SOLTBILITY RELATIOXS OF ISOMERIC ORGXKIC COMPOUNDS YIII.
Solubility of the Aminobenzoic Acids in Various Liquids B Y CHARLES L. LAZZELL* AND JOHN JOHNSTON
In a previous paper1 there were presented series of measurements of the solubility of the three nitroanilines in water, alcohol, benzene, chloroform, carbon tetrachloride, ether, ethyl acetate and acetone; the corresponding solubility curves for the three isomers are in general very similar, yet differ appreciably in some cases, these differences being evidently somehow correlated with the melting temperature (presumably also with the heat of melting) of the crystalline isomer. These results indicated the desirability of investigating similarly a related series of isomers to learn mole as to the degree of similarity which may be expected in such parallel cases. Consequently we have measured the solubility, in the same solvents, of the three aminobenzoic acids, which differ formally from the nitroanilines only in the substitution of a carboxyl group for a nitro group; in chemical behavior they differ specifically in the pronounced amphoteric character of the aminobenzoic acids in aqueous solution, and in the readiness with which they decompose a t elevated temperatures. There are few data available on the solubility of the aminobenzoic acids. Flaschner and Hankin* determined the solubility of each in water a t temperatures ranging in the case of the ortho from 84', of rneta from 66", of para from q j o , up to the respective melting point; de Coninck3 worked with the meta in water from oo--700, and there are scattered data in various solvents at temperatures I o O - Z ~ O . The solvents used in the work here presented are methyl, ethyl, and butyl alcohol, ethyl acetate, benzene and chloroform; the temperature range is from 25' to the melting temperature of the respective acid except in the case of butyl alcohol in which fewer measurements were made. The materials used, selected from the purest stock obtainable, were purified as follows: Ortho-aminobenzoic Acid. The C.P. acid was crystallized several times from water at about Soo, boiling water being avoided because at that temperature some decomposition of the acid occurs.4 Norite was used as a decolorizer prior to the first crystallization from water. Finally the acid was crystallized from hot chloroform, which yielded a slightly yellow crystalline material. A white product can be obtained if the acid is sublimed, but
' From a part of the dissertation presented to the Graduate School of Yale University, in June, 1927, by Charles L. Laszell in candidacy for the degree of Doctor of Philosophy. Coilett and Johnston: J. Phys. Chem., 30, 70 (1926). Flaschner and Rankin: Monatsheft, 31, 23 (1910). Oechsner de Coninck: Compt. rend., 116, 758 (1893). 1Iachl.tster and Shriner: J. Am. Chem. Soc.: 45, 5 7 1 (1923).
CHARLES L. LAZZELL AND JOHN JOHNSTON
I332
there is some decomposition, which necessitates a further crystallization from water. The melting point of the acid as purified was 146.1';that given in the literature is 144O-145~.The melting points given in this paper were determined by the usual capillary tube method; all readings were corrected for emergent stems and the thermometers used were compared with thermometers certified by the Bureau of Standards. Meta-aminobenzoic Acid. The C.P. acid was crystallized several times from hot water, then from 95% ethyl alcohol, and finally from boiling water, which in this case causes no decomposition. The meta acid can readily be
TABLE I
a)
Final Experimental Values of the Solubility, in Terms of Molal Percentage, of ortho-Aminobenzoic Acid in:Benzene b) Ethyl Alcohol t 146.I
C 100.00
80.64 71.26 64.69 61.74 50.88 51.03 34.96 29.26
135.2
129.9 126.3 125. I
119.6 119.3
e)
d) Ethyl Acetate t
C
146.I 110.8
100.00
100.4
88.9 76.5
65.03 52.82 29.73 14.71
f) t
2 5 . 0
Butyl Alcohol C
100.00
146.I
100.00
25.92
77.'
