Eleclrochemical Applications of Ion Exchange Alembranes ill OJemical Transformations 66

Chapter 3 Application of Ion Exchange Membranes -Electrochemical Organic Transformations

3.1. Introduction

E lectro-organic synthesis largely depends on the choice of a suitable

solvent and supporting electrolyte. Due to poor solubility of organic

compounds in aqueous media and poor conductivities of organic

solvents, in general, two-phase (aqueous-organic) is often employed. In

such cases, a phase transfer catalyst is used for improving the system efficiency.

However, this makes the electro-organic synthesis, on the whole, more complicated.

Solid polymer electrolyte i. e. ion-exchange membrane reactors (SPE) have been shown

to be promising for electro-organic transformations. The mobility of counter ion affects

the electrode reactions possible. However, the studies on SPE reactors are confined to

metal-membrane composite electrodes only. Besides few disadvantages such as the

involvement of metal-membrane composite electrodes, confinement of these studies to

very costly Nafion membranes and greater threat possed by the adhering capability of

the metal film of such composite electrodes during their function, they have been

reported to be used in literature.

3.1.1. Oxidation of methylsulfoxide to methyl sulfone. Dimethylsulfone (DMS02) is

useful as a high temperature solvent in extractive distillation, in electroplating baths, in

making ink, adhesives and many other substances of organic or inorganic nature!.

Molten DMS02 is a suitable electrolyte for lithium intercalation batteries2 It is found in

primitive plants and in the adrenal cortex of cattle. It has reportedly been used in the

preparation of epoxide catalysts for polymerization reactions]

Ph. D. Thesis o/Afr. Sanjaykumar S. vaghela Bhavnagar University, Regln. No. 654, 4dOl2000

Electrochemical Applications of lmJ Exchange ,Uembranes in Chemical Transfonnations 67

The synthesis techniques, properties and numerous practical applications of methyl

sulfone and other sulfones have been reviewed earlier4 The oxidation of organo sulfur

compounds, in fact, is important as stated by Vedemikov and Maksimov5 from the view

point of effluent deodorization and utilization of sulfur compounds from the wastes of

pulp and paper industries.

Devis and Sorensen6 patented the process of preparation of methyl sulfone from

methyl sulfide by heating the later to 120-125°C in a bomb containing HN03 (6 N) or

N-oxides as oxidants and OS04 as catalyst. A yield of 71 % methyl sulfone was reported

at the end of three hours. They, further reported7 the synthesis of sulfones by the

disproportionation of sulfoxides in the presence of HN03 (6 N) or N-oxides and OS04 at

110-120°C. In this case methyl sulfoxide was reported to give 83% methyl sulfone.

Goheen and Bennett8, reported the oxidation of methyl sulfoxide to methyl sulfone in

hot HN03. About 86% of methyl sulfone was obtained in 0.64 equivalents of HN03 at

120-150°C.

Vedemikov and Maksinov5 synthesized methyl sulfone by passing methyl sulfide

vapors through 30% H2S04 at an elevated temperature (11 0 -120°C). Hydrogen

peroxide was added to catalyze the reaction. Seree de Roch and Menguy9 patented the

liquid phase oxidation of alkyl/aryl sulfides or sulfoxides using an alkyl hydroperoxides

at JO-150°C. Group IV-VII metal acids, oxides or salts were employed as catalysts.

Sulfones were reported to be formed in excess hydroperoxide at >50°C and sulfoxides

in excess sulfide at low temperatures. Methyl sulfone was not reported to be achieved

by this method. Boehme and Sitorus 10 in their communication, reported that ethanolic

solutions of thioethers produce methyl or alkyl/aryl sulfones when alkaline H20 2 was

added to it.

Thompson II reported the formation of stoichiometric amounts of methyl sulfone

when ozone in Et20 was added to methyl sulfide or methyl sulfoxide at -30 to -40°C in

the presence of triaryl phosphites. Akamatsu l2 e/ al. reported the ozone oxidation of

methyl sulfide derived from the pulp and claimed a yield of 25% sulfone and 75%

sulfoxide with 7% ozone. Akamatsu, Ueshima and Kimural3 patented the methyl

sulfoxide and methyl sulfone preparations by the oxidation of methyl sulfide with 0 3 at

O-IOO°C. According to them, the percentage of methyl sulfide should be between 2-19.7

Ph. D. Thesis ofA1r. Sanjaykumar S. Vaghela Bhavnagar University. Regtn. No. 654. 4110/2000

Electrochemical Applications of Ion Exchange Jlembranes in Chemical Tramfonnatio1Js 68

moles to avoid explosions. A mixture of 3:7 molar solution of Me2S and 20% 0 3 gave

85% of methyl sulfoxide and only < 15% of methyl sulfone at 30° C.

Mallievskii 14 et al. have reported the sulfides and sulfoxides oxidation to get

sulfones by atmospheric oxygen in the presence of variable valence metal compounds.

Acetic acid medium at 20-130° C was found to give sulfones in the purest form. While,

Bennett, Goheen and Mac Gregorl5 reported the formation of 10-30% methyl sulfone as

side product in the preparation of methyl sulfonyl chloride (MeS02CI) by the

chlorination of methyl sulfide under aqueous conditions at 25° C.

Methyl and other alkyl/aryl sulfoxides were converted photochemically to sulfones

by Schenck and Krauch 16 via photosensitized O-atom transfer mechanism. The yield of

methyl sulfone was around 55-99%, depending upon the type of photosensitizer used.

Hubenett l7 et al. patented an electrochemical process for the preparation of dialkyl

sulfones from sulfoxides. They used Pb02 electrodes as anodes and an aqueous solution

of 0.05-1.0 N salt/acid as an electrolyte to affect the reaction in a single compartment

cell at 20-40° C. About 79% of methyl sulfone was reported to be obtained by this

method from methyl sulfoxide at a current density of 40 rnA cm-2 in 0.2 N H2S04 at 20°

C. In an other patent, Bennett and Goheen l8 reported electrolytic preparation of methyl

sulfone from methyl sulfoxide. They used a high density graphite anode and carried out

the electrolysis at 5° C in 0.4 N HCI medium at a current density of 10 - 54 rnA cm-2

and voltage of 3-6 V. The yield of sulfone was reported to be improved to 100% and the

current efficiency has gone up to 76-93% when a salt or oxide of W, V, Mo or Se was

added as catalyst. Although, the yields of sulfone and current efficiencies in the above

processes are good, but the requirement of a supporting electrolyte, saturation of the

medium with the sulfone before electrolysis and the problems such as the separation of

supporting electrolyte and catalyst from the reaction mixture/product truly limit the

wide utility of these processes.

