a kinetic study of the chemical oscillating system comprising mannitol-acetone-bromate-h2so4

8/11/2019 A Kinetic Study of the Chemical Oscillating System Comprising Mannitol-Acetone-bromate-H2SO4

1/5

Indian Jo

urn

al of Chemistry

Vo l. 4 1A, March 2002 ,

pp

. 532-536

A kinetic

st

udy of

th

e chemical oscillating

system compris

in

g mannitol-ace

ton

e

bromate-H

2

S0

4

Shi-G ang Sh en' , Han-Wen Sun, Jin-Hu an Shan

& JL n -li L

iu

Collcge

of

Ch emical

and

Environm

en

tal Sc ience Hebei

University. Baod ing 071002. P. R. China

Rl'Cl il'ed

24

Ma .l 1; rel'ised 16 OClUbl.'r 2001

A new type of chemical osc

ill

at in g system comprising

lll


2/5

NOTES

533

Tab le I- The in

iti

al co

nc

entra

ti

on range of

th

e reacta

nt

s a

nd

tempera ture range

in th

e osc

ill

ating system (Concentration unit : mol dn'-

')

IAc tlo

0. 17-4.0

1.02

1.

02

1.

02

1.

02

1.02

.

[MAlo

IBrO

,'

lo

0.01 88 0.06

75

0.009-0.05 I 0.0675

0.

01

88

0.Q3 8-

0.1

35

0.01 88

0.0675

0.0188 0.0675

0.01 88

0.0675

[Mn

2

+1o

[H

2

S0

4

1

0

T K

0.0025 2.58

298

0.0025 2.58 298

0.0025 2.58

298

0.0001 25- 0.0250

2.58 298

0.0025

1.

30- 4.

10

298

0.0025

2.58 293-323

Time,s

Fig. I-The osci11ating curve of the potential with time [System: [Actlo = 1.02 mol dm'), [MAlo = 0.0188 mol dm') mol dm ,

[8r0.

1'10=

0.0675 mol dm , [Mn

2

+10 = 0.00250 mol dm

3

, [H

2

S0

4

1

0

= 2.58 mol dm

3

, temp.=298 0.1 K].

and the system exhibited a periodic oscillation

between

brown and

pale yellow. n the latter stage,

the solution colour became light, and the oscillating

cycle did not change much during the whole

oscillating process. With time, the oscillating

amplitude began to

show

a trend of

slow

increase, and

after a period

of

stable amp litude, the amp litude

began to

decrease gradually

until

the

oscillation

stopped.

Th e effect

of

temperature

and

the apparent activation

parameters

The mannitol-acetone-bromate-H

2

S0

4

chemical

oscillating system is very sensitive to temperature

changes. When the temperature increased, the

induction period tieS), oscillating cycle tp(s), and

oscillating life tt( s) decreased regularly.

A very good linear relationship was obtained

when fitting In(t

;

t

s

), In(tpt

s

) and In(tt s) with

I K

(shown in Fig. 2) , the linear correlation

coefficient

s

are greater than 0.

995,

and the

corresponding

lin

ear

equations are:

In(t; s) = E/RT

+

A;

In(tp s) = -Er/

RT

+ AI'

In(tl s) =

-E /RT

+ A,

in

which A;, A

I

and A, are the intercept

of

the line,

E;/R

,

Ep/R and E,

/R

are the slopes

of

the fitting line,

respectively. Compared with the Arrhenius equation

In (k) = EAIRT + A, (;-', tp l, and

t,

-' are very similar to

E

-5 A

c

-6

=

-7

3.

05

3.10 3 .15 3 .20 3 .25 3 .

30

3 .35

3.40

3.45

Fig. 2- The plot

of

In (f1s) with

r lK

A:

In

(tj l

s

) with

r lK:

8 :

In(tp

l

s

) w

ith

r K; C:

In(t, s) with

r

K.

[S

yste

m: [A

c

t]

o =

1.

02

mol dm-\ [MAlo = 0.0188 mol dm

3

,

[8r03'

]0= 0.0675 mol dm .

[Mn

2

+]

o = 0.00250 mol dm-

3

, [H

2

S0

4

]O

= 2.58 mol dn'-' ]

the reaction rate constants,

but

E

Ep and

E

should be

con-esponding to

the activation parameters, which are

called the apparent activation

parameter

in thi s paper,

and their values are E = 45 . 14 kJ mol , Ep = 60.20 kJ

mol , and E 67 .30 kJ mol , respectively. Th e results

are in good

agreement

with the inves

ti

gations of An

et al.

