J . Chem. Soc., Furuduy Trans. I , 1989, 85(9), 2705-2712

Transfer and Partition Free Energies of 1 : 1 Electrolytes in the Water-Dichloromethane Solvent System at 298.15 K t Angela F. Danil de Namor,* Rafic Traboulssi and Franz Fernandez Salazar

Department of Chemistry, University of Surrey, Guildford, Surrey GU2 5XH

Vilma Dianderas de Acosta, Yboni Fernandez de Vizcardo and Jaime Muiioz Portugal

Departamento de Quimica, Universidad Nacional de San Agustin, Arequipa, Peru

Solubility data at 298.15 K for 1 : 1 electrolytes in dichloromethane are reported. The results are used for the calculation of the transfer free energies for these electrolytes from water to dichloromethane. These data are compared with partition free energies as obtained from distribution ratios of these electrolytes in the mutually saturated solvent system. Except for Et,NCl, where large differences are observed between transfer and partition data, agreement between AGP and AG; values for 1 : 1 electrolytes in the water - dichloromethane solvent system is found. This finding leads to the conclusion that in the partition of 1 : 1 electrolytes in this solvent system, mosb of the ions are unhydrated in the dichloromethane phase. Single-ion AGP values for five anions and nine cations based on the Ph,As Ph,B convention are calculated. Single-ion AGP values derived from experimental data are compared with corresponding values derived from theoretical considerations. Discrepancies of ca. 1 kcal mol-' or higher are observed for some ions.

~~

Equilibria and derived free energy data for the of electrolytes and ions in the water-organic solvent systems have been reported in a number of papers. For a given electrolyte or ion, results derived from experimental data which refer to the process involving two mutually saturated phases may differ (depending on the solvent system under consideration) from data involving the transfer of the same electrolyte or ion between the two solvents in their pure state. Agreement between partition and transfer free energy data has generally been found for those systems in which the organic phase is constituted by a water-immiscible ~o lven t .~ - '~

This field of research is of considerable importance since it can be related to a number of processes (solvent extraction, phase- transfer catalysis, transport of ions across membranes etc.) in which two-phase systems are involved.

Comparisons between transfer and partition free energies of electrolytes in water-non- aqueous solvents are of particular interest for systems involving a low dielectric medium, given that : (a) there is very little quantitative information regarding thermodynamic parameters for the transfer of electrolytes from water to solvents of dielectic constants lower than 10; (6) the possibility of using transfer free energy data to evaluate the influence of the anion or cation on the direct partition of 1 : 1 electrolytes in these solvent systems requires further experimental evidence, and (c) the scope and limitations of existing theories can only be argued on the basis of experimental data. These data are also required for the development of new theoretical approaches related to ion-solven t interactions. In the light of these observations, the water-dichloromethane solvent system was selected for our studies.

and

t Paper presented at the Third International IUPAC Symposium on Solubility Phenomena, held at the University of Surrey, 23-26 August, 1988.

2705

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online / Journal Homepage / Table of Contents for this issue

2706 Transfer and Partition Free Energies

Halogenated alkanes, in particular dichloromethane, have been used in synthetic as well as in extraction processes. The weak coordinating properties of these solvents make them suitable reaction media for solution studies. Dichloromethane is a water- immiscible solvent of low dielectric constant. Ion-pair formation constants for a number of 1 : 1 electrolytes (tetra-n-alkyl ammonium halides, perchlorates and picrates) in the water and dichloromethane solvent system and ion-pair formation constants in aqueous dichloromethane for these electrolytes at 293 K have been reported by Gustavii and Schill.'*

Beronius and Brandstrom,12 using conductance and partition measurements, determined the ion-pair formation and partition constants of tetra-n-alkyl ammonium picrates in aqueous dichloromethane at 298 K. Conductivity studies of a number of salts in anhydrous dichloromethane and derived ion-pair formation constants for these electrolytes in this solvent at 298 K have been reported by Svorstol and Songstad.16~17 This information is useful in the calculation of solution free energies, AGZ, for the dissociated electrolytes in this solvent given that in a solvent of such a low dielectric constant ( E = 8.9 at 298 K),16 the dissolution of a salt results in the formation of ions as well as ion pairs in solution.

