Russ
ian
Chem
ica
l
Bu
l
le
t
in
,
In
terna
t
iona
l
Ed
i
t
ion
,
Vo
l
.
62
,
No
.
7
,
pp
.
1595—1598
,
Ju
ly
,
2013
1595
Publishedin Russianin Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1595—1598, July, 2013.
10665285/13/62071595 © 2013 Springer Science+Business Media, Inc.
Comparat
ive
conduct
imetr
ic
stud
ies
o
f
sa
l
icy
l
ic
ac
id
in
methano
l—water
m
ixtures
at
25
C
Z
.
Chaaraou
i
,
аA
l
i
H
.
A
lTa
iar
,
band
Ad
i
l
A
.
O
thman
ba
Depar
tmen
t
o
f
Phys
ics
,
Facu
l
ty
o
f
Sc
iences
,
Un
ivers
i
ty
o
f
Sc
iences
and
Techno
logy
o
f
Oran
"Mohamed
Boud
ia
f"
,
P
.O
.B
.
1505
E
l
M´naouar
,
31003
Oran
,
A
lger
ia
.
Fax
:
00213
4156
0353
.
Ema
i
l
:
zahraaz@yahoo
.com
b
Depar
tmen
t
o
f
Chem
is
try
,
Facu
l
ty
o
f
Sc
iences
,
Un
ivers
i
ty
o
f
Sc
iences
and
Techno
logy
o
f
Oran
"Mohamed
Boud
ia
f"
,
P
.O
.B
.
1505
E
l
M´naouar
,
31003
Oran
,
A
lger
ia
.
Fax
:
00213
4142
5763
.
Ema
i
l
:
ade
la
l
io
thman@gma
i
l
.com
The conductivity of salicylic acid in methanol—water mixtures was measured at 25 C. Experimental data were analyzed usingthe Hsia—Fuoss and Fuoss78 conductance equations and a comparison was made. The Hsia—Fuoss and Fuoss78 methods were also usedto deter mine the thermodynamic association constants and the limiting molar conductivities for all solvent compositions. The limiting equivalent conductance decreases with an increase in the methanol contentinthe binary mixtures overthe whole range of solvent compositions, butthe variation does not give a constant value of Walden product. The electrolytes werefoundto be practically completely associated in all solvent mixtures studied. The association constant of salicylic acid decreases asthe dielectric constants ofthe mixturesincrease.
Key words: salicylic acid, association constants, Walden product, electrolyte conductivity.
Sa
l
icy
l
ic
ac
id
(SA
,
ohydroxybenzo
ic
ac
id)
is
a
pheno
l
ic
compound
presen
t
in
p
lan
ts
.
I
t
is
an
impor
tan
t
in
termed
ia
te
in
the
produc
t
ion
o
f
asp
ir
in
,
and
i
ts
der
iva
t
ives
are
a
lso
used
in
pharmaceu
t
ica
l
and
po
lymer
indus
tr
ies
to
manu
fac
ture
d
is
in
fec
tan
ts
,
an
t
isep
t
ics
,
and
de
tergen
ts
.
Thermodynam
ic
assoc
ia
t
ion
cons
tan
t
va
lues
o
f
SA
in
some
a
lcoho
l—wa
ter
so
lu
t
ions
were
de
term
ined
po
ten
t
iome
tr
ica
l
ly
.
1—3There
are
a
few
s
tud
ies
on
the
conduc
tome
tr
ic
behav
ior
o
f
SA
in
so
lven
t
m
ix
tures
.
4—9In
th
is
paper
,
we
presen
t
the
conduc
tance
da
ta
o
f
sa
l
icy
l
ic
ac
id
a
t
25
C
in
me
tha
no
l—wa
ter
m
ix
tures
con
ta
in
ing
from
0
to
90
.59
we
igh
t
%
o
f
MeOH
.
To
de
term
ine
the
thermodynam
ic
assoc
ia
t
ion
cons
tan
ts
,
K
A,
the
l
im
i
t
ing
mo
lar
conduc
t
iv
i
t
ies
,
0,
and
the
Wa
lden
produc
t
va
lues
,
the
conduc
tance—MeOH
con
cen
tra
t
ion
da
ta
were
ana
lyzed
us
ing
the
Hs
ia—Fuoss
and
Fuoss78
equa
t
ions
.
