Indian Journal of Chemical Technology Vol. 6, September 1999, pp. 288-293

Synthesis and characterization of poly (ortho-anisidine) using quinolinium fluorochromate (QFC) [C9H7NH(Cr03F)] as an oxidizing agent

Shipra Dubey, Dan Singh & R AMisra*

Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India

Received 5 October 1998; accepted 29 July 1999

Poly(o-ani sidine) has been prepared using quinolinjum fluorochromate C9H7NH[Cr03F] (QFC) as an oxidizing agent and the polymer was obtained in good yield. The detailed electrochemical studies have been performed in the presence of QFC in aqueous and non-aqueous media. TG analysis exhibited that the synthesized polymers have relatively high thermal stability. Conducti vity of the polymers was found in the range of 10.9 ·to 10.3 Scm· l and the magnetic susceptibility measurement show the paramagnetic behaviour. The study also include' tbe structural elucidation and external morphological properties of the synthesized polymers.

Polyanilines have emerged as one of the most interesting and useful conducting polymers as evinced in the synthesis and detailed studies of substituted polyanilines 1-7 in the recent years . It has been shown that the substituted polyanilines (i.e. polyanisidine and copolymerss) have greater life time than that of parent polyaniline .. Polyaniline derivatives have been prepared by chemical and electrochemical methods. The search for novel oxidants for polymerization is an area of interest. So far, quinolinium fluoro­chromate9 (QFC) having Cr(VI) has been used as an ox idizing agent for the oxidation of ' primary, secondary, allylic alcohols, hydrocarbons and other organic substrates . It has recently been reported lO for the first time the polymerization of o-toluidine using QFC as an ox idizing agent. The present study describes the detailed investigation of the poly­(o-anisidine) prepared by the QFC used as an ox idi zing agent. Earlier studies9 have confirmed that the QFC is reduced to C9H7NH[Cr02F] having Cr(IV) and thus acts as a two-electron oxidant. The. present study confirms QFC to be an effic ient reagent in the synthesi s of organic conducting polymers.

Experimental Procedure Materials

o-Anisidine (Aldrich) was purified by distillation under reduced pressure. Dichloromethane (Glaxo), acetonitrile (BDH), dimethy l formamide (GSC) and dichloromethane (Glaxo) were purified by double disti lI ation. Tetra-n-butylammonium perchlorate (TBAP, F lu ka, m.p . 210°C), tetra-n-butylammonium

bromide (TBAB, spectrochem 103°C), tetra-n­butylammonium chloride (TBAC, Aldrich, m.p. 73-7S°C) and all other chemicals were used without further purification. Quinolinium fluorochromate (QFC) used as an oxidizing agent was prepared as reported earlier9

•

Methods Polymerization of (o -anisidine). using QFC as an

oxidizing agent-Poly (o-anisidine) was prepared using quinolinium fluorochromate used as an oxidizing agent. To a stirred solution cum suspension of QFC (0. 12M) in O.IM acid (H2S04, H3P04, HCI04,

NH2S03H and other dopants) was added to a solution of O.IM o-anisidine in SO mL anhydrous dichloro­methane/aqueous acetonitrile ( 10:90). The reaction was ' stirred for about Sh at IS±2°C under nitrogen atmosphere to afford a solid polymer mass.

Polymerization of o-anisidine using K2S20 {l as an oxidizing agent-A solution of K2S20 S (O. 12M) in O.IM acid (H3P04, HCI04, NH2S03H) or NaF (0. 1M) was added to solution of n-anisidine (O .IM) in the same acid. The reaction mixture was sti rred for 4-S h at IS±2°C under nitrogen atmosphere. The resulted polymer mass was worked-up as usual by filtration, washing and drying.

Electrochemical polymerization in the presence and absence of catalytic amount of QFC-Electro­polymerization was carried out in one compartment cell using stainless steel foils (6.2S cm2

) as anode and cathode. A solution of o-ani sid ine (0.1 M ), QFC (O.OOI M) in a catalytic amount and H2S04 (O. IM) in

DUBEY e/ al.: SYNTHESIS OF POLY(ORTHO-ANISIDINE) 289

t -« E --C GI I­'­::J U

-0.6 -0.4

10.01 lilA

Cathodic

-0.2 0.0 Potential (V)~

Fig. l-Cyclic voltmmetry of o-anisidine in aq . acetonitrile containing H2S04 (0 ! M) and QFC (0.00 I M).

aqueous acetonitrile (10:90 mL) or o-anisidine (0. 1M) and supporting electrolyte (0. 1M) in dichloromethane in absence of QFC was kept in a cell at IS±2°C under nitrogen atmosphere. The electrolysis was carried out at constant current (1=20 rnA, c .d .=3 .2 rnA cm-2) with D.C. regulated power supply without stirriQ..& and was terminated after 4 h. During electrolysis the black green polymer mass covered the anode surface which was removed at in terval of I O-IS min . A good amount of the polymer mass also escaped in reaction medium as black green insoluble mass and was recovered from it.

