Electrochemical fluorination of acetonitrile

159

ELECTROCHEMICAL

FLUORINATION

OF ACETONITRILE

MASATAKE

and NOBUATSU

WATANABE

HARUTA

Department Kyoto

of Industrial

University,

To Professor

Chemistry,

Yoshida,

George

Sakyo,

H. Cady

Faculty Kyoto

of Engineering,

(Japan)

on his 70th birthday

SUMMARY

An electrolytic nickel

cell with

anode was used

electrolysis

duration,

anode

acetonitrile

and pulsed

fluorination

of acetonitrile.

rate of helium current

flush

efficiency

of fluorination formation

yields

that the extremely

imposed

high

the barrier

obtained,

Pulsed

the mechanism

on the

The time dependence with

the film

electrolysis

did not

compounds.

potential,

it was

anodic

overpotential

across

the anodic

for electron

of

of the flow

duration

observed.

of fluorinated

of anode

operating

effects

in connection

anode.

the

on the electrochemical

Appreciable

were

disk below

of gas bubbling,

concentration

gas and electrolysis

of the decay

the potential

electrolysis

of CF3CN

on the nickel

analysis

the effects

potential,

was discussed

lead to improved

a gas dispersion

to study

transfer.

From

the

indicated

was mainly

due to

film of nickel Based

of electrochemical

which

on the results

fluorination

was

discussed.

INTRODUCTION

Inancarlier acetonitrile fluoride with

paperonthe

in a stationary

[ll, it was

comparable

shown

current

electrochemical solution

referred

that one of the advantageous

chemical

fluorination

allowed

with

retention

of liquid

that CF3CN

efficiencies

fluorination hydrogen

and C2FSNF2

were

to each other. features

is that the complete of the original

of

obtained

It is often

of electro-

fluorination

functional

groups

is [2,31.

160 The present

investigation

of the fluorinated acetonitrile,

Since

product

i.e.,

electrochemical

CF3CN

it was

nation

with

sis was

electrolysis

period

information

relating

be discussed

formation

Donohue

of organic

lead to improved

In addition potential enabled

current

us to have better overpotential

it varied

in liquid

knowledge

on nickel

the types

that pulsed

hydrogen

fluoride

compounds. of anode

was analyzed, about

of

from the results

the decay

interruption

time

elcctroly-

fluoride

of fluorine

analysis,

This

Pulsed

[5] predicted

compounds

reaction

may provide

in connection

anode.

of wet hydrogen

to the product

during

in detail

whether

yields

on the fluori-

to the mechanism.

et al.

electrolysis

of the flow

can be evaluated

on the nickel

the

of acetonitrile,

of fluorination

rather

out to examine

formed.

electrolysis

anodic

The time dependence

fluorides

disk below

the effects

and pulsed

of the pulsed

should

to investigate

duration

will

acid

a gas dispersion

concentration

carried

products

cell with

potential,

the film

of of

of the electrolyte

of the perfluorinated

the induction

significant dependence

group

the mechanism

anode

reaction.

from which

that agitation

yields

was used

rate of helium, electrolysis

the yield

the functional

and to elucidate

reported

[41, an electrolytic anode

retaining

to improve

fluorination.

led to the improved

nickel

was undertaken

which

the extremely

for the fluorine

high

evolution

and

fluorination. Fluorination

of acetonitrile

methods.

Bigelow

fluorine

gas and Nerder

The obtained variety with

et al.

results

of operating

those

of other

has been

[6] reported

carried

the direct

[7] the fluorination

of electrochemical conditions methods

were

described

out by other

fluorination

by

by HgFZ.

fluorination

discussed

under

a

and compared

above.

EXPERIMENTAL

Electrolytic

cell

The electrolytic of Teflon transparent

with

Kel-F

Kel-F

cell used fittings

for this study was constructed

and a Teflon

tube was used as a "sight

lid. A piece glass"

of

to observe

161 the solution

level

the internal

arrangements

shown

in Fig.1.

the Teflon Each

condenser

skirt

vapor

is connected

by methanol

of about

in product

bubbled

into the solution.

of the cell to allow

to the wall

pre-electrolysis fluorination.

hydrogen

disk

dry helium screen

is to be

electrodes used

were

for the

for electrochemical

The two Pt conductance of electrical

by

each reflux

to reflux

and they were

of the cell,

or as the cathode

the measurement

-30°C

is

compartment.

