SOLUBILITY OF SUCCINIC ACID I N BINARY MIXTURES BY WILDFB, D. BANCROFT AND F. J. C. BUTLER
Many cases are known of a maximum solubility of a solid in some mixture of two consolute liquids.' Holleman and Antusch consider the possible explanations for aqueous alcohol to be: the formation of alcohol hydrates in solution; the formation of complex molecules of the solute in solution; the formation of a compound between solvent and solute. There is no evidence for the existence of alcohol hydrates in solution. If this is the sole cause of the abnormality, the position of the maximum must be independent of the temperature. While the absolute amount of the hypothetical compound will vary with the temperature, the percentage composition a t which there is a maximum formation of the compound at any temperature will be independent of the temperature. We have made a study of the behavior of succinic acid, substituting mass concentrations for the volume concentration used by Herz and Knoch. At 20' they found the maximum solubility a t about 35% by weight of water; we find it at about 45% by weight at 40'. Seidell found that the position of maximum solubility of acetanilide in aqueous alcohol was displaced by change of temperature. I n these two cases there is therefore no justification in assuming that a compound of acetone and water or of alcohol and water plays any important part. This is what one would have expected anyway from the partial pressure curves of aqueous acetone and aqueous alcohol. There is no evidence from these of any appreciable amount of any hydrate being formed. There is no evidence for the existence of any appreciable amounts in solution of any compound between succinic acid and water or acetone though the non-existence of such compounds has not been proved. Nobody has even made an attempt to show how the maximum solubility of succinic acid in aqueous acetone could be accounted for on the assumption of polymerization or depolymerization of succinic acid. The explanations suggested by Holleman and Antusch seem therefore to be inadequate. There is one other factor that has not yet received adequate consideration, namely reversible polymerization and depolymerization of either or both of the solvents. If succinic acid is more or less soluble in monomolecular water than in polymolecular water, the solvent action of the water will change with changing concentration of the water. Experiments were made on the solubility of succinic acid in binary mixtures of methyl, ethyl and propyl alcohols. The data areshown graphically in Fig. I. The solubility curves are so near straight lines that any variation from them Cf. Holleman and Antusch: Rec. Trav. chim., 13, 2 7 (1894);Herz and Knoch: Z. anorg. Chem., 41,315 (1904).45,262;46, 193 (1905);SeidekJ. Am. Chem. SOC 29, 1088 (1907);Dehn: 39, 1399 (1917);Highfield: Trans. Faraday Soc., 22, 57 (1926)' Dikelkamp: Z.qhysik. Chem., i23, 99 (1926);Angelescu and Dumitrescu: 132,217 (1928j;Wilson and Wnght: J. Chem. Soo., 1928,3111;Duff: 1931,881,1196.
2516
WILDER D. BAKCROFT AKD F. J. C . BUTLER
can be disregarded for the time being. In terms of our hypothesis this means that there is practically no change in solubility of succinic acid with changing polymerization of the alcohols. Similar data forwater with acetone, methyl alcohol, ethyl alcohol, and propyl alcohol are shown graphically in Fig. 2 . In all cases there is a maximum solubility and this maximum solubility was predicted from the experiments of Herz and Knoch with aqueous acetone. I t seemed probable that other acids of the same type would behave similarly and in Fig. 3 are given the data for adipic acid for water with acetone, methyl alcohol and ethyl alcohol FIG.I at 40'. I n each of the three cases there is a maximum solubility as expected. As might - also have been expected there is less of a maximum relatively with aqueous methyl alcohol than with the other pairs of liquids because the relative effect ascribed to monomolecular water will be less the greater the solubility in the organic liquid.
I R ,d
10
c
0
o m s of
60
a ,
M
60
w
W ~ W RI* r n c of MLYN~T
AF:-Aqueous BG:-Aqueous CG:-Aqueous DG:-Aqueous EG:-Aqueous
FIG.2 acetone at zoo acetone at 40' propyl alcohol at 40' ethyl alcohol at 40' methyl alcohol at 40'
1
I
o
m
w
II)
OOUI
EF
UI
ro
P
wnra IXIOOP.OC
AD:-Aqueous BD:-Aqueous CD:-Aqueous
07. M IOLWF
FIG.3 acetone at 40" ethvl alcohol a t 40' meehyl alcohol a t 40'
SOLUBILITY OF SUCCINIC ACID I N BINARY MIXTURES
2517
If we make the explicit assumption that the solubility due to an alcohol is a linear function of the concentration in the aqueous alcohol mixtures, just as it has been shown to be in the mixtures of two alcohols, the difference between the calculated value for the alcohol and the found value for the mixture represents the assumed solubility of succinic acid in the water. By recalculating to the basis of one hundred grams of water, we get thedatagiveninTable1. TABLE I M = weight percentage of methyl alcohol in aqueous alcohol. E = weight percentage of ethyl alcohol in aqueous alcohol. P = weight percentage of propyl alcohol in aqueous alcohol.