6

who obtained practically the apparent energy

of activation (Ep=61.03kJ mol ) for the

BZ

oscillating

system containing H

2

S0

4

, BrO}', lactic acid, acetone

and Mn

2

+.


3/5

534

I

NDI N

J CHEM. ,

SEC

A,

M R

CH 2002

Tli

e /j

e lS

/,tlie reactallt cOllcelltratioll

It

is found from the experiment that both

th

e

induction period tieS ) and th e osc illation cycle tp(s) of

the chemical osci lIati ng reaction are affected by th e

concentrati ons

of

th e reac tants; In (t/s) and In (t,,/s)

have good

lin

ear relationship with

In

([A ct]om

or'

dm'},

In

([MAl

o

mor'

dm' ),

In

([BrOJ' ]o mor' dm\

In([Mn2 ]o mo

r'

dm\ and

In

(

[H

2

S0

4

]0

mor'

dm' ) in

th e concen tration range as shown in Table

I.

Their

lin

ear relationsh ips can be expressed as:

In(t;ls) = ai+bi In ([Act]o

mor'

dm' ) +Ci In ([M

A]o

mo

r'

dm' ) +d

i

In[Br0

3'

]0 mor ' dm

3

)

+ ei InClMn 2 ]u

mor'

dm' ) + f I n [ H S mol dm' )

In

(t

i s )

,=

ap+b

p

m

~ m +C

p

In

([MA]o

mol dnl') +d

p

In[BrO, ]0 mol dnl' )

+ e

p

In ([Mn

2

]0

mor ' dm' ) + fp In[H

2

S041o mol dm\

I

Based on

th

e expe

ri

rnental data (w

hi

ch are

compose d

of

37 experimental data, eac h represents

the average of three parallel experim ental results), th e

correlati on coefficie

nt

s in

th

e above two formulae can

be

determined

by

plural

lin

ear fitting: ai = 6.88, b

i

=

-0.48, Ci = - 1.1 5, d

i

= 1.03, ei = -0.18, fi

=

-2.94; a

p

=

5.10, b

p

= -0.55, c

p

=

-1.48 , d

p

=

0.93, e

p

=

0.70,

1 1 =

- 1.28. The plural linear correlation coeffici ent s are

0.999 and 0.998, respect ively. Therefor

e, th

e

relationship of

th

e induc

ti

on pe

ri

od

ti eS)

and

oscillating cycle tp(s) with

th

e initial co

nc

entration

of

th

e reactan ts can be ex pressed a

s:

t (s )=969[ Act ]

O,OA8

[M A]0, ' ,'5

B

1'0

3

]0

OJ

[M n

2

]o,O'8

S

~ \

m o l dm

'J

)'

72

s

tp(s)= o , o s s A [ B r 0 J i ) ~

[M n2 ]o070[1-I

2

S04h ' 2s (mol

dm

) 6 8

s

It

can be seen from the above relationship , that

increas

in

g IAc

t]

o, IMA10 and

can

in

crease

th

e rate a

nd

sho

rt

en induction pe

ri

od t

ieS)

and

oscillation cyc le tp(s);

In

creas

in

g IMn

2

+Jo can sho

rt

en

th e induction period tieS) and elongated th e oscillating

cyc le tp(s);

In

creas ing [BrO, ' ]0 can elongate th e

induction period t

ieS)

and osc ill ating cyc le tp(S) .

Th

e j

illl

ctions of reacta

nt

s

Keep ing other reaction conditions consta

nt

, water

was added in place of acetone. It was found th at

adding potassium bromate solution produced large

quantities

of

Br2. The system colour changed to

brown and gave off a browil gas. After th e induction

peri od,

th

e potenti al decreased witho

ut

go in g up , and

th

e brown colour did not disappear, and no osc illating

react ion took p

la

ce. The ex istence

of an

induction

period demonstrates that

th

e accumu lati on process

of

HBrOz ex ists

in th

e osc illating

t c m . In

acidic

med ium, under th e cata lytic condit ion

of

Mn

2 , an

oxidation-reduction react ion takes place between

BrO, ' and MA produc

in

g Br2

wh

ich causes

th

e

solution colour to change to brown. The existence

of

large amount

of

Br2 preve

nt

ed

th

e accumulation of

HBr0

2. The brown colour

di

sappeared quick ly after

adding acetone and the osci llation took place . When

nitrogen was rapidly bubbled through

th e sys tem with

no acetone added, some osci Iations were observe

d.

