T H E SOLUBILITY RELATIOKS OF T H E ISOMERIC DIHYDROXYBENZENES * BY W. H.WALKER, A . R. COLLETT AND C. L. LAZZELL
In previous communications to this Journal, Collett and Lazzell have reported a series of measurements of solubility for several systems of disubstituted benzene derivatives, namely the nitranilines,’ the aminobenzoic acids,? and the nitrobeazoic acids.:l h survey of the literature revealed that no systematic investigation of the solubilities of the dihydroxybenzenes in a series of solvents has ever been reported. Most of the data obtained by previous investigators has been collected by SeidelL4 Lang5has obtained complete data for the solubilities of these isomers in acetone. The present investigation was undertaken with the primary object of obtaining data for another system of disubstituted benzene derivatives which could be used in our study of the solubility relations of systems of this type. Incidentally these solubility measurements are of value, since the dihydroxybenzenes are of considerable commercial importance. In this paper are presented solubility measurements, from about 2 5 O C to the respective melting temperature of the solute, for the three dihydroxybenzenes in benzene, carbon tetrachloride, water, acetone and absolute ethyl alcohol. Chloroform and ether were also used as solvents but it was found impossible to secure reliable data for quinol in chloroform and for resorcinol in ether. A few of the values recorded in Seidell and the International Critical Tables have been incorporated with the data presented herein, so as to secure greater ranges of temperature for purposes of interpolation. Each of the values so used has been properly identified in the tables which are included in the body of this report. Materials In the preliminary attempts to purify the isomers it was observed that the products of crystallization were susceptible to the influence of sunlight and air. Crystals, which were obtained in transparent condition, soon became discolored upon exposure to air and sunlight, especially in the case of quinol. Because of this fact all further purification of the isomers Kas carried out in a dark room and the purified materials u-ere dried and kept in an atmosphere of hydrogen over calcium chloride or sulfuric acid. On observing these precau* Presented before the Division of Physical and Inorganic Chemistry a t the Cincinnati Meeting of the American Chemical Society, September, 1930. Collett and Johnston: J. Phys. Chem., 30, 70-82 (1926). 2 Lame11 and Johnston: J. Phys. Chem., 32, 1331-41 (1928). Collett and Lazzell: J. Phys. Chem., 34, 1838-47 (19303. 4 A. Seidell: “Solubility of Inorganic and Organic Compounds” 2nd Ed.: 1-01 I, pages 323, 575 and j80, Vol. 11,pages 1234, 1383 and 1389. 5 International Critical Tables, Vol. IV, page I I I .
3260
W. H. WALKER, A. R. COLLETT AND C. L. LAZZELL
tions the discoloration of the purified material was avoided. This action of air and sunlight may account for the wide divergence in the melting points which have been recorded in the literature for these compounds. Two solvents, water and alcohol, were employed in the purification of the solutes by repeated crystallization; the process being carried out until no further change in the melting point was observed. All melting points were secured by the capillary tube method using thermometers certified by the Bureau of Standards and corrected for stem emergence. Catechol: The best grade of catechol secured from the Eastman Kodak Company melted a t 103-104' C; the purified product melted at 104.4-104.6' C. International Critical Tables give 105' C. Resorcinol: Merck's U. S . P. resorcinol was purified and yielded a product melting at 109.4' C. International Critical Tables give 110' C. Quinol: J. T. Baker's C. P. quinol was purified and yielded fine glistening needle shaped crystals, whose melting point was I 72.9' C. International Critical Tables give 170.5' C. Andrews, Lynn and Johnston,' purifying t,hese isomers by sublimation in an atmosphere of carbon dioxide, obtained the following melting temperatures by means of time-temperature cooling curves using thermocouples: catechol, 104.3' C; resorcinol, 109.6-109. 7' C ; and quinol, I 72.3' C. The melting points obtained by Andrews, Lynn and Johnston would naturally be expected to be somewhat lower than those obtained by the capillary tube method owing to the error of super heating which is inherent in this method. Acetone: C . P. acetone was dried over calcium chloride and twice distilled using a Glinsky column; the fraction used boiled between jj.9-60.0' C a t 747 mm. Ethyl Alcohol: 95y0 ethyl alcohol was refluxed with lime, distilled, dried with sodium and redistilled twice; the major fraction boiled at 78.4' C under 760 mm pressure. Benzene: Thiophene free Kahlbaum benzene was dried over sodium and distilled; redistillation yielded a major fraction boiling between 80.3-80.4' C at 760 mm. Chloroform: Merck C . P. chloroform, dried over calcium chloride, was twice distilled and the final fraction was secured at 60.3-63.4' C and 737 mm. Carbon tetrachloride: C. P. carbon tetrachloride, dried over calcium chloride was twice distilled using a Glinsky column; the major fraction boiled a t 75.1-75.Z0 C at 740 mm. Ether: U. S . P. material was washed three times with distilled water, dried over calcium chloride and twice distilled. The fraction boiling at 34.7-34.9' C at 760 mm was used. Method The experimental data on solubility presented in this article were chiefly obtained by the synthet,ic method. This consists essentially of subjecting known quantities of solute and solvent, which are sealed in small glass bulbs, 1