with

The two nickel

showing

is separated

A gas dispersion

gases.

in the bottom

view

in the cell

of 1

and a cathode

of the cell

mounted

attached

a capacity

into an anode

cooled

fluoride

of the electrodes

The cell with

compartment

A cross-sectional

in the cell.

electrodes

conductivity

were

used

of liquid

for

hydrogen

fluoride. The reference the reported

for fluorination and with

were

apparent

electrochemical a diameter #600

were

degreased

were

carried

sandpaper

cell,

available purity

through

remove glass

hydrogen

99.9%)

the reflux

for the

rods with

by sanding

surface.

dried.

Then,

they

All experiments

became

grade)

was

extremely

fluoride

was distilled

condenser

then pre-electrolyzed

(supplied directly

from a

into the refrigerated for about

a day until

low. Acetonitrile

used without

by

further

the

(guaranteed

purification.

of products

The effluent through

nickel

prepared

to smooth

and vacuum

of 99.9%

materials

conductivity

Analysis

benzene

were

purity

The anodes

zone melted

all

used

out at O'C.

and was

reagent

were

anodes

with

area_of_.?O-25cm2.

The electrodes

to which

Allnickel

in the form of plate

and buffing

with

Co. Ltd.,

cylinder

referred.

measurements

Commercially Daikin

used was Cu/CuF2[8],

were

surface

of 2.5mm.

with

Starting

electrode

potentials

the reflux hydrogen

gases

fluoride

tube cooled

produced

condenser

by an electrolysis

and sodium

and the products

in liquid

nitrogen.

fluoride were

Since

were

pellets

collected

products

passed to in a

remained

162 1:

Ni anode

2: Pt conductance 3: Reference 4: working

electrodes

electrode

electrode

electrochemical 5: to reflux

(Cu/CuF2) for

measurements

condenser

6: Transparent

Kel-F

tube

7: Ni screen

electrodes

8: to reflux

condenser

9: Teflon

skirt

10: gas dispersion

disk

11: drain

Fig.1.

Electrolytic

in the electrolyte

cell

even after

they were

purged

the glass

tube until

products.

The collected

with

a known

volume

the measurement each product gram

was determined except

were

finished,

amount

The molar

in

free from the

were vaporized

total

was

gas and collected

became

in a bottle

was determined formation

ratio

by of

by the peak area of gas chromato-

by the corresponding experimentally identified

correction

for all products.

factor,

which

All products

by i.r. spectra.

Measurements

Potentiodynamic grams)

products

and their

of the pressure.

for one were

Electrochemical

helium

the electrolyte

was determined

calibrated

the electrolysis

out by bubbling

obtained

current-potential

curves

in the usual manner

using

(cyclic voltammoa motor-driven,

163 slow

function

The output stat.

generator

(maximum

of the function

scan rate,

generator

The current-potential

curve

was

0.2V/sec).

applied

was recorded

to a potentio-

on an X-Y

recorder. Pulsed pulse

electrolysis

generator

was carried

(Hokuto Denko,

potential

were

displayed

nication

Industrial,

out by using

CPG-05)

on an oscilloscope

VP-541A)

a current

and the decay

of the

(Matsushita

Commu-

and photographed.

RESULTS

In Table

1 the current

the products

obtained

acetonitrile

under

efficiencies

by the electrochemical

a variety

Electrofluorination

are tabulated

of operating

of acetonitrile

denoted

fluorination

yielded

as X in the Table

of

conditions.

C2F5H and NF3 as the main products, C2F6' relatively small amounts of CF4 and CF3H. compound

for all

CF3CN,

C2F5NF2,

together

with

Identification

was unsuccessful,

of the

however,

its i.r.

spectrum showed strong absorption bands at 1240, 1230 -1 and 970cm due to the C-F and N-F bonds and its retention time in gas chromatography This product C2F5NF2,

and hence

of the current efficiency discharge required

Effect

of fluoride

between

formation

was calculated

of C2F6

change

of the molar

efficiency

flush

The

of the

atom

Fig.3

ratios

shows

that

gas is shown

in

noticeably

the current current

up

efficien-

efficiency

do not show any signifithe similar

of the main

be noted

of the main

increases

total

of C2F5NF2

flow rate.

