Electrochemical synthesis of new polymeric reagents

Ekcrmchtmimha, Vol 37, No 4, pi 751-755. 1992 Ptmted ttt Gnat Bntarn

ELECTROCHEMICAL

0013+%/!32 ssao+ooo 819=PerpmonhpEc

SYNTHESIS OF NEW POLYMERIC REAGENTS*

R TABAKOVIC,~E Gu&,t

I TABAKOVI@#and M ZUPAN$$

tFaculty of Technology, DJU~OPucar Stan Umveraty, 78000 Banjaluka, Yugoslawa, %Laboratoryfor Orgamc and Bloorgamc Cbermstry, Department of Cbenustry and J Stefan Institute, E KardelJ Umverslty, 61000 LJublJana, Yugoslavnl (Recerved 6 March 1991) Abatraet-Crossbnked poly [styrene4vmyl (N-metbylpyndmmm lo&de)] (1MaPVPI), poly [styrene4 vmyl (pmdmmm hydrolotide)] (PVPHI) and denvatwes were transformed to new polymenc reagents, dlffermg m amons, by usmg a supportmg electrolyte carrymg the desired amon through antic oxuiation of the released lo&de at a controlled potential The exchange reachon was studied by means of electroanalflcal tecbmques A new and simple electrochenucal method for the syntbes~s of oxldmng, reducmg, nucleopiubc and acldlc polymenc reagents IS described Key words synthesis of polymenc reagents, polyvmylpyndmmm iodide denvatwes, amon exchange

INTRODUCTION Chermcal functionahzation of polymer resins represents an mterestmg dmzchon for the preparation of new reagent catalysts, separation media etc Crosslinked polystyrene beads have found a wde range of uses[ l-5] However, croaalmked polyvmylpyndme or crosshnked copolymers of styrene and 4vmylpyndme have received much less attention, m spite of the fact that pyndme, by Itself or m conJuncbon Hrlth other reagents, has wade application [6] Polyvmylpyrtdme was found to he useful as an HCl acceptor [7], while the salt wth HF was used for halofluormatton of orgamc molecule@-91 Vanous complexes Hnth halogens have been used for mdd

halogen mtroductlon mto orgamc molecules[lO-141, whde several ox&zmg[lS-181 and reducmg[ 191 reagents were also prepared Insoluble beads bearmg pyndme units also form a stable complex wth boron tnfiuonde, which was used for the formation of various acetales and esters[20] Kawabata et al showed that a polymenc reagent electrochermcally generated from crosslmked poly(vmylpyndmmm) brormde can be used for selective oxidation of alcohols[21], alkylbenzenes[22] and sulphldes[23] The use of much less than a stolchlometnc amount of the chemical oxldlzmg agent, the reusablhty of the polymer and easy work up, as well as the nuld reaction conditions make this method a useful alternative to conventional methods Recently, the preparauon of the poly(vmylpyndmmrn hydrobromlde perbromlde) mod&d electrode has been reported by the electropolymenxatlon of vmylpyndme UI srru[24] The present paper describes a simple and versatile electochermcal synthesis of new polymenc reagents lDe&cat~ to the late Professor Manuel M Bauer $Authora to whom the correspondence should be addressed

by using controlled potential electrolysis, through the transformauon of crosshnked poly [styrene4-vmyl(N-methylpymhmum mdlde)] (IMe-PVPI) or poly [styrenesvmyl(mum hydromdule)] (PVPHI) to new polymenc reagents dd%rmg m amons, by merely using a supportmg electrolyte carrymg the desired amon

EXPERIMENTAL Materials and apparahcs The eqmpment and acetomtnle punticauon for the voltammetnc measurements have been described prevlously[25] A standard three&&ode electrochenucal cell was used for all expernnents, with a Pt &SC (2r = 2 mm) and gauze (3 x 5 cm) for analytmal expenments and large scale electrolysis, respecuvely The potent& are related to see. All expenmentals were carned out at room temperature. The ir spectra (KBr pellets) were recorded on a Perkm-Elmer M377 spectrophotometer. The startmg polymers 1-18 (Table 1) were prepared accordmg to the pubhshed procedure[l l-131 All the supportmg electrolytes were commemlally avrulable General procedure for preparation of products

In the anodlc compartment of the &vlded cell was a F+tgauze (3 x 5 cm) anode and a Nl cathode tilled wth a 0 1 M solution of the correspondmg electrolyte m the appropmte solvent (see Table 1) 0 3-O 5 g of the polymer (l-19 was added and the nuxture was stured for 1 h The potentml was mamtamed at a fIxed value (see Table 1) with imhal currents generally 15CL250mA. Electrolysis was dmcontmu& generally when the current dropped to 5-20 mA. The polymenc product was filtered and washed thoroughly wtth water, methanol and acetoniuile. 751