I3 ' 7 0
50.7
44.86 26.80
7.62
t
146.I 120.8 108.0 76.8
25.0
Methyl Alcohol
C
25.0
75.7 Chloroform
1.57
93 ' 9 86.5 77.3 68.2
25.0
C
43.14 29.07 18.83 11.24
125.5
108.3 101.6 93.3 89.5
16.35 I3 ' I3 8.71 0.81
100.00
73 ' 92 38.I9 33.03 26.94 22.19 7.75
146.I
110.3
22.22
C)
t
C IOO.OO
25.0
t
146.I 104.6 80.I
SOLUBILITIES O F ISOMERIC ORGANIC COMPOUNDS
'333
TABLE I1 Final Experimental Values of the Solubility, in Terms of Molal Percentage, of meta-Aminobenzoic Acid in :b) Ethyl Alcohol
Zenzene
a)
IO0,OO
67.04 34.92 19.54 12.60 7.54 5.53 4.23 0.008
100.00 ' I3 5.63 3.65
32
0.0;
e) Methyl Alcohol C
I . 52
t
177.9 163.6 140.5 115.5
98.6 25.0
d) Ethyl Acetate C
177.9
100.00
152.7
4 7 . I9
132.9 124.8
11.76 I .30
t
177.9 145.I 110.5 25.0
25.0
f) t
9.i3 I.7 0
25.0
20.07
78.06 47 ' 9 2 24.11 11.89
t
777.9 109.6 86.2
100.00
100.00
25.0
c) Chloroform C
C
t
177.9 161.j 156.7 153.5 150.4 143.7 138.5 134.4
Butyl Alcohol C
t
29,35
177.9 138.7
20.72
127.2
100.00
sublimed in vacuo, yielding a very pure product. The product from either crystallization or sublimation was perfectly white, and had a melting point of I 7 7 .go; that given in the literature is I 74'. Para-aminobenzoic Acid. The C.P. acid was crystallized several times from water a t So0, boiling water causing decomposition as in the case of the ortho acid, then from 95% ethyl alcohol, and finally from water a t 80". Upon slow cooling the crystals came out of water in long colorless needles, which color slightly upon exposure to light; they have a melting point of 187', which is the same as given in the literature, 186'-187'. The mode of purification of the several solvents was identical with that described in the earlier paper and so need not be repeated here except to note that the methyl alcohol boiled a t 66.5'-67' a t 765 mm., and the butyl alcohbl a t I 16.5' a t 760 mm. The method of experiment was also identical with that previously described; the only difference being that in the analytical method, used only a t 2 jo,a weighed sample of the saturated solution was titrated with 0. I molar sodium hydroxide previously standardized against the pure acid. The results are again satisfactorily concordant throughout the range. The solubility of each of the three aminobenzoic acids was de-
I334
CHARLES L. LAZZELL AND J O H N JOHNSTON
TABLE I11 a)
Final Experimental Values of the Solubility, in Terms of Molal Percentage, of para-Aminobenzoic Acid in :Benzene b) Ethyl Alcohol
C
100.00
53.42 32.37 28.50 18.24 15.66 14.14 4.98
e)
t
187.0 165.0 160.2
155,2
159.8
30.00
115.0
156.5
22.04 20.04 15.29 13.56 4.97
99.0 88.7 81.3 75.8
155.2
'54.8 '39.9
2.11
121.7
25.0
100.00
29.90 5.25 0.13
t
d) 187.0 156.4 136.7 25.0
Methyl Alcohol C
100.00
26.87 17.75
5.94
187.0 108.3 86.5
25.0
t
100.00
187.0
48.40 41.95 34.75
136.6
23.07
1 1 2 ,I
f) t
140.I
Ethyl Acetate C
t
12.19
e)
187.0
65.j 2 48.01
0.04
Chloroform C
C 100.00
144.0 131.2
82.1
Butyl Alcohol
C
t
100.00
187.0
55.10
1j3.2
33.36
134.5
25.0
termined over the range from 25' upwards in benzene, chloroform, ethyl alcohol; a less complete series with ethyl acetate, methyl alcohol, butyl alcohol; the last two constituting with ethyl alcohol a group of closely related solvents. The final experimental results are presented in Tables 1-111, C being the molal percentage (C = I O O N where ?i is the mole fraction) and t the temperature centigrade. These data were plotted on a large scale in terms of C versus t ; from these curves were read off, a t IO' intervals, values of the solubility, and these are listed in Table IT', the sequence of solvents being in order of diminishing solubility of the respective acid in the lower part of the temperature range. The values for water are derived similarly from the data of Flaschner and Rankin: those in the column headed "Ideal" were calculated from the integrated form of the solubility equation on the basis that the molal heat of melting, and its dependence upon temperature, is expressed by the following equation, derived directly from calorimetric datal : 1 Andrews, Lynn and Johnston: J. .Im. Chem. Soc., 48, 1274 (1926). Details of the method of calculation may be found in J. Phys. Chem., 29, 1041 (192ji.
