halides, especially for LiCl, in nonaqueous solvents. 1 5) For instance,. Brookes et al. ... distance. (a = 2.15 A) for LiCl in acetone .... to the Cl- solution, the E1/2 of ...
CHEMISTRY
LETTERS,
The
pp.
449-452,
Polarographic
Study
and
Masashi
Hironori
Kochi
of
Chemistry,
been
applied
The
formation
that
the
deduced of
to
or
of
of
some
polarographic of the positive in
the
In the
have 1 5)
ion-pair
contact radii have In
method to potential of
presence
of of
to
study
have
halide (Li+)2Cl
cations
been
ions
made
on
been
(Lewis)
Bronsted
(X-)
in
X-12)
as
follows
of (at
the
first
(the C1 and
(see
Eq.
3)
C2 are to
constants.
decrease
When
the
in
a
the
been
sum
solved,
triple-ion
formation a new
method makes wave of a
of
new
species
use base in
method. of
halide
ions of
can wave,
second is
acetone
developed
oxidation
first
reported
occur i.e.
in
via
steps.
i.e. of
examined
mercury
more
wave,
function
are
two
the
negative more
in
11,12) wave)
positive
wave)
concentration
(or
25℃):
(the
where
this
solvents
wave
of have
especially
1)
because not
A number
waves The
nonaqueous
LiCl
have
we
by
anodic acids.
for
al.
impossible
acids.
(the (,E1/2)
A)
acid)
halides,
constants. The (mercury dissolution)
6-10)
the
(HR =
et
possibility 6-10)
formation anodic
discovered
alkali
problems
the
acetonitrile.
(HR)2Cl
Brookes
practically
studies,
of
for
instance,
These
in
has
(HA = benzoic
(a = 2.15
A.
formation
,
reported
was
complex of the
excess
and
potential of
IMAI
University,
ions
(Li+)2(HA)Cl-
For
2.41
investigation,
halide
half-wave
activity)
of Japan
Anions
Yoshihiko
complex
as
(the
The
and
Kochi
of
been
previous
obtain shift
a large
present
presence
Science,
distance
is
solvation.
solvents the
HAGIWARA,
of
Halide
Society
Acetonitrile
such
measurements
suggestions
presence
nonaqueous
in
waves
,
solvents.
conductivity
strong
anodic
complexes,
phenomena
in nonaqueous value
method
(Li+)(HR)Cl
crystallographic
although
between
Acids
Minoru
Faculty
the
of
inconsistent
from
the
Interaction or
NAGAI,
polarographic
p-bromophenol), was clarified.
Many
the
Cation
The Chemical
780
A new
LiCl,
1987
on
Lithium
HOJO,*
Department
for
1987.(C)
activity
wave)
second an
acid
of
X ,
(1)
wave) HA is E1
1/2
(2) added, may
which shift
reacts
positively
with
X
and
E2,1/2
negatively.
(3)
Combining
Eqs.
1
the
wave
(cf.
first
and
3, Ref.
we
have
the
following
equation
about
the
shift
in
E1/2
of
6): (4)
where absence
(B 1/2) of
c and (E1/2)s HA, respectively.
are
the half Equation
wave potentials 4 can be extended
of
X in the presence to a more complicated
and
450
Chemistry
Fig. 2.
Shift
Letters
,
1987
in E1/2 of the first
wave
Fig. 1. D.c. polarograms of Cl in acetonitrile of Cl with changing concentration of containing various supporting electrolytes and acids , acids and Li+. [Et4NCl] = 0 .5 mM. [Et4NCl] = 0.5 mM. (1) Base current of 0.1 M Et4NClO4; (△) Benzoic acid; (□) p-bromophenol; (2) 0.1 M n-Bu3NHClO4;(3) 0.1 M p-bromophenol, 0.1 M (○) LiClO4; (▼) n-Bu3NHClO4; (●) the Et4NClO4; (4) 0.1 M benzoic acid, 0.1 M Et4NClO4; (5) second wave, LiClO4. Et4NClO4 was added 0.1 M LiClO4; (6) 0.1 M Et4NClO4. to adjust the ionic strength to 0.1 M. case,
in which
time
(Eq.
two
(E 1/2)c formation
The
absence
kinds
of
reacting
agents,
HA and
MT, are
present
at
the
same
5). (E 1/2)s + 0.059 constant(K') for
of
both
HA and
M+ is
log K' + 0.059 Reaction 6 can taken
as
p log [HA] + 0.059 q log [M+] (5) be obtained if E1/2 of X in the
(E1/2)s. (6)
The
incomplete
dissociation
acetonitrile
was
of
ignored
in
Tetraethylammonium in
acetonitrile
to
the
this
as Cl-
is
solution,
positively.
