.74 26.24 0.4 0.74 35.26 0.2 0.75 42.234.0 0.62t 13.94* 5.0 0.556t 14.35* 10.0 0.640t 15.17*

[CPB] X 10' ,0.4 0.70 27.06 0.4 0.72 32.80 0.2 0.74 40.183.2 0.629t 13.94* 4.8 0.559t 13.94* 8.0 0.648t 14.76•••·

[crAB] X 10'0.2 0.74 26.65 0.2 0.73 32.20 0.2 0.74 37.312.0 0.630t 13.94* 3.0 0.566t 14.35'" 4.0 0.640t 14.76•••.·

Anionic[Manoxol-IB] X 10'

0.2 0.73 27.06 0.2 0.74 35.26 0.5 0.74 36.902.0 0.632t 14.35* 3.2 [0.554t 13.94* 8.0 0.64t 14.16·

[Manoxol-OT] X 10'0.2 0.74 26.24 0.2 0.74 31.16 0.3 0.75 40.18·1.6 0.630t 13.53'" 2.4 0.558t 14.35* 4.8 0.638t 1~.17*

[SlS] X 10'37.310.4 0.74 25.83 0.4 0.74 34.44 0.4 0.74

4.0 0.624t 13.94* 5.0 0.560t 14.35* 8.0 0.634t 14.76·[DBS] X Ie'

0.2 0.74 27.88 0.4 0.72 32.80 0.8 0.75 38:953.2 0.635t 14.35* 4.8 0.560t 13.94* 7.2 0.633t 14.35*

[Tergitol-7] X 10·0.750.2 0.73 27.06 0.4 0.74 31.16 0.5 37.72

3.2 0.630t 13.53* 4.0 0.564t 14.35* 6.4 0.630t 14.76·**[XL-Anionic] X 10'

0.8 0.73 26.65 0.4 0.73 35.26 0.4 0.75 3Q.776.4 0.630t 13.94* 8.0 0.56t 1435* 10.0 0.647t 15.17·

**[Methyl red] X 10·0.[ 0.72 27.06 0.2 0.74 29.93 0.2 0.74 38.541.0 0.634t 13.53* 2.0 0.570t 13.94* 4.0 0.635t 14.76*

Non-ionic**[Gelatin] X 10

1.0 0.74. 26.24 1.0 0.73 32.80 2.0 0.74 34.0310.0 0.62Ot 13.94* 12.0 0.550t 14.35* 20.0 0.630t 14.76*

**[friton X-I00] 10'1.0 0.73 25.42 1.0 0.74 36.90 0.8 0.73 36.49

10.0 0.6 13.9'4* 16.0 0.554t 14.35* 10.0 0.637t 15.17***[2-Ethyoxyethanol] X 10!

0.2 0.74 28.29 0.4 0.74 32.39 '0.5 0.74 40.182.0 0.620t 13.94* 4.0 0.535t 13.94* 20.0 0.630t 15.58*

**[Ethyldigol] X 1032.0 0.73 25.42 2.0 0.73 32.80 4.0 0.74 36.90

16.0 0.62Ot . 13.53* . 20.0 0.550t 14.35* . 80.0 0.642t . 14.76***[Decon-90] lOx'

0.2 0.73 27.06 1.0 0.74 37.42 2.0 0.75 ·38.5415.0 0.620t 13.94* 20.0 0.546t 14.35* 40.0 0.635t 15.17* .

*Denote th

INDIAN J. CHEM., VOL. 18A, NOVEMBER 1979

TABLE2-m.s.p., s.s.c. ANDc.m.c. VALUESFORIONICANDNON-IONICSURFACTANTSFORTHEMAXIMAOF0-, m- ANDp-NITROTOLUENES

o-Nitrotoluene m-Nitrotoluene p-Nitrotoluene

m.s.p. s.s.c. c.m.c. m.s.p, s.s.c. c.m.c. m.s.p. s.s.c. c.m.c.X 10· x 10· X 10· X 10" X 10" X 10· X 10· X 10· xl0·(M) (M) (M) (M) (M) (M) (M) (M) (M)

0.0050 0.0015 0.00135 0.0060 0.00160 .0.00107 0.01000 0.00120 0.001070.0030 0.0010 0.00087 0.0040 0.00090 0.00076 0.00640 0.00064 0.000620.0024 0.00075 0.00065 0.0032 0.00084 0.00069 0.0048 0.00040 0.000470.0058 0.0025 0.00182 0.0064 0.00160 0.00143 0.01200 0.0040 0.003020.0040 0.0016 0.00158 0.0050 0.00160 0.0010 0.01000 0.00320 0.001480.0032 0.0012 0.00115 0.0048 0.00120 0.00092 0.0080 0.00160 0.001070.0020 0.00080 0.00077 0.0030 0.00060 0.00060 0.0040 0.00120 0.00074

200.0 75.0 59.6 320.0 50.0 42.2 800.0 160.0 158.01.6 0.5 0.4 2.4 0.7 0.6 4.8 0.8 0.6