The limitations of the above methods are that they involve expensive catalysts,

corrosive chemicals, cumbersome procedures, or the use of OMS which has a pungent

odorl . In electrochemical methods, the yields of sulfone and current efficiencies in some

of the above processes are good, but the requirement of adding a supporting electrolyte,

saturation of the medium with the sulfone before electrolysis and the problems such as

Ph. D. Thesis aJMr. SanJuykumar S. Vaghela Bhavnagar University, Regt". No. 65{ 4110/2000

Electrochemical Applications of Ion Exchange Afembranes in Chemical TransfomlGtions 69

the separation of supporting electrolyte and catalyst from the reaction mixture/product

limit their wide utility.

3.1.2. Oxidation of benzyl alcohol to benzaldehyde. The electrooxidation of benzyl

alcohol was investigated by A. Kunugi 19 et at. employing a Pt-Nafion composite

electrode in both polar and non-polar solvents. The benzaldahyde formed in different

solvents was reported to be in the range of34 - 62% and benzoic acid in the range of 9 -

28%. S. M. Lin and T. C.Wen20 have reported the electrocatalytic oxidation of benzyl

alcohol in alkaline medium on Ru02-coated titanium electrode. J. S. D021 et at. have

studied the indirect anodic oxidation of benzyl alcohol in the presence of phase-transfer

catalyst in a continuous flow stirred-tank electrochemical reactor (CSTER).

3.1.3. Reduction of maleic acid to succinic acid. Succinic acid or butanedioic acid

(C4~04) is a constituent of plant and animal tissues. It is found in beer, molasses, meat,

eggs, peat, fruits, honey and urine. It has wide applications ranging from scientific, such

as radiation dosimetry and use in standard buffer solutions to agriculture, food,

medicine, plastics, cosmetics, textiles, plating, photography and waste-gas scrubbing 22

The hydrogenation of maleic acid has been reported in aqueous cobalt chloride and

potassium chloride solutions to give 41% succinic acid in the presence of Zn/Hg and

22% in its absence23. Succinic acid has also been prepared24 chemically by treating

maleic acid with 50% H3P02 at room temperature in aqueous NaOHIEtOH with an

average yield of 83%. It has been reported to be obtained in 99.5% yield when a

mixture of maleic acid, water and Pd/C was autoclaved at 1000 C while bubbling with

hydrogen containing

Electrochemical App/icaliotU if /"" Exc/umge MemhrtllW. in o,emical TrumfQmlQlioIU 70

The yield of succinic acid in some of the above processes is good, but, the requirement

of adding a supporting electrolyte in the electrochemical processes, saturation of the

medium with succinic acid before electrolysis, requirement of costly catalysts or

reagents, and the problems associated with the separation of supporting electrolyte,

catalyst or unreacted reagents from the reaction mixture/product limits application.

3.2. Experimental

3.2.1. Materials. Interpolymer cation and anion exchange membranes (300 cm x 60 cm)

were either purchased from Nuchem Weir Ltd. Faridabad or prepared from styrene

divinyl benzene copolymer (prepared initially) by attaching with sulfonic acid (to

function as a cation exchange) or tertiary amine (to act as anion exchanger) as patented

from this laborato~. Dimethyl sulfoxide (S. D. Fine Chemicals Ltd., India), maleic

acid (S. D. Fine Chemicals Ltd., India) and benzyl alcohol (Sisco Research Laboratory)

were used as received. Expanded precious triple metal oxide coated electrode

(Dimensionally Stable Anode, DSA) was purchased from Titanium Tantalum PToducts

Limited (TITAN), Chennai, India. An expanded stainless steel sheet to serve as cathode

was procured from Hy-Tech Engineering, Bhavnagar.

3.2.2. General description of the fabrication of membrane flow cell. Fig. 3.1 shows a

View of the two Cathode Anode

compartmental

electrochemical

membrane flow cell.

The capacity of the

each electrode

compartment of the cell

was about 20-30 mi. A

dimensionally stable

anode which is an

expanded titanium

sheet with a precious

triple metal oxide

coating was used. A

Ph. D. Thew of Mr. Sanjfl}fumror S. Vo[!}lela

Fig.3.L A look oftlle membl3De flow reactor

Bhavoogor Univenity. Regtn. No. 654. 4110/2000

Electrochemical Applications of Ion Exchange Afembralles in O,emical Trans/omlGtiolls 71

fine stainless steel mesh or expanded sheet was served as the cathode. Both of these

electrodes were separately fitted inside the electrode chambers made of TeflonIPVC.

They were separated by about 4-6 mm by the conditioned indigenous anion/cation

exchange membrane between them. The anolyte or catholyte solution of desired

concentration was passed through the respective compartment at a regulated flow rate,

under gravity, while a solution of a desired electrolyte or distilled water depending on

the nature of the experiment carried out was circulated through the other compartment

at the rate equaling to that of the other side, with the aid of inlets and outlets provided to

the cell.

3.2.3. Methods. (a) Galvanostatic electrolysis. (i) Oxidation of Methyl sulfoxide to

methylsulfolle. Galvanostatic oxidation of methyl sulfoxide to methyl sulfone was

carried out in two ways viz. batch process in an undivided cell and a divided membrane

flow reactor. In batch process, the undivided cell had provisions for introducing

expanded DSA (area 48 cm2) and stainless steel cathode. 20 grams of DMSO (0.256

moles) was dissolved in 500 ml of 0.53 M H2S04 or 0.2 M Na2S04 as the case and

oxidized at current densities of25.0, 62.5 and 100.0 mAcm-2 till the charge equivalent

to two Faradays was passed.

A rectangular Perspex cell of 18 cm x 15 cm consisting of an expanded DSA (area

60 cm2) and a stainless steel cathode was used as a flow reactor. A cation exchange

membrane35•36 (an interpolymer of polyethylene and styrene-divinyl benzene copolymer

with sulfonic acid as functional group having aerial resistance, 1.5 Q cm-2, ion

exchange capacity, 1.8 m equiv g -I and moisture content, 29.8% after drying) of 100

cm2 exposed surface area was placed between the cathode and the anode, which are

separated by 3-4 mm, thus dividing the cell into two compartments each having an inlet

and an outlet. The anolyte consisted of 250 ml of aqueous solution containing 20 grams

of DMSO and the catholyte was 250 ml of 0.1 M H2S04. both of which were

recirculated through the respective compartments. The flow in both the cases was

regulated at 10 ml min - I The current passed corresponding to anode was of 35 rnA

cm -2 The cell voltage between the cathode and the anode, and the potential at the anode

vs Ag/ AgCI (3M NaCl) were monitored.