The
in
the E1/2
M (1
Fig.
E1/2
of
the
species
may
not
interact
are
shown
in
2.
The
slope,
affected of
none
the
was
Cl-
by
2 are
the was
reported
the
mV was
observed
Figure
124
wave
height,
The
formation
slope
of
the
formation for
constant
3
shows
of Li+,
of
the
first
mV (50
these
105,5
effect
1.
(more HA.
-
and
one)
shifts
constants of
benzoic
heteroconjugated
the
formation
was the
first
supporting was
not
affected,
by Eq.
was
as
potentials
changed
benzoic
control
from
acid character
(heteroconjugated
Kolthoff
added
shifted
half-wave
of
diffusion
heights)
(HA)
wave
120 mV (p = 2),
(Li+)2Cl
the
wave)
species)
respectively.
4.
The
and
Chantooni
species.13,14) of
wave
acid
presence
(HA)2Cl-
obtained acid.
the
The and
ca.
of
in
reversible.
in
as
benzoic
positive
for
and
were 2:1
Et4NClO4
negative
200 mM).
(HA)Cl-
waves
(more
The
n-Bu3NHClO4)
(ca.
When
reversibility, of
that
and
anodic
wave
wave with
LiClO4,
waves dm-3)
Table
59 mV (p = 1)
to
the
anodic
M = 1 mol
the
formation
similar
(e.g.,
ΔE1/2/Δlog[HA],
HA) to
the
listed
bromophenol
formation
of
wave.
shown
Table
Fig.
20 mM of
two
and
second
HgX3-
59 mV (5 -
1
of
the
salts All
gave
0.1
shown
added study.
chloride
containing
electrolyte,
the
The proposed
effect slope with
In of
p-
have of
115
the
(M-2 ).
of
the
coexistence
of
LiClO4
and
p-bromophenol
(HR)
Chemistry
Table
Letters,
1.
1987
D.c.
451
polarographic
containing
a) Concentrations c) The values e) No wave Table
2.
data
various
of halides
for
anodic
supporting
are all
waves
electrolytes
0.5 mM. h) Supporting
The
by precipitation,
overall
(R3NH+)pcl-
formation ,
f)
(Li+)pCl-
,
(log
etc.)
by
ions
electrolytes ion.
K)
the
of
in
acetonitrile
25℃
at
d) vs, Ag/0.1
Pyridinium
constants
halide cations
of the second waves are not shown here, was observed
of
are 0.1 M perchlorates. M AgClOa-MeCN electrode.
(m = 1.28 mg/s, chloride
analysis
τ=1.0s)
"complexes"((HA)pCl-,
of
the
anodic
wave
of
Cl-
on the E1/2 of Cl- . In the presence of 50 mMLi , the E1/2 shifted 60 mV (and not 120 mV) to the positive upon a 10-fold increase in the concentration of HR. Similar potential shifts were observed with other concentrations of Li+. On the other hand, the E1/2 was shifted ca. 60 mV positively by a 10-fold increase of the Li+ concentration in the presence of a fixed concentration of p-bromophenol (e.g. 50 mM). The values of p=1 and q=1 in Eq. 5 indicate the formation of (Li+) (HR)Cl-. Fig. 3. Shift in E1/2 of the first wave of Cl_ with changing concentrations of both Li+ and p-bromophenol. [Et4NCl] = 0.5 mM. (1) 10; (2) 20; (3) 50; (4) 100 mMof LiClO4. Et4NClO4was added to adjust the ionic strength to 0.1 M. 200
mM of
HR),
that
the
cates
mM) changes
the
(E 1/2)c
ca.
concentration. ca.