It should

The current

gas

flush

flow rate, while

efficiency

formation

rate of helium.

ratio.

of fluorine

efficiencies

of CF3CN

and NF3 decreases.

with

to

of the product.

the current

increasing

compound

on the basis

ion and the number

and the flow rate of helium

The current

and the current cant

and molar

for the formation

40% with

cies

efficiency

to that of C2F5NF2-

in C2F5NF 2 for the calculation

of the flow rate of helium

products

to

close

to be an analogous

it is included

of each product

The relation

Fig.2.

was very

can be presumed

products

the molar

dependence on the flow

formation

0

50

0

Temp. ("C)

Flow rate(Id/mi.n.)50

5.5

2.7

6.0

9.4

1.4

50

0

8.2

7.0

5.7

0.7

50

0

5.4

0.7

50

0

13.5 16.7

6.5

0.5 6.6

0

12 0

12

1.2

1.0 6.7

1.1 6.4

5.7 57.1

25.8 57.3

3.5

3.4 0.9

2.0 2.6

2.4

2.7 4.2

2.8

39.0 38.5 30.6 65.0 75.4 68.9

3.7

3.0

8.7 20.5 27.8

0.4 5.2

1.1 6.3

7.1 0

4.5

0.8

4.0

0.8

68.2 50

0

12

5.0

3.1

1.8

2.2

6.0

7.9

74.7 81.5 64.8 71.6

4.6

3.2

34.6 39.8 32.4 30.2

0.8

26.7 26.2 23.1 21.9

4.7

0.9

52.6

0

12

0.1 trace trace trace trace trace trace trace trace

11.4 42.4 42.1 26.6

7.9

2.2

5.2

6.8

0

12

6.75 6.95 6.75 6.75 7.05 6.0

1.0

8.6 19.7 29.9 40

0

12

7.1 18.9 14.3 11.8 11.9 10.4

0.6

4.3

0.6

50

0

-

7.5

I

0.9

trace trace

14.7 18.1 20.5 14.0 13.6

0.8 7.5

trace

4.0

6.0

4.5

04

Ave. C.D. (fi/an2)

I

Current efficiencies of electrochemicalfluorinationof acetonitrile.

Cont. (M)

1.

Potential (V)

Table

165

C2F5NF2

et=";

10 2fl 30 40 50 6P 7C 8@

10 20 30 40 50 60 70 80 FLOW RATE, ML/P!lN.

FLOW RATE, ML/PIN.

Effect of flow rate Fig.2. on current efficiency. CH CN: 1.01.1,Current density : 22mA/cltJ, electrolysis duration: lhr.

ratio

of CF3CN

increases

and it exceeds

appreciably

to CF3CN,

of C-N bond

show appreciable

this hand,

ratios

C2F6

with

the molar

and NF3

increasing

above

resulted

decreasing

decreases

formation

ratio

from the scission

trends

in their molar

the investigated

are observed.

of C2F5NF2

range

flow rate

40nl/min..

up to the flow rate of 40ml/min.

flow rate no further

throughout

Fiq.3. Effect of flow rate on molar formation ratio. CH3CN: l.OM, Current density : 12mA/cm2, electrolysis duration: lhr.

50% at the flow rates

In contrast

formation

u

and above On the other

remains

constant

of the flow rate.

Consequent-

ly, it is evident that the replacement of hydrogen in the methyl group of acetonitrile takes place in preference to the addition

reaction

introduction rapid

of the helium

removal

results

of fluorine

of CF3CN

about

2%, which

occurred. bonding

molar

formation

indicated

of C-C bond

formation ratios

ascribed

and that

ratios

the

flow rate allows

interface,

which

of C2F6

and NF3

of CF4 and CF3H was only

that the scission

This may be partly energy

group

flush gas at a high

from the reaction

in the decreased

The sum of the molar

to the nitrile

of C-C bond

to the relatively

(80-90kcal/mole)

compared

hardly high

with

that

166

of C-N bond

(70kcal/mole).

the following

experiment

Based was

on the results

carried

described

above

out at a flow rate of

50ml/min.