This study involves the solubilities of 1 : 1 electrolytes in anhydrous dichloromethane at 298.15 K from which the solution free energies, AG:, for the dissociated (M++X-) electrolytes are calculated. These data are combined with corresponding AGZ, values in water in order to obtain the transfer free energies, AG:, for these electrolytes from water to dichloromethane. These data are then compared with values for the partition free energies, AG:, for the same electrolytes as obtained from distribution ratios in the mutually saturated solvents.

The Ph,As Ph,B convention'' is used for the calculation of single-ion AG," values from water to dichloromethane. Single-ion AG: values derived from theoretical calculation^^^ for a number of solvent systems are discussed in relation to single-ion values derived from experimental data in the same ~ y s t e m s . ~ * ~ ~

Experimental Dichloromethane (Merck, 99.5 % pure) was purified according to the method suggested by Bekkevol et aLZo The water content of the solvent, as measured by Karl Fischer titration, was < 0.005 %.

Sodium perchlorate, sodium iodide, lithium chloride and caesium chloride (all BDH AnalaR grade) were dried at 105 "C for several days before use.

Potassium, rubidium and caesium tetraphenylborates were prepared by adding an aqueous solution of the corresponding alkali-metal chloride to an aqueous solution of NaPh,B (BDH) until complete precipitation of the appropriate salt was observed. The mixtures were filtered and the salts were recrystallised twice from an acetone-water mixture and dried in a vacuum for several days at 333-353 K.

Tetra-n-alkyl tetraphenylborate salts were prepared by adding a solution of sodium tetraphenylboron in methanol to the corresponding tetra-n-alkyl ammonium hydroxide solution until complete precipitation was observed. The salts were recrystallised from an aqueous acetone (1 : 3) solution and dried for several days in a vacuum oven at 323 K.

Tetraphenylarsonium tetraphenylborate, Ph,As Ph,B, was prepared from aqueous solutions containing equimolar quantities of Ph,AsCl (Fluka) and NaPh,B (BDH). The salt was recrystallised from acetone-water (3 : 1) solution. Crystals were dried in a vacuum oven at 353 K for several days.

Solvents used for the recrystallisation of the tetra-n-alkyl ammonium iodide salts (all AnalaR) were; water for Me,NT, and water-methanol mixtures for Et,NI, Pr,NI and Bu,NI. The salts were dried over P,O1, at 323 K in a vacuum oven for several days.

Tetraphenylphosphonium iodide (Ph,PI) was prepared by reacting Ph,PCl (Fluka)

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

A. F. D a d dt, Narnor et al. 2707 with KI. The salt was recrystallised twice from water-methanol (3 : I V/V) and dried in a vacuum oven at 323 K for several days before use. Tetra-n-ethyl, tetra-n-propyl ammonium perchlorates (Fluka) and tetra-n-alkyl ammonium bromides (all AnalaR reagents) were dried under a vacuum for several days prior to use. Tetraphenylarsonium perchlorate was prepared from Ph,AsCl and KCIO, and recrystallised from an acetone- water solution.

Tetra-n-alkyl ammonium picrates were prepared by adding a warm concentrated solution of picric acid in water an amount in excess of the appropriate hydroxide in order to ensure complete precipitation of the salts. The crystals were filtered, washed and recrystallised from water. The compounds were dried in a vacuum oven at room temperature for several days.

For solubility measurements, saturated solutions were obtained by adding an excess amount of the salt to the solvent. The mixtures were left for several days in a thermostat at 298.15+0.05 K. Aliquots of the saturated solutions at 298.15 K were removed and the solvent evaporated to constant weight. Analyses were performed at least twice.