R

152

TABAKOVIC et

al

Table 1 The electrochemical transformation of polyvmylpynduuum lodlde denvatives Substrate R 1H 2H 3H 4H 5H ! :H 8 CH; 9 CH, 10 CH, 11 CH, 12 CH, 13 CH, 14 CH, 15 n-C,& 16 n-C& 17 n-C,& 18 n-C,&

Product Y-

Solvent/supportmg electrolyte-(0 1 M)

FCH,COOIO, ClOi IOi CF,COO-

CH,CN/Et,NClO, CH,CN/Et,Np-TsO CH,CN/H,O (8 3) NaBH, CH,CN/H,O (4 l), KF CH,CN/Et,NCF$O, CH,CN/Et,NCl CH,CN/Et,NBF, CH,CN/Et,Np-TsO CH,CN/H,O (8 3) NaBH, CH,CN/H,O (9 ) NH,NO, CH,CN/H,O (4 l), KF CH,CN/CH,COOH (9 1) CH,COONa CH,CN/H,O (1 1), HIO, CH,CN/Et,NClO, CH,CN/H,O (8 3) NaIO, CH, CN/CF, COONa

Cr& SzOb-

CH,CN/H,O (4 1) Na,Cr,O, CH,CN/H,O (7 3) (NH,),S,Q

ClOi $sOF-’ CF, SO, ClBFi ;;s”. NO;

RESULTS AND DISCUSSION

Voltammetry The electrochemical behavlour of the insoluble polymer (IMe-PVPI), added m acetomtnle solution containing the supportmg electrolyte, was studied m some detad A single compartment cell containing a see was employed, the counter electrode was a platlnum sheet and the workmg electrode was a polished disc of platinum (diameter = 1 mm) Typical cychc voltammograms of polymer (lMe-PVPI), run after &fferent time intervals of mlxmg (900 rpm) in acetomtnle-tetraethylammomum perchlorate (0 1 M) solution, are shown m Fig 1 The cyclic voltammogram (cv) of I-methyl-y-plcohmum iodide 1s also gven for the mu-pose of comparison (Fig 1b) The shape of the ~1)sshown in Fig la and b are essentially the same cus show two anodlc waves around 0 35 and 0 65 V It 1s known[26] that the iodide ion displays two anodlc waves m acetomtnle at the Pt electrode within the potential range examined The first two waves are due to the processes shown m Scheme 1 [equations (1, 2)] The increase of both waves as a function of time can be attnbuted to the ion exchange pven by equation (3) A number of nucromoles of iodide were generated as a function of time The quantity of iodide generated was read as the peak current of the first wave and the resulting curves obtained m acetomtnle by using different supportmg electrolytes are shown m Fig 2a The curves show that the system approaches equlhbnum at different time intervals dependmg on the amon used Smular kmds of experiments were done m order to examme the influence of the alkyl group attached to the pyndme mtrogen on the amon exchange reaction, and the results are shown m Fig 2b Knowmg the amount of rodlde present m the polymer (IMe-PVPI) and the concentration of supportmg electrolyte, the released concentration of iodide, cf equation (3), was determmed from the $,-concentration cahbratlon curve obtained wth I-methyl-y-plcohmum iodide The eqwhbnum

Appkd p&&al/V 07 07 11 08 07 07 07 07 11 10 08 07 14 07 13 10 13 10

Charactensbc u bands for Y(KBr)v/cm-’ 1095 1195, 1115, 1030, 1005, 815 1410, 1350, 1120 1080, 1005, 815 1255, 1220, 1150 1025, 630 Refs[6, 11, 121 1120, 1080, 1030 1190, 1115, 1030, 1010, 815 1400,1340,1000 1410, 1380, 1355, 830 1065, 1020, 825, 660 1700, 1400, 1060, 1035, 525 760,740 1100 830 1450, 1200, 1170, 1120, 830, 800, 715 930, 765, Ref [18] 1265, 1040, 670

constants, K, were calculated and the results are shown m Scheme 1 On the bases of our observations, it 1s obvious that the stenc hindrance due to the presence of a more

volts vs

SCE

lb)

Fig 1 Cyclic voltammograms at a Pt electrode (2r = 1 mm) wth a scan rate of 0 1 Vs-’ m CH,CN (25 ml)-Et,NClO, (0 1 M), (a) 1 Me-PVPI (14 5 mg) at different time intervals, (b) I-methyl-y-pxohmum lo&de (c = 1 mM)