Effect

of the electrolysis

Fig.4 formed

shows

from

at a constant electrolysis

duration

the current

the electrolysis current

density

duration.

efficiencies* of 0.5M

of 8mA/cm2

The current

of the main

solution

products

of acetonitrile

as a function

efficiencies'of

of

C2F5NF2,

of the electrolyand NF 3 are nearly constant irrespective C2F6 sis duration, whereas the current efficiency of CF3CN appreciably

increases

with

increasing

duration

of electrolysis

within

60

50

0

20

40

60

80

100

120

Ill0

I60

IIt%> NINUTES Current efficiencies of products as a function of Fig.4. electrolysis duration. CH3CN: 0.5M, Current density:8mA/cm2, Flow rate: 50ml/min.

*

The current

the value a given

efficiency

at a given

electrolysis

shown

time but does duration.

in Fig.4 does

not

the time averaged

reprt?Sent

value

for

2

167 hours

and tr.ereafter it remained

current

efficiency

CF3CN.

There

shows

the similar

is an induction

as long as those

already

151 and ammonium

bifluoride

However,

in the present

the time averaged shorter

than

was plotted.

Fig.5, CF3CN

during

with

and C2F6. nitrile

group

the induction

Effect

of anode

Fig.6

the molar

potential.

other

potential. the molar

tion

formation

ratio

with

the electrolysis shorter

anode

CF3CN

and the

of the

is favored

lysis,

so that it was more the induction

was not observed

dissolution

of the nickel

that nickel

dissolved

leads

of the

with

to an increase

to an acceleration

potential

in the current

decreased

resulted

influenced

Any noticeable

because

in the

coulomb

electro-

by the results change

with

efficiency

anode

for the

anode (calculated on the assumption 2+ ), which amounted to 0.5 to 1.5%.

as Ni

in

at the

of fluorina-

be primarily

for the constant

in

be due to the

of fluorine

This would

anode

is observed

of all the products

largely

period.

This might

concentration

anode

duration

trend

products

as a func-

ratios

appreciably

potential

potential.

at higher

of the main solution

formation

decreasing

of C2F5H.

higher

during

ratios

do not vary

efficiencies

electrolysis

potential

of

of C2F5NF2

fluorination

produced

of 0.5M CH3CN

and therefore

Current

increasing

ratios

that

in

ratio

of electrolysis

further

formation

in anode

i.e.,

surface

rate.

As shown

formation

formation

that

a slightly

However,

density,

electrode

time

of CF3CN,

period.

the molar

duration

The molar

than CF3CN

fact that an increase current

become

potential

shows

tion of anode

is

period.

from the electrolysis

products

would

at a given

efficiency

the induction

for the molar

of water fluoride.

in the electrofluorination

the current

period

is

efficiency

period

efficiency

to

which

of hydrogen

the current

that

increasing

tendency

for the electrolysis

in the preferentially

during

formed

be noted

The total

2 hours,

so that the induction

it is indicated

Thus,

increasing of about

investigation

during

is the case

unchanged.

[91 solutions

the induction

increases

opposite

reported

it is only

appreciably

period

if the current

It should

of acetonitrile changes

one,

2 hours

nearly

168

c2F6

20 .

o-

~ * . . . ' . 20 4Q 60 80 IO0120140160 TIWE , PIINUTES

Fig.6. Molar formation ratios of products as a function of anode potential. CH3CN: 0.5M, Flow rate: 50ml/min., electricity passed: 50 coulombs/cm2.

w

60

5.5

6.0

6.5

7.0

7.5

POTENTIAL, V VS ClJ/CUF2

TOTAL

i

O

0.1

CONC.OF

0.5

I.0

ACETONITRILE, Pr

Effect of concentration on Fig.7. current efficiency. Anode potential 6.OV, Flow rate: 50ml/min.

169

Effect

of concentration

of acetonitrile

In Fig.'? are shown products

obtained

acetonitrile. cally

with

the current the three

The total

current

concentration,

fluorination relations

with

current

efficiency

increases

[lo]. Similar

the investigated

with

of increasing

increased

suggested

concentration

yield

hand,

logarithmic

of CF3CN

are

the current

concentration.

of concentration

was up to 1.OM

in the electrolyte

of acetonitrile,

that concentrations

for the better

g

range

solubility

logarithmi-

and concentration

for C2F5NF 2 and C F . On the other 2 6 efficiency of CF3CN increases Linearly with Although

of

in the electrochemical

observed

because

of the main

concentrations

efficiency

as observed

of N-nitrosodiethylam~ne

between

efficiencies

different

not less than

it might

be

l.OM are preferable

of CF3CN.