For salts with low solubilities, large volumes of saturated solutions were taken for analysis. For partition measurements, both solvents, dichloromethane and water, were mutually saturated for a period of at least one day before use in these measurements. Standard solutions of the appropriate electrolyte at different concentrations either in water or dichloromethane were prepared. The volumes of the two solvents used for these measurements were in some cases the same (Pr,NClO,, Bu,NCIO, and KPh,B) or it was varied (Et,NI, and is CsPh,B) so a similar distribution of the electrolyte in each phase could be achieved. Tubes containing the mixtures were sealed and left in a shaker for a period of 2 h, then in a water bath at 298. I5 k0.05 K for several hours. The phases were separated and aliquots of each phase were taken for analysis. Samples were analysed either by the gravimetric method or by the methods previously des~r ibed .~ . 7 * 8

Measurements were done at least twice. Results are expressed in terms of the defined calorie; 1 cal = 4.184 J for the isothermal process at 298.15 K.

Results and Discussion Solubility data in dichloromethane at 298.15 K for 16 electrolytes are listed in table 1. Note that from the 27 electrolytes considered, 1 1 showed solvate formation when exposed for a few hours to an atmosphere saturated with dichloromethane. The tetra- n-alkyl ammonium and tetraphenylphosphonium bromides solvated very rapidly in this solvent. No solvate formation was detected for the alkali-metal bromides in dichloromethane. However, no consistent values for the solubility of these electrolytes were obtained and, therefore, we were unable to calculate the standard free energy of solution for electrolytes containing the bromide anion in dichloromethane.

The abnormal behaviour of tetra-n-methylammonium salts in this solvent observed by Svorstol et d . 1 6 when carrying out conductance measurements of 1 : 1 electrolytes in dichloromethane was found by us for two salts (Me,NCIO, and Me,NPh,B) and therefore no accurate data for the solubility of these two electrolytes in this solvent could be obtained.

Our results for tetra-n-methylammonium iodide and picrate are shown in table 1. Also included in this table are the literature values21 for the solubility of tetra-n- methylammonium and tetra-n-ethylammonium iodides in dichloromethane.

Taking into account the ion pair formation constant, K,, and the ion-size parameter, h, for the individual electrolytes in dichloromethane, the molar ionic concentration, ci, and the mean molar ionic activity coefficients (using the extended Debye-Huckel equation) were calculated. The data were used to obtain the thermodynamic solubility product, K,O (expressed as pK,”) and the standard free energies of solution, AGZ, for the dissociated electrolytes in dichloromethane. Details are given in table I .

90 F A R I

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

h)

00

Tab

le 1

. So

lubi

litie

s, s

olub

ility

(io

n-ac

tivity

) pr

oduc

ts o

f 1 :

1 el

ectro

lyte

s in

dic

hlor

omet

hane

and

free

ene

rgie

s of

tran

sfer

(m

olar

scal

e) fr

om w

ater

to

dich

loro

met

hane

in

kcal

mol

-' at

298

.15

K

2

NaC

lO,

Et4

NC

104

Pr4N

C10

4 Ph

4PC

104

NaI

M

e4N

I M

e4N

I Et

,NI

Et4

NI

Pr4N

I B

u4N

I Ph

4PI

Me4

NB

r E

t4N

Br

Pr4N

Br

Bu4

NB

r Ph

4PB

r Li

Cl

CSCl

Ph

4AsC

1 K

Ph4B

R

bPh4

B

CsP

h4B

E

t4N

Ph4B

Pr

4NPh

4B

Bu4

NPh

4B

Ph4A

sPh4

B

Me4

NPi

E

t4N

Pi

1.31

x 10

-5

7.61

x

7.68

x l

o-'

4.10

x

6.27

x 1

0-4

1.12

x 10

-4

1.50

x 1

0-4b

3.

29 x

lop

2 3.

77 x

ve

ry s

olub

le

very

sol

uble

2.

20 x

lo-

' so

lubl

e so

lubl

e ve

ry s

olub

le

very

sol

uble

ve

ry s

olub

le

very

sol

uble

very

sol

uble

4.

75 x

10-

5

1.16

x 10

-3

2.92

x 1

0-3

2.94

x 1

0-3

5.46

x 1

0-3

9.19

x 1

0-3

6.02

x 1

0-3

very

sol

uble

ve

ry s

olub

le

6.9

x lo

p2

6 x

lo4"

4.