Work-up- The polymer mass obtained from electrochemical and/or chemical method was filtered, washed thoroughl y with distilled water and dried under controlled temperature at 70°C for S-6 h. The polymer powder was pressed (- 10 pascals) to form a pellet for conductivi ty measurement and it was measured wi th the help of Keithly electrometer. Magnetic susceptibility of polymer samples was determined by Gouy' s method at room temperature

f

c .. .. .. j

U

-0.8

I 5~A Anodic

-0.4 0.0 0.4 Potentiat (v)_

0.8 1.2

Fig. 2-Cyclic voltammetry of o-anisidine in DMF containing QFC (0.01).

USIng mercury tetrathiocyanato cobalt (II), Hg[Co(CNS)4] as reference material. Cyclic voltammogram was recorded with an EG & G Parc Model-362, scanning potentiostat and Servogor 733, x-yet) recorder, scanning electron micrograph was carried with JSM 840-A SEM unit with the film deposited on stainless steel foi l. IR spectrum of polymers was recorded with a JASCO-FTIR-S300 infrared spectrometer using KEr pellet. The presence of counter ion was confirmed by functional group analysis .

Results and Discussion The polymerization of o-anisidine was achieved

using QFC and K2S20 g in the presence of variol,ls dopants . It was also performed electrochemically using catalytic amount of QFC in presence of different electrolytes. The e lectropolymerization was also carried without using QFC in the medium. Electrical conductivity, yield and magnetic susceptibility per two ring unit mol of polymer are given in Tables I and 2. The result shows that yield and conductivity of the polymer varied with the nature of the solvent, electrolyte and oxi dizmg agent used. The variation in the yield and the conductivity may resu lts from possible variation in the chain length of the polymer under the influence of solvent and electrolyte. The poly (o-anis idine) obtained by QFC oxidation was found to have poor conductivity

290 INDIAN J. CHEM. TECHNOL., SEPTEMBER 1999

Table I- Yi e ld , conductivity and magnetic susceptibility of poly(o-anisidine) in the presence o f different electrolyte/dopants by chemical

and electrochemical method

[c.d .= 3 .2 mA cm·l , T= 15±2°C , volume of reaction mixture=50mL, t=5h at s tai nless steel 6.25cml)

usi ng QFC (O.12M) as oxidizing agent in chemical polymerization

S. Solvent Electrolyte! Yield Conductivit;t (Scm' I ) Magneti c ~ cff.

No. Dopants (g) h·doped susceptibility (BM .) (emu/two ring unit)

Chemical

I. I. ? -Dichloromethane 1.00 Non conducting 4.8x I0' .1 1.2

2. Aq . Acetonitri le( 10:90) (O . IM) H2SO4 0.67 1.20x I O·y 0.02x I0·h 4.5x IO·J 3.2

:l. Aq . Acetonitrile( 10:90) (O.IM) [-!)P04 0.91 Non conducting 3.40x I0·J 3.4x I 0.1 1.0

4. AlJ . Acetoni trile( I 0 :90) (O. IM) HclO4 1.03 0.27x I0·Y 0.83x I0·h 5 . 7x I 0'~ 1.3

5. Dichlorc methane Il-Bu4NBr 0.45 0.0IxI0·9 1.20x I O·h 1.8x I O·l 0 .7

6. Dichloromethane n·Bu4NCI04 0.77 0.18xI0'Y 11.2x IO·h 1.7 x I 0'] 0.7

7. Aq . Acetonitrile( I 0:90) LiCI 1.08 0.19x I0·9 o 26x IO·h 5.8x I0·J 1.3

8. Aq . Acetoni tril e( I 0:90) NaF 1.10 0.04x I0'Y 0.07x I0'" 4.9x I0·J 1.2

9. Aq . Acetonitrile( 10:90) NH2S0JH 0.85 0.87x 10 9 O. ll x IO'" 4.7x IO·J 1.1

10. Dichloromethane BU4NCI 0.73 0.0I x I0·9 O.92x IO'" 3 .8x IO·J 1.0

II . [)i chloromethane I'-CHJ-Ct;H5S0JH 0.65 0.35x I0·9 2.80x I0'" 3. lx I0·J 0 .9

Electrochemical

I. Aq . Acetonitri le( 10:90) (0.1 M) H2SO4 0.31 0.30x I0·3 3 .8x IO'] 1.0

2. Acetonitrile Il -Bu4NCI04 0.57 0.67x I0'" 3.0x I0·J 2.6

T ab le 2-Yie ld , conductiv ity and magnetic susceptibility of poly(o-anisidine) formed in the presence of different electrolyte/dopants by

c he mical method (us ing K2S 20 R (O.12M) as oxidizing agent) and electrochemical [c.d.=3 .2 rnA cm·2, T= I 5±2°C, vo lume of reaction

mixture=IOO mL, electrolysis time=5h at stainless steel 6 .25 c m 2) .