J. Am. Chem.
SOC., 48, 1282 (1926).
SOLUBILITY RELATIONS OF ISOMERIC DIHYDROXYBENZENES
326 I
to a very gradual rise in temperature and recording the point at which the last crystal goes into solution as the saturation temperature. Details of the method used in obtaining these solubility measurements may be found in a previous paper.' A sketch of the apparatus employed is shown in Fig. I . One important modification in the procedure was made necessary by the fact that if air was allowed to remain in the small glass bulbs, oxidation of the solute apparently took place, especially at the higher temperatures. This difficulty was avoided by sweeping out the air with dry hydrogen just before the bulb was sealed.
FIG.I A-Electric Hotplate-3 heats B- liter Pyrex Beaker C-$ ample Bulb D-Faraday six-inch bell with gong removed
Several determinations of solubility for these isomers a t 25' C were made by an analytical procedure. The values so obtained are indicated in the table of results. The procedure was as follows: duplicate samples of the given solute were placed in 2 5 0 C.C. ground glass stoppered bottles with the chosen solvent; care being taken t o have an excess of solute present. These bottles were then suspended in a thermostat at 2 5 f 0.1' C and kept there for 24 hours with frequent shaking. The solute was then allowed to settle for an hour and samples of the solution (50 to roo c.c.) secured by means of pipettes equipped with filter plugs; transferred to tared glass stoppered Erlenmeyer flasks and immediately weighed. The solvent was then removed by evaporation at room temperature under reduced pressure (about 2 0 - 3 0 mm) and the amount of solute present obtained by again weighing the flasks. The results presented in the tables are in all cases the mean of a t least two measurements. 'Collett and Laazell: J. Phys. Chem., 34, 1839 (1930).
3262
W. H. WALKER, A. R. COLLETT AND C. L. LAZZELL
Experimental Results The experimental measurements of solubility which were obtained for the three dihydroxybenzenes are listed in Tables 1-111; C being the molal percentage of each isomer (C = IOO K,where N is the mol fraction of the dihydroxybenzene) and t, the temperature in degrees centigrade. A few values taken from Seidell (loc. cit.) are indicated by * and a few taken from the International Critical Tables by 1. Values which were obtained by the analytical method previously described may be identified by $ which follows them. All other data given below were obtained by the synthetic method. Thermometers used were calibrated by comparison with thermometers certified by the United States Bureau of Standards.
