[CONTRIBUTION FROM THE
RESEARCH LABORATORY OF ARMOUR AND
COMPANY]
THE SOLUBILITIES OF THE NORMAL SATURATED FATTY ACIDS. 11. C. W. HOERR
AND
8 . W. RALSTOK
Received M a y 8, 194.6
An earlier report from this laboratory (1) presented the solubilities of the normal saturated fatty acids from caprylic to stearic acid, inclusive, in water, ethanol, acetone, 2-butanone, benzene, and glacial acetic acid. This paper reports the further investigation of the behavior of these acids in cyclohexane, tetrachloromethane, trichloromethane, ethyl acetate, butyl acetate, methanol, isopropanol , n-but anol , nit roet hane, and acetonitrile. Several of the acids employed in this investigation possessed slightly higher freezing points than those of the acids used in the previous study (1). The freezing points of the present acids are listed in Table I. The solubilities of these acids were determined in highly purified solvents by the method previously described (1, 2). RESULTS AND DISCUSSION
The solubilities of the fatty acids in cyclohexane are similar to their behavior in benzene (1)in that they form eutectics with both solvents. The compositions and freezing points of these eutectics are listed in Table 11. The solubilities of the acids above the freezing point of cyclohexane are listed in Table 111, and the systems are shown graphically in Fig. 1. The solubilities of the acids in tetrachloromethane and in trichloromethane are listed in Tables IV and V, respectively, and the solubility curves in trichloromethane are shown in Fig. 2. The acids are generally more soluble in trichloromethane than in any other solvent investigated. I n the above three solvents, as with benzene, the fatty acids are paired, with the next higher odd-numbered homolog being the more soluble of the pair. I n each of the following solvents, all of which are more polar than trichloromethane, the adjacent homologs are also paired. In these instances, however, the paired solubility curves intersect at moderate dilutions. Thus, the next higher odd-numbered homolog is the less soluble of each pair a t temperatures below the intersection, and the solubilities of the acids decrease without alternation as the series is ascended. I n the less polar solvents, this intersection of the paired solubility curves occurs above lauric acid at ordinary temperatures, while in the more polar solvents it occurs also in the lower acids. The solubilities of the acids in ethyl and in butyl acetates are listed in Tables VI and VII, respectively, and the curves in ethyl acetate are shown in Fig. 3. The solubilities in these solvents correspond qualitatively to those in acetone and in 2-butanone (1 ) whose polarities approximate those of the acetates. The solubilities of the acids in methanol, isopropanol, and n-butanol are listed 329
330
C. W. HOERR AND A. W. RALSTON
TABLE I FREEZING POINTS OF PURIFIED FATTY ACIDS
c
30, OF ATOMS
ACID
.
Caprylic. . . . . .. . . . . . . . . . . . Nonylic. . . . . . . . . . . . . . . . . . . Capric, . . . , , , . . . . . . . . . . . . . Undecylic . . . . . . . . . . . . . . . . . Lauric. . . . . . . . . . . . . . . . . . . . . Tridecylic . . . . . . . . . . . . . . . . .
8 9 10 11 12 13
P.P.,
"c.
ACID
Myristic. . . , . . . . . . . . . . . . . Pent adecylic . . . . . . . . . . . . . Palmitic. . . . . . . . . . . . . . . . . Heptadecylic . . . . . . . . . . . . . Stearic. . . . ... . . . , . . . . . . . .
16.30 12.25 31.24 28.13 43.92 41.76
-~ 14 54.15 15 52.54 16 62.82 17 60.94 18 69.32
TABLE I1 EUTECTICS FORMED BY ACIDSWITH CYCLOHEXANE NO. OF
c ATOMS
WT. % ACID
8
TEMP.,
-14.0 -17.5 -3.2 -5.9 $3.2 1.9 5.6 5.4 6.4 6.3 4 . 6
22.0 23.9 14.1 16.2 6.8 8.6 2.4 2.9 0.4 0.7
9 10 11 12 13 14 15 16 17 18
OC.
