SOLUBILITIES OF SOME NORMAL SATURATED ALIPHATIC


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[CONTRIBUTION FROM

THE

RESEARCH LABORATORY OF ARMOUR AND COMPANY I

SOLUBILITIES OF SOME NORMAL SATURATED ALIPHATIC HYDROCARBONS A. W. RALSTON, C. W. HOERR,

AND

L. T. CREWS

Received March 24, 1944

In view of the extensive experimentation upon the aliphatic hydrocarbons, it is noteworthy that the literature contains few references to their behsvior in organic solvents. Hildebrand (1) has recorded some solubilities of several hydrocarbons containing 4 to 8 carbon atoms, but in this cme the hydrocarbons have been considered primarily as solvents and not as solutes. Except for a few investigations of ebullioscopic behavior (2) and viscosities of solutions (3), physical measurements of the higher hydrocarbons have dealt predominantly with the differences between the normal aliphatic homologs and their isomers. Solubility determinations of a wide variety of paraffin-chain compounds (4) have indicated that their polar groups do not exert as great an influence upon their behavior in solution as had previously been thought. Many of the physical properties of the aliphatic compounds, such as the melting points and refractive indices, are markedly dependent upon the nature of the polar groups, and their dipole moments appear to be a specific function of the polar groups. The slopes of the Solubility curves of these compounds, however, are so consistently similar, irrespective of the polar groups, that the nature of the solubility curve appears to be a specific function of the length of the alkyl chain. The solubilities of several representative hydrocarbons have been determined in order to compare their behavior with that of the polar compounds. The slopes of the solubility curves of polar aliphatic compounds have been attributed to molecular association (4). It is evident, however, that the zero dipole moments of the aliphatic hydrocarbons (5) preclude any possibility of dipole-dipole coupling. This paper presents the solubilities of octane, dodecane, hexadecane, heptadecane, and dotriacontane in 11 organic solvents. EXPERIMENTAL

The highly purified normal aliphatic hydrocarbons used in this investigation were prepared by i,he following methods. Octane was obtained by the reaction on n-butyl bromide with sodium, and was subsequently distilled through a Stedman packed column. Dodecsne was prepared by catalytic hydrogenation of dodecene and purified by vacuum distillation in a Stedman packed column. Hexadecane and dotriacontane were obtained simultaneously by reaction of hexadecyl iodide with sodium. Hexadecane was separated by vacuum distillation, crystallized from acetone, and then subjected t o two further vacuum distillatione. Dotriacon tane was recrystallized three times from trichloromethane a t -30". Heptadecane was prepared by Dr. W. 0. Pool by heating stearic acid (f.p. 69.3') to 350" in the presence of Raney nickel catalyst. Pure heptadecane was separated from a small amount of lower unsaturated hydrocarbons by two vacuum distillations in a Stedman packed column. The freezing points of these hydrocarbons are listed in Table I. The solubility measurements were made with the equipment and in the manner previously described (40). 319

320

RALSTON,

EOERR, AND CREWS

RESULTS AND DISCUSSION

In the non-polar and slightly polar solvents, the solubility curves of the normal aliphatic hydrocarbons are qualitatively similar to the curves of the polar aliphatic compounds of corresponding chain lengths. As the polarity of the solvents increases above that of acetone, the solubility of the hydrocarbons decreases abruptly. The hydrocarbons are practically immiscible with the strongly polar solvents such as methanol, ethanol, nitroethane, and acetonitrile. The polar aliphatic compounds, on the other hand, are generally miscible with these strongly polar solvents. Even such long-chain compounds as laurone and myristone are appreciably soluble in acetonitrile, although they resemble the hydrocarbons in other behavior. Thus, a polar group imparts a definite solubilizing effect upon a paraffin-chain compound, particularly in a polar solvent. TABLE I FREEZING POINTS OF PURIFIED HYDROCARBONS HYDROCA~BON

Octane

(0.OF

c ATOXE

P.P., O C .

8

-56.84

Dodecane

12

-9.64

Hexadecane

16

18.18

Heptadecane

17

21.72

Dotriacontane

32

70.16

F.P.,

"C.(LIT.)

-57.3(6); -56.90(7); -56.82(8);-56.5(9); -56.8(10, 11, 12); -57(13); m.p. -56.84(14); m.p. -57.0(15). -9.73(7); -9.61(8); -12.0(9); -9.6045 .003(12) ; m.p.-12(16). 17.9(11); 18.145 f .003(12); 17.6(17); 18.10(18); m.p. 18.2(19); m.p. lS(20); m.p. 17.8(21). 22.0(12); m.p. 21.2(15); 21.92(22); m.p. 22.5(23,24);m.p. 21 (25); m.p. 21.8(26). 69.6(27);m.p.70(28,29,30);m.p.70.0(31); m.p. 68-70(32); m.p. 69.8(33); m.p. 71(34); m.p. 70.5(35); m.p. 74-75(36); m.p. 70.2(37); m.p. 69.9(38); m.p. 69.6(39).