TABLE I Experimental Values of the Solubility of Ortho-dihydroxybenzene (Catechol) in Terms of Mol Percentage Benzene
t 100.00 104.5 83.59 97.0 74.85 93,3 61.32 88.9 48.j2 85.1 34’.81 82.0 C
Chloroform t
C
100.00
20.03
77.2
21.37
11.05
70.6’
10.69 5.49
5.29 59.6 0.8621 2 5 . 0
c Acetone 100.00
82.21 jo.78 58.66 55.1 t 49.5 t
t 104.j
91.0
IO?. j
85.29 71.98 j9.r~ 46.21 35.93
98.0 92.0 86.6 82,3 79.0 73.7 65.8 55.3
2.322:
C
2 5 . 0
Water
100.00
t
104.5
47.11 37.23 37.10
66.2
77.4 j3.z
42.2
23.01
41.2
18.0
6.88* C
Ether
57.1
56.7
Carbon tetrachloride C t 100.00
85.97 72.31 59.08 45.74 36.36 19.45 10.47 4.35 0.156:
104.5 98.3 94.6 92.6 91’5 91.1 90.5
88.j 83’5 25.0
Alcohol C 100.00
96.05 69.84 59.10 45.45
t 104.j 101.7
81.5 67.9 43.1
20.0
t
104.j 84.53 95.0 73.37 85.6 j6.13 60.j 41.03 9.8
100.00
* A. Seidell: “Solubilities of Inorganic and Organic Compounds,” Vol. I and 11, Second Edition. t International Critical Tables, Vol. IV, page I I I . t Analytical data.
SOLUBILITY RELATIONS O F ISOMERIC DIHYDROXYBENZEKES
3263
TABLE I1 Experimental Values of the Solubility of Meta-dihydroxybenzene (Resorcinol) in Terms of Mol Percentage C
Benzene
t
109.4 85.17 1 0 1 . 7 68.j6 97.3 Two liquid layers 9.34 93'4 5.16 87.4 2.95 i9.3 2.02 72.6 100.00
1.14
61.1
0.244:
25.0
Chloroform C t
109.4 85.19 102.3 Two liquid layers j.68 90.0 5.15 89.4 1oo.00
2j.o
0.5211
Carbon tetrachloride C t
109.4 8j.31 104.1 Two liquid layers 100.00
0.84
100.7
0.65 95'4 0.2311 2 5 . 0
Triple point 94,S"C. Triple point 103.7"C.
Triple point 95.9"C. Acetone
C 1oo.00
85.49 67.93 59.12 49.5 t
t
C
Water
t
109.4 98.3 75.1 51.8
100.00
12.0
48.62
64.4
37.80 36.76 33.18 26.35
50.4 49.3
72.15
63.28 53.95
109.4 88.5 80.j 70.7
Alcohol C 100.00
81.92 67.85
53.13 39.34* 37.2 *
t
109.4 95.8 83.8 60.1 20.0
10.4
44.5
33.61 * A. Seidell: "Solubilities of Inorganic and Organic Compounds," Vol. I and 11, Second
Edition. t International Critical Tables, Vol. IV, page Analytical data.
III,
TABLE I11 Experimental Values of the Solubility of Para-dihydroxybenzene (Quinol: Hydroquinone) in Terms of Mol Percentage
c Acetone 100.00
82.84 71.55
j8.78 46.45
40.61 38.37 35.17 34.11 29.54 2j.98 21.25
t
172.9 160.3 148.4 131.3 105.3
90.2 82.4 69.5 66.5 58.8 54.8 45.6
C
Benzene
100.00
81.68
t
172.9 163.8
75.06 1 6 1 . 0 68.03 158.8 Two liquid layers 13.21 154.1 5.70 143.2 5.21 141.2 0.0364: 25.0 Triple point 1 5 7 , IT.
C
Water
t
172.9 6j.18 147.2 60 35 141.8 j2.95 136.0 49.11 131.7 39.24 120.3 35.29 114.6 13.55 81.9 10.25 75.3
100.00
1.19%
25.0
1.16*
20.0
3264
W. H. WALKER, A. R. COLLETT AND C. L. LAZZELL
TABLE 111 (continued) Ether C
Carbon tetrachloride C t
t
100.00
172.9
100.00
57.78 46.06 35.24
14j.0
86.73 1 6 7 . 2 Two liquid layers 1.89 1 5 4 . 0 1.42 147.3 0 . 8 j 137.3 0.69 1 3 2 . 4
21.62
133.2 117.3 89.9
172.9
C
Alcohol
100.00
t
172.9
93.85
16i.9
67.61 j i . O j
146.0 I34.j
44.33
115.1
34.71
91.2 43.0
22.18
0.008Ij 2 5 . 0
Triple point 163. z°C.