Synthesis of new polymenc reagents

753

16

12

[CIA] 8

60 80 mmutes

0

1 20

’

I ’ I 10 60 minutes

’

I

60

s

1

100

Rg 2 Effects of trme on the rate of amon exchange reactlon m acetomtde (25 ml), (a) 1 Me-PVPI (14 5 mg) wth the correspondmg supportmg electrolyte (0 1 M) except for NH,NO, (c = 0 025 M), (b) the polymers (14 5 mg) m CH,CN (25 ml)-Et,NClO, (0 1 M)

bulky alkyl group attached to the pyndme mtrogen has a negattve influence on the amon exchange reaction. Some other factors, such as the rate of &&ion of the amon mto the polymenc matnx and an ion-pairmg effect may play an equally important role on the rate of the amon exchange reaction This reaction was proven to be quite senstttve to the nature of the solvent when the reactron was camed out m the presence of another amon When acetomtnle was used as solvent, the current &d not flow smoothly and hence the reaction was very slow The ad&non of water improved the soluhhty of the supportmg electrolyte and also gave nse to a smooth reaction Typical voltammograms of polymer (1 Me-PVPI) run after drfferent ume mtervals of nnxmg m acetomtnlcwater (4 1) m the presence of KF as a supportmg electrolyte (0 1 M) are shown m Fig 3a The cychc voltammorgram of 1-methyl-y ptcohmum iodide is gtven for the purposes of comparison (Fig. 3b), wtth the same solvent-supportmg eiectrolyte system. The eqtuhbnum, cf cquatm (3), can be shrfted towards product formation by the electrochemmal

oxtdation of the released iodide The global stotchtometry of the process seems to be 21- +I, + 2e Coulometry at a controlled potenual correspondmg to the second wave (E = 0 7 V) of the cychc voltammogram was carned out m a divided cell at a Pt gauze anode (2 x 3 cm) after nnxmg (130 mm) 14 5 mg of polymer (IMe-PVPI) in CH,CNAl 1 M Et,NClO, solution with an tmual current of 18 mA, and the current-ume curve was recorded and the quantity of electnctty passed was measured durmg the electrolysis by means of an electronic integrator Electrolysts proceeded smoothly and after 10mm the current dropped to the residual current (0 2mA) The u- spectrum of the polymer (lMe-PVPI) confirmed[lO, 111 that more than 90% of the pyndme nngs were transformed, and analysts by coulometry at the controlled potenual of t&de gave the theoreucal capacny of 2.52 nullieqtuvalents of perchlorate amon of fully loaded resin. On the basrs of smular analyses, the numbers of meqv g-l of other polymenc products were estimated to be between 1 and 3.3 meqv g-1

R TAEZAKOVIC ei al

754

EQUILIBRIUM CONSTANTS FOR THE ANION-EXCHANGE REACTION Y-= ClO,-

R=CHa K

Y-

R

K

NO,-

0 0270

H-

O 0127

BF,-

0.0116

CH,-

0 0092

CF,SOz-

0 0100

C,H,

0.0065

ClO,-

0 0092

p-TsO-

0 0071

CF,COO-

0 0067

Cl-

0 0063 Scheme1

I

I

0

I

I

I

Voltsvs SCE

I

#

I

05

The electochemlcal transformation of the polyvmylpyndmmm iodide denvatlves (I-18) to new polymenc reagents was performed according to Scheme 2 The polymer was nuxed m the correspondmg solvent-supportmg electrolyte for 1 h, and the preparative anodlc oxldatlons were typically performed using a controlled potential correspondmg to the plateau of the wave of the current-potential curve obtained with a rotatmg disc electrode (see Table 1) The oxldatlons of polymers were camed out at a Pt gauze anode (4 x 5 cm) The oxldatlons of polymers were camed out at a Pt gauze anode (4 x 5 cm) The electrolysis was terminated when the current decayed smoothly to the residual current and the polymenc product (la-l 8a) was filtered and washed thoroughly with water, methanol and acetomtnle The polymenc product was added to an acetomtnl+tetraethylammomum perchlorate (0 1 M) solution and after mmng (2 h), the cychc voltammogram was recorded and did not indicate the presence of itide ion even m traces All the bands expected were seen m the infrared spectrum of the isolated products C-H stretchmg at 3040 cm-‘, c=C and C=N at 1620 and 1510 cm-‘, nng vlbratlons around 1250cm-‘, C-H deformations around 820cm-’ and characteristic vibrations for the amons (see Table) The IT spectrum of the electrochermcally obtained polymer from 6 and 17 was identical wth the product obtained by independent synthesa[ 11,181 The electrochermcally based synthesis of new polymerrc reagents proceeded smoothly, except m the case of reachon m the presence of NaIO, where instead reaction with polymer took place and resin contammg IO; was isolated The problem was overcome

cg

I bl

1m

0

Voltsvs SCE

05

Fig 3 Cychc voltammograms at a Ptelectrode(2r = 1 mm) wth a scan rate of 0 1 VP-’ m CH,CN/HIO (4 1)