60
mV in
values
60
-
mV in
While, the
given
opposite
that
in
(E 1/2)s the at
value
direction
the
The E1/2
ized
by
2 were at
a
direction fixed
data
each
in Fig.
value .
fixed
The
(negatively)
E,
a 10-fold
concentration
of with
a
E1/2 of
Li+
10-fold
standardvalue
of
(HR)2„Cl-
(20
figure
indi-
rearranged
concentration with
be rearranged:
3 was
the
As the
used.
3 can
in Fig.
subtracting
(HR).,Cl-
Fig.
positive
(7)
of
HR (e.g.,
increase (e.g., increase
of 50
mM) of
-
200 the
Li+
shifts the
452
Chemistry
HR
concentration.
following
These reaction
data
occurs
show
with
that
the
p=-1
addition
of
and
q=1
Li+
in
the
in
can
be
Eq.
5.
Letters,
Thus,
presence
of
1987
the
HR.
(8) The
equilibrium
last
two
and
M+
constant
terms (cf.
exchange
in
-p
of
Eq.
= q
5 will
= 1).
reaction
the
of
exchange
be
cancelled
Thus,
Eq.
9,
reaction
we
log
by
equalizing
obtained
KP X is
log
given
obtained the
Kex
= 1.36
to
be
of
p-bromophenol)
easily.
The
concentrations for
Eq.
of
8.
For
HR
the
0.81,. (9)
The
coexistence
similar Ke
to
x =
of those
Li+
shown
0.17 and 1.3 The coexistence
ined.
In
this
following
and in
for
n-Bu Fig.
(n-Bu effect
case,
3NH+
(.instead
3.
The
exchange
constants
3NH+)2Cland (Li+)2Clof Li and benzoic acid
we obtained
p = 1 and
q
= 2
,
in
also were
5,
results
obtained
respectively. on the ClEq.
gave
wave
to
was
which
indicated
light
of
be
also
log
examthe
reaction: (10)
The
(Li+)2(HA)Cl
species
= C6H5COOO- ) which
The
was
paper
for
kindly
be
very
probable
previously
data
was
to
reported
polarographic
This
seems
Br-
looked
in
the
A
(HA)Lit
(A-
. 6)
and
I-
over
are
also
by Professor
listed
in
Table
Kosuke
Izutsu
1.
of
Shinshu
University. References 1)
H.
C. Brookes,
M. C. B.
2)
J.
N.
3)
M. Salomon,
4)
L.
G.
Savedoff,
5)
J.
E.
Prue
6)
M. Hojo
and
Y.
Imai,
Bull.
Chem.
7)
Butler
and J. and
J.
C.
Hotz, Synnott,
Phys.
Chem.,
J.
Am. Chem.
P.
J.
and J.
73,
Sherrington,
Y.
Imai,
Anal.
Chem.,
Y.
Imai,
Anal.
Sci.,
9) M. Hojo
and
Y.
Imai,
J.
11)
"Encyclopedia Dekker,
12)
Y.
A.
Dekker, I.
14)
M. K.
57, 1,
Bunseki
(.1982),
"Modern
New York
M. Kolthoff Chantooni,
Jr.,
9(a),
Polarographic
(1980),
and
of
Vol. p. I.
Faraday
A,
2602
Soc.,
56,
509
1971,
2415.
(1970).
(1985).
32,
57,
1795
(1961).
(1983).
Interfacial E77
the p.
1963
(1985). Electrochem.,
209,
297
(1983).
Elements,"
ed by A.
J.
Bard,
Marcel
58.
Methods
in
Analytical
Chemistry,"
Marcel
101.
M. K. Chantooni, and
92,
Soc.,
(1966).
Chem.
Kagaku,
Chem.
Soc.,
Jpn., 185
Electroanal.
of Electrochemistry
New York
M. Bond,
13)
Imai,
664
Trans.
and
J.
(1969).
88, Soc.
and
and
Spong,
Am. Chem.
Soc.,
M. Hojo
(1986). M. Hojo
H.
3299
8) M. Hojo
10)
A.
Jr.,
M. Kolthoff,
J.
Am. Chem. J.
Am. Chem. (Received
Soc., Soc.,
91, 92,
November
4621 7025 21,
(1969). (1970). 1986)