* Seidell: “Solubilities of Inorganic and Organic Compounds,” Vol. I and 11, Second Edition. t International Critical Tables, Vol. IV, page I I I . 1Analytical data. The results presented in the above tables have been plotted on a large scale in terms of C versus t and from these curves values of solubility have been obtained at ten degree intervals of temperature. Table IV was constructed from these values. I n a few cases extrapolations were made beyond the experimental data but where this was done the values have been enclosed in parentheses. From the integrated form of the ideal solubility equations have been calculated the values listed under the column headed “Ideal.” These calculations were based on a changing value for AH, the molal heat of fusion, with temperature. The dependence of AH on temperature has been expressed by the following equations which were obtained by Andrews, Lynn and Johnston‘ from calorimetric measurements. Ortho Meta Para
AH AH AH
Dihydroxybenzenes 23.49t - o.oj3t2calories 23.2jt - 0.061t’ calories 23.00t - o.ozzt2 calories
= 3563 = 3172 = 3167
+ + +
When these expressions are converted to functions of the absolute temperature they yield the following: Ortho Meta Para
AH = -6800 AH = -7724 AH = - 4 7 5 2
+ jz.43T - o.oj3T2 + j 6 . j i T - o.061T2 + 2j.01T - o.ozzT2
The insertion of these expressions for AH in the unintegrat,ed form of the dlnX AH ideal solubility equation 2 = -and its subsequent integration between dT RT2 the limits T A and T gives
J. Am. Chem. SOC.,48, 1281 (1926). Details of the method of calculation may be found in J. Phys. Chem., 29, 1041 (1925).
SOLUBILITY RELATIONS O F ISOMERIC DIHTDROXYBENZENES
3 265
m
bic
r-m
0
0
0
r
H
w.o c. 0. ii
. b. h .
N
3
d 0
0
&&
0
W
roo
r - 0 *
4
E
a
8
5
Q r
h-
m-ffi
w - m l.N 0 d r o L o W i c h C . 0
W
g
-E~ c:
-
Loo r o o 0 . . . w. r o.f f i. d. o.
W O W
h
v v
c/
o o o o o o o o o m 0 0 0 0 0 0 0 0 0 4 m d m W h m
N
5.2 2
O O O O O O O O O d . . . 0 0 0 0 0 o o o o m N
m d *.a
-03
ci 0
- *0
3266
W. H. WALKER, A. R. COLLETT AND C. L. LAZZELL
s
-
h
0
-
0
0
0
0
d
~ 0
~ 0
m
m 0
0
*
o o
~
h o
*
o
0
0
m
w
m
m
a
0
a
n
N
o
a
o
E
o
~
o
o
SOLUBILITY RELATIONS OF ISOMERIC DIHYDROXYBENZENES
3 267
where KA is the mol fraction of solute, TAthe melting temperature of the solute, and T any absolute temperature a t which the solubility is desired. In the above expression all the constants have been grouped as K1 KBand KB, and below are listed the values calculated for each isomer. 377.5 382 4
K1 3 931 4 408
Kt - 2 6 38 -28 42
0
445 9
2.324
-17.60
0.00480
TI
Ortho Meta Para
K1 o 01156
01332
Discussion of Results I t will be noted that no data are given in the above tables for quinol in chloroform. Attempts were made to secure such data but it was noticed that successive determinations of the saturation temperatures of bulbs containing low concentrations of quinol gave lower and lower results. In higher mol concentrations of quinol the solute darkened with melting and two liquid layers were produced. I n a particular instance one of the bulbs exploded with considerable violence. These phenomena indicated that there was a probable reaction between solute and solvent with ultimate decomposition. In order to further investigate this probable reaction between quinol and chloroform, a quantity of each of these substances was placed in an autoclave and heated to I 25' C for several hours. A cursory examination of the reaction mixture revealed that only carbonaceous material remained and that considerable quantities of hydrogen chloride had been formed. I t will also be noted that no data are given for resorcinol in ether. When bulbs containing 3 to 45 mol per cent of resorcinol were made it was found that the saturation temperature was below 30' C. However on standing, a light brown solid precipitated and in the case of a bulb containing 5 mol per cent no apparent solution of this precipitate was noticed even at twenty degrees above the original saturation temperature. A bulb containing 5 5 mol per cent of resorcinol gave a saturation temperature of 69' on