So one

of th

e main functi on of acetone is to eliminate

excess ive of Br2 and to produce Br' simultaneously,

I e.,

Br' c

an

be oxidized

by

BrO

,'

,

wh

ich is favourable

fo

r

th

e accumulati on

of

1-1 Br02, so this is an

osc

ill

a

ti

on switch.

In

creas

in

g

th

e amo unt

of

acetone

increased

th

e acc umulati on, and

th

e induc tion period

became shorter. This accelerated

th

e whole oscillating

process, and the osci Iati ng cycle became sho rte

r.

Keeping the oth er conditions constant , adding

small amount of bromoacetone shortened th e

induction period . It indicates th at th e accumulati on of

bromoacetone is very important dur

in

g

th

e induction

period. Bromoacetone was partly oxid ized

by

Mn

'+

to

produce Br', which was fav ourabi e for

th

e

accumulat ion of HBr02 and shorte ned

th

e induction

period. The reaction process is as fo

ll

ows:

Mn

3

++CH,COC I-I

2

Br--;; Mn

2

+fBr'+Oxidation

Pro duct I .. . (2)

In

th e same way, water was added in th e system

re

pl

ac

ing MA. The so lution colour changed to pink

after adding bromate solution. The potenti al did not

decrease

af

ter th e first increase and no osc illating

reaction took place. Then MA wa s added agai n,

th

e

so luti on colour changed to brown, and th e osc ill

ati

ng

ph eno menon took place.

It

indi cated that Mn

2

+ was

regenerated through reduction

of

Mn

3

+

by

MA , i.e.,

Mn ]+ + MA

--;; . .

Mn

2

++ Oxidation product

II

... (3)

If without MA, [Mn' +] (or pote

nti

al) did not

decrease , no osc

ill

at in g reac tion could take plac

e.

Moreover, if

MA

wa s added again after

th

e osc illati on

stopp ed,

th

e oscill a

ti

on reac tion took place again. Th is

indicates th at MA was cons

um

ed in the reaction and

could not be rege nerated, w

hi

ch ac ted

as th

e reaction


4/5

NOTES

535

substrate. MA played the role

of

the reductant and

participated in the formation of Br2 at the same time.

So with the increase in the initial concentration of

MA, the rate of regeneration of Mn

2

+ through the

reduction of Mn

3

+ by MA increased, and the induction

period t;(s) and oscillating cycle tp(s)

became

shorter. .

On replacing

Mn

2+ by water, though no oscillation

occurred, the solution colour changed to light-brown

gradually. This indicates that though there is no Mn2+

as catalyst, Br0 3 can partly oxidize MA.

This

is

because alcohol is more easily oxidized than acid

6

.

7

.

This reaction shown as processes E in the following

section is the side reaction

of

the oscillating reaction,

consumes part

of

MA. In the presence

of

Mn2+,

Br0

3

and MA reacted rapidly to produce Br2, so that the

colour of the solution changed rapidly to brown. Here

Mn

2

+ plays the catalytic role, which is shown n

mechanism

in

the following section.

Br2 produced was removed in reaction

I)

to

produce B( at the same time. The B( thus formed can

be oxidized by Br03 which is favourable for the

accumulation of HBr02. The reaction process 10 took

place as process A.

At the beginning of the reaction (the induction

period), the concentration of

B (

is very low. The

catalytic process takes place predominately. With the

increase

in

the concentration of Mn2+ , it may cause

Reaction (II) and 10) proceed very fast and more

Br

2

is produced.

This

further causes reaction 1) to

produce more

B(

and then reaction (4) accelerates the

accumulation of

HBr0

2. The

time to reach the critical

value o( the oscillation is very short, so the induction

period t;(s) becomes shorter with the increase in

[Mn

2

+]o.