I335
SOLUBILITIES OF ISOMERIC ORGANIC COMPOCNDS
TABLE IV Solubility of the Aminobenzoic Acids in Various Solvents, as Interpolated a t a Series of Temperatures, expressed in Terms of Mol Percentage, C. a) ortho (m.p. 146.1') Temp. 25
30 40
jo 60 70 80 90 IOO
Ideal
Et0.k
11.3 12.6 15.5 19.0 23.2 28.2 34.1 40.9 48.7
14.71 15.2 16.8 19.2 22.2
26.2 31.6 39.0 45.8
(SzHsOH
7.75 9.0 11.6 14.6 18.5 23.0 28.4 35.2 43.8
CHjOH
Butyl Alc.
7.62 8.6 10.8 13.5 17.2 22.1
27.8 (35.0) (43.5)
26.6 32.6 40.0
CHClJ
GHs
1.57
0.81
2 .O
1.3 2.3 3.6 5.3
3;o 4.4 6.4 9.0 13.0 19.5
9.9 13.5
28.5
20.0
HiO'
7.2
0.6 .9 2.4
34.3
31.2
52.5
55.2
70.6
74.2 91.8
88.8
*From Flaschner and Rankin, m.p. 144.6OC. Values extrapolated much beyond the experimental range where the slope of the curve seems uncertain are enC!obed {n parenthmes.
b) Temp.
Ideal
25
6.3 7.0 8.8 10.9 13.5 16. j
30 40 50 60 70 80 90 IO0
20.2
24.5 29.5
meta (m.p. '77.9O)
CHaOH CzHsOH I . 70
I . 52
2.2
1.8 2.5 3.2 4.0 4.6 6.0 8.4
3.4 4.6 5.7 5 .O 8.6 10.8 15.0
12.7
EtOAc Butyl Alc
1.30 1.4 1.6 1.8 2.0
2.5
3.3 4.7 6.8
CHCls
CsH,
0.05
0.008
.3 '7 1.1 1.5 1.9 2.2 2.
j
2.8
Hz0" 0.I
.2
.2
.4 '7
'3 .4
1.0
'5
1.3 1.6 1.8
.6
2.2
IIO I20
130 140 150 160 170
* From Flaschner and Rankin, m.p. 174.4;vdlues below 67" from de Coninck.
'7 .9 1.4 3.5 12.6 26.3 39.9 54.0 70.0 87.0
CHARLES L. LAZZELL AND J O H N JOHNSTON
I336
TARLE I V (continued) c) para (m.p. 187.0') Temp.
Ideal
CsHsOH
EtOAc
25
7.1 7.9 9.6 11.7 14.1 17.0 20.4 24.3 28.8
4.97
5.1
5.4
6.5
5'4 6.0
7.8
7.0
9.5 11.8 14.8 18.4
8.1 9.7 11.7 14.3 17.7
30 40 50
60 70 80 90 IOO I10 120
33.9 39.8 46.1 53.8 62.0
130 140 150 160 170
81.v
180
91.9
71.1
* From
22.4
27.3 33.1 40.4 49.7 59.9 70.8 (81.6) (92.4)
27.7
33.8 (41.1) (49.8) (59.6) (70.1) (80.9)
Butyl Alc.
0.04 .2
'7 .8
0.7 1.1 2.4
1.0
1.2
(2.4)
1.4
27.8 35.4 44.4 54.8 (66.3) (78.8) (91.3)
(2.6) (3,o)