30 -

s kz =20-

c2F6

-0 D -*

IO -

l

0

CF3CN

q

q

EL-

e

-$I-IO0

300

500

700

Do

CURRENTON LENGTH,MSEC,

Fig.8.

Effect

of pulsed

l_OnA/cm2, electrolysis

electrolysis.CH3CN:

duration:

0.5M,

Zhrs.,interruption

Current

density:

length:

12Omsec.

170

Potential decay curve. density: lOmA/cm2.

Fig.9. Current

Pulsed

Pulsed

electrolysis

was attempted

current

at a current

of the continuous

observed

current

from the results

electrolysis

interruption

length

of

frequencies.

is shown

the potential

the state

is maintained

current during obtained

reported

that

interruption

results

interruption.

feature

et al.[5]

difluoride during

a rapid

decay with

for fluorine surface

of pulsed

of ohmic

time

essential

between

electrolysis.

interrup-

polarizatior

to 3.6V more It is suggestec

to the fluorinatior

Thus,

the assumption

fluorination

in current

on pulse

to ozone.

current

evolution.

interruption.

and the decrease current

diffe-

that pulsed

led to the considerable

potential

logarithmically

which

do not take

is quite

of anode

current

on time are

of fluorination This

fluoride

After

the results

for all the products,

by Donohue

the counterbalance

the subsequent

current

of current

of oxygen

of electrode during

represents

ratio

than the potential

is negated

types

interruption.

in Fig.9. decays

without

the length

of wet hydrogen

curve

of w

efficiencies

in the formation

The decay

anodic

with

that any different

during

change

on length

electrolysis

changes

in the current

indicates place

that

current various

of pulsed electrolysis at a constant 2. in 0.5M CH3CN solution. The current of lOmA/cm

density

No appreciable

tion

with using

8 shows the results

efficiencies

rent

0.5M,

electrolysis

120msec. Fig.

CH3CN:

during

efficiency

is the reason

for the

Electrochemistry

of the hydrogen

(a) Cathodic

reduction

fluoride-acetonitrile

curve

for the anodically

system

polarized

nickel Fig.10 polarized current

shows

a cyclic

at 5.2V

is observed

to increase

rapidly

reaction.

Anodic

fluorine

evolution

that

fluorine,

being

by the curve

potential

sweep

reduction

charge

could

noticeable

cathodic

implied

in the cathodic Accordingly,

calculated

be assigned

of the reduction

with

at SOmV/sec.

that

the reduction

current

was observed

the following

reduction

2.0

in Fig.11,

300

rates

above

high

50mV/sec.,

in the anodic

scan,

was not completed sweep

experiments

Cathodic reduction curve of nickel polarized at 5.2V in 0.7M KF solution. sweep rate: SOmV/sec.

the

rate approaching

even

4.0

on the

sweep

of fluorine

POTENTIAL,V vs Cu/CuF2 Fig.10.

of

thus obtained

As shown

decreasing

At the sweep

the reduction

I.0

is

from the area

charge

scan at such relatively

0

indicates

to the amount

rate of 50mV/sec.

-2.0 -1.0

curve surface

surface.

increases

value

sweep

coulombs

evolution

at 2.6V due to the

at the electrode

rate was examined.

a limiting

rapidly

Since

electrode

Cathodic

ca. 2.6V and it begins

due to the hydrogen

reduced

at the electrode

for the nickel for lominutes.

below

increases

reaction.

The dependence

which

at -1.OV

the reduction

surrounded fluorine

at potentials

current

the species

voltammogram

in 0.7M KF solution

rates.

were

made

at a

172 The relations

between

tion time are shown coulombs

obtained

0.5M CH3CN

limiting

charge

gradually

at 100 minutes.

charge

1 shows

electrode

The reduction

and thereafter

value

Curve

for the nickel

solution.

to 30 minutes

the reduction

in Fig.12.

and the anodiz;

the reduction

anodized increases

increases

The time required

at 5.8V in rapidly

approachinq for the

80

0.030.05

0.1

0.2

SWEEP RATE, V/SEC

Fiq.11. Reduction coulombs of nickel polarized at 5.2V in 0.7M KF solution as a function of sweep rate.

20

40

60

80

100

120

140

TIME, MINUTES.

