THE INFLUENCE O F A THIRD SUBSTANCE ON T H E CRITICAL SOLUTION TEMPERATURE O F PHENOL AKD WATER JOHN DUCKETT AND WILLIAM HAMILTON PSTTERSON
The result of investigation of critical solution temperatures of several pairs of liquid systems especially with small additions of a third component has been published by Timmermansl in an extensive paper with bibliography. Since the following work has been in progress, two papers have appeared2 dealing with the change of mutual miscibility of phenol-water mixtures on the addition of a small quantity of another component. Critical solution temperatures has also been made use of as a criterion of purity. The addition of a third substance may raise or lower the temperature a t which two liquid phases become one. I n phenol-water mixtures the addition of most electrolytes raises this temperature considerably. The maximum rise is expected when the added substance is soluble in one of the liquid constituents only. If it is soluble in both, the rise may be small, or the critical solution temperature may be much depressed, the maximum lowering occurring when the third substance is equally soluble in both liquids4. Critical Solution Temperature The purpose of this investigation was t o ascertain the effect of the nature and concentration of the added substance on the mixture of phenol and water (36.1 phenol and 63.9 water) which gives the maximum temperature for mutual solubility. We have found this t o be 66.0' for phenol M.Pt. 41' and pure water in the above ratio. (Other workers have given values 65.3'70'.-Friedlander5, 66.06'). Above 66.0' an opalescence is shown (the critical opalescence); at and below 66.0' however the turbidity in a tube 1 5 mm. diameter becomes such that the stirred mixture is no longer transparent, so this temperature has been selected as the basis. The disappearance of the opalescence is gradual; a range of 2' as a rule suffices to make the liquid quite clear, even when a third substance has been added. The homogeneous solut>ionof a phenol-water mixture was found to give the Tyndall cone effect and examination of the scattered light with crossed Nichols showed it to be plane polarised with a critical change in the angle just before turbidity set in, as distinct. from opalesence. This has not been observed hitherto and deserves fuller investigation. Z. physik. Chem. 58, 129-213 (1907). C. R. Bailey: J. Chem. Soc. 123, 2579 (1923); Boutaric and Nabot: Compt. rend. 176, 1618 (1923). SCrismer: Bull. Soc. chim. Belg. 9, 145 (1895) etc.; Orton and Jones: J. Chem. Soc. 115 105.5 (1919). Cf. Rooaeboom, "Die heterogenen Gleichgewichte", I11 Part 2 (1913); Bancroft: J. Phys. Chem. 1, 414 (1897). 6Z.physik. Chem. 38, 389 (1901); Scarpa, 65, 8': J. Chim. phys. 2, 447 (1904). 2
JOHN DUCKETT AND WILLIAM HAMILTON PATTERSON
296
The following results were obtained on adding a third component to the phenol-water mixture giving a C.S.T. of 66.0". (1) Salts which raise the Critical Solution Temperature Soluble in Water c = grams of salt per I ,000 grams of total solution Mol. c =molecular concentration i.e., c/Molecular Weight C.S.T. =Critical Solution Temperature of mixture e =elevation of C.S.T. produced by addition of salt E =molecular elevation mol.
C
1
'
550
2.313 4.430 4.775 8.194 9.080 9 * 642
C.
NaC1 C. S.T.
,02649 ,03954
69.25 70.65 74.3 74.6 79.9 81.3 82.2
.0757I ,08162
.1401 .I552
,1648
e
E
3.25 4.65 8.3 8.6 13.9 15.3 16.2
1-23 118 I IO I 06
99.2 98.6 98.3
KC1 .02379 .06885 .09401
68.45
I959
82.2
2.45 6.5 7.9 9.9 . 16.2
.2085
83 ' 2
17.2
72.5 73.9 75.9
,1180 *
103 94.4 84.0 83.9 82.7 82.5
KBr 4.481 6.772 9.200 15.15 18.47 22.51 27.46
.03766 .os692 .07732 . I274 .I552 .1892 ,2308
69.5 71.I
72.4
75.8 77.5 79.7 82.2
3.5 5.1 6.4 9.8
92.9 89.6 82.8
11.5
74.1 72.4
13.7 16.2
77.0
70.2
KI 4 . I49 9.740 20.01
25.30 32.09 37.96 57-51
.85
. I933
67.85 69.80 72.95 74.4 76.15
.2288 .3465
77.75
3.8 6.95 8.4. 10.15 11.75
83. I
17.1
.0250
.os868 .1205
. I524
I
74.0 64.8 57.7
55.1 5 2 4
51.4 49.4
CRITICAL SOLUTIOK TEMPERATURE
297
NHdC1 C
mol.
C.