2.0
ortho: A H = 3192 meta : A H = 3389 para : A H = 3082
.2
.3 .4 .6
22.0
92.0 Flaschner and Rankin, m.p. 186.0.
Hz0 0.7
CsHs
28.7 39.3 51.1
63.7 (76.7) (90.3)
7 ' 2
18.3 38.0 (73.8) (92.3)
3.0 5.0 10.0
30.3 68.4 (90.0)
6.2 17.0 31.7 45.2 58.6 72.0
84.3 94.6
+ 25.13t - o.og34t2 + - o.084t2 + 21.56t - o.0603t2 25.29t
The corresponding values of the coefficients in the ideal equation
(TA - T) i- KZlog$T + KdTA - T)
log r\J, = K1
~
are : ortho meta para
TI
K,
419.2 451 . O 460. I
5 ' 546 4.741 3.470
K* -38.32 -35.82 -27.43
KI 0.02042
0.01836 0.01318
Discussion of Results There is again a general similarity in shape between the solubility curve of each of the three aminobenzoic acids in any one solvent, as is apparent from Fig. I . The curves for the meta and para isomers in water, benzene and chloroform exhibit reverse curvature, implying an approach to the region of two liquid layers; in the case of the ortho, this characteristic is marked only with water, though with benzene there is an indication of similar behavior. The general similarity of the curves led us in this case again' to seek some function of the solubility which would yield superCf. Collett and Johnston: Zoc. at., p. 80
SOLUBILITIES OF ISOMERIC ORGANIC COMPOUNDS
'33 7
posable curves; but none of these attempts succeeded. Nor did we find i t possible to superpose the corresponding curves for the aminobenzoic acids and the nitroanilines. There are therefore real differences between the curves, associated with specific differences in the chemical nature of both solute and solvent. The order of the several liquids with respect to their solvent power is, for the lower, and larger, part of the temperature range, that of the corresponding set of column headings in Table IV. This order is the same except for
the ortho in ethyl acetate, ethyl and methyl alcohols a t the lower temperatures. The solubility of the ortho is greatest in ethyl acetate up to about IIO', at which point (about 3 j o below the melting point of the solid acid) it is exceeded by that in the methyl and ethyl alcohols, and thereafter the order for all three isomers is the same. The solubility of each isomer is nearly the same in ethyl as in methyl alcohol; for ortho ethyl is slightly better, for meta methyl is somewhat better, and for para the pair of curves cross at about 140'. The order of solubility of para-nitroaniline in the five solvents common to both investigations is the same as that of ortho-aminobenzoic acid ; but the ortho- and meta-nitroanilines each show a different order as between chloroform, benzene and ethyl alcohol. It is again apparent therefore that one is not justified in assigning an order of solvent power to a series of liquids, based on gradations in their physical properties, even when one is dealing with solutes as closely related as those under discussion. If now we consider the course of the curves downwards from the melting temperature of the solute, we find that initially all are close to one another and to the ideal, but that they soon diverge and separate into two groups.
CHARLES L. LAZZELL AND JOHN JOHNSTON
I338
The first group, nearer the ideal, comprises the more polar liquids, ethyl acetate, the three alcohols (and water a t the higher temperatures); the second, further from the ideal, comprises the less polar liquids, chloroform and benzene, the last being (with the exception of water) the poorest solvent in all cases. With the, presumably less polar, nitroanilines as solutes, this grouping of solvents is less well marked, the alcohol curve occupying an intermediate position. Instead of comparing solubilities a t a fixed temperature, it is perhaps more logical to make the comparison a t a fixed distance below the melting temperaTABLE V Solubility of the Hydroxybenzoic Acids in Several Solvents a t a Series of Temperatures, interpolated from the data of Sidgwick and Ewbank'; in terms of Mol Percentage. A. ortho (m.p. I59.0') Temperature
gg%C*HsOH
Butyl Alc.
50
21.j
70
150
28.I 36.6 48.1 65.2 88.7
70
18.8
90
22.0
20.8
I10
190
26.5 33.6 44.6 60.8 85.3
32.4 42.8 62.8 (86' 5 )
70
18.2
90
22.5
20.2
IIO
27.0
130
32.6 39.8 49.0 68.0
24.6 29.5 36.0 49.0 71.4
90 I IO 130
130 150 170
IjO 170
190
* Includes (1898).
Benzene
21.1
1.0*
27.8 35.9 47.6 (65.4)
2.4
Heptane
-
7.3
1.3
23.2
3.5
-
47.6 88.2
(77,s)
B. meta (m.p.
201.3")
11.1
Water 0.07**
0.2
.4 2 0 .j
50.3 (84.5)
o.9t 3.4 10.9
25.5
0.9 2.2
11.4 66.8
Triple point 197O
C. para (m.p. 213.0') 16.4
22.2
36.3
o.9t 3.2
0.5 1.3
3.6 14.2
Triple point 208.j"
10.5
20.4 31.6 45.6 (66.9)
data at temperatures 12-64' by Walker and Wood: J. Chem. SOC.,73, 618
* * Includes data by Walker and Wood (loc. cit.), by FlaschnerandRankin (loc. cit.),and by Alexejew, W e d . Ann. 28, 305 (1886). On undercooling two liquid layers are realized; critical solution temperature 89.5' (S.and E.). t Includes data by \Talker and Wood, and by Flaschner and Rankin. 'Figures in brackets are extrapolated.