S . o . So lve nt Electrolyte/ Yeild

Dopants (g)

Chemical

I. Aq . H1P04 (0.1 M) 0.5

2. Aq. HC I04 (0.1 M) 1.0

3. Aq. NH cS03H (0.1 M) 0 .9

4. Aq. NaF (0.1 M) 0.8

Electrochemical

I. Di chlorometh ane I1-Bu4NCI04 0 .3

2 . Aq . HC I ( 1.5M) 0 .2

(which is enhanced to some extent iby h doping) than the poly (o-anisidine) prepared by using K2S20 g as an oxidizing agent. Thi s may be due to lower extent of doping of the polymers during polymerization process, possibly owing to the steric factors operating for the entry of anionic part, Cr03r. The other factor responsible for this may be possible change in chain length of the polymer in the presence of QFC. The magnetic measurement of the polymer observed per two rIng unit mole snows the paramagnetic behav iour.

Conductivity (Scm· l

)

b.32x I0·7

0.73x I0·4

0.45x I0·5

0.14x lQ·7

0 . ll x lQ·3

0.38x I0·4

Magneti c

susceptibility

(emu/two ring unit)

1.00x 10·3

0.70x lQ·3

0.14x lQ·3

0 .40x IO·3

0.60xlQ·3

Cyclic voltammetric studies

I-l clT

(B.M .)

1.5

1.3

0.5

0.9

1.2

The polymerization of o-anisidine was examined by cyclic voltammetry. Fig. 1 presents the cyclic voltammogram of o-anisidine (0.1M) in aqueous acetonitrile (10:90) containing QFC (0.001M) and H2S04 (0. 1M) recorded in the range of 0.0 to -0.6V versus SCE using platinum foil as working microelectrode (0.16 cm2

) and platinum wire as auxiliary electrode in an undivided cell under nitrogen atmosphere. The anodic peak appears at -0.31 V and the corresponding cathodic peak at -0.34V,

DUBEY el at. : SYNTHESIS OF POLY(ORTHO-ANISIDINE) 291

Table 3-Analytical data of poly(o-anisidine) with different anion

S. No.

2

3

4

5

6

7

8

Cathodic

Io.05mA

0.6 0.4

Polymer

Poly (o-anisidine) Sulphate

Poly (o-anisidine) Phosphate

Poly (o-anisidine) Perchlorate

Poly (o-anisidine) Bromide

Poly (o-anisidine) Chloride

Poly (o-anisidine) Fluoride

Poly (o-anisidine) p-toluene sulphonate

Poly (o-anisidine) Sulphamate

Anodic

0.2 0.0 -0·2

t ~ Z UJ a: a: :> u

~ E/V vs. SCE

Fig. 3-Cyclic voltammogram of o-anisidine (0. 1) in 1.2-di­chloroethane containing tetra-n-butylammonium perchlorate (0.05M) on a platinum microelectrode with different scan rates of (a) 20 mVs· t • (b) 100 mVs· t

• (c) 200 mVs· t and (d) 500 mVs· t•

Found (Calc.) % C H N

53.31 4.17 9.15

(49.55) (4.4) (8.25)

51.04 5.35 7.19

(49.55) (4.71) (8.25)

52.03 3.67 7.84

(49 .19) (4.09) (8.19)

58.09 4.01 9.91

(52.17) (4.34) (8.69)

67.96 5.35 9.84

(60.54) (5 .04) (10.09)

65.28 5.90 11.05

(64.36) (5.36) (10.72)

63 .24 5.26 5.96

(61.01) (4.26) (6.77)

48.9 3.4 11.91

(50.3) (4.9) (12.5)

0.0 c 'E 1.0 " '# 2.0 GI > 3.0 -0 > 4.0 ... GI '0 5.0 -1/1 .... 6.0

400 600 800

Temperature (oCI

Fig. 4-TGA and DTA curve of poly(o-anisidine) with a heating rate of 10°C/min.

the redox peak current was found to increase with the increase in scan rate.

In non-aqueous (DMF) medium when QFC (0.01M) was used as an electrolyte, the cyclic voltammogram (Fig. 2) of o-anisidine (0.1 ) shows a single anodic peak at 1 .OV and the peak current decreases at multiple sweep cycle. During the CV as the potential was applied, it was observed that electrode surface got covered by black polymer mass spontaneously. The voltammograrn shows no reduction peak correspondi ng to the anodic peak and reveals a typical irreversible reaction indicating that the polymer is formed on the electrode surface through the oxidation of o-anisidine.