Exper
imenta
l
Salicylic acid (puriss. p.a., >99.5%, Aldrich) was used with out purification. Methanol (purity > 99%) and triply distilled water with a specific conductivity of less than 1 S cm–1 was used for the preparation of binary mixtures. Densities of the mixtures were determinedin a 20 mL pycnometer at 25.00±0.05 C. Viscosities of the mixtures were measured with a Falling Ball viscometer (Gilmont Instruments) to an accuracy of 0.2—1%. The densities, viscosities, and dielectric constants ofthe solvent mixtures arelistedin Table 1.
Conductivity measurements were carried out using a CDM230 conductivity meter (Radiometer Analytical SAS, France) equipped with a CDC641T cell comprising two platinized platinum electrodes. Taking into account the sources of er ror (calibration, measurements, impurities), the molar con ductivity values are accurate to within 0.02%. During the ex periments, the cell was calibrated using aqueous KCl solu tion at least five times and then immersed in a thermo stat where the temperature was maintained with an accuracy T = ±0.05C.
All solutions were made up by weight. The volume concen trations (in mol L–1) were calculated usingthe densities ofthe solvent mixtures. The molar conductivities, , were calculated
Table 1. Properties of methanol—water mixtures at 25 C a b/g cm–3 c/P Dd 0 0.9958 0.00891 78.48 19.79 0.9714 0.01526 69.85 37.54 0.9345 0.01572 61.50 49.97 0.9186 0.01569 55.76 72.55 0.8686 0.01356 45.32 90.59 0.8223 0.01033 36.63 aWeightfraction of MeOH (%).
bDensity of solvents. c Viscosity of solvents. dDatatakenfrom Ref. 10.
Chaaraou
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from the experimental electrolyte conductivities corrected for the electrolyte conductivity ofthe pure solvent.
Experimental data were analyzed using the Hsia—Fuoss 11 and Fuoss78 12 conductance equations.
The Hsia—Fuoss method is based on the assumption11 that the conductance of a partially dissociated (1: 1) electrolyteis relatedtoits concentration с:
= [0 –S(c)1/2 +E(c)ln(c) +
+ J1(c) + J2(c)3/2]/(1 + KAcf2), (1) where isthe degree of dissociation,KAisthe association con stant ofion pairs, and fisthe mean activity coefficient offreeions.
The activity coefficient was calculated accordingto Ref. 13: f = exp{–A(c)1/2/[1 + BR(c)1/2]}, (2) where A = 2.791•106(DT)–3/2, B = 50.29(DT)–1/2, R is the di
ameter of the Gurney cosphere of the ion, D is the dielectric constant, and T is absolutetemperature.
The S, E, J1, andJ2 values were calculated usingthe known equations.14
Equation (1) is resolved for 0 and KA which minimize the standard deviation
2 =[
jcalc –jexp]2/(n – 3), (3) where n isthe number of data points.
The Fuoss78 method. The limiting molar conductivity, 0, andthe association constant, KA, were deducedfromthefollow ing equations:
=p[0(1 + RX) + EL], (4) = 1 –KAc2f2, (5) lnf = –/[2(1 + R)], = e2(DkT)–1 (6) andthenthe standard deviation was minimized:
2 =(jcalc –jexp)2/(n – 2). (7) The expressions for RX and EL in Eq. (4) are the explicit relaxation and hydrodynamicterms, respectively.12
Resu
lts
and
D
iscuss
ion
The
conduc
t
iv
i
ty
o
f
SA
in
me
thano
l—wa
ter
m
ix
tures
(36
.63
D
78
.48
;
0
.0089
P
0
.0157
P)
was
measured
a
t
25
C
in
the
concen
tra
t
ion
range
2
.29
•10
–6mo
l
L
–1 c
1
.12
•10
–2mo
l
L
–1.
A
t
a
me
thano
l
concen
tra
t
ion
o
f
90
.59%
,
the
resu
l
ts
were
uns
tab
le
;
hence
we
take
the
aver
age
va
lue
o
f
the
conduc
t
iv
i
ty
.
Ca
lcu
la
t
ions by bo
th me
thods revea
led no m
in
imum
in
R—
% p
lots
in accordance w
ith pub
l
ished data
12(R va
lues
were
used
equa
l
to
the
B
jerrum
d
is
tance
,
see
Re
fs
6
,
8
,
and
15)
.
The
in
i
t
ia
l
0and
K
Ava
lues
were
es
t
ima
ted
us
ing
the
Os
twa
ld
law
. The mo
lar conduc
tance o
f SA a
t
in
f
in
i
te
d
i
lu
t
ion
,
0,
the
s
tandard
dev
ia
t
ions
%
based
on
the
ob
served and ca
lcu
la
ted
va
lues
, and
the SA assoc
ia
t
ion
cons
tan
ts ob
ta
ined us
ing
the
two me
thods are
l
is
ted
in
Tab
le
2
.