6 x

104d

2.

7 x

104d

2.

1 x

103d

1.

0 x 1

05~

1.

8 x

105b

1.

8 x 1

05b

4.2

x 10

4d

4.2

x 10

4d

1.68

x lo

3"

3.8

x lo

6"

1.66

x 10

4"

1.55

x 1

04

"

1.48

x 1

04

c

8.0

x 10

3d

2.3

x 10

3d

1.03

x 10

5f

1.77

x 10

4f

4.2b

10

.17

4.9d

5.

84

5.2d

4.

83

12.8

d 4.

92

4.3"

8.

28

4.9"

8.

94

4.9c

8.

79

5. Id

6.

15

5.1d

6.

09

solv

ate

form

atio

n so

lvat

e fo

rmat

ion

11.5

" so

lvat

e fo

rmat

ion

solv

ate

form

atio

n so

lvat

e fo

rmat

ion

solv

ate

form

atio

n so

lvat

e fo

rmat

ion

solv

ate

form

atio

n 3.

6'

10.9

4 so

lvat

e fo

rmat

ion

3.4"

7.

33

3.7"

6.

87

3.9"

6.

84

6.4d

6.

35

solv

ate

form

atio

n so

lvat

e fo

rmat

ion

9.7d

5.

74

4.4f

7.

26

5.5f

5.

55

-

13.8

7 7.

96

6.59

6.

71

11.2

9 12

.20

11.9

9 8.

39

8.31

5.54

14.9

2

9.99

9.

37

9.33

8.

67

7.82

9.

91

7.57

-3.8

0'

- 2.

40'

4.86

' 10

.96h

2.33

g 2.

33g

1.15

h 1.

15h

- 7.

30'

7.12

h

-2.1

5h

1 0.2

0h

1 1 .6

0h

1 2.0

0h

14. 5

6h

23.6

0h

3.75

h 4.

37h

17.6

7 5.

56

1.73

18.5

9 9.

87

7.24

7.

16

-4.2

5

-

- 1

.58

17.0

7

-0.2

1 - 2.

23

- 2.

67

- 5.

89

- 1

5.78

6.

36

3.20

17.3

1 5.

63

- 3.

73

19.0

2 10

.70

10.7

0 7.

34

7.34

-

-2.0

2

-

-

-

-

- 5.

72

-

6.46

3.

10

2 p a 3

=L

__

_~

__

a Th

is w

ork.

' Re

f. (2

0).

" Est

imat

ed v

alue

s.

Ref

. (16

) and

(17

). " C

alcu

late

d vi

a th

e B

jerr

um e

quat

ion.

f R

ef. (

12).

Ref

. (4)

and

(18

). R

ef. (

5).

From

sin

gle-

ion

valu

es g

iven

in ta

ble

2.

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

A . F. Danil de Namor et al. 2709

Table 2. Single-ion free energies of transfer (molar scale) from water to dichloromethane based on the Ph,AsPh,B convention in kcal mol-' at 298.15 K ; comparison with corresponding data in

1,2- and 1 , 1 -dichloromethane

AGP A Cpf ion H,O -+ DCM H,O + 1,2DCE

A GPf H,O + 1,lDCE

Ph,B- Pic-

I- Br- c1- Ph,As+ Ph,P+ Bu,N+ Pr,N+ Et,N+ Me," CS' Rb+ K+ Na'

ClO,

- 7.89 f 0.05" 0.93 f 0.10 3.46 k0.30" 5.17 f 0.25" -

1 1.85' - 7.89' - 7.19 f 0.40

-

- 1 .73d 2.17 f 0 . 10" 5.53f0.10 5.22" 5.66e 7.68e

13.85 f 0.40"