The hydrocarbons form eutectics with benzene, cyclohexane, tetrachloromethane, and trichloromethane. The compositions and freezing points of the respective eutectics are listed in Table 11. The solubilities of the hydrocarbons above the freezing poink of the solvents are listed in Tables III-VII, and these solubilities are illustrated by the diagrams of several representative systems shown in Figs. 1-8. These hydrocarbons exhibit a pronounced correlation between their solubility and the polarity of the solvents. Thus, the solubilities of any of the hydrocarbons investigated decrease progressively as the dielectric constants, E, of the solvents (5) increase in the following order: benzene 2.3, trichloromethane 4.9, butyl acetate 6.0, ethyl acetate 6.2, 2-butanone 18, acetone 21, methanol 33. The hydrocarbons are, however, somewhat more soluble in isopropanol and in n-butanol than would be anticipated on the basis of the dielectric constants of these solvents.

321

SOLUBILITIES O F ALIPHATIC HYDROCARBONS

TABLE I1

EUTECTICS FORMEDBY

THE

HYDROCARBONS c ATOMS

NO. OF SOLVENT

a 12 --

Wt. % solute.. . . . . . . . Temp., "C.. . . . . . . . . . .

Benzene Cyclohexane Tetrachllxomethane

17

91.8 -58.4

65.1 -17.9

32.4 -1.3

37.2 -1.9

Wt. yo solute.. . . . . . . . 39.1 Temp., "C.. . . . . . . . . . . -71.6

28.5 -32.9

17.6 -12.5

17.5 -10.8

Wt. Yo solute.. . . . . . . . Temp., "C.. . . . . . . . . . .

39.1 -66.3

9.9 -34.2

3.5 -26.2

3.3 -25.6

Wt. % solute.. . . . . . . . Temp., "C.. . . . . . . . . . .

25.3 -67.8

0.3 -63.6

-

-

i i

Trichloromethane

16

-

32

TABLE I11 SOLUBILITIESOF WOCTANE~ C. P E P

100

G. SOLVENI

SOLVENT

-75.0"

-70.0'

37.5 1.1

68 3.2 13.3 1.7 4.4 9.9 15.4

___-

Trichloromethane. . . . . . . . . . . . . . . . . . . . . . . . . . . . Ethyl et'her... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ethyl acetate.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Butyl acetate.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acetone 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13utanone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isopropanol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . %-Butanol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q

m

b

SOLYENT

-55.0"

275 550 25.0 120 5.3 31.2 36.0 45.1

m ca m 00

8.0 m

m W

TABLE IV SOLCBILITIES OF TL-DODECANE~

I

I

Tetrachloromethane.. . . . . . . . . . . . . . . . Tr.ichloromethane.. . . . . . . . . . . . . . . . . . Ethyl ether . . . . . . . . . . . . . . . . . . . . . . . . . Ethyl acetate.. . . . . . . . . . . . . . . . . . . . . . Butyl acetate.. . . . . . . . . . . . . . . . . . . . . . Acetone h . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-Hut an0 ne. . . . . . . . . . . . . . . . . . . . . . . . . Isopropanol. . . . . . . . . . . . . . . . . . . . . . . . . n-Butanol . . . . . . . . . . . . . .. . . . . . . . . . . . .

30

-6Q.00

147 7.9 26.4 2.8 8.0 15.9 22.1

above -56.8" with solvents listed, except acetone. above -5.5".

_______

30

8.8 z1.0 3.0 7.1 12.2

-65.0"

G. P E R

-60.0'

0.5 0.9 -

0.3 0.4 -

0.5

-5O.OO

I

1.3 3.4 0.9 -

0.7 0.1 1.0

above -9.6" with solvents listed, except acetone. above 16.5".

100 G. SOLYENT

-40.0°

-30.0"

-20.00

-15.0"

4.9 10.0 0.3 2.6 0.5 1.3 0.7 2.0

19.8 39.1 2.8 7.4 1.2 3.2 2.7 4.6

114 117 186 13.6 34.6 3.3 12.0

260 317 490 106 178 6.2 41.8 21.1 31.4

9.0

13.6

'

TABLE V WHEXADECANE'

SOLUBILITIES OF

G. PER 100 0 . SOLVENT

SOLVENT

Benzene. . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclohexane. . . . . . . . . . . . . . . . . . . . . . . T e t rachloromethane , .. . .. . . . . . . . . . . Trichloromethane. .. . . . . . . . . . . . . . . . Ethyl ether .... . . . . . . . . . . . . . . . . . . . . Ethyl acetate., . . . . . . . . . . . . . . . . . . . . Butyl acetate.. , . . . . .: . . . . . . . . . . . . . Acetone b , . . . ... . . . . . . . . . . . . . . . . . . . . 2-Butanone. . . . . . . . , . . . . , . . . . . . . . . . Isopropanol. . ... . . . . . . . . . . . . . . . . . . . n-Butanol . . . . .. . . . . . . . . . . . . . . . . . .

.

Q

b

m

m

-20.0"

-10.00

5.5 2.2 5.4

-

-

=0.2

-