From
the
da
ta
o
f
Tab
le
2
i
t
fo
l
lows
tha
t
a
t
me
tha
no
l
concen
tra
t
ions
h
igher
than
50%
,
the
%
va
lues
found
by
the Hs
ia—Fuoss me
thod are
larger
than
those de
ter
m
ined
us
ing
the
Fuoss 78
equa
t
ion
.
The
0va
lues
ca
lcu
la
ted
by
bo
th
me
thods
are
approx
i
ma
te
ly
equa
l
.
The
l
im
i
t
ing
conduc
tance
o
f
SA
in
aqueous
so
lu
t
ion
ca
lcu
la
ted
by
the
Hs
ia—Fuoss
equa
t
ion
is
in
good
agreemen
t w
i
th
the pub
l
ished da
ta (384
.2
,
9385
.2
,
4and
384
.23
S
cm
2mo
l
–1(see
Re
f
.
6)
.
In
F
ig
.
1
,
the
0va
lues
o
f
SA
in
me
thano
l—wa
ter
m
ix
tures
are
compared
w
i
th
those
found
ear
l
ier
.
9The
l
im
i
t
ing
equ
iva
len
t
conduc
tance
decreases
as
the
con
ten
t
o
f
me
th
ano
l
in
wa
ter
increases
,
thus
sugges
t
ing
s
tronger
ion—so
l
ven
t
and
so
lven
t—so
lven
t
in
terac
t
ions
.
F
igure
2
shows
tha
t
the
mo
lar
conduc
tance
o
f
SA
de
creases
w
i
th
increas
ing
the
concen
tra
t
ion
o
f
me
thano
l
in
wa
ter
as
a
resu
l
t
o
f
reduc
t
ion
o
f
the
d
issoc
ia
t
ive
power
o
f
the
so
lven
t
.
A
t
me
thano
l
concen
tra
t
ions
above
50%
,
sma
l
l
er
conduc
tance
var
ia
t
ions
are
observed
.
The
p
lo
t
o
f
the
Wa
lden
produc
t
vs.
compos
i
t
ion
o
f
the
so
lven
t
m
ix
tures
(F
ig
.
3)
passes
through
a
max
imum
be
tween
12
and
20%
o
f
me
thano
l
,
as
was
found
in
th
is
b
inary
m
ix
ture
for
var
ious
e
lec
tro
ly
tes
.
16—18The
presence
o
f
th
is
max
imum
shows
tha
t
the
l
im
i
t
ing
conduc
tance
o
f
the
so
lu
t
ions
decreases
more
s
low
ly
w
i
th
increas
ing
the
me
tha
no
l
concen
tra
t
ion
in
the
m
ix
ture
than
i
t
wou
ld
be
expec
t
ed
from
the
increase
in
v
iscos
i
ty
o
f
the
so
lven
t
m
ix
tures
in
the
wa
terr
ich
reg
ion
.
The
cons
tancy
o
f
the
Wa
lden
prod
uc
t
a
lso
fa
i
ls
in
genera
l
for
sma
l
l
ions
in
m
ixed
so
lven
ts
.
19In
F
ig
.
4
,
the
dependences
o
f
the
thermodynam
ic
d
is
soc
ia
t
ion
cons
tan
t
PK
ao
f
SA
on
the
inverse
d
ie
lec
tr
ic
con
stant of so
lut
ions ca
lcu
lated by the Hs
ia—Fuoss and
Table 2. Conductance parameters of salicylic acidin methan ol—water mixtures at 25 C calculated usingthe Hsia—Fuoss (in numerator) and Fuoss78 (in denominator) equations 0 KA•10–3 (%) R/Å /S cm2 mol–1 /dm3 mol–1 0 385.60±0.02 0.985±0.001 0.026 3.57 386.06±0.04 1.004±0.001 0.024 3.57 19.79 249.89±0.01 1.676±0.003 0.022 4.01 249.99±0.02 1.699±0.002 0.002 4.01 37.54 170.00±0.01 3.963±0.009 0.038 4.56 170.03±0.01 4.000±0.005 0.022 4.56 49.97 150.16±0.01 5.966±0.009 0.068 5.02 150.16±0.02 6.013±0.006 0.054 5.02 72.55 106.87±0.01 19.735±0.071 0.080 6.43 105.45±0.01 19.126±0.007 0.042 6.43 90.59 71.05±0.01 925.222±1.754 0.087 7.65 70.29±0.01 900.897±0.215 0.076 7.65E
lec
troconduc
tance
o
f
sa
l
icy
l
ic
ac
id
Russ
.Chem
.Bu
l
l
.