(25 ml)-KP (0 1 M), (a) 1 Me = PVPl(14 5 mg) at dlffmnt time intervals, (b) l-methyl-y-ptcohmum Iodide (c = 1 mM)

syllthesls of new polymellc reagents

_flTR

%

+

@+$R

0R

H, CHJ, n&H9

0

CtO$? BF4? pTsO? CF,SOg CF@O~CH,COO~ I?ClS)B&?

l/21,

(la-18a)

(l-18)

Y

75s

IOE 102 [S,O,]?

NO2

[Cr,O,]”

Scheme 2

when instead of the polymenc iodide denvative, resin in the chlonde form was used

In summary, we have developed a new and simple electrochenucal synthesis of polymenc reagents supplementmg other methods for the synthesis of oxldlzmg, reducmg, nucleophlhc and acl&c polymenc reagents The correspondmg chenucal nucleophdx displacement reasons are usually very slow, or even impossible The synthetic utility of these polymexx reagents IS under mvestrgation m our laboratory Acknowledgement-This work was supported by the U S Yugoslav Joint Board for Sclentdic and Technologxal Cooperation under Grant No 456

6 J M J Frcchet and M V deMefUu, i&. Pofjm J 16, 193 (1984) 7 M L Hallensleben and H Wurm, Attgew Chem 88, 192 (1976)

* A Gregor&& and M Zupan. J Fluorine Chem. 60,291 (1984) 9 i Gkgorhd and M Zupan, Bull Chem Sot Jp, y 3083 (19871

10 J M J Frechet,M 11 t: 14 15

16 17 N K Mathur, C K Narang and R E Wdlrams, m Polymers as Au& m Organrc Ckemrstry (Edited by P Hodge and D C Shemngton) Acadenuc Press, New York (1980) N K Mathur, C K Narang and R E Wdbams, in Polymer-Supported Reactions m Organrc Synthesu @ted by W T Ford) John Wiley & Sons, Chxhwter (1980) N K Mathur, C K Narang and R E Wdbams, m Polymertc Reagents and Catalysts (Edited by P Laszlo) hencan Che&al Society, Washuqton, -DC (1986) N K Mathur. C K Narann and R E Wdhams. m Preparattve dhemutry U&g Supported Reagents (mted by D C Shemngton and P Hodge) Acadenuc Press, San Diego (1987) N K Mathur, C K Narang and R E Wtiams, m Syntheses and Separations Using Functronal Polymers John Wdey & Sons, &Chester (1988)

EA 3v4-M

18 19 20 21 22 23 24 25 26

J FarrallandL J Nyens, J Macromol. Sci Chem 11, 507 (1977). Y Johar, M Zupan and B Sket. J them Sot Perkin Trans I, 2059 (1982) B Sket and M Zupao, Synth Comm. 19,248l (1989) B Za~c and M Zupan, Tetrahedron 45, 7869 (1989) B Sket, P Zupet and M Zupan, J ckem Sot &kh Tram I, 2279 (1989) J M J -Frechei, J %rnock and M J Farrall, J org Cbrn 43, 2618 (1978) J M J Frechet, P Darhng and M J Farrall, J org. Chem 46, 1728 (1981) T Brunelet and G Gelbard. Noun J Chtm 7, 483 119831 .-- --, Z Zdravkovslu and M Zupan, Synth Comm 19,1317 (1989) fi M Menger, H Shmoz& and H C Lee, J org Ckem 45,2724 (1980) B Sket and M Zupan, J Macrom Set Chem 19,643 (1983) J Yoshxla, R Naka~ and N Kawabata. J org Chem 45, 5269 (1980) J Yosluda, K Oguara and N Kawabata, J org Chem 49, 3419 (1984) J Yoshuia, H Sofuku and N Kawabata, Bull them Sot Jpn 56, 1243 (1983) G Mengob, M. M Musuuu, M Nn and N Garrard, hiixtrochim Acta 32, 55 (1987). E Gund and I Tabakov& J org Chem. 53, 5081 (1988) G Dryhurst and P Elvmng,J anal Chem 39, 605 (1967)