2.230 5 ' 576 7.145 9.543 12.83 15.09
,04169 . io42 . I336 .I783 ,2400 ,2819
1.913 7 ' 230 I3 ' I4 21.32 31.17 39.26
,01952 ,07377 ' 1341 ,2176 .3181 .4006
C. S. T.
e
69.2 73.25 74.9 77.4 80.7
3.2 7.25 8.9 11.4 14.7 16.7
s2.7
E 76.8 69.6 66.7 63.9 61.3 59.2
NH4Br 67.45 70.90 73.95 77.8 82.4 86.0
1.45 4.90 7.95 11.8 16.4 20.0
74.3 66.4 59.3 54.2 51.6 49.9
" 4 x 2 0 '3
,05368 .0836 . 1442 ,1972 ,2940 ,4451
68.5 69.6 71.8 73.5 76.0 80.35
I . 586 5.732 6.247 15.90 25.66
2.5
3.6
5.8 7.5 10.0
14.35
1.25
3.65 3.95
8.75 12.8
46.6 43 ' 1 40.2 38.1 34.0 32.2
79.6 64.3 63.9 55.6 50.4
Na2S04.roH20 I47 5.023 6.689 8.861 2
*
10.07
,00667 . 01 56 .0208 .0275 .0313
68.6
75.75 73.2
7.2
75.1
9.1 10.25
76.25
&SO* 2.057 4.241 9,262 10.87 12.49
2.6 5.75
. 01I 8
69.7
.0244 ,05323 ,0625 ,0718
79.4 81.4 83.45
72'75
390 369 347 331 328
JOHN DCCKETT S X D WILLIAM HAMILTON PATTERSON
298
c
Mol.
c
6.169 9.642 15.27
.0325 .os08 .0804
15.95
.0800
21.99
.I157
7.122
10.67 13.87 21.95 23.83
a0375 . o 562 .0730 .I154 '1254
d. Na. H. Tartrate C. S.T.
e
E
5.2
I 60
73.5
7.5
148
77.0
11.0
77.35 81.3
11.35 15.3
137 135
71.2
Na. H. Racemate 71.7 74.3 76. I 81.2 82.2
5.7 8.3
132
152 148 138 132 129
IO. I
15.2 16.2
Results in the case of some of the above salts have been also given or requoted by Timmermans (loc. ciC). A comparison with our numbers is only possible in a few instances since we have not worked above I O O O C . , as pressure affects the initial solution temperature. For potassium chloride one number only is comparable and this agrees with ours; in the case of potassium chloride the three values and potassium sulphate the one value which can be compared, show small differences. Our endeavour has been to arrive a t strictly comparable numbers over a range of small salt concentration. The importance of these figures lies, in the first place, in the value of E for the various salts and secondly in the characteristic curves for individual salts on plotting the change of E with increase in the concentration. From the curves the following average values for E are obtained:-
n m . C. 0.03-0.1 NH4X03 KI KK03 IrJHhBr NH&1 KBr KC1 NaCl Na. H. Tartrate KzS04 NaZS04
46.5 66 66
68.5 75 87 93 112.5 I45 256 3 I 5 extrapolated
Mol. c. 0:1-0.2 40 56 56.5 59 66.5 75.5 83 IO0
128
i. e. the same order is obtained for each concentration. The curves for potassium iodide and potassium nitrate, above very low concentrat'ion, are nearly identical.
299
CRITICAL SOLUTION TEMPERATURE
The above results show that most of the effect must be due to ions and that the cations and anions may be arranged in order of their power of elevating the C. S. T.
Cations. Na > K >Tu”, Anions. SOr>H. T a r t r a t e > C l > B r > I = N 0 3 This is the Hofmeister series with the exception that the iodide ion is equal to, instead of greater, than KO3 ion. Thus such a phenomenon as the coagulation of neutral egg albumen is linked up with the mutual miscibility, in presence of electrolytes, of water-phenol mixtures and is also related to changes of surface tension. Numerical values may be assigned to each ion and all the substances investigated will be found to be in agreement: an assumption is necessary however which the data are insufficient to justify; a criticism which applies in general to all such series. (2) Substances which raise the Critical SolutionTemperature Solublein Phenol
Azobenzene C
Mol.
c
.9747 .885 3.748 9.262
.00536 ,01035 .ozos9 .os089
247
. OIOSO
I
2
‘
8.420 11.53
6.222 9.714 10.54 11.24 11.76 13.30
5.137 6.510 8 * 950
9,158 14.12
.03934 .os392
.04861 .0759 .0823 .0878 .og18 .ro4o
,0338 .0428 ‘0589 .0603 e0929
C. S. T.
e
67.6 69.0
I.6
72.0
80.6
Salol 68.8 76.5 80.4 Naphthalene 75.8 81.1 81$85 82.9 83.6 85.7 Ca.mphor 74.15 76.2 79.45 79.65 87.0
3.0 6.0 14.6
2.8 IO.5
14.4
9.8 15.1
15.85
16.9 17.6 19.7
8.15 10.2
13.45 13.65 21
.o
JOHN DUCKETT rlND WILLIAM HAMILTOS PATTERSON
300
Palmitic Acid C. S. T. 67.8 72.3 75.2 82.0
Mol. C.
