THE SITSTEM, BESZOIC ACID, ORTHO PHTHALIC ACID, JY-ATER BY H . LEE WARD AXD STAXClL 6. COOPER
The above ternary system is of some theoretical importance, since binary mixtures of water and benzoic acid show a separation into two liquid phases and an upper critical solution temperature while mixtures of phthalic acid and water do not do so at the temperatures required for saturation with the solid pha3e. I t is probable in this case also that there is a separat,ion into two liquid phases at, temperatures in which the solution is supersaturated wit,h phthalic acid, as is indicated by some isolated measurements of Flaschner and Rankin’ as quoted by Seidell.? The t,ernary system would be expected to show a transition between the two types of curves. The problem is also of technical importance, since a method bas been devised for the production of benzoic acid by passing phthalic anhydride and steam over a catalyst, such as zinc oxide, at temperatures from Z G G ~ - ~ G O ~ . ~ The binary 35-stmi benzoic acid, water has been investigated in the higher teriiperature ranges by hlexejew4 by means of the synthetic method and his results have been confirmed and extended by the xork of didgwick and llubank,j employing the same method. Additional data at the lover tcniperatures is given by 130urgoinGand inany other observers have obtained the solubility of benzoic acid in water at room tcniperatures. The solubility of phthalic acid in water has been obtained at ten degree intervals between z j o and 8;” by IIcMaster, Bender and JYeil.’ They employed the analytical method and approached equilibrium from both sides. Sonic determinations by the synthetic method have been made at still higher temperatures by Flaschner and Rankin. S o melting point curve for mixtures of benzoic acid and phthalic acids appears to be available and there is no published data on the ternary system. Preparation of Materials The water used vias laboratory lled water which was twice redistilled after treatment with barium hydro and potassium permanganate. The benzoic acid was LIallinckrodt’s C.S.P. qualit.y, prepared from toluene. I t gave a melting point of 1 z 2 . j ’ by the capillary tube method, and Flaschner and Rankin: Monatsheft, 31, 23 (1910). of Inorganic and Organic Compounds,” 490 (1919). Conover: U. S.Patent, 1645180 (Oct. 11, 1927). Alexejew: Ivied. Ann.. 28, 305 (1886). 6 Sidgwick and Eubank: J. Chern. SOC., 119, 9 3 (1921). 6 Bourgoin: Ann. Chirn. Phya., (5) 15, 171 (1878). hlcMaster, Bender and Weil: J. Am. Chern. SOC.,43, 12oj (1921).
* Seidell: “Solubilities
BENZOIC ACID, PHTHALIC ACID, WATER
1485
this was checked by heating a much larger amount in a sealed tube in the apparatus used in the solubility measurements. Titration of the acid with tenth-normal sodium hydroxide, using phenol phthalein as a n indicator showed 99.967purit'y. The phthalic acid was furnished by the LlonFanto Chemical Company. Titration indicated 99.975 purity and heating showed 0 . 0 2 5 ~ash. The material melted with decomposition at 193.3' when heated in a sealed capillary tube. Experimental Method The synthetic method was employed throughout the investigation. The shaking apparatus con,sisted of a vertical piston operated by a crank attached eccentrically to a wheel which was rotated by an electric motor. The heating bath was a liter beaker containing glycerine. The temperatures of complete solution were recorded by short-stem thermometers, accurate to within one or two tenths of a degree. In most cases the mercury column was completely immersed in the bath. If this Tvas not the case a stem correction was made. The sample tubes were thin-walled test tubes, five-eighths of an inch in