the first trial; 67' on the second and 65.5' on a third trial. Mol concentrations of resorcinol higher that 5 5 per cent formed solutions so viscous that proper agitation of the crystals in the bulb was impossible. Thus no reliable data could be obtained. This anomalous behavior of resorcinol in ether may be due to compound formation and seems worthy of further investigation. Fig. 2 is a plot of the data obtained in this investigation. By referring to the curves for the ortho compound it will be noted that the solvents employed form curves of two general types; those showing only simple curvature, such as acetone, falling in one group and those showing double curvature, such as CCla, falling in another. The solvents in the first group are mainly polar liquids, while those of the second group are non-polar. I t is interesting to note the position of the various curves with respect to the ideal curve. Those for alcohol, acetone and ether fall below the ideal; that for water almost coincides with the ideal, and those for chloroform, benzene and carbon tetra-
3268
W. H. WALKER, A. R. COLLETT AND C. L. LAZZELL
chloride are at a considerable distance above the ideal. Intersection of the alcohol and ether curves occurs at 69 mol per cent and of the ideal and water curve at 37 mol per cent. Inspection of the curves obtained for the meta isomer show the same grouping of solvents, as was noted in the case of the ortho compound; the
20
40
60
a0
FIG.2
polar liquids, such as acetone, possessing high solvent power and the nonpolar liquids low solvent power In fact the non-polar group of solvents possesses such low solvent power that the solute melts to form a second liquid layer before solution takes place. S o attempt was made in the cases of chloroform, carbon tetrachloride and benzene to determine the critical solution temperature and no particular efforts were made to secure accurate values for the triple point. Only one pair of curves intersect, namely that for chloroform
SOLUBILITY RELATIOXS OF ISOMERIC DIHYDROXYBENZENES
3 269
and benzene. For resorcinol the curves for the polar solvents all lie below the ideal and non-polar all lie above. Referring to the curves for para dihydroxybenzene it will be observed that again the polar liquids are the best solvents; the non-polar group forming two liquid layers as in the case of resorcinol. As before the critical solution temperature was not determined and only the approximate value of the triple point recorded. Two intersections will be noted, water and ether at 3 2 mol per cent and acetone and alcohol at 24 mol per cent. This last intersection is discussed more fully in a succeeding paragraph since it is produced by compound formation. In this instance the acetone and alcohol curves lie below, the water and ether slightly above, and the chloroform and benzene curves far above the ideal curve.
FIG.3
X graph of the solubilities of the three isomers in acetone is shown in Fig. 3. This figure is of interest for two reasons: first because of the crossing of the solubility curves for catechol and resorcinol at about 63 mol per cent, signifying that resorcinol is the more soluble below 64' C even though its melting temperature is higher than that of catecho1;and second because of the abrupt change of slope in the curve for quinol. This break in the curve occurs at 62' and 33 mol per cent and indicates compound formation between quinol and acetone. When the curve for the compound is extended as shown by the dotted line, in Fig. 3, a maximum is reached at about 50 mol per cent which indicates an unstable compound of I mol of acetone to one of quinol with a melting point of 68 to 69' C. Lang' had previously worked on the solubility of the isomers in acetone and our results show good agreement with his in the cases of catechol and resorcinol. Our data for quinol, however, do not agree at all since he reports the formation of a compound of I mol of acetone and I mol of quinol which has a melting temperature of 148' C. Since the original datn International Critical Tables, Vol. IV, page
I I I.