At the beginning of the oscillation, Mn

3

+

returns to Mn

2

+ through reactions (3) and (2). When

[Mn2+]o is large, though the rate of reaction (3)

becomes faster, every oscillation reaction consumes

large amount of MA, causing [MA] to

become

lower;

and during each cycle the time of

Mn

3

+

changing

to

[Mn2+] becomes longer with the increase in [Mn

2

+]o

;

so the oscillating cycle tp(s)

becomes

longer with the

increase in fMn2+

].

When

Br03

is not in the reaction

sys tem, the solution colour does not change, and no

oscillating phenomenon takes place. If Br03 is added

at the last stage of the oscillating process, the

oscillation restarts. This indicates that in the

oscillating system, Br031 is consumed and not re

formed. Without the catalysis of Mn2+, BrO) can still

oxidize part

of

MA and

consume

part

of

MA ,

(Process E) . So , on increas in g the concentration of

Br03 , more

MA

is consumed. Therefore, with the

increase in

[Br03

], the induction period t;(s) and the

oscillating

cycle

tp(s)

become

longer.

The effect o he radical inhibitor

Keeping other conditions constant, acrylonitrile

was added into a reaction system, the oscillation

stopped immediately. Also on adding ethanol into the

reaction system, the oscillation stopped immediately

after a few oscillations. Acrylonitrile and ethanol are

both radical inhibitors; it indicates that radicals are

involved in the oscillation reaction. It is reported \ J

that the possible radical reaction process may tak e

place as process B.

iscussion o he oscillating mechanism

Based on the above discussions, it is proposed that

the system may undergo the following five

processes

1.12:

Process A:

.. . 4)

HBr0

2

+

B(+ W

HOBr

. .. 5)

... 6)

. .. I )

Process B:

... (7)

... 8)

... 9)

4 M n 2 H ~

4Mn

3

++HOBr+HBr0

1

II ) ,

Process C: Mn

3

+ transformed to Mn

2

+ through reacli ons 3)

and (2)

Process D: B( was rege nerated by reactions ( I) and (2)

Process E: BrO)' oxidized MA through reactions (4) , (5) a

nd

10)

shown as follows:

H O B r M A ~ 1I2Br2

+0xidation

Product

I .. . 10)

The existence of the induction period indicates that

the mechanism is an automatic catalytic process

dominated by Br02 produced in reaction (8) during

Process B. The catalyst is

HBr0

2. B( plays the role

of

kinetic control.

The

multitude

of

[Br'] determined th e

rate

of

the self-catalytic oxidization. When fBr' ] is


5/5

536

INDI AN

J

CHEM., SEC. A, MARCH 2002

large enough, Process A

dominates

, and Process B is

inhibited, which causes the formation rate o f

Br0

2to

become slower.

The

outcome of Process A is to make

Process B dominating by removi ng

B

fro m system.

The proceeding of Process B results in [Mn

3

]

in

Reac tion

(9)

increasing constantly, which causes

Process C to proceed leading to regeneration

of

Mn

2

+.

At the sa me time,

B

is formed through Process D.

These processes go round and round, the oscillating

phenomenon of [B ] or [Mn

3

+]/[Mn

2

+] begins to take

place.

eferences

Zhao X

Z,

Zhao H X,

Xu

Y T Zang Y R, HI/ax l e

TOlI

gbao

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2

Li

H X, Liu M. Wang S X, Xu H H Fu C J,

Acta Ph

ysC

hilll

Sillica, 6 1990)609.

3

Lu

C H. Xu Z Q, XU J D

Ni

S S. llaxll e TOlIg ao. 2 1992)

30.

4 Shen S G, Zhao J G, San J H Dang G S. J.

f-lel

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Ulliversit

y

5 1995) 21.

5 Yuan C L, Li Z X Wang J C, Acta Phv-Chilll Si

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icu.

10

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6

An

C

J,

Zhuang L, Liu Y

Lin

Z X. Acta Chilli Si

ll

ha.

55

19

97) 259.

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C

J, Gan N Q, Liu

yi

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Li J

F Lin Z X.

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8 Rastogi R P, Verma M K Yadav R D, /I/{lia

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ll

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24A 1985) 721.

9 Trivett T L Meyer E A, J Bacterial , l07 1971 ) 770.

10

Field R J Burger

M,

Oscil/ lliolls al/ I

tr

avel/illg waves ll

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a kinetic study of the chemical oscillating system comprising mannitol-acetone-bromate-h2so4

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