diameter. They were allowed t o st,and in cleaning solution, washed, and dried at 110'. After weighing, the sample of the acid was introduced and the tube again weighed. The desired amount of water was then added from a pipette and the exact amount determined by weighing after sealing. The tube was then heated in the bath with vigorous stirring until solution took place and the approximate solution temperature noted. The bat'h was then removed and the tube cooled with shaking until crystallization or the separation of the liquid phase took place. The heating was then carried out as before except at a much slower rate and the exact temperature of solution recorded. The chilling in order to form small crystals of uniform size is absolutely necessary for the success of this method, as has been shown by Ward.8 In some cases it was found possible to cause the separation of a metastable phase and determine its solution point. I n the case of the ternary systems the procedure was the same except that a mixture of the two acids was used instead of a single acid. Five mixtures of benzoic and phthalic acid were made up by thoroughly grinding weighed amounts of the acids and subsequently shaking them mechanically. The mixtures contained 90) 80, 6 6 . 6 7 , 50 and 33.33 per cent of benzoic acid respectively. Experimental Results The results of the solubility measurements appear in Tables I to TIIT and in Figs. I to 3 . 8
Ward: J. Phys. Chem., 30, 1316 (1926;
1486
H. LEE WARD AND STANCIL S. COOPER
TABLE I Grams Benzoic Acid .OI33
Solubility of Benzoic Acid in Water Grams Weight yo Solubility Water
3 ' 9694
Benzoic ,334 ,628
jo
3.9560
,0441 ,0848
3.9856 4.016;
1.093 2.067
I303 ,1891
4.03'7
3.130
4,4797
3.966
.02
'
2368
3.9831
5,509
,3096
4
6.471
,3091 ,4371 . j23I
3 989; 3 4689
,5069 ,4935 ,4912
I
2
4i51
Olji 0692 5i09
,5580
3093 2 j86 Ii92
,6198
0866
all
none
,5757
Temperature 24.6'
;;:;
1
Benzoic Acid
88.3
{
89,7
{ TWO liquid phases.
95 3
Solid phase, { Benzoic hcid.
93.2
j.190
11.19 20.61
116
I
::g
32.34 46.37 61.36 69.01 7.: .68 8s . ; 2
109
7
IO1
I
95 lo' I22
I O 0 00
''7
TKO liquid phahes.
1
Solid phase, Benzoic Acid
Critical Solution Teniprrature I i;.z0C. Cornposition of critical inisture; 3 2 ri benzoic acid Invariant Point, 94.6OC. Composition of 3Jistures at Invariant Point 4 . 5 7 5 Benzoic Acid, 95.43'; Water 7 3 .jC; Benzoic Acid, 26. j:;; Kater
TABLE I1 Solubility of Phthalic Acid in Water Grams Phthalic Acid 0.028;
0.0538 0.0668
0.0954 0,1187 0,2306
0.3271 0.5613 0.74jO 0.5459
Grams Water 3,9i90 4.0083
Weight S; Phthalic hcid 0 .j16
1.324
3.9838
I
4 0974
2
3.9787 4.1024 3 9801 4.1769 3.9743 I ,3070
2.89;
,647 .2j6
Solubility Temperature
25.8"
43.7 48.9 58.0 63.7
j ,322
77.8
7,594
8j.j
11.85
94.8
15.79 29.46
I O 1 .I
113.8
I487
BENZOIC ACID, PHTHALIC ACID, W A T E R
TABLE I1 (Cont'd) Weight yo Phthalic Acid
Grams Water
Grama Phthalic Acid 0.5156 0,6896
0.5005
50.73
131.6
0.2739
71.57
157.5
100.00
'93.3
none
all
Solubility Temperature
TABLE I11 Melting point curve for mixtures of Benzoic and Phthalic Acids Grams Phthalic Acid
Grams Benzoic Acid
Weight 5 Phthalic Acid
Solubility Temperature 122 jo
Iione
all
0 000
0.0508
5 698
1 .oooo
0.8408 9.0000
IO 00
0.1419
0.84j2
'4.37
2 .oooo
8,oooo
20.00
3.3333
33.33
j .oooo
6.6667 j . 0000
6.6667
3.3333
66.67
Solid Phase
Benzoic Acid 120 I
{ ;: ; 138
Phthalic Acid Benzoic Acid
2
4
50.00
Phthalic Acid
175 I
none all 100.00 I93 3 Eutectic temperature I 17.3' Eutectic mixture 9 1 . 3 5 benzoic acid, 8.7% phthalic acid
TABLE It7 Solubility of Mixture, Benzoic Acid 90% Phthalic Acid 1oCc, in water Grams Mixture
Grams Water
0,0397 0.1413 0.2351 0.4103 0.4330 0.5226 0.4967
3.9778 4.0313 3.9717
j388 0.5481 0 .