3270
W. H. WALKER, A. R . COLLETT A N D
C. L .
LAZZELL
of Lang is found in his thesis (Zurich) and appears not to have been published elsewhere it has not been available for comparison with the data as published in the International Critical Tables. This compound formed by I mol of acetone and I mol of quinol was previously reported by S.Habermann’ who noted its very unstable character when exposed to air. The solubility curves for the three isomers in ethyl alcohol all show the same type of curvature. The values given by Speyers*for resorcinol in alcohol deviate considerable at temperatures above 30’ from t,hose recorded in this article. Water, of all those investigated, is the solvent which most nearly forms ideal solutions with the dihydroxybenzenes; the curve for quinol lying just, above the ideal, that for resorcinol below and that for catechol crossing the ideal curve. Comparison of our data with that of Speyers (loc. cit.) for resorcinol and water again shows deviations which increase with increasing temperahres. Apparently there seems to be some factor in the method employed by Speyers which causes inaccuracies in the results obtained at the higher temperature. This error in the method used by Speyers has also been observed and discussed by other worker^,^ who were unable to check data given by Speyers. Ether forms solubility curves of the same general type with catechol and quinol and may be considered a very good solvent for these compounds. As previously explained no reliable data could be obtained for resorcinol in ether. Chloroform was not found to be very satisfactory as a solvent since it possesses low solvent power for the dihydroxybenzenes. The curve for catechol shows a reverse curvature which indicates that the region of two liquid layers is not far distant. Resorcinol in chloroform has a region of two liquid layers between 1 2 - 6 2 . 5 mol per cent. Quinol also reached this region of two liquid layers with chloroform but as stated at the beginning of this discussion a reaction apparently takes place with decomposition of the solute. Benzene is a very poor solvent for quinol and resorcinol since in these two cases a region of two liquid layers exists, for the former between 5 and 75 mol per cent and for the latter between 16 and 60 mol per cent. Although there is only a difference of five degrees between the melting point of catechol and resorcinol yet that is sufficient to remove the catechol and benzene from the region of two liquid layers. The curve does however show the double curvature characteristic of the near approach to that field. The only data available in the literature for comparison was that of Rothm ~ n d . The ~ agreement is not very close except in the case of the triple point determination and a few determinations a t lower temperatures. By far the most unsatisfactory solvent for the dihydroxybenzenes is carbon tetrachloride which forms two liquid layers with quinol and resorcinol over the greater range of concent,rations. I n case of ca.techo1 no region of two liquid layers was observed but it will be noted that the greater portion of the curve lies about parallel to the concentration axis, indicating a very close approach to the four phase region. 1
Monatsheft., 5, 329 (1884) through Abstracts J. Chem. Sac., 48, 53 (1885).
* Seidell: loc. cit.
H. Lee Ward: J. Phys. Chem., 30, 1317 (1926); Sunier: J. Phys. Chem., 34,2582 (1930). 2. physik. Chem., 26, 475 (1898).
SOLUBILITY RELATIOSS O F ISOMERIC DIHYDROXYBENZENES
32
I
Comparison of this system of isomers with the nitro benzoic acids (loc. cit.) shows considerable variation with respect to the solvent power of the various liquids over a range of temperature. Owing to the frequent crossings of the curves for this system it is impossible to assign a definite order of solubility for the solvents, as was done for the nitro benzoic acids, since this may vary for the same isomer depending on the particular temperatures selected. A consideration of the completed results of this investigation yields further evidence in support of the statement made in a previous communication1 that the validity of certain rules of solubility which are current may be seriously questioned. h study of the curves in Fig. I for the isomers in benzene reveals that if a mixture containing all three of the isomers were subjected to repeated crystallization from this solvent it would be possible to obtain pure catechol. Details of the method used to calculate the number of crystallization necessary for complete separation may be found in a previous article.z
summary The solubility curves of the three dihydroxybenzenes were determined from approximately 2 s0C to the respective melting temperature, in carbon tetrachloride, benzene, ethyl alcohol, water, acetone, chloroform and ether. Reliable data for resorcinol in ether, and quinol in chloroform could not be obtained. The synthetic method was employed except in a few determinations a t 2 5 T which were secured by an analytical method. Evidence supporting the existence of an unstable molecular compound of one mol of quinol to one of acetone has been obtained, A brief discussion of the results and a comparison with previous data are given. Department of Chemistry, West Virginia Cniuersity, Morgantow, West Virginia. Collett and Lazzell: J. Phys. Chem. 34, 1846 (1930). Collett and Johnston: J. Phys. Chem., 30, 70 (1926).