1 .6i 3.4i 5.3i

1 2.9i

- 2.2i 1 .oi 4.0i 5.3' 5.8i 6.4i 7.0i

- 7.87 & 0.06

4.1 1 f0.05 6.07 f 0.05 9.48 f 0.1 1

12.81 - 7.87 * 0.06 - 7.53 & 0.06 - 4.34 - 2.14 * 0.06

1.08 f 0.08 3.63 f 0.05 5.79 5.99

6.19 5.99 11.13h

3 .F 5.4' 9.Y

13.1i

- 5.4i -2.1i

l . l i 4. l i 5.Y 6. l i 6.7' 7.4i

- 6.55 f 0.05

5.26 k 0.06 7.14 f 0.10

10.02 * 0.02

- 6.55 & 0.02 - 6.43 & 0.03 - 2.64 - 0.65 f 0.06

-

2.72 f 0.07 4.32f0.10 6.79 6.99 7.19 6.9g

a Average differences between observed and calculated AGP values given in table 1 for transfers involving this ion. From AGP value for CsCl. ' From ACP value for Ph,AsPh,B. From AG: value of Pr,NC10,. From AG: values for M+Ph,B- where M' = K', Rb' or Cs', respectively.

Suggested values, ref. (19). * See text.

From ref. (19) adjusted to the Ph,As Ph,B convention (see text). From theoretical calculations, ref. ( 1 5).

The transfer free energies, AG,", for the process as described by

M+(H,O) + X-(H,O) + M+(CH,Cl,) +X-(CH,Cl,) (1) are also included in this table. AG," values required for these calculations are those from the literature (see footnote table 1).

Self-consistency of the AG," (M++X-) values given in table 1 is tested through the calculation of a set of single-ion AG," values based on the Ph,As Ph,B convention. These are shown in the second column of table 2. In this column, average differences between observed and calculated AGP values for the electrolyte containing the partricular anion and cation are also given. These differences give an estimated average error of 0.20 kcal mol-1 in the AG," values (estimated error of AG: values in CH,Cl, is between 0.10 and 0.15 kcal mol-'). Therefore, the observed AG," values are in excellent agreement with the calculated AG,". (M++X-) values as shown in the last two columns of table 1.

For comparison purposes, we include in table 2, single-ion AGP values of transfer from water to 1.2 dichloroethane (1,2DCE) and to 1-1 dechloroethane (1,l DCE)."

These data, originally based on the AG," (Ph,P+, Ph,As-) = AG: Ph,B- convention, have been adjusted to the AG," Ph,As' = AG," Ph,B- convention. For this adjustment, single-ion AG: values for the Ph,As+ and Ph,B- ions from water to 1,2-dichloroethane and to 1,l-dichloroethane were obtained from direct AG," values for the Ph,As Ph,B salt as well as from a combination of AG," values of R,N Ph,B, Ph,As C10, and R,NC10, salts. The recalculated single-ion values slightly differ from previous reported values. The AG," data given in table 2 indicate that anions are generally more favourably transferred (AG," more negative) to dichloromethane ( E = 8.9 at 298 K) than to 1,2DCE (E = 10.23 at 298 K) or indeed to 1,lDCE ( E = 9.9 at 298 K).

As far as the alkali-metal cations are concerned, it is quite clear that in transfers from

90-2

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

2710 Transfer and Partition Free Energies

-*I -4

Fig. 1. Single-ion AGP values (Ph,As Ph,B convention) for the alkali-metal cations us. the cation size. 0, PC; x , AN; 0, DMF; A, DMSO; B, N M ; 8, NB, 0, AN; +, DCM.

water to dichloromethane a definitive size effect is observed with AG," values becoming increasingly more positive as the size of the cation decreases. This effect is generally observed for the alkali-metal cations in transfers from water to most dipolar aprotic solvents [propylene carbonate (PC),22 acetonitrile (AN),3. benzonitrile (BN),23 nitromethane (NM)' and nitrobenzene (NB),] as shown in fig. 1 . In this figure, single- ion AG," values for these cations from water to N,N-dimethylformamide (DMF) and to dimethyl sulphoxide (DMSO) based on the Ph,As Ph,B convention are included. It is quite clear from these results that the presence of basic oxygens in the structure of DMF and DMSO leads to a strong interaction between alkali-metal cations and these solvents. Therefore, no appreciable variation in the AG," values is observed by increasing the size of the cation (Li+ to Cs').