Fig.12. Reducticn coulombs as a function of anodization time. Curve 1: polarized at 5.RV in 0.5M CH3CN solution, Curve 2: polarized at 5.2V in C.7M KF solution.

up a

173 reduction

charge

to be steady

of fluorination

shown

was as long as the induction

in Fig.4.

Reduction

on the electrodes

anodized

they

for 100 and 120 minutes,

are anodized

cathodically in Fig.12.

reduced.

than the corresponding the fluorine

reduced

increases

with

coworkers

reported

film

ones

the growth

fluorination

reaching

a limiting

of sorbed

film

the nickel

the reduction

in 0.7M KF solution

as that

the reduction

in 0.5M CH3CN

coulombs

to the curve minutes

value

fluorine

formed

(b) Analysis A steady

is shown

were

after

the existence

is observed

1300mV/decade.

slope

anodic

film of nickel

than by assuming Tafel

equation

barrier

of anode curve

Points

within

that

10 2.

the

for the fluori-

potential

taken

when

on open

for the steady

30 minutes reverse

reasonably

as a barrier

high value

an extremely

at the electrode-electrolyte

Tafel-like run with

a slope

of the observed

transfer

coefficient unsymmetrical

interface.

is

indicating

by assuming

for electron

low transfer

state

at each

polarization

surface.

explained

circuit

in 0.5M CH3CN

at each potential,

The extremely

implies

2,

similarly

in the curve

for nickel

approximately

an abnormaly

which

is observed

from 5 to 6V in the initial

can be more

time

is used

of a film on the electrode

relation

on

in the curve

than that

surface

5 minutes

of about

also made

acetonitrile.

is noted

for approximately

Tafel

for

at the same current As shown

increase

polarization

in Fig.13.

recorded

were

of this difference

containing

A hysterisis

potential. done

in the

concentration

anodization

is higher

of the decay

state

experiments

with

at the electrode

in a solution

solution

sorbed

of the electro-

and the steady

polarized

a sharp

1. However,

and a limiting

be one of the causes

curve

it

and his

as the time required

solution.

increases

It might

nation

that

fluorine.

For comparison,

density

thickness

Hackerman

strongly

period

could be regarded

larger

suggests

and therefore

film.

was

the induction

circles

are much

in the film rather

surface

of the anodic

and then

by shaded

1, which

or trapped

that the fluorine

[ll]. Consequently,

chemical

plotted

on the electrode

after

respectively

thus obtained

in the curve

is sorbed

adsorbed

were

coulombs

period

were made

for 30 and 15 minutes,

The results

The reduction

than merely

again

experiments

the rather

in the energy

174

6-

0.1

1

10

CURRENTDENSITY,nAh2

Steady-state polarization Fiq.13. nickel in 0.5PI CH3CN solution. If electron process

tial operates the film, steady

transfer

in the overall

across

curve

for

the film is the rate-determining

electrode

reaction,

the whole

the film. For the electron

across

the following

Tafel-

state polarization

like relation

curve

shown

overpoten-

current

is given

through

by the

in Fig.13.

i = kc,exp(aFnf/RT) where

i is current

fering film,

through

the film,

usual

the decay

factor

operating

on opening

+ bloge

-

after

are equation,

and the others

density circuit

is given

trans-

in the

meanings

in the Tafel

the film,

current

of electron

of electron

physical

coefficient

have

by eq.(l),

is represented

by

(2)

blog(t+e)

nf -t=o is the potential

just before

opening

opening

circuit.

circuit

and

b and 0 are given

by

b=

2.3RT/nF

(3)

0=

(bCf/2.3kce)exp(-nFnf't=o/RT)

(4)

Cf is the differential

that a linear slope

When

of potential

t is the time passed

where

of which

across

meanings.

'if = nf-t=o where

k rate constant

c, concentration

from the transfer

nf potential their

density,

c( expotential

different

(1)

relation

of b, when

the slope

the potential

log(time).

of the film.

A linear

It is evident

nf and logt is obtained

The slope b in eq.(2)

of the logarithmic

In Fig.14 against

t>>B.

capacity

between

representation decay

a

with

of es.(l).

on open circuit

relation

with

is identical

is observed

is plotted

in the region

175 of 10

-3

- lo-lsec.,

of which

is in fair agreement

tial

with

curve.

polarization

slope

that obtained

Consequently,

for the electrochemical

table

the anodic

of electron

barrier

speculative,

of electron however,

state

high overpoten-

at nickel

is attribu-

from fluoride

ion

film on nickel.