292 INDIAN 1. CHEM. TECHNOL. , SEPTEMBER 1999

~

c 100 i 0·0

80 -I -I 0.4~ too 60 > J:

0.8 !;i ~ III 40 > ~ 1.2 a:

III 20 0

' · 6 1ft 0 -0 200 400 600 800

TEM PERATURE (oC)

Fig. 5-DTG curve of poly(o-anisidi ne) with a heating rate of I DOC/min.

SMPL 10 : 50-73 DATE RUN : MOl'1. /l"7 ST A 1500 ~~:E 10 : SA~.-'~m g~~ 1 ; AI PL Thf1'moI ScI,ne •• OP£RATOR : A K 9 COMMENT : eANARAS UN IV

110 1/,0

100

90

C 80 .. ~ 70 .t

6 0

50

Tn

19.t. 74 C

OTA

120

100

20

. 0

~ ~

o 100 20 0 3 4 0 500 600 00 1 0 Oeg, C

Fig. 6-TGA and DTG curves of C10 4' doped poly(o-anisidine) with a heating rate of 5°C/min in nitrogen.

On the other hand, the cyclic voltammetry of o-anisidine (0.1 M) in 1,2-dichloroethane containing only tetra-n-butylammonium perchlorate (0.05M) (Fig. 3) exhibits the anodic peak at 0.28V and the peak current was observed to increase with the increase of scan rates.

Thermal properties Thermal stability of the polymers was determined

by thermogravimetric analysis carried out under nitrogen/air. The TG (Fig. 4a) and DTG (Fig.4b) analyses of chemically prepared poly (o-anisidine) obtained by the QFC oxidation show three inflection points. The weight loss observed initially below 100°C may be due to loss of moisture from the polymer matrix and further weight loss in the range of 190-310°C could be attributed to decomposition of polymer chain unit. On further heating, -44% of the polymer sample remains at 400°C which seems to be thermally stable up to 900°C. Maximum decompo­sition of polymer chain at 300°C is shown by DTG curve (Fig. 4b) . DTA (Fig.4a) of the same polymer material shows a single exothermic peak at 294°C. The TG and DTG analyses (Fig. 5) of electro-

(a)

Fig. 7-SEM picture of S04-2 doped poly(o-anisidine) magnification (a) X 1546 (b) 3865.

chemically prepared perchlorate doped poly (o-anisi­dine) in the presence of catalytic amount of QFC show the weight loss in the range of 250-300°C.

Morphological properties The morphology of the polymer film obtained by

the QFC oxidation was studied using scanning electron microscope (SEM) at two magnification is presented in Fig. 6a and b which show very irregular type of external morphology.

Structural studies The structural elucidation of synthesized polymers

were made only by infra red spectroscopy as these polymers were found insoluble in organic solvent. The IR data of these polymers doped with various anions show in general a weak band between 3460-3220 characteristics of NH2 and NH stretching vibration . The Cl04- in polymer matrix was confirmed by peak at around 1120 or 1080 cm-I whereas for

DUBEY et al.: SYNTHESIS OF POLY(ORTHO-ANISIDINE) 293

Ae

•

cr~~tO !~NH" R It : R R

A: Dopant anion

R. o-OCH3

Scheine I

CHEI'1./ ELECTROCHEf1. )

USIN~ <iFC

Scheme 2

Polymn

d

PO/ anion absorption at IllS cm- I is observed. The other dopants like sulphamate and p-toluene sulphonate anions gave absorption peak at 1170, 1300 and 1250 cm· 1 respectively. The two bands around 1580 and 1508 cm- I are assignee! to quinoid and benzenoid phenyl ring respectively . The analytical data of carbon, hydrogen and nitrogen composition are given in Table 3. Based on elemental analysis and other physicochemical properties discussed, the possible structural backbone can be assigned to the poly(o-anisidine) as given in Scheme 1.

Mechanism The polymerization process can be rationalized to

proceed via cation radical intermediate. Th'e oxidation of o-anisidine gives a cation radical that couples together in a head-to-tail manner (Scheme 2).

Conclusion The present study is affirmative that quinolinium

fluorochromate used as an oxidizing agent for the polymerization of o-anisidine has proved to be a mild and efficient reagent and gives the polymer in good yield. However, unexpectedly the conductivity of the polymer was found in low~r range.

Acknowledgement RAM thanks the Head, Chemistry Department for

laboratory facilities and to CSIR, New Delhi for financial support in form of Emeritus Scientist. S. D. and D S thanks CSIR for fellowship .

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