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Electrochemical Applications of Ion Exchange AJembranes in D,emical Transformations 72

The progress of the electrolysis was followed in both the cases, by recording UV-vis

or IH_NMR spectra of I ml sample withdrawn periodically and diluted suitably. After

the completion of the electrolysis, the solution was evacuated (after neutralization in

case of H2S04 as electrolyte) using rotary evaporator and the resulting solid was

recrystallized from ethanol. DMS02 thus obtained as white prisms, had melted at 109

dc. Cyclic voltammetry. Cyclic voltammetric studies were made in the conventional

three electrode cell with provisions for introducing the working, reference and counter

electrodes. Glassy carbon (area 0.0314 cm2), AglAgCl (0.222 V vs NHE) in 3 M NaCI

and a platinum wire served as the working, reference and counter electrodes,

respectively. Cyclic voltammograms for DMSO in the concentration range of 0.05-0.10

M, were recorded in acetonitrile-O.I M BU4NBF4 medium.

(ii) Reduction of Maleic acid to succinic acid A rectangular Teflon cell of area IS

cm x 10 cm fitted with a stainless steel, copper or lead cathode of area 40 cm2 and a

dimensionally stable anode (DSA) or lead anode was used as the flow cell (Fig. 3.1). An

interpolymer of polyethylene and styrene divinyl benzene copolymer attached with

sulfonic acid to function as a cation exchanger purchased from Nuchem Weir Ltd.,

Faridabad, India, was used as the conducting solid polymer electrolyte. It had dry

resistance 1.5 ohms cm-2, ion exchange capacity 1.8 meq g-l and moisture content

29.8% after drying. The cation exchange membrane, measuring about 66 cm2 exposed

surface area, was placed between the cathode and the anode at a distance of 2-4 mm,

thus dividing the cell into two compartments each having one inlet and one outlet. A

100 ml solution consisting of the desired quantity of maleic acid was used as the

catholyte, while a 100 ml of 0.1 M solution of H2S04, Na2S04 or NaOH was used as

anolyte. The quantity of current consumed was 2 faraday mole- l Both solutions were

recirculated at 10 ml min-1 through the respective compartments until the end of

electrolysis. Cathodic current densities in the range 18.7 - 31.2 rnA cm -2 were used. The

cell voltage between the anode and the cathode at a given current density was noted.

The electrolysis was continued beyond the calculated time and stopped corresponding

to the maximum yield of the product observed by regular analysis every minute after the

completion of the theoretical time.

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Electrochemical Applications 0/ Ion Exchange Membranes in Dlemical Trans/onnations 73

The progress of the reaction was followed by recording lH~NMR spectra of I mlof

the sample withdrawn periodically during electrolysis. After completion of electrolysis,

the solution was concentrated and allowed to crystallize as white prisms which melted

at 187°C.

Cyclic vo/lammetry. Cyclic voltammetric studies were made in a conventional three

electrode cell with provisions for introducing the working, reference and counter

electrodes. A hanging/static mercury drop electrode (HMDE/SMDE) (0.017 cm2), a

saturated calomel electrode (SCE) and a platinum wire served as the working, reference

and counter electrodes, respectively37 Cyclic voltammograms for maleic acid (1 mM)

were recorded in 1M H2S04, or 0.1 M CH3COONa-H2S04 and 0.1 M KH2P04-

Na2HP04 solutions in the pH range 1.0 -8.1.

(iii) Oxidalion of benzyl alcohol A rectangular Teflon cell of area 15 cm x 10 cm

fitted with a stainless steel, copper or lead cathode of area 40 cm2 and a dimensionally

stable anode (DSA) used as the flow cell (Fig. 3.1). An interpolymer of polyethylene

and styrene divinyl benzene copolymer attached with sulfonic acid to function as a

cation exchanger purchased from Nuchem Weir Ltd., Faridabad, India, was used as the

conducting solid polymer electrolyte. The cation exchange membrane, measuring about

66 cm2 exposed surface area, was placed between the cathode and the anode at a

distance of 2-4 mm, thus dividing the cell into two compartments each having one inlet

and one outlet. A 100 ml 1

solution consisting of the

desired quantity of benzyl

alcohol was used as the

anolyte, while a 100 ml of

0.1 M solution of H2S04

used as catholyte. The

quantity of current

consumed was 2 faraday

mole-1 Both solutions

were recirculated at 10 ml

'" U I: III -e 0.5 5l .c 0:(

O+-~--~----~----~----

o 0.2 0.4 0.6 0.8 Benzaldehyde, 1M] x 10-3

Fig.3.2. Plot of Absorbance against Concentration of Benzaldehyde in 0.1 % (v/v) benzyl alcohol.

Ph. D. Thesis of Mr. Sanjaykumar S. Vaghela Bhavnagar University, Reg/II. No. 654, 411012000

Electrochemical Applications of Ion Exchange AJembranes in Olemicai Trans/onnalions 74

min- l through the respective compartments until the end of electrolysis. Anodic current

densities in the range 5-60 rnA em -2 were used. The cell voltage between the anode and

the cathode at a given current density was noted. The electrolysis was continued beyond

the calculated time and stopped corresponding to the maximum yield of the product

observed by regular analysis every minute after the completion of the theoretical time.

The amount of benzaldehyde was estimated by Uv vis spectrophotometry38 by

following the absorption band at Amax.= 283 nm, (t::, 664 ~l em-I; Fig. 3.2)

characteristic of benzaldehyde.

3.2..1. Instrumentation. Perkin Elmer Series II-2400, CHNS/O Analyzer for C, H,

N-analysis; Bruker Avance DPX-200-FT NMR-200 MHz spectrometer for IH_NMR

spectra and Perkin Elmer Spectrum (GX FTlR system) for IR data were used. Shimadzu

Uv vis spectrophotometer was used to record Uv spectra. All pH measurements were

made with Adair and Dutt digital pH meter.

EG&G P ARC Models PAR 174A Polarographic Analyzer and PAR 175 Universal

Programmer coupled to a high precision Houston X-V recorder were used to record all

sampled-de, differential pulse (DPP) and cyclic (cv) voltammograms. A three electrode

assembly, PAR 303 SMDEIHMDE comprising of a dropping mercury (DME, 3.85 mg

S-I ) or a hanging mercury drop (HMDE, 0.021 cm2) as working, platinum wire as

auxiliary and SCE (or Ag/AgCI) as reference electrodes was employed for recording all

electrochemical data.

EG&G PAR model 273A PotentiostatiGalvanostat coupled with three electrode cell

assembly and Gateway 2000 (4DX2-66) computer loaded with M 270 Research

Electrochemistry were utilized for electrokinetic measurements. A glassy carbon of area

0.0314 cm2 was served as the working electrode, while its potentials were measured

against Ag/AgCI (0.22 V vs NHE) in 3 M NaCI. A platinum wire served as a counter

electrode.

Controlled potential coulometry (CPC) was performed on EG&G PAR model 173

PotentiostatiGalvanostat coupled to models 179 digital coulometer. A coulolmetric cell

used here was assembled with a working Hg-pool (I in convex surface diameter)

electrode in the main compartment, a platinum mesh as counter and a SCE reference

electrodes. The solution was uniformly agitated throughout the experiment.