Fig.14. Potential decay curve; CH3CN: 0.5M, Initial condition:

The mechanism

This value

from the steady

the extremely

fluorination

to the slow transport

through

is b=1240mV/decade.

potential vs_ loqt nlots. 6.3V, lOmA/cm‘(

transfer

tunneling

through

through seems

if the film is semiconducting,

the film is quite

the space

to be most

charqe

layer,

plausible.Ll21

DISCUSSION

The agitation noticeable with

its maximum

group

The introduction facilitates

further

of helium

the rapid

fluorination.

compared

without

and NF3,

extent

of its low boiling

which

since

it

owing

Doint

to

(-68°C).

flush gas into the electrolyte of CF3CN

prevents

Thus, methods

of perfluorinated

C2F6

led to a

fluorination

to a considerable

removal

and therefore

gas

of CF3CN

in a solution

to further

of C2F5NF2,

irrespective

ling or by the other yields

subject

flush

efficiency

efficiency

was

in the electrolyte

the nitrile

interface

current

in the formation

dissolved

by helium

in the current

[ll. CF3CN

agitation resulted

of solution

increase

from the reaction

it from being

agitation

can be recommended

compounds

subject

of solution

retaining

to

by gas bubb-

for improved

functional

groups.

176 Noteworthy observed methods nation

defferences

between described

of acetonitrile

by fluorine

and polymers

C2F5NF2

pounds

retaining

amount

of fluorocarbons

nitrile

group were

addition

of fluorine

to replacement According yielded

to Nerdel, CH3CF=NF,

that only

of hydrogen

reaction

than

methods,

the electrochemical

CF3CN

with

formation

ratio

flow rate

of helium,

It should

be also noted

fluorocarbons amount

10% in total.

These

indicated

fluorination

features

group

contrary

to the greater reaction

electrochemical

proton

toward which attack

electrode may present

Since

reaction

condition

on the methyl

of

than

reaction fluoride

of acetonitrile

with

toward

which

is a

is protonated

by hydrogen

has an orientation

a favorable

to the addition

hydrogen

group

group

of

of hydro-

to the fact that

and solvated

and its nitrile

sequence

of fluorination

of addition

nitrile

of the fluorine

fluorination

is a two-dimensional

surface.

less than

the replacement

selectivity

that

and a trace were

to the reaction

in preference

facility

increasing

fluorination

ratios

charged

acetonitrile

with

only C2F5H

methods,

to the above

of yielding

and NF3 decreased.

of electrochemical

This

fluorination

strong

[13], Thus,

were

methods

50%. The molar

appreciably

may be attributable

at the electrode

positively

capable

of C2F6

contrary

group.

occurs

donor,

In contrast

was

formation

took place

to nitrile

to become

molar

that,

fluorine

replacement

hydrogen

by the chemical

gen in methyl

by the above

in the electrochemical

of which

took place

by fluorine

of the addition

not less than

those

by HgFZ

indicated

group

group

facility

increased

the

in preference

etc., which

reaction.

ratio

whereas

retaining

of CF3H,

evidently

of CF3CN

place

the than

that

of acetonitrile

in methyl

method

formation

more

by fluorine.

of fluorinations

the replacement

molar

takes

to nitrile

in view of greater

Further,

was much

group

CH2=CFNF2

of fluorine

The results

occured.

are reasonable

group

in methyl

CH3CF2NF2,

and no com-

it is indicated

the fluorination

the addition

and the replacement hardly

to nitrile

the fluori-

fluorocarbons,

obtained.[61

Therefore,

of hydrogen

that

nitrogen

hydrogen

are

and the chemical

gas yielded

containing

retaining

of perfluorocarbons.

of acetonitrile

method

It was reported

previously.

CF2=NF,

that

of fluorination

the electrochemical

fluoride

its methyl

solution

group

side,

for the preferential

group.

Consequently,

the

following

reaction

chemical

sequences

fluorination

can be considered

rate-determining I_

HF2-

ror the electro-

of acetonitrile.

CH3CEN

&

CF3CzN

CH3CrN

2

CF2HCeN

,

F+e+HF

F,

CF3CF2NF2

5

CF2HCF3+

(5)

5

(6)

C2F6 + NF3

(7)

NF3

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in Fluorine

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