0.5'50 0.3912 0.4981 0.5286
all
Weight yo Mixture o 988
Solubility Temperature
3.465 j
,588
91.1,
3.4771
10.56
I
,6169
21.I2
I
. I934
0
i758
0.532'
30 46 3 9 03 50.32
0.3723
59.55
92.8
0.2008
71.95 78.24 89.64 94.69
93.0
0.1087
0.0576 ,02957
none
100.00
109 . o 103'9 Io'
ioj 8 101
3
94.7
i
I
'
\
117.2 I 20. I
Two Liquid phases
1
\
(
IOO. 2
105 . 6
Benzoic Acid
1
Solid phase Benzoic Acid Solid phase Phthalic Acid
I 488
H. LEE WARD A S D STANCIL S. COOPER
TABLE V Solubility of Mixture, Benzoic Acid 80 per cent Phthalic Acid 2 0 Der cent, in Kater Grams Mixture
o ,0600
Grams IYa t ei-
Kciqht
5; &fixture 1.494
0.1213
3.9567 3.9125
3 .ooS
0.2113
3.9175
j.118
0,3195
3.9516
0.39iI 0,5333 0,4998 0.6733
3,2765 2.9913 I ,9816 2 Ioooo
1 5 .I 3 20.14
o.jj16
I.OOO.$
35.54
0.6014
0.7006
46.I 7
0.j116 0.4981
0.3io4
j
0,2066
70.68
0.4980
0,0767
86.66
0.5358
0.0516 0.0319
91.34
,482 I O .80
Solubility Temperat w e 61 . I Solid phase
1
(
;6,6 Benzoic Acid 86.5 , ( 8;.2 Two liquid phases Solid phase Benzoic Acid 93 5 9 6 .j Two liquid phases
)
2j.10
Solid phase Benzoic Acid Two liquid phases
a . 00
Solid phase Benzoic Acid Solid phase (Phthalic Acid Solid phase Benzoic Acid ’’ ’’ Phthalic ” ” Benzoic ”
91.22
0.5311
o ,0303
0.5769 all
O.OI2i
94.58 9j.81
none
100.00
135.6
Phthalic Acid
TABLE VI Solubility of Mixture, (Benzoic Acid 66.67 per cent, Phthalic Acid 33.35 per cent) in water Grams Grams Weight yo Solubility Mixture
Water
0.0733
Mixture
0,3381
3.9274 3.9132 3.9021 3.9925
0.4029
3.2766
10.95
0,5199 0.4979
2.9623
14.93 26.21
0.1213
0.2422
1.401j
I
Temperature
,832
3.007 j ,845 7.806 81.4
88.1
Two liquid phases Solid phase Benzoic Acid
BENZOIC ACID, PHTHALIC ACID, WATER
I489
TABLE VI (Cont'd) Grams Mixture
Grams Water
Weight Mixture
0
4977
I
1852
29 5 7
0
0
809i
0
5042 2723
37 83 49 72
0
493' 4986 4998
0
5584
o 279.4
0
0
64 i3 66 66
0.5650
0.1917
74.68
0,5210
0.0852 none
86.01
All
IO0
.oo
Solubdity Temperature
:z ' 1\ 8.i 7 8i
Solid phase, Benzoic Acid
8j.7
Solid phase, PhthalicAcid Solid phase, Benzoic ' I
{91 4 87 . g
Solid phase, Phthalic
"
1j1.6
TABLE VI1 Solubility of hlixture iBenzoic Acid j o per cent, Phthalic Acid j o per cent) in Water Solubility Grams Weight % Grams Mixture
Water
o 0213 o oj03 0 I081 o 1761 o 3087 0 iTi3
3 9600 3 9140 9331 1 2i58
Mixture 0
535
2 1 6i5 597 3 956
3 9195 3 8232
7 30' 16 90
0.5320
2.0427
0.4890
1.4;'s
20.66 21.93
0.3864
0.8036
32.46
o 4602
0 .