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Electrochemical Applications OJ/Oil Exchange Alembranes in Owmical Tranifomrations 75

An Aplab D. C. Power supply (model L 1285 and model L 1288SR) were employed

as the constant current source.

3.3. Results and discussion

3.3.1. Galvanostatic transformation of methyl sulfoxide to methylsulfone. The results of

galvanostatic oxidation studies on DMSO in different media at different current

densities and reactor types are given in Table 3.1. It can be seen that, under the batch

reactor conditions, the percentage yield ofDMS02 in 0.53 M H2S04 increased by 8.3%

when the current density was increased from 25.0 to 62.5 rnA cm-2, while the CE

rose by about 9%. When the current density was further enhanced to lOa rnA cm-2, the

yield ofNa2S04 medium, the yield ofDMS02 along with the CE was reduced, possibly

due to competing oxygen evolution. In 0.2 M increased slightly (4.2%) at 62.5 rnA

cm-2, though the cell voltage was relatively much higher (10 V) which is generally

Table 3.1. Data on the galvanostatic oxidation ofDMSO to DMSO, at DSA in membrane and batch flow reactors

DMSO Elcctrol)1e Anode Current Cell current 'Cell % Yield cCE 0/0** (g) (M) density (A) voltage of

(rnA ern-2) (V) DMSO,'

20 'H,S04(0.53) 25.0 1.21 4.0 71.0 78.0 20 'H,S04(0.53) 62.5 3.02 5.0 79.3 87.1 20 'H,S04(0.53) 100.0 4.83 6.0 71.1 78.2 20 'Na,S04(0.2) 62.5 3.02 10.0 83.5 91.9 20 b 35 2.20 2.5 '96.2 95.1 20 c 35 2.20 2.5 '97.5 98.1

'wlth respect to the Isolated "eld of DMSO" •• CE for DMSO, fonnatlOn'Batch reactor, bMembrane flow reactor, 0.1' M H,S04 as cathol)te, 'Membrane flow reactor, 0.1 M Na,S04 as cathol)tc.

not advisable. The cell voltage in all other experiments was between 4 - 6 V while the

potential at the anode maintained to about + 1.5 to +2.0 V vs Agi AgCI, depending on the

current density applied and the DMSO composition used. The percentage yield of

DMS02 and the CE were relatively high even at low current densities in flow reactor as

compared to those obtained in batch reactor (S. No.5, 6; Table 3.1) The yield and CE

values were further improved when Na2S04 was used as catholyte. However, the H2S04

medium is preferable as the cell voltage is less. In both the cases, the flow of counter

ion, W across the membrane occurs from the water auto decomposition equilibrium at

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Electrochemical Applications of Ion Exchange Membranes in Chemical Transformatiolls 76

the membrane-solution interface of the anode compartment into the cathode

compartment and carries the cell current.

Product analysis

The IH-NMR spectrum of DMSO exhibited a single sharp peak at 2.66 (5

corresponding to six protons of the two symmetric methyl groups. With the progress of

electrolysis, the intensity of this signal was reduced and a new peak at 3.05 (5

corresponding to six protons

of two symmetric methyl

groups was observed whose

intensity increased. The IH_

NMR spectrum of DMSO

(5%) after 7 h electrolysis is

depicted in Fig. 3.3. The low

intensity peak at 2.66 (5 and

the high intensity peak at ppm 3.00 250

3.05 (5 correspond to the Fig.3.3. IH-NMR spectrum showing the 96% conversion of (5%) unconverted (4%) and (CH3hSO to (CH3hS02 after 7 hr. electrolysis at 15 rnA crn-2

converted (96%) DMSO,

respectively. The isolated products obtained by using both the reactors showed a single

peak at 3.05 (5 indicating DMS02 as the sole product.

The FT-IR spectrum of the isolated DMS02 exhibited strong absorption bands at

1136 cm-I corresponding to symmetric S=O stretch and at 1298 and 1336 cm-I due to

asymmetric S=O stretch. Besides, the other absorption bands observed at 3020, 936,

763 and 699 cm-I are typical for DMS02 as reported in the literatureW The strong band

at 1030-1080 cm-I corresponding to S=O stretch ofDMSO was absent in these spectra.

DMSO showed absorption maximum at 208 nm (959 ~I em-I) while no such

absorption was found for the product in the uv-visible spectra. This is as per Iiterature40

reports that sulphone shows absorption due to IT-IT* transition in the far uv at

wavelength less than 180 nm but not in the near uv whereas sulphoxide shows weak

absorption in the near uv due to n-IT* transition at wavelengths longer than 200nm. The

Ph. D. Thesis afAlr. Sanjaykumar S. Vaghela Bhavnagar University, Regtn. No. 654, 411012000

Electrochemical Applications of Ion Er:challge ~fembralles in O,emical Trans/ormations 77

elemental analysis of the purified product indicated % C as 24.74 and % H as 6.05

which are close to the calculated values 25.52 % and 6.42 %, respectively for DMS02.

Cyclic voltammetry and mechanism of electrooxidation. Typical cyclic

voltammograms obtained at a gc electrode for various amounts of DMSO in

acetonitrile-O.I M n-Bu4NBF4 are shown in Fig. 3.4. A single irreversible anodic peak

is observed at around 1.9V corresponding to the two-electron oxidation of DMSO to

DMS02 as follows.

•

Fig. 3.4a shows the cyclic

voltammetric response for the solvent-

supporting electrolyte system. It can be

seen that with increasing concentration

of the added DMSO to the acetonitrile-

0.1 M n-Bu4NBF4, a peak starts to

appear, whose height Increases,

indicating the oxidation of DMSO to

(3.1)

DMS02 (Fig. 3.4 b,c) Further 2 1.5 1 0.5 o

enhancement in the current was seen

with the addition of 2 mmoles of

water (Fig. 3.4d), indicating the

E, V vs Ag/AgCI

Fig.3.4. CV of CH3CN.o.! M Bu,NBF, containing (C(CH3hSO (a) 0.00 M, (b) 0.05 M, (c) 0.10 M, (d) 0.10 M with 2 mmols ofHoO at gc electrode

participation of trace quantities of water present in the solvent in the electrochemical

oxidation of sulfide to sulfone at + I. 9 V, as per equation 3.1 above.