,
In
t
.Ed
.
,
Vo
l
.
62
,
No
.
7
,
Ju
ly
,
2013
1597
var
ia
t
ions
were
a
lso
found
for
SA
in
wa
ter
m
ix
tures
w
i
th
e
thano
l
,
51propano
l
,
8and ace
tone
.
6The PK
a
va
lues
in
aqueous so
lu
t
ions ca
lcu
la
ted by
the
two me
thods are
in
exce
l
len
t
agreemen
t
w
i
th
those
found
by
o
ther
me
thods
o
f
ana
lys
is
.
4,7—9Increased assoc
ia
t
ion upon add
ing me
tha
no
l
was
exp
la
ined
by
s
tab
i
l
iza
t
ion
o
f
an
ion
ow
ing
to
for
ma
t
ion
o
f
an
in
terna
l
hydrogen
bond
be
tween
the
carboxy
l
and
hydroxy
l
groups
.
4,7,8Fig. 1. Limiting equivalent conductance (0) plotted vs. methanol content () in methanol—water mixtures: published data6 (1) and results of calculations bythe Fuoss78 (2) and Hsia—Fuoss (3) methods. 400 350 300 250 200 150 100 50 1 2 3 0/S cm2 mol–1 0 20 40 60 80 100 (%)
Fig. 2. Molar conductance plotted vs. solvent mixture com positions at 25 C: = 0 (1), 19.79 (2), 37.54. (3), 49.97 (4), 72.55 (5), and 90.59% (6). 350 300 250 200 150 100 50 0 1 /S cm2 mol–1 0.02 0.04 0.06 0.08 C1/2/mol0.5L–0.5 3 2 4 5 6
Fuoss78
me
thods
are
compared
w
i
th
the
va
lues
ob
ta
ined
us
ing
the
Lee—Whea
ton
conduc
tance
equa
t
ion
.
6S
im
i
lar
Fig. 3. Walden product plottedvs. solvent mixture composition. 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 20 40 60 80 100 (%)
Fig. 4. PKa values plottedvs.inverse dielectric constant of solu tion: results of calculations carried out usingthe Lee—Wheaton conductance equation6 (1) and by the Hsia—Fuoss (2) and Fuoss78 (3) methods. 6.0 5.5 5.0 4.5 4.0 3.5 3.0 1 2 3 pKa 1.2 1.6 2.0 2.4 2.8 D–1•102
Chaaraou
i e
t
a
l
.
1598 Russ
.Chem
.Bu
l
l
.
,
In
t
.Ed
.
,
Vo
l
.
62
,
No
.
7
,
Ju
ly
,
2013
Summ
ing up
,
the conduc
t
iv
i
ty o
f SA
in me
thano
l—
wa
ter
m
ix
tures
was
measured
a
t
25
C
and
the
resu
l
ts
ob
ta
ined were ana
lyzed by
the Hs
ia—Fuoss and Fuoss78
me
thods
.
I
t
was
found
tha
t
the
l
im
i
t
ing
conduc
tances
and
assoc
ia
t
ion cons
tan
ts d
i
f
fer s
l
igh
t
ly
from
those ob
ta
ined
by
o
ther
me
thods
o
f
ana
lys
is
.
The
0va
lues
de
term
ined
by
the
Hs
ia—Fuoss
,
Fuoss78
,
and
Lee—Whea
ton
6me
thods
vary
w
i
th
the
concen
tra
t
ion
o
f
me
thano
l
in
the
m
ix
tures
in
the
same
way
.
Th
is
con
f
irms
the
va
l
id
i
ty
o
f
app
l
ica
t
ion
o
f
the
former
two
me
thods
.
The
0va
lue
changes
as
the
so
l
ven
t compos
i
t
ion changes
,
thus
ind
ica
t
ing ra
ther s
trong
ion—so
lven
t
in
terac
t
ions
.
20—25I
t seems necessary
to s
tudy
the
tempera
ture depen
dence
o
f
conduc
t
iv
i
ty
to
ge
t
more
in
forma
t
ion
on
the
be
hav
ior
o
f
SA
in
b
inary
m
ix
tures
.
The
lack
o
f
trans
ference
da
ta
in
the
l
i
tera
ture
prec
ludes
de
ta
i
led
in
terpre
ta
t
ion o
f
the concen
tra
t
ion dependence
o
f
conduc
tance
.
Re
ferences
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