SOLUBILITIES OF ISOMERIC ORGANIC COMPOUNDS
'339
ture of the solute. If this is done, the order of decreasing solubility in ethyl alcohol is para, ortho, meta, whereas in benzene it is ortho, para, meta over a range of 60' below the melting temperature but ortho, meta, para a t lower temperatures. Thus it appears that the relative solubility of a group of isomers cannot safely be inferred from the order of their melting temperatures, but depends also upon factors associated with the difference in their chemical properties. As an illustration of this statement the ortho and para, with chemical properties similar in many respects, show similar curves in ethyl alcohol, whereas the meta, with rather different properties, shows a somewhat different type of curve; this is true for the nitroanilines as well as for the aminobenzoic acids.
TABLE VI Solubility of the Sitrobenzoic Acids, in terms of Mol Percentage, from the data of Sidgwick and Ewbank. ortho (m.p. 146.8') CsHs
C7Hia H20* 0.2
1.4 0.9 4 8 28.8 24 6 Triple49.8 6 9 . 7 point 7 7 . 0 139.6'
meta m.p. 141.4')
para (m.p. 242.4')
CsHs
CsHs
2.6 6.0 17.4 45.5
CiHls HzO*
ClHia
H20'
T.P 76.8" 33.2 Triple 5 5 . 0
8 0 . 1 point 8 3 . 0 135'
0. I
0.6 5 . 2 Triple 1 3 . 5 1 4 . 6 point 3 5 . 6 4 9 . 0 234' (60.1)
* Includes data by Flaschner and Rankin.
TABLE VI1 Solubility of the Chlorobenzoic Acids, in terms of Mol Percentage, from the data of Sidgwick and Ewbank (for benzene and heptane) and of Flaschner and Rankin (for water). Temp,
ortho (n1.p. 140.3') CsHo
SO
io
90 110
130
CiHis
3.5
9.5 2 4 * 23.6 4j.6 6 . 8 38.8 84.1 60.0 80.2
IjO I
HzO
io
190 2IO
* Two liquid layers
meta (m.p. 154.5') C6He
c7H1s HzO
2.3 6.2 1.1 14.6 3.0 * 34.8 7.9 6 1 . 9 26.7 4 4 . 6 93.2 (90.4) 8 7 . 2
para (m.p. 241.5') CaHo
CIHM
H20
0.9 1.9
4.0 8.4 26.5 31.6 53.8
1.0
1.7 4.0
10.4 25.7
0.8 16.1 (49.6)
I340
CHARLES L. LAZZELL AND JOHN JOHNSTON
Comparison may also be made with the data of Sidgwick and Ewbankl on the solubility of each of the three hydroxybenzoic acids in water, 99% ethyl alcohol, butyl alcohol, benzene and heptane; of the nitrobenzoic acids in water, benzene and heptane; and of the chlorobenzoic acids in benzene and heptane. Their results, originally in terms of weight percentages, have been computed in terms of mols, and plotted along with such other data as are available; values interpolated a t even temperatures are presented in Tables V-VII, the solvents being arranged in order of diminishing solvent power.
FIG. 2
The curves for these sets of isomers in benzene as solvent are shown in Fig. 2 . In these cases the solubility curves again exhibit the same kind of disparities although superficially there is a general similarity. The hydroxybenzoic acids are each about equally soluble in ethyl alcohol (907~) and in butyl alcohol, but much less soluble in benzene. The solubility in heptane is much less than in benzene, for all of these groups of acids; in water the order of solubility is irregular, as might be expected from the appearance of two liquid layers in some of the systems. Moreover there is no obvious relation between solubility and the melting temperature of the solute, although it does happen in some instances that solutes which melt about the same temperature have nearly identical solubility curves in some solvent over a considerable range of temperature. S o one solvent seems to offer any special advantage in the separation of the isomers by recrystallization; for the ratio of the temperature co-
' Sidg\