3,3.2. Voltammetric studies all the reduction of maleic acid to slIccinic acid Cyclic

voltammetry. Cyclic voltammetric study was carried out in 1 M H2S04 and in different

buffer solutions. In buffers, the range of pH employed was 0.0 to 8.1. Fig. 3.SA, shows

the voltammetric responses of 1 mM maleic acid in 1 M H2S04 at different scan rates. It

showed only one peak in the reductive scans and no response in reverse scans. At 0.5

Vis (Fig. 3.SA(a)), it gave a sharp peak (E1I2-Ep = 24 mY) at Ep = -0.570 V which

shifted negligibly with the decrease in scan speed as seen in Fig. 3.SA(b-c) Similarly,

Ph. D. Thesis aJAfr. Sanjaykumar S. Vaghela Bhavllagar University, Regln. No. 654, 411012000

Electrochemical Applications of 10 II Exchange Membranes in Chemical Transfonnations 78

the Ep!2-Ep values varied little in the range 25-35 mV. The plot, ip liS square root of scan

speed (Fig. 3.5B(a)) was linear and passed through the origin which together with the

above results revealed that the

reduction of maleic acid seen in

Fig. 3.5A, is an irreversible two-

electron diffusion controlled

process. The peak position, its

intensity and the slope of the

plateau of the peak

corresponding to the maleic acid

reduction at -0.570 V (Fig.

3.5A(a)) were altered

considerably when the

concentration of the acid was

reduced. The changes

·'-~'-'~~~-~. ..... ~/}c·· * ...... .

pH. Between pH 2.Y"'" 4.5; the· Fig.3.6. (A) Cyclic voltammetric response of ImM maleic acid at HMDE in buffered and unbuffered media

plateau of the peak appeared to be (a) 0 (b) 2 (c) 3 (d) 4 (e) 5 (I) 7 (g) 8.1 Scan rate = 0.1

split in two at slow scan speeds (,s; Vis (8) Plot of E"" vs pH

Ph. D. 711esis o/Afr. Sanjaykllmar S. Vaghela Bhavllagar University, Regtn. No. 654, 4/10/2000

Electrochemical Applications of Ion Exchange Membranes ill Glemical Transfonnations 79

0.2 Vis) as seen in Fig. 3.6A (c, d) which is explained in latter part of this discussion.

The decrease in peak intensity (ipe) in the pH range 0-2 (Fig. 3.6A(a, b» is explained

for the decrease in hydrogen ion activity which takes part in the electrochemical

reaction while that at pH ~ 8 is attributed to the slow participation of the deprotonated

maleic acid species and the protons of the medium. However, the overall peak height

(ipe) at all the pH values increased with the increase in the scan speed. The plots of ipe vs

square root of scan speed were linear and passed through the origin as seen in Figs. 3.5

B(b and c) for pH, 5.0 and 8.1, respectively. Moreover, the peak height at a given scan

speed and pH was increased linearly with the increase in the concentration of maleic

acid. This indicated that the electrode reaction at all pH investigated here was still under

diffusion controlled.

The ipe, and Ep/2-Ep data measured at three different scan speeds and pH pertinent to

Fig. 3.6A are summarized in Table 3.2. The ipe value at a given scan speed, was large at

pH = 0 and decreased with increase in the pH. On the other hand the Ep value at a given

pH, was nearly constant and shifted negligibly to positive potentials with decrease in

scan speed. But, at a given scan speed, the peak position shifted considerably to more

negative potentials with the increase in pH of the solution indicating the involvement of

hydrogen ions in the reduction process. The plot ofEpc vs pH for 0.1 Vis is shown in the

Fig. 3.6B. The plot is linear with an average slope of -0.125 VlpH.

Table 3.2. Cyclic voltammctric data of Maleic acid reduction at HMDE in different buffer solutions. 100 I

pH Scan i" -Ep Ep12-Ep" pH Scan i" -Ep Epl2-E~ 'peed (vI,)

(1lA) (V) (mY) speed (vIs)

(1lA) (V) (mY)

0.0 0.05 13.77 0.559 24 4.10 0.05 8.66 1.078 102 0.10 19.48 0.556 23 0.10 12.60 1.094 110 0.50 38.97 0.574 39 0.50 25.59 1.118 118

1.0 0.05 11.02 0.685 24 5.05 0.05 9.06 1.212 70 0.10 15.15 0.688 35 0.10 12.20 1.204 70 0.50 2933 0.696 32 0.50 2362 1.181 70

2.02 0.05 10.24 0.787 79 7.00 0.05 7.87 1.456 55 0.10 14.57 0.748 56 0.10 11.02 1.464 55 0.50 31.50 0.740 63 0.50 2205 1.496 87

3.00 0.05 8.27 0.881 70 8.10 0.05 4.72 1.543 55 0.10 11.42 0.905 87 0.10 5.91 1.551 63 0.50 24.41 0.960 134 0.50 9.45 1.574 86

Ph. D. Thesis o[}.dr. Sanjaykumar S. Vaghela Bhavnagar University. Regtn. No. 654, 4/10/2000

Electrochemical Applications of Ion Exchange ~fembranes in Olemical Tramformations 80

It is noted from the data in Table 3.2 that, at all scan speeds, the EpI2-Ep values were

in the range of23-39 mV in 1 M H2S04 as well as in buffer solutions of pH = 00 - 1.5.

But, it increased to 55 - 87, 102-134 and 55 - 87 mV in the pH ranges 1.5-3.0, 3.0-4.5

and 5.0-8.1, respectively. This may be the resultant effect of decrease in hydrogen ion

activity and transformation of maleic acid into mono- (HOOCCH=CHCOO-) and di-

COOCCH=CHCOO- ) cations (discussed in the later part of this section) with the

increase in solution pH. The large Epl2-Ep values in the pH range 3.0-4.5 may be the

reduction of HOOCCH=CHCOOH and HOOCCH=CHCOO- at closely separated

potentials.

Product identification. The solutions after the electrolysis were studied by IH_NMR

spectra in D20 which showed the yield of -100 % succinic acid in 0.1 M H2S04 and

99.6% sodium succinate in 0.1 M Na2S04 at pH 8.1. It is interesting to note that the

product yield in both cases was nearly same.

The products from the electrolyzed solutions stated above were isolated and

characterized. The compound obtained from 0.1 M H2S04 showed a peak at Ii = 2.44

ppm corresponds to the protons of two symmetric methylene (-CH2) groups in IH_

NMR and a strong absorption band at 1695 cm-I corresponding to >C=O stretch, apart

from other bands in FT-IR spectra for succinic acid. The product obtained from 0.1 M

Na2S04 showed a peak at Ii = 2.18 ppm in IH_NMR spectra and a broad IR band

centered at 1563 cm -I corresponding to >C=O stretch for disodium salt of succinic acid.

The peak at Ii = 6.38 or 5.91 ppm in IH_NMR and the strong band at 1637 cm-I in FT-

IR corresponding to -HC=CH- in maleic acid were absent. The elemental analysis of

the purified product, succinic acid indicated % C as 40.55 and % H 5. \0 against the

calculated values 40.64 and 5.12, respectively.

