M U T U A L S O L U B I L I T Y A N D T I E L I N E D A T A
C O L E M A N J. M A J O R 1 AND O SC A R J. S W E N S O N , Cornell University, Itliaca, N. Y.
¡\Iutual solubility and tie line data are presented for the system acetic acid-cthyl ether—water. Data at 25° C. were determined using reagent and commercial grade ether.
Additional data were obtained for commercial ether at 2 0 ° C. The tie line data have been successfully correlated by each of four different methods. Data on the water side of the mutual solubility curve were obtained by a new method based on the difference in foaming tendency be
tween a homogeneous and a heterogeneous solution of the three components.
I
N TH E course of a laboratory investigation on liquid-liquid extraction, mutual solubility and tie line data were required on the system acetic acid-cthyl ethor-water. Although a number of investigators have studied this system (I, 3, 5-13, 16, 18, 19, 30), the published data are not sufficiently extensive to permit construction of a complete ternary diagram. The present study was undertaken for the purpose of obtaining the necessary datá with both reagent and commercial grades ethyl ether.The equilibrium data for the system are presented in Tables I and II and the ternary diagrams are given in Figures 1 and 2.
The mutual solubility curve of Figure 1 for commercial ether lies below that of the reagent grade because the commercial ether used in this investigation contained, as an impurity, approxi
mately 3.5 weight % ethyl alcohol. Figure 2 shows that very lit
tle difference exists between the data for 25° C. and for 20° C.
1 P re s e n t a d d re s s , S h a rp ie s C h e m ic a ls , I n c ., W y a n d o t t e , M ic h .
The tie line data of Table II indicate that, at low concentra
tions of acetic acid, the acid concentration in the ether phase is lower than that in the water phase; at high concentrations of ace
tic acid tho reverse is true. This is illustrated graphically by Figures 1 and 2, where the tie lines actually undergo a reversal in slope as the acid concentration is increased.
G R A D E O F M A T E R I A L S
A c e t i c A c id . Baker and Adamson reagent glacial acetic
acid was used. Direct titration with standard alkali and phenol- phthalein indicator showed the acidity to be 99.8% by weight.
Density data on the acid at various temperatures arc presented in Table III. At 25° C. the density of the acid was 1.0439 grams per ml. whereas tho accepted literature value is 1.0440 for the pure acid.
E t h y l E t h e r . The reagent grade was obtained from one-
pound bottles labeled “ Ether Anhydrous Merck” . The specifi
cations indicated that principal impurities were 0.1% ethyl alcohol and 0.05% water. The commercial grade was obtained from 5-gallon metal containers labeled “ Ether U.S.P. Merck” . It was an alcohol derivative containing approximately 3.5 weight
% ethyl alcohol.
Density data on the two grades are presented in Table III.
The density of the reagent grade at 25° C. was 0.7071 gram per ml. as compared with tho accepted literature value of 0.7078 for the pure ether.
Wa t e r. Ordinary distilled water from the laboratory supply system was used.
ACETIC ACID ACETIC ACID
Figure 1. Mutual Solubility Curves and Tie Lines for Acetic Acid-Ethyl Ether—Water System at 25° C.
Figure 2. Mutual Solubility Curve and Tie Lines for Acetic Acid-Commercial Ether-Water System at 20°
and 25° C.
A u g u s t , 1 9 4 6 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 8 3 5 components were measured by volume from standard burets.
The density data of Table III were used in computing the weights of material added.
Measured volumes of acetic acid and ether were added from burets to a glass-stoppered Erlonmeyer flask of 125-cc. capacity.
Water was added dropwise to this solution until the mixture be
This procedure yielded data for the ether side of the solubility curve. The end points in all cases were
tion was used. Sasaki (17) showed that homogeneous solutions o f acetic acid, ethyl ether, and water tend to form foam when shaken in a flask; heterogeneous solutions of these components, however, represented by points below the water side of the mutual solubility curve, show little or no