Chemical reactions in molten salt solvents are of great interest at the moment. Experimental data on the subject are presented in some detail, e.g. in Refs. [I-3].
React. Kinet. Catal. Lett., Vol. 46, No. 2,
SOLVENT
EFFECT
ON
REACTION
S.A. Institute
of G e n e r a l
RATES
301-304 (1992)
IN M O L T E N
SALTS*
Kirillov
and
Inorganic
252601,
Chemistry,
Kiev
USSR
Received July 8, 1991 Accepted October 8, 1991
Predominant
solvation
to be c h a r a c t e r i s t i c reactions
~
p~C~B~eHHNX
tion
Chemical
reactions
at the m o m e n t .
of
in some
these
additions as
to
solvents
their The nism
reactions
effect
of
The
considerations This
effect
salt
e.g.
was
the
study
active found
containing
weakly
containing
strongly
are
accelerated
[7]
been
rate
solvents
actions
solvents
has
by t h o s e
[5]
and
particles
was
polarizing
or e v e n
* P r e s e n t e d at E U C H E M C o n f e r e n c e 2-8, 1990, R i o - P a t r a s , G r e e c e
change
salts
definition
rate
of
in Ref.
[6].
and mecha-
the
effect
reactions
showed are
cations,
on M o l t e n
small
and
of to
formation. who
cations
polarizing
and
of m o l t e n
to a n a l y z e
complex
are
insufficiently.
of c h e m i c a l
by D u k e ,
of g r e a t
subject
given
on the
studied
CO~5BaTalJ~Mg
[I]
the
was
B
A classifica-
in Ref.
salt
first
[I-3].
properties
in Ref.
on the on
in R e f s
peaK~MM
are
on the
Dynamic
active
present
solvents
data
suggested
[4].
reactions
solvents
3~eKTpOXMMMHeCKMX
in m o l t e n
determined
a i m of the
salt
electrochemical
~peMMymeCTBeHHa~
was
the m o l t e n
of c h e m i c a l
and
is s h o w n
xapaKTepHa
detail,
it in Ref. were
M
Experimental
electrochemically
molten give
COdeX
KOM~eKca.
presented
chemical
complex
salts.
XI4MMqeCKMX
aKTHBHOFO
interest
for
in m o l t e n
~OKa3aHO,~TO
of a c t i v a t e d
their Salts,
that
when
substituted acid--base
re-
mechanism
[8].
September
Akad4miai Kiad6, Budapest
KIRILLOV: SOLVENT EFFECT
Duke
attributed
cationic
field
ic radii. tivity
The
these that
and the c a t i o n i c suggested
Gibbs
activation
energy
rate
ions d e p e n d s correlation
et al.
between
on the i n v e r s e
cationic
for o t h e r
of s m a l l e r
the
of m o l t e n [9]. They
for e l e c t r o c h e m i c a l
also h o l d s
of r e a c t a n t s
for the c a t i o n s
relation
composition
by F l e t c h e r
This
to the a c t i v a t i o n
is s t r o n g e r
semi-empirical
first
melts
effects
solute
salt
radius
was
that the
reduction
chemical
ion-
reac-
solvents
showed
by
of n i t -
of solvent.
reactions
in
[10,11]. Let us m a k e
Gibbs
activation
tween
the G i b b s
use of the t r a n s i t i o n energy
is c o n s i d e r e d
energies
of a c t i v e
state
theory,
where
to be a d i f f e r e n c e
complex
the
be-
X # and reactants
A. 1
AG*~
=
GX#-
ZGA. 1
This
gas
equation
phase
is,
processes.
strictly
For
l
speaking,
reactions
applicable
in s o l u t i o n s
AG~,
only
to
GX# and
GA. are c o n s i d e r e d to u n d e r g o c h a n g e s due to the i n t e r a c t i o n l of a c t i v e c o m p l e x and r e a c t a n t s w i t h s o l v e n t (solvation)
AG#
If the have
= GX,
solvation
AGsolvx#
media will tionic
- G s o l v X* -
to the gas phase, The solvents
302
(stronger case
solvation
in c o n d e n s e d
and the
ionic
we w i l l
smaller
interactions)
the r e a c t i o n
rate
cawill
increases.