Mechanism of electro reduction of maleic acid Both, the HOOCCHxCHxCOOH

(where x = I for maleic or 2 for succinic) acids are dibasic acids. They dissociate

stepwise in two well separated pH regions. Their acid dissociation constants (pK. and

pK2.) corresponding to the equilibria I and 2, are reported to be 1.75 and 5.82 for

maleic acid, and 3.92 and 5.12 for succinic acid, respectivel/1 These values reveal that

the species HOOCCHxCHxCOOH, HOOCCHxCHxCOO- and -OOCCHxCHxCOO- of

Ph. D. Thesis of Mr. SallJaykumar S. Vaghefa Bhavnagar University. Regtn. No. 654. 4/10/2000

Electrochemical Applications 0/ Ion Exchange Alembralles in Olemieal Trans/annalians 81

both maleic and succinic acids all exist in equilibrium at pH < 7 but they convert into a

single species -OOCCHxCHxCOO- at pH > 7.

The split in the plateau of the peak seen in Fig. 2 A(c and d) could probably due to

the resolution of the reduction steps corresponding to viz. HOOCCH=CHCOOH and

HOOCCH=CHCOO- present at equilibrium (Eq. 3.2).

HOOCCHxCHxCOOH, • HOOCCHxCHxCOO- + H+ (3.2)

(3.3) .. Then, the reduction peak at low negative potentials may be attributed to the

involvement of HOOCCH=CHCOOH while the other at more negative potentials is due

to HOOCCH=CHCOO- in the electrode process. This assumption is supported by the

observation that a single reduction peak was observed at pH;?: 5 (Fig. 3.5A(e-g» due to

the complete conversion of HOOCCH=CHCOOH to HOOCCH=CHCOO-.

Comparison of pKa values also revealed that one of the carboxylic acid in both

maleic and succinic acids behave nearly as a strong acid while the other as a weak.

However, the more acidic carboxylic group of maleic acid is relatively stronger than

that of succinic acid while, the second carboxylic acid of maleic acid is relatively a

weak as compared to that of the succinic acid. Based on these facts and the cyclic

voltammetric (Ep12-Ep) data given in Table 3.2, the pH dependent nature of the cyclic

voltammetric peak at -0.570 V (Fig. 3.4A) is explained by the following mechanism of

electrode reactions.

pH 0.0-2.5

HOOCCH=CHCOOH + H+ + 2e-

HOOCCH2CH2COO- + H+

pH 2.5-4.5

HOOCCH=CHCOO- + 2fT' + 2e-

HOOCCH2CH2COO- + H'

pH 4.5-6.5

HOOCCH=CHCOO- + 2H+ + 2e-

Ph. D. Thesis a/Afro Sanjaykumar S. Vaghela

--.. HOOCCH2CH2COO-

HOOCCH2CH2COOH •

------c.~ HOOCCH2CH2COO- and/or

(3.4)

(3.5)

(3.6)

(3.7)

Bhavnagar University. Regtn. No. 654. 4/10/2000

Electrochemical , .... pplications of Ion Exchange A-Iembranes in Olemical TrallsfomlGtions 82

-OOCCH=CHCOO- + 2H+ + 2e-

-00CCH2CH2COO- + H+

pH >6.5

-OOCCH=CHCOO- + 2H+ + 2e-

-~.. -00CCH2CH2COO-

HOOCCH2CH2COO--(3.8)

(3.9)

(3.10)

In 1 M H2S04 or in the pH range pH 0.0 - 2.5, maleic (HOOCCH=CHCOOH and/or

HOOCCH=CHCOO-) acid reduces at the electrode by taking 2e - from the electrode and

2W (one from its more acidic carboxylic acid group and the other from the medium) to

give HOOCCH2CH2COO- which rapidly protonates to succinic acid (Eqs. 3.4 and 3.5).

But, in the pH region 2-5-4.5, wherein HOOCCH=CHCOOH converts totally into

HOOCCH=CHCOO-, it reduces by taking 2e- from the electrode and 2H+ from the

medium to give HOOCCH2CH2COO- which again protonates to HOOCCH2CH2COOH

(Eqs. 3.6 and 3.7) by abstracting a proton from the solution. In the pH region 4.5-6.5

maleic acid mostly presents as a mixture of HOOCCH=CHCOO- and

-OOCCH=CHCOO-, and they under go 2e--2H+ change simultaneously at the electrode

producing HOOCCH2CH2COO- and -00CCH2CH2COO-, respectively (Eqs. 3.6 and

3.8). The latter product may be in equilibrium with the former one or may rapidly

proto nates to the former in a succeeding chemical step (Eq. 3.9). On the contrary, at all

pH > 6.5, where the maleic acid exists solely as -OOCCH=CHCOO- reduces by 2e--

2H+ to give a single product i.e. -00CCH2CH2COO- (Eq. 3.10).

Electro reduction of maleic acid can occur by (i) the direct electron transfer from the

electrode, (ii) the reaction of activated hydrogen ions and/or (iii) the reaction of

adsorbed hydrogen ions with it. The reaction (iii) will be more likely to occur at

reversible and low overpotential electrodes at which hydrogen is easily dissolved. In

case of mercury cathode, reaction (iii) was ruled out and hence, the reduction may take

place either by (1) or (2). But the very low values obtained for the transfer coefficient

indicated the possibility of the reduction by direct electron transfer. The electro-

reduction of maleic acid was concluded to take place through activated hydrogen ions.

3.3.3. Ga/vanostatic transformation of maleic acid to succinic acid using a membrane

flow cell. Excellent yields (95-99%) of succinic acid were obtained in the galvanostatic

Ph. D. Thesis o/AIr. Sanjaykumar S. Vaghela Bhavnagar University, Regtn. No. 654, 4/10/2000

Electrochemical Applications of Ion exchange fl.,fembralles in Q,emical TransfomlOtions 83

reduction of maleic acid at SS, Cu and Pb cathodes vs DSA in the membrane cell. The

important data obtained under different experimental conditions with different electrode

pairs at different current densities are presented in Table 3.3. It can be seen in Table 3.3

that, at a given current density (I8.7 and 25 rnA cm-z) with O. I M HzS04-DSA anode,

the membrane flow cell yielded 0.4-3.3% more of succinic acid with Pb cathode than

with the other two electrodes, indicating the specificity of Pb-cathode for this process.

On the basis of succinic acid yields, the current efficiency improved marginally in the

order SS < Cu < Pb. However, the use of SS cathode is preferable as it is stable and

gives no harmful impurities. Moreover, the yield of succinic acid in all cases was found

to decrease as the current density increased from 18.75 to 31.25 rnA cm -z, which may

be accounted for by competing hydrogen evolution. The yield and coulombic

efficiencies were high when O. I M Na2S04 and 0.1 M NaOH instead of 0.1 M H2S04,

were used as anolytes. However, the H2S04 medium in the anode compartment is

preferable as the cell voltage is low. In both cases, the flow of counter ion -Na+ from

the anode compartment or H+ ion from the water auto decomposition equilibrium at the

membrane-solution interface of the anode compartment across the membrane to the

cathode compartment carry all the cell current.