Owing to experimental difficulties associated with solubility measurements of alkali-metal salts in 1,lDCE and in 1,2DCE, Abraham and Danil de Namor19 were unable to obtain reproducible AG," (hence AGF) values for electrolytes containing alkali-metal cations in these solvents. Therefore, these authors suggested a set of single- ion AG," values for the transfer of alkali-metal cations from water to 1,lDCE and to 1,2DCE and these are the values given in table 2. Examination of fig. 1 seems to indicate that the suggested AG," values for sodium and possibly for potassium (table 2) in transfer from water to these solvents must be in error. A value of AG," (Na+) (H20 + 1,2DCE) = 1 1.13 kcal mol-' [derived from combination of AGF (NaClO,) (H20 + 1,2DCE) = 15.24 kcal mol-' and a AG," (ClOJ ( H 2 0 + 1,2DCE) = 4.1 1 kcal mol-' (table 2)] seems to be a more reasonable value for the AG," for this cation from water to 1,2DCE.

Using an electrostatic model of solvation, single-ion AG," values (theoretical values) from water to a number of solvents, including dichloromethane and 1,2-dichloroethane have been ~a1culated.l~ These data adjusted to the Ph,As Ph,B convention are included in table 2. In transfers from water to dichloromethane, differences of ca. 1 kcal mol-I or

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

A . F. Danil de Namor et al. 271 1

Table 3. Partition constants and derived free energies of partition for 1 : 1 electrolytes in the water4ichloromethane solvent system

at 298.15 K

electrolyte K P " AG; a AGP

Et,NClO, 9.6 x 10-5 5.48 5.56' Pr,NClO, 3.7 x lo-' 1.95 1.73' Et,NI 7.8 x 6.97 7.20'

. - ~ _ _ _ ~ _ _ . . - ~ _ _ _ _

________.~- _ _ _ _ _ _ ~ ~ ~ ~

CsPh,B 2 . 1 4 ~ lo2 -3.17 - 2.67' Bu,NClO, 4.9 x lo-' 0.42 -

Et,NCl 1.43 x lo-' 1.15 1 4.02d Me,NPi 1.35 x 10-5b 6.64b 6.36' Et,NPi 8.99 x lo-"* 2.70b 3.20' Pr,NPi 0.17 x 10lb -0.32b - 0.130~

_______ _ _ _ _ _ ~ _ ___ ~ ~~ ~~

a This work. * From ref. (12). ' From table 1 . From table 2.

-3 -2 1' J-1

Fig. 2. Partition ratios (log P) of Et,NCl us. the initial concentration of electrolyte in the organic phase at 298.15 K .

slightly higher are found between the theoretical and observed AG," values for the tetra- n-alkylammonium (Me,N',Et,N+), C1- and K+ ions. There is indeed a very large discrepancy (ca. 7 kcal mol-l) for the sodium cation in this solvent system. The discrepancy found for this cation in the water-dichloromethane solvent system was also observed to a lesser extent (ca. 2.7 kcal mol-') in the water-nitrobenzene solvent system. Again, in the latter solvent system, not very satisfactory agreement between the theoretical and observed AGP values was found for the tetra-n-alkylammonium, chloride and picrate ions.

Values for the partition constants (K, ) of a number of electrolytes (Et,NC10,, Pr,NClO,, Et,NI, CsPh,B, Bu,NClO,, Et,NCl) are reported in table 3. These data are referred to the process

M + ~ H 2 0 s a ~ d C H 2 C 1 ~ ~ + X ~ ~ H ~ o ~ a ~ d C H 2 C 1 2 ~ M+(CH2C12satdH20) +X-(CH2C12satdH20) (2)

Kp values are calculated from distribution ratios of 1 : 1 electrolytes carried out at different electrolyte concentrations. Corrections for ion-pair formation constants for these electrolytes in the organic phase were applied in all cases. Good agreement is found between the AG; and AG: values for all electrolytes (except for Et,NCl) in the water-dichloromethane solvent system. It is quite clear from the differences observed between AGE and AG," values for Et,NCl (ca. 13 kcal mol-l) that the C1- ion in the water-dichloromethane solvent system must be heavily hydrated. The distribution ratios for tetra-n-ethyl ammonium chloride (log P) us. the initial concentration of the electrolyte in the organic phase is shown in fig. 2 . For this particular electrolyte, distribution ratios are approximately constants, independently of the salt concentration.