i440
38.22
0,4717
0.7138
0.5545
0 . j0I j
39.78 j2 .48 66.50 8 2 .56
0.4311
0.2184
0,4777
0.1009
all
none
IO0
Temperature 17
oo
1;q '( ;8 8
81
::i: {:: / 80
Solid phase, Benzoic Acid
Solid phase, Phthalic Acid '' " Benzoic *kcid
2
.oo TABLE
TI11
Solubility of Mixture (Benzoic Aleid33.33per cent, Phthalic Acid 66.6;per cent) in water Grams Grams Weight Fb SolubilitMixture
Water
Mixture
0.0293 o 0683
3.8876
0,748
3 9048 3 9470 3 8240
I
o
1327
o 1982
719
3 245
4 927
Temperature
19.5'1
1
4o j
j6 8 63 8
)
Solid phase, Pht haliclcid
1490
H. LEE WARD A S D S T A S C I L S. COOPER
TABLE VI11 (Coni'&) Solubility of Nisture (Benzoic Acid 33,33 per cent, Phthalij Acid 66.67 pcr ecnt) in water Grams Grams JVcight CE Solubility Mixture
Kater
0.3016
3.4151
0 3200
I . i I l 4
I5,i5
o 8148 0.6832 o 8163
2.j276
0.8267
0.7oj6 all
21.38 34,63 49.74 70.90
none
1.2906 0.2897
Mixture
8.11;
Temperature 72.2'
81.4 88 . 4
1
Solid phnse, Phthalic Acid 125.j
100.00
Discussion of Results The solubilities obtained for benzoic acid at temperatures b e t w e n 2 5' and 80" agree satisfactorily with those of Bourgoin.6 Where deviations occur the results of the present authors show slightly greater solubilities. h comparison with the work of Sidgwick and Eubankj and Alexejew4 shows minor deviations. The triple point is found to be 94.6' instead of 95.0' as given by the former authors and the critical solution temperature 1 r i . 2 ' instead of I I j.5'. The single experimental result of Sidgwiek and Eubank in this region giyes a solution temperature of 116.2' but they, evidently relying on the more numerous experiments of Xlesejew, give a lower critical temperature. The melting point of benzoic acid, 1 2 2 . 7 ' is the same as that found by Sidgwick and Eubank. The solubility determinations for phthalic acid show unexpectedly large which were made by deviations from those of Llcllaster, Bender and the analytical method. The average percentage deviation in the per cent phthalic acid amounts to 3 . 7 5 with a maximum of 6. jC;. The temperature deviations amount, to slightly more than a degree with a masinium deviation of 1.8'. Singularly enough, the errors a t the lower temperatures are less than a t the higher ones, the greatest being between 5 5 and 75'. The material used in the two sets of observations was from the same source and showed essentially the same purit,y on analysis. The thermometers used agreed within the limits of the experimental errors of the measurements. Since the error obtained is considerably greater than that usually obtained in the synthetic method, (which is considerably less t,han half a degree) it becomes necessary t,o account, for the large discrepancy. It was noticed that the solutions supercooled very readily and it was difficult to secure crystallization. Moreover, when the crystals did form, they were much coarser than is usually the case and apparently much less material separated than would have been expected. As a consequence the point at which the last of the crystals disappeared was unusually difficult to determine. Also when the original coarse crystals mere dissolved in the preliminary measurement the temperatures were very much higher than the solubility point obtained in the second heating. This slowness in the attainment of equilibrium is also
BENZOIC ACID, PHTH.4LIC ACID, WATER
1491
apparent in some unpublished results of ,\Ic,lIaster, Bender and Weil. They found that the same equilibrium could be reached from both sides at z jowhen six hours was allowed, the average weight per cent of solute being 0.7014. At two hours on approaching equilibrium from the unsaturated condition the per cents dissolved were 0.448j and 0.6367, while approaching equilibrium from the supersaturated condition the per cent was 0.7788. The figures for four hours were 0.6648 and 0.7014,and 0.7138 and 0.7067 respectively. The attainment of equilibrium from the supersaturated condition is usually more rapid than from the unsaturated because of the large number of small crystals formed in the former case.
Keight per cent
FIG.I
The above phenomena niay be due simply to the physical characteristics of the crystals, but the slowness of attaining equilibrium both on crystallization and solution suggests the presence of a tautomeric equilibrium in the liquid phase. This would account for the greater errors a t the intermediate temperatures, for a t the higher temperatures the equilibrium would be more rapidly reached and at the lower temperatures the amount of material, which must undergo tautomeric change, would be small due to the considerable amount of solid separating. Dr. J. H. Gardner of this laboratory has noticed this time lag in the crystallization process in the case of a number of derivatives of phthalic acid such as the ortho phthalaldehyde acids and the nitro phthalic acids, and in some of these cases derivatives of the tautomeric forms have been isolated. He suggests
as a possible tautomeric form in the case of phthalic acid. Whatever the cause of the slow attainment of equilibrium, it is important to note that in
H. LEE WARD A S D STAKCIL S . COOPER
1492
cases where the material, whose solubility is to be determined does not separate rapidly on supercooling and in a finely divided form, considerably greater errors may be expected from the synthetic method than in the more usual cases. The effect of the introduction of a second polar group on the solubility of phthalic acid in water is shown by the fact that, while this acid has much the higher melting point, its molecular solubility is greater than that of benzoic acid at' all temperatures below the critical solubility temperature of the latter. That benzoic acid ?holm the critical solubility phenomena in water
2
I:
Keight per cent
FIG.2
solution while phthalic acid does not, is probably caused by the high melting point of phthalic acid and not by its greater solubility. The logarithm of the mol fraction of phthalic acid when plotted against the reciprocal of the absolute temperature s h o w the usual reversed "S" type of curve.$ The high temperature end of this curve is very difficult t o determine because of the uncertainty as regards the.arnount of water present in the vapor phase. Correction for this was made bj- riicasuring the empty space in the tube and assuming Raoult's larv t o hold. The deviations from this law are probably in the direction of increascd vapor pressure for the water, and hence the solubilities obtained at the higher temperatures are too small. The results agree fairly well with those of FIaschner and IZankin' for temperatures above 95'. They honw-er give the melting point of phthalic acid as 231' which is very much higher than the value 191' ns given in the Critical Tables and the 193.3 found in this research. In addition to the Iosa of water to the vapor phase there is also a possibility of the fornintion of phthalic anhl-dride at the higher tenlperatures. This does not seen1 to be of great importance since no abnormality appears in the curves for rriistures of benzoic and phthaiic acids. The very marked effect of the presenct of phthalic: acid on the critical solution temperature of benzoic acid is shoxn in curws A and I3 of Fig. z as compared with the phthalic acid watcr curw of Fig. I . For maniple when Mortimer: J. Am. Chem. Soc.. 44,
1416 i 1 9 2 2 1 ;
45, 633 (1923).
BENZOIC ACID, PHTHALIC ACID, WATER
I493
so%, of water is added to a benzoic acid which contains ioc0 of phthalic acid, the critical solution temperature is fourteen degrees lower than for pure benzoic acid and another 10% of phthalic acid lowers it eleven degrees more. Since the critical solution temperature can be easily measured with a n accuracy of half a degree, the above facts suggest the possibility of a method for the analysis of mixtures of benzoic with small amounts of phthalic acid. The ternary diagram appears in Fig. 3. The lines K I and K D represent the 6 j0 isotherms and the region KDXI has not been explored. It contains of course the ternary eutectic ice, benzoic acid, phthalic acid. Phthalic acid water
The Ternary System :-Benzoic
FIG.3
.hid-0-Phthalic
Acid-and
Water
separates in the region H S K I C while solid benzoic forms in the region BGLEDKSH. In the region of GLEF two liquid phases are formed with the highest critical solution temperature of 1 1 7 . 2 . The coordinates of the ternary diagram are expressed in weight per cent.
Summary The solubility curves for benzoic and phthalic acids in water have been obtained by the synthetic method from 25' to melting points of the acids and the values compared with those given in the literature. The synthetic method is not entirely satisfactory in the case of 2. phthalic acid on account of the slowness in the attainment of equilibrium, due perhaps t o a tautomeric change in water solution. 3. The melting point curve for mixtures of benzoic and phthalic acids has been determined. 3 . The complete ternary melting point diagram for the system benzoic acid, phthalic acid, water has been obtained with the exception of that portion of the diagram which lies at temperatures below 70'. j. A method of analysis has been suggested for mixtures of benzoic acid with small amounts of phthalic acid. I.
Tt'ashzngton l'nwersaty, St. L O U I SMassoun. ,