Table 3.3. Data on the galvanostatic synthesis of succinic acid at different cathodes III a membrane flow cell

MA Anol}1e Cathode Cathodic Cell current Cell % Yield CE' fg (0.1 M) current fA Voltage of f%

fmA cm-2 N SA' 5 H2SO4 SS' 18.7 0.75 4 96.4 96.6

25.0 1.00 5 95.3 95.5 31.2 1.25 6 95.2 96.2

5 H2SO4 Cu' 18.7 0.75 4 98.4 98.6 25.0 1.00 5 96.1 96.3 31.2 1.25 6 95.4 95.5

5 H2SO4 Pb' 18.7 0.75 4 98.8 98.8 25.0 1.00 5 98.6 98.9 31.2 1.25 6 95.3 95.5

5 Na,S04 SS' 25.0 1.00 9-13 95.5 95.7 5 NaOH SS' 25.0 1.00 16-24 96.5 96.7 5 H,S04 SS' 25.0 1.00 5-6 93.8 93.9 5 Na,S04 SS' 25.0 1.00 9-13 96.6 96.9 5 NaOH SS" 25.0 1.00 15-20 80.4 80.5 , . " , With DSA as anode, \\Ith Pb as anode, calculated on the basiS of maXimum YICld of

product obtained.

Ph. D. Thesis ofJfr. Sanjaykumar S. Vaghela Bhavnagar University, Regtn. No. 654, 4/10/2000

Electrochemical Application8 of Ion Exchange ,Membranes in a,emical Transformations 84

The percentage yield of succinic acid obtained at SS was negligibly affected when

DSA anode was replaced by Pb anode, in both the cases wherein H2S04 or Na2S04

were used as anolyte. The data indicated that, with Pb anode, the use of H2S04 as

anolyte is preferred over

Na2S04 as the rise in the

cell voltage in the case of

latter was objectionable.

On the other hand, the %

yield of succinic acid

formed at SS cathode and

the CE was considerably

decreased when Pb and

o I M NaOH anolyte were used. This may be

attributed to the drastic

increase in cell voltage.

Also a weak electro

dissolution of the anode of

I I I

J , _,---.-J "._ .. ~\'-. __ _

Fig.3.7. 1 H-NMR spectrum showing the 98.4% conversion of 5% Maleic acid to succinic acid after electrolysis

lead under these conditions and the migration of Pb2+ to the cathodic compartment is

likely to cause a decrease in the yield and current efficiency.

The reaction of maleic acid reduction at the cathode in the membrane flow cell is

simultaneously followed by recording the 'H_NMR at regular intervals. The untreated

solution exhibited a single sharp peak at 6.33 Ii corresponding to -CH=CH- (ethylenic)

protons. The intensity of this was reduced as the electrolysis was in progress.

Simultaneously, a new peak at 2.56 Ii corresponding to four protons of two methylene

groups (-CH2-CH2-) was observed whose intensity increased with the progress of the

reaction at the anode. The 'H_NMR spectrum of electrolyzed solution (containing

initially 5% maleic acid), after 138 minutes of electrolysis, is depicted in Fig. 3.6. The

low intensity peak at 6.33 Ii and the high intensity peak at 2.57 0 correspond to the

unconverted maleic acid (1.4%) and converted succinic acid (98.4%), respectively. The

Ph, D. Thesis ofAfr. Sanjaykumar S. Vaghela Bhavnagar University. Regln. No. 654, 411012000

Electrochemical Applications of Ion £xchange }rlembranes ill Chemical Tramjomlatiolls 85

product isolated at the completion of electrolysis showed a single peak at 2.57 0

confirming the formation of succinic acid as exclusive product. The peak at 4.8 0

corresponds to protons of water.

3.3. -I. Galvanostatic transformation of benzyl alcohol to benzaldehyde. The

e1ectrooxidation of benzyl alcohol to benzaldehyde was carried out in a membrane cell

wherein the plain ion exchange membrane was placed between the cathode and the

anode at a minimum distance (2 -3 mm) to act as an SPE and make the oxidation

reaction feasible in the absence of supporting electrolyte. The data obtained for

galvanostatic oxidation with different percentages of benzyl alcohol in pure water at

different current densities are presented in Table 3.4. The product benzaldehyde was

estimated by UV -vis spectrophotometry and was compared with a standard sample.

Table 3.4. Data on the galvanostatic oxidation of benzyl alcohol at a dimensionally stable anode in a membrane flow cell.

% 'Catbol}1e Anode Anode Cell Cell % Yield of Benzyl (0.1 M) current current Voltage Benzaldehyde alcohol rnA cm-' fA N

I H2SO4 DSA 5 0.16 14-7 15.7 10 OJ3 41-13 15.6 20 0.65 54-26 15A 30 1.00 58-27 17.2 40 1.31 49-32 20A 50 1.65 61-32 33.7 60 1.97 51-42 29.0

2 H2SO4 DSA 30 1.0 57-18 9.5 3 H2SO4 DSA 30 1.0 53-18 13.6 4 H2SO4 DSA 30 1.0 71-15 12.7

• Catbode - Stamless Steel.

The Data in Table 3.4 reveals that the yields (10-29%) of benzaldehyde obtained in

the galvanostatic reduction of benzyl alcohol at DSA in the membrane cell were not

encouraging. However, the yield increased with the increase in current density

indicating the feasibility of the oxidation of benzyl alcohol to benzaldehyde at DSA, but

the cell voltages at all current densities were more than the normal values due to high

resistance caused by the substrate. Further, it is noticed that the yield of benzaldehyde

decreased as the % benzyl alcohol increased due to decrease in the solution

conductivity. Because of theses reasons, the studies were not further extended.

Ph. D. Thesis of AIr. Sanjaykumar S. Vaghela BhavnagarUniversity, Regtn. No. 65.f, 411012000

Electrochemical Applications of/on E'Cchange Alembranes in a,emical Transformations 86

3.4. Conclusions

The results obtained in the present study indicate the potential applications of SPE

reactors with plain Membranes (Membrane flow cells) for the water based

transformation of some of the organic compounds. The advantages in specific example

exploited here are summarized below. They may be further investigated for their

commercial utilization.

Oxidation of methyl sulfoxide. The difficulties involving with expensive catalysts,

corrosive chemicals, cumbersome procedures, or the use of dimethyl sulfide which has

a pungent odor, the requirement of adding a supporting electrolyte, saturation of the

medium with the sulfone before electrolysis as required in the conventional methods

and the separation of supporting electrolyte and catalyst from the reaction

mixture/product are overcome by the use of membrane flow reactor.