In the light of these results we conclude that most of the ions seem to enter the organic phase as unhydrated entities. Therefore, in the water-dichloromethane solvent system,

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online

2712 Transfer and Partition Free Energies

the AG,O values considered in this work, can be used (except chloride) for a quantitative evaluation of the anion/cation effect on the direct experiment involving the partition of these electrolytes in the two mutually saturated solvents.

The financial support given to Rafic Traboulssi (Hariri Foundation), Franz Fernandez Salazar, Vilma Dianderas de Acosta, Y boni Fernandez de Vizcardo (Overseas Development Administration and The British Council) and to Jaime Munoz Portugal (Concytec, Peru) is gratefully acknowledged.

References 1 B. G. Cox and W. E. Waghorne, Chem. Soc. Ret.., 1980, 9, 381. 2 S. Ahrland, Pure Appl. Chem., 1982, 54, 1451. 3 Y. Marcus, Pure Appl. Chem., 1983, 55, 977. 4 A. F. Danil de Namor, A. Hill and E. E. Sigstad, J . Chem. SOC., Faraday Trans. I , 1983, 79, 2713. 5 A. F. Danil de Namor, E. Contreras and E. E. Sigstad, J. Chem. SOC., Faraday Trans. I , 1983,79, 1001. 6 S. Glikberg and Y. Marcus, J . Solution Chem., 1983, 12, 255. 7 A. F. Danil de Namor and L. Ghousseini, J. Chem. Soc., Faraday Trans. I , 1984, 80, 2843. 8 K. Gustavii and G. Schill, Acta Pharm. Suecica, 1966, 3, 241. 9 K. Gustavii and G. Schill, Acfa Pharm. Suecica, 1967, 3, 259.

10 R. Modin and G. Schill, Acta Pharm. Suecica, 1967, 4, 301. i l J. Rais, Collect Czech. Chem. Commun., 1971, 36, 3253. 12 P. Beronius and A. Brandstrom, Acta Chem. Scand., Part A, 1976, 30, 687. 13 M. Gerin and J. Fresco, Anal. Chim. Acta, 1978, 97, 165. 14 J. Czapkiewicz and B. Czapkiewicz-Tutaj, J . Chem. Soc., Faraday Trans. I , 1980, 76, 1663. 15 M. H. Abraham and J. Liszi, J . Znorg. Nucl. Chem., 1981, 43, 143. 16 I. Svorstol, H. Hoiland and J. Songstad, Acta Chem. Scand., Part B, 1984, 38, 885. 17 I. Svorstol and J. Songstad, Acta Chem. Scand., Part B, 1985, 39, 639. 18 B. G. Cox, G. R. Hedwig, A. J. Parker and D. W. Watts, Aust. J . Chem., 1974, 27, 477. 19 M. H. Abraham and A. F. Danil de Namor, J . Chem. SOC., Faraday Trans. I , 1976, 72, 955. 20 S. Bekkevoll, I. Svorstol, H. Hoiland and J. Songstad, Acta Chem. Scand., Part B, 1983, 37, 935. 21 M. H. Abraham, J . Chem. SOC., Perkin Trans. 2, 1972, 1343. 22 M. H. Abraham, Monatsch. Chem., 1979, 110, 517. 23 A. F. Danil de Namor and H. Berro a de Ponce, J . Chem. Soc., Faraday Trans. I , 1987, 83, 1569.

Paper 8/04470H ; Received 4th November, 1988

Publ

ishe

d on

01

Janu

ary

1989

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Ir

vine

on

31/1

0/20

14 0

0:19

:36.

View Article Online