40.0 16.0 12.6 50.0 15.8 12.6 80.0 10.0 9.832.0 12.0 10.6 48.0 12.4 10.2 72.0 16.0 12.33.2 0.6 0.5 4.0 12.0 1.0 6.4 1.3 1.2

64.0 32.0 20.9 80.0 24.0 18.6 100.0 12.0 11.510.0 5.0 4.5 20.0 7.0 6.8 40.0 8.0 6.5

10000 5000 4000 12000 3800 3240 20000 3400 32401000 150 110 1600 300 300 2000 280 260

20000 9500 5620 40000 16000 11200 40000 20000 2000016000 8000 5000 20000 1000 6170 80000 20000 155001500 2.50 110 2000 800 410 4000 1000 560

Surfactant

CationicLPCCPCCDBACLPBTDPBCPBCTAB

AnionicManoxoI-IBManoxol-OT

SLSDBS

TergitoI-7*XL-Anionic

*Methyl red

Non-ionic*Gelatin*Triton X-1OO*2-Ethoxyethanol

*EthyldigoI*Decon-90

*Concentrations expressed in percentage.

concentrations of cationic, anionic and non-ionicsurfactants on Emax, imax, Ell 2 and id of the maximaof 0-, m- and p-nitrotoluenes has been studied. InTable 1, only the initial concentration at which maxi-ma appear and the concentration at which these disap-pear have been mentioned. It is found that Emax ofall the three maxima gets shifted to less negative poten-tials (positive shift) as the concentration of cationic,anionic and non-ionic surfactants is increased.

The decrease in the value of imax from the stagewhen no surfactant is present to the point just pre-ceding the elimination of the maxima is different forthe three isomers. This decrease in imax is in thefollowing order : p-Nitrotoluene> m-Nitrotoluene> o-Nitrotoluene.

A negative shift in El/2 of all the three isomerstakes place with the addition of surfactants beyondthe stage of the suppression of the maxima. Thevalue of t« tends to decrease with the increasing con-centrations of the surfactants beyond the stage of justsuppression. These effects indicate the inhibitionsof the electrode processes of 0-, m- andp-nitrotoluenesby thesurfactants.

Characteristic properties of surfactants vis-a-vistheir relative efficacies in the suppression of the maximaof 0-, m- and p-nitrotoluenes - The values of charac-teristic properties, viz. m.s.p., s.s.c. and c.m.c. of the

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surfactants for 0-, m- and p-nitrotoluenes are listed inTable 2. A perusal of this table reveals that m.s.p.,s.s.c. and c.m.c. values for cationic surfactants aremuch less than those for anionic ones. From this,it follows that the amount of surfactants required tosuppress maxima of similar sign is greater than thatfor those possessing dissimillar chargess.

On the basis of m.s.p. values, the order of relativeefficacies of cationic, anionic and non-ionic sur-factants in suppressing the negative maxima of 0-, m-and p-nitrotoluenes has been established as below :

Cationic surfactants - LPC and CPC; and LPB,TDPB and CPB possess the same polar head butdifferent carbon chain lengths. The following orderexists for their efficacies : CPC > LPC; CPB >TDPB > LPB.

Thus, with the same polar head the efficacy of acationic surfactants increases with the increase incarbon chain length.

In the case of CTAB and CDBAC which possesthe same carbon chain length but different polar head,it is found that the former is more effective than thelatter.

Anionic surfactants - In the case of Manoxol-IBand Manoxol-OT which possess the same polar headbut different carbon chain lengths, it is found that thelatter, with longer carbon chain, is more effective in

GITA RAM & MUKHTAR SINGH: POLAROGRAPHY OF 0-, m & p-NlTROTOLUENES

suppressing these negative maxima. The efficaciesof the anionic surfactants are in the following order :Manoxol-OT > Tergitol-7 > DBS > SLS > Mano-xol-IB; Methyl red > XL~Anionic.

Non-ionic surfactants - The efficacies of the non-ionic surfactants in suppressing the maxima are in thefollowing order : Triton X-lOO > Decon-90 >Gelatin> Ethyldigol > 2-Ethoxyethanol.

AcknowledgementThanks are due to the Principal, Agra College,

Agra for providing necessary facilities.

References1. !IEYROVSKY, J. & KUTA, J., Principles of polarography

(Academic Press, New York), 1966,434.

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2. LAL, S. & SRIVASTAVA, S. N., Indian J. Chem., 6 (1968),385.

3. COLICHMAN, E. L., J. Am.Chem. Soc., 72 (1950), 4036.

4. SEMERANO, G., Arch. sa. Biol (Italy), 20 (1934), 325.5. MEITES, L., Polarographic techniques (Interscience, New

York), 1955, 35.

6. DEVRIES, T., KROON, J. L., J. Am. Chem. Soc., 75 (1953),2484. .

7. HEYROVSKY, J. & KUTA, J., Principles of polarography(Academic Press, New York), 1966,437.

8. HEYROVSKY, J. '& KUTA, J., Principles of polarography(Academic Press, New York), 1966, 299.

9. MALIK, W. U. & HAQUE, R., J. polarogr. Soc., 8 (1962),36.

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