Reduction of maleic acid. The present study finds a novel and simple method of

electrochemical preparation of succinic acid from maleic acid using an ion conducting

polymer electrolyte flow cell. It demonstrates the advantages of using a highly

conductive solid ion exchange membrane film between the two electrodes in the flow

cell wherein the use of supporting electrolyte is avoided. Thus, the additional separation

steps otherwise required in conventional methods are not required. The most advantage

is that the required hydrogen is generated from water.

Ph. D. Thesis ofAfr. Sanjaykumar S ~ aghela Bhavnagar University. Regtn. No. 654. 4; 10J 2000

Electrochemical Applications of Ion Exchange Alemhranes ill O,emieal Transformations 87

3.5. References

L Budavari, S., (Ed.), All Encyclopedia of Chemicals, Drugs alld Biologicals, 11th

edn, Merck & Co., New Jersey (1989) 962.

2. Pereira-Rames, 1. P., Messina, R. and Perichon, 1., } Appl. Electrochem. 83

(1986) 379

3. Bailey, Jr. and France, Brit. 926,452, May 15, (1963).

4. Truce, Kinglor and Brand, Org. Chem. Sulfur, Ed. S. Oae, Plenum (1977) 527.

5. Vedemikov, V. G. and Maksinov, V. F., USSR Patent 166333, Cl C07c, 19th

Nov. (1964).

6. Devis, H. R. and. Sorenson D. P., U. S Patent 2,870,163, Jan. 20, (1959).

7. Devis, H. R. and Sorenson D. P., U. S Patent 2,870,215 Jan. 20 (1959).

8. Goheen and Bennett} Org. Chem. 26 (1961) 1331.

9. Seree de Roch and Menguy Fr. 1,540,284 Cl. C 07c, Sep. 27, (1968).

10. Boehme and Sitorus Chem. Ztg. 96 (1972) 37-8., CA, (1972) 77, 8496Ot.

1 L Thompson J. Am. Chem. Soc. 83 (1961) 845.

12. Akamatsu, Kamishima and Kimura CA 65 (1965) 18826c.

13. Akamatsu, Ueshima and Kimura Japan Patent 70,07,539, 70, Cl. 16 B 7, Mar.

16, (\ 970)

14. Mallievskii, Vints, Perfenov and Enanuel, U. S. S. R. Patent 323,966, Cl. C 07

C 147/14, Feb. 05, (1979).

15. Bennett, Goheen and Mac Gregor} Org. Chem. 28 (1963) 2485.

16. Schenck and Krauch Ber. 96 (1963) 517.

17. Hubenett and Dorffurt German Patent. 1,034,171, Cl. 120, July 17, (1958).

18. Bennett and Goheen U. S Patent. 3,418,224; Cl. 204-78; 24 Dec. (1968).

19. Kunugi, A., Yasuzawa, M,. Kan, K., Ogumi, Z .. and Takehara Z. 1., Electrochim

Acta 40 (1995) 1785.

20. Lin S M. and Wen T. C, } Appl. Electrochem. 25(1), (1995) 73. (CA:

122:91443y)

21. Do, J. S. and Do, Y. L., Electrochim Acta. 39 (1994) 2299.

22. Kirk, 1. and Othmer, D. F., The Encyclopedia of Chemical Technology, Ed. H.

G. Mary, 3rd edn, Vol. 21, 1. Wiley & Sons, New York (1983),p848; 4th edn,

Vol. 22, 1. Wiley & Sons, New York (1997) 1074 Ph. D. Thesis ofAfr. Sanjaykumar S. J aghela Bhavllagar University, Regtn. No. 654, 4/1012000

Electrochemical Applications of Ion Exchange ~fembranes ;n Owmical Transfonnations 88

23. Lysyak, T. V., Kolomnikov, I. S. and Kharitinov Yu. Ya., Koord. Khim. 9

(1983) 1000.

24. Wang, X. and Yedi, G.; Chill. Chem. Lett. 4 (1993) 407.

25. Yamada, S.; Hidefumi, H., Shoichi, M. and Yoji, A. JP 09 31,011 [9731011]

(Cl. C07C55/10), 4 Feb. 1997 Appl. 95/181,199, 18 July 1995; pp6.

26. Ryuichi, I. and Akira, K, JP 09 95,464 [97 95,464] (Cl C07C55110), 8 Apr.

1997 Appl 95/253,656, 29 Sep. 1995; pp6.

27. Murib, 1. H. and Frank C. E., U. S. Pat. 3,923, 881 (Dec. 2, 1975), (National

Distillers & Chern. Corp).

28. Kyrides, L. P. and. Bertsch, J. A., US Pat. 1,927,289, 19 Sep. 1933.

29. Pomilio, 0., Z. Elektrochem. 21 (1915) 444.

30. Norris, J. F. and Cummings, E. 0., US Pat. 1,457,791 June 1943.

31. Vasudevan, D.,J. Appl. Electrochem. 25 (1995) 176.

32. Gora, 1.; Smigielski, K., Kula, 1., Pol PL 148,885 (Cl C07 C5511O), 31

Mar. 1990, Appl 269,881, 30 Dec. 1987; pp2.

33. Smigielski, K, Gora, J and Kula, J, Hung, J. Ind Chem. 20 (1992) 117.

34. Govindan, K P., Narayanan, P. K Indian Patent No. 124573 (1969).

35. Ramachandraiah, G. and Ray, P., .J. Phys. Chem.B 101 (1997) 7892.

36. Shahi, V. K, Prakash, R., Ramachandraiah, G., Rangarajan, Rand Vasudevan,

D., J. Colloid lllter. Sci. 216 (1999) 179.

37. Vasudevan, D., Vaghela, S S. and Ramachandraiah, G., J. Appl. Electrochem.

30 (2000) 1299.

38. Ency. 0/ Industrial Chemical Analysis Eds. Snell, F. D. and Hilton, C. L. InterScience Publishers Vol 7 (1968) 99.

39. Grasselli, J G. (Ed.), Atlas 0/ Spectral Data alld Physical cOllstanls/or Organic Compollnds, CRC Press, OH (1973) B-917.

40. Silverstein, R. M. and Bassler, G. c., Spectroscopic Identification 0/ Organic Compollllds 1. Wiley & Sons, New York (1963) Chapter 5 pp. 92, 93 and 97.

41. Martell, A. E. and. Smith, R. M., Critical Stability Constants, 5 Plenum Press,

New York, first supplement (1982) 313.

Ph. D. Thesis oJAir. Sanjaykumar S. Vaghela Bhavnagar University. Regtn. No. 654, 4/10/2000