of r e a c t a n t s
< E A G s o l v A. ) i n c r e a s e s 1
is p r e d o m i n a n t ,
in the gas phase,
solvent In this
The p r e d o m i n a n t
complex
IAGI.soiv" A.•
A.I ; AG # for r e a c t i o n s
than
of salt
be e v e r - d e c r e a s i n g .
(AGsolvx,
of a c t i v e
> ZAGs~
be lower
radii
( ~GA'I l -
AG#
in m o l t e n
media
compared
1
and hence
reactions are l i s t e d
whose
decreases
rates
below:
were
the p r o c e s s
studied
rate.
at least
in t h r e e
KIRILLOV: SOLVENT EFFECT (I)
NO~
>
NO~ + 1 / 2 0 2
[10,12,13]
(2)
C104
>
C1- + 2 02
[11]
(3)
C104
C15
C1- + 2 02
[11]
4NOj-ClO~
~
4.o F +el
[10,14]
5)
NO2 + I/2 0 2
>
NO;
[12,13,15]
6)
ClOy + I-
>
IO~ + el-
[16]
(4)
7)
BrO3
Br$
Br- + 3/2 0 2
[7]
8)
2BrO; + Cr20~-
>
Br2 + 5/2 02 + 2 CrO~-
[17]
9)
P2ot+2
>
2 Po~
E18]
>
NO2 + O 2-
(I0)
No]
NO; + 2 e-
+ 2 No~ + i/2 o 2
[9]
0@8~ I
0m88 I
-o-.._o.i~ 320
154 ~O-..
1901
152
A
E 300
O
180 I
%
6 [ ~
21(]
r
1.3
1.4
1.0
1.4
140
200
100 0.7
0.8
0.9
1.0 1/r,(~ -1)
Fig.
I. Dependence of activation free energies for reactions 5-7 (left) and 8-10 radius of the solvent
(right) on the cationic
303
KIRILLOV: SOLVENT EFFECT
Gibbs
activation
been c a l c u l a t e d cation radius Refs.
energies
and AG # values
of the solvent
[10,11]).
are plotted
(Fig.
gies for all these reactions
complex
signs of their charges. as c h a r a c t e r i s t i c
the inverse I-4,
solvation
ener-
cationic
of the a c t i v a t e d
in addition
contains
to r e a c t i n g
species having opposite
This p h e n o m e n o n
for m o l t e n
see
I, Gibbs a c t i v a t i o n
In other words,
the a c t i v a t e d
have
decrease with d i m i n i s h i n g
i.e. p r e d o m i n a n t
complex takes place.
against
I; for reactions
As is seen from Fig.
radius of solvent,
species
for all these reactions
should be c o n s i d e r e d
salts.
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V.D.
Prisyazhnyi,
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82
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D.H. Kerridge: VB. A c a d e m i c
3.
The C h e m i s t r y
Press,
I.K. Delimarskii: Naukova
Dumka,
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S.V. Volkov:
New York
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Kiev
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5.
S.A. Kirillov:
6.
S.I. Chernukhin, Safronova:
Elektrokhimiya,
7.
F.R.
Duke,
E.A.
8.
F.R.
Duke,
W.W.
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916
M.L.
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66,
2114
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S.A. Kirillov,
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E. Freeman:
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E. Freeman:
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F. Paniccio,
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Chem.,
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15.
D.W.
James:
16.
F.R.
Duke:
Fused Salts.
McGraw-Hill,
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F.R.
Duke,
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J.Phys.Chem.,
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J.L. Copeland, A.S. Matculf, B. Hubble: J.Phys.Chem.,80, 236 (1976).
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