M
x = calculated grams of succinic acid per hundred grams water. Temperature, 40'. X E X P
0
15.7
IO
19.8
20
21
30 40
24.8 29.2 34.1 38.7 43 .o 48.1
50
60 70 80 90
.o
0
15.7
IO
18.5 23.9 29.5 35.0 41.8 47.4 53.7 59.8 62 . o
20
30 40 50
60 70 80 90
52.1
X
0
15.7
IO
20.5
20
26.1 31.5 36.9 42.2 48.0 54.5 60.9 66.2
30 40 50
60 70 80 90
TABLE I1 M = weight percentage of methyl alcohol in aqueous alcohol. E = weight percentage of ethyl alcohol in aqueous alcohol. x = calculated grams adipic acid per hundred grams water. Temperature, 40'. M x M x E x E x 0
IO 20
30 40
5.2
50
21.5
4.1 4.8 8.3 14.6
60 70 80 90
28.9 36.7 40.9 42.8
0 IO
5.2
50
6.6
60 70 80 90
20
11.5
30 40
'9.4 28.3
41.9 51.4 63.7 76.9 94.5
In each case there is a smooth curve with increasing apparent effectiveness as the concentration of the water in the mixture of the two liquids becomes less. Since water is monomolecular in dilute solutions, this means that the apparent solubility of succinic acid in monomolecular water at 40' is approxmately four times as great as in pure water at the same temperature. This cannot be the whole truth, however, because the solubilities do not extrapolate to the same value in the three cases. There is therefore another factor to be taken into account and we cannot at present state what that factor is. We
2518
WILDER D. BANCROFT AND F. J. C. BUTLER
may point out empirically that the apparent solubility in water comes out lowest in the alcohol in which succinic acid is most soluble. Succinic acid is about twice as soluble in methyl alcohol as in ethyl alcohol and about four times as in propyl alcohol. A similar result is obtained for adipic acid as shown in Table 11. The general relations are much the same as with succinic acid, but the change in apparent solubility is much greater and the difference between the end values is much greater. Data for t'he solubility of succinic acid in mixtures of acetone with methyl alcohol, ethyl alcohol and propyl alcoeaan# OF m w c IN roo a e+ 5 o ~ w r hol are shown graphically in Fig. 4. FIG.4 There is a maximum solubility in aceAD:-Acetone-prop 1 alcohol at 40" tone and propyl alcohol and in acetone BD:-Acetone-ethSYalcohol at 4oo CD:-Acetone-methyl alcohol at 40' and ethyl alcohol; but none in acetone and methyl alcohol. In terms of our hypothesis this means that there is a change in the solubility of succinic acid with changing polymerization of acetone. If we assume that the solubilities due to the alcohols are linear functions of the concentration, the apparent solubilities in acetone are given in Table 111. The apparent, solubility of succinic acid in monomolecular acetone at 40' is approximately four times that. in pure acetone a t the same t'emperature. The apparent solubility is greatest in the propyl alcohol solutions in which
TABLE I11
ll1 = weight percentage of methyl alcohol in alcoholic acetone. E = weight percentage of ethyl alcohol in alcoholic acetone. P = weight percentage of propyl alcohol in alcoholic acetone. x = calculated grams succinic acid per hundred grams acetone. Temperature, 40'. M o IO 20
30 40 50 60
70 80 90
X
6.60 8.89 11.31 13.63 16.27 18.22 19.57 21.77 22.90 24.60
E
x
P
X
o
6.60 8.52 I O . 52 13.10 15.37 17.64 19.70
o
80
6.60 8.21 10.04 12.03 13.95 15.92 17.85 20.53 23.35
go
28.70
IO
20
30 40 SO
60 70 80 90
20.70
21.45 22.50
IO 20
30 40 50
60 70
SOLUBILITY OF SUCCINIC ACID I N BINARY MIXTURES
2519
E.
FIQ.6 AC:-Acetone-ethyl alcohol a t 40" BC:-Acetone-methyl alcohol at 40"
AE:-CCL-acetone a t 40' BE:-CClr-prop 1 alcohol at 40" CE:-CCl&hyfalcohol at 40" DE:-CCla-methyl alcohol at 40'
the solubility of succinic acid is the least; but it is least in the ethyl alcohol solutions and not in the methyl alcohol solutions, as was the case in the aqueous solutions. No explanation is offered for this discrepancy. The solubility data for adipic acid in mixtures of acetone with methyl alcohol and with ethyl alcohol at 40' are shown graphically in Fig. 5 . There is a maximum solubility in the ethyl alcohol solutions and no maximum in the methyl alcohol solutions. This is qualitatively identical with what was found with succinic acid. The calculated data for the apparent solubilities of adipic acid in acetone are given in Table IV. The apparent solubility of adipic acid in monomolecular acetone a t 40' is three to four times the solubility in pure acetone a t that temperature. The
TABLEIV M = weight percentage of methyl alcohol in alcoholic acetone. E = weight percentage of ethyl alcohol in alcoholic acetone. x = calculated grams adipic acid per hundred grams acetone. Temperature, 40'. M 0
IO 20
30 40
X
M
8.71 11.94 16.00 19.00 22.65
50 60
70 80 go
x
23.22 24.83 26.07 26.50 25.80
E 0
IO 20
30 40
x
E
50 60
8.71 11.74 14.98 17.96
80
21.05
90
70
x
24.08 28.05 29.53 31.55 32.90
2520
WILDER D. BAXAROFT AND F. J. C. BUTLER
higher apparent solubility occurs in the ethyl alcohol solut,ions and adipic acid is less soluble in ethgl alcohol than in met,hyl alcohol. Succinic acid is pmctically insoluble in carbon tetrachloride. Data for the solubility in mixtures of carbon tetrachloride with acetone, methyl alcohol, et'hyl alcohol, and propyl a,lcohol at 40' are shown graphically in Fig. 6. A11 the curves are slightly concave as seen from above. This is not surprising because carbon tetrachloride would tend to precipitate succinic acid from solution in an alcohol and succinic acid would increase the partial pressure of carbon tetrachloride in an alcoholic solution. This would give a curve which would be concave as seen from above. The general results of this investigation are as follows: I. In binary mixtures of methyl alcohol, et'hyl alcohol, and propyl alcohol, bhe solubilities of succinic acid are practically linear functions of the concentrations of the solvent. 2. With binary mixtures of water and the alcohols, water and acet,one, and acetone and the alcohols, the solubility curves for succinic acid and for adipic acid, so far as determined arc convex as seen from above. 3. There are no maxima in the solubility curves for succinic acid and adipic acid in mixtures of acetone and methyl alcohol. There is a maximum solubility in each of the other curves which are convex when seen from above. 4. The solubility curves for succinic acid in binary mixtures of carbon tetrachloride with acetone, methyl alcohol, et'hyl alcohol, and propyl alcohol, are concave as seen from above. The solubility of succinic acid in carbon t,etrachlorideis pract'ically negligible. 5 . If a maximum solubility is due solely to t'he formation of a definite chemical compound between the two liquids, the concentration a t which the maximum solubility occurs must be independent' of the temperature. 6. With acetone-water mixt,ures and succinic acid the concentration showing maximum solubility changes with varying temperature. The existence of a hypothetical hydrate of acet'one cannot therefore be the sole factor and is probably not an important factor in causing the maximum solubility in this syst'em. 7. Since 'the solubility curves of succinic acid in binary mixtures of methyl ethyl, and propyl alcohols are very nearly straight lines, we must assume that the solubility of succinic acid does not vary much with varying polymerization of t,he alcohols. 8. From the existing data it seems probable that succinic acid and adipic acid are more soluble in depolymerized water and acetone than in the polymerized liquids. 9. Since t,he calculated values for the apparent solubility of succinic and adipic acids in depolymerized water and acetone vary with the nature of the other liquid, there must be still another factor to be taken into account. IO. In all cases but one t'he apparent' solubility of succinic or adipic acid in depolymerized water or acetone comes out higher the less soluble the organic acid is in the other liquid. No explanation is offered for this. Cornell Universitg.