C
1.731 6.039 8.923 16.41
,00676 ,0236 '0349 .0641
C
I .8 6.3 9.2 16.0
E 266 267 2 64 250
Stearic Acid* 2.816 4.318 7 ' 7-07 11.31
.00991 .0271
69.1 70.6 73.9
3 .o 4.6 7.9
.0398
77.1
11.1
.OIjZ
,
303 303 292 279
Among substances of this class azo-benzene and salol were tried since Boutaric and Kabot (loc. cit) make use of these compounds to show that the identical rise is obtained from equimolecular concentrations. An anomalous result in the case of naphthalene they explain by its solubility in water. The figures given above, based on the maximum point of the binodal curve (not used by Routaric and Kabot) show that equimolecular concentrations give different values for E. The values are approximately constant for each individual substance. Timmermans has given values for azobenzme haphthalene and camphor. (3) Substances Soluble both in Phenol and Water
Urea C
5.656 13.55 30.07 69. I O
mol. c.
C. S. T.
0943 ,2258
64.7 62.9 59.0 49.2
'
,5010 1.152
e -1.3 -3.1
-7.0 -16.8
E -13.8 -13.8 -14.0 -14.6
Hg(CN2 29.38 33.01 38.39 48.01 58.84
,1166 . I310 . I524 . I905 '2335
26.62 48.40 54.49
,0778 .I415 . I693
60.8 59.9 58.8 56.7 54.3
Cane Sugar 65.8 65. 65 65.6
-5.2
-6.1 -7.2
-9.3
-11.7
- * 2' - .35' .4'
Phenyl-a-naphthyl-methyl-benzyl-arsonium iodide MW = 5 I 2 I . 267
4.167 5.406 12.61
.00247 .00814 ,0106 .0246
*Kahlbaum sample-not
pure.
64.0 60.2 59.0 55.3
-2O.O
-5.8 -7.0 -10.7
-44.6 -46.6 -47.3 -48.8 -50.1 -2.57 -2.47 -2.51
-809 - 7=3 - 663 -434
CRITICAL SOLUTION TEMPERATURE
301
Cane sugar leads to a very small lowering of C. S. T. as it is soluble in both water and phenol. Bancroft (loc. cit.) had classed it with potassium nitrate i. e. insoluble in phenol. Phenyl naphthylmethylbenaylarsonium iodide is of interest as being of high molecular weight. It leads to anomalous values for E, decreasing with concentration; it extends the range of critical opalescence. Viscosity Comparative viscosity determinations were made (water at I j' being taken as unity) of ( I ) phenol-water mixture (as above) and also with the addition of each of the three classes of third component i. e. ( 2 ) sodium chloride, (3) naphthalene, (4) mercuric cyanide.
FIG.I
( I ) and (3) show inflection at the respective C. S. T.s i. e. 66'0 and j4'5 the viscosity of the heterogenous system just below the C. S. T. being less than the homogeneous phase just above the C. S. T.; ( 2 ) and (4) show points of inflection. These results are shown graphically in Fig. I .
Conductivity Conductivity measurements were made with a dipping electrode in one or other of the layers or the homogeneous solution. In some cases the formation of an emulsion brought about discrepancies.
302
JOHN DUCKETT AXD WILLIAM HAMILTON PATTERSON
Fig. 2 shows variation of specific conductivity; the lower outer line the phenol phase with rising temperature the upper outer line the aqueous phase. The dotted lines extend this into the metastable region above the C. S. T. The straight middle line gives the values of K for the single phase by falling temperature (I(being almost constant); the inner branches the respective conductivities of the two phases below the C. S.T.
It may be noted that the relative distances of the two outer lines from the middle line are in the same ratio in which phenol and water are mixed to give the maximum C. S. T. When a third substance is added, e. g. sodium chloride, this ratio is greatly changed.
FIG.3
Colloids Dialysed colloidal gold, ferric hydroxide, and silver (by the Bredig method) were found to raise appreciably the C. S. T. The results are not included owing to difficulty in allowing for traces of electrolyte and changing stability. Optical Isomerides Fig. 3 gives the result for actual C. S. T. plotted against molecular concentration for sodium hydrogen racemate and d. sodium hydrogen tartrate. Both substances lic on the same curve.
CRITICAL SOLUTION TEMPERbTURE
30 3
Summary The following are the main results:(I). I n the region of critical opalesence phenol water solutions polarise light with a change in the angle a t the C. S. T. The homogeneous solution above the C. S. T. is of the nature of an isocolloid. A series corresponding t o the Hofmeister series is arrived a t by (2). examination of the effect on C. S. T. of substances soluble only in water. (3). The change of C. S. T. by substances soluble in phenol only cannot be used for determination of molecular weight. (4). An optically active substance and a racemate have the same effect on the C. S. T. ( 5 ) . Viscosity and conductivity changes in the region of the C. S. T. are shown by curves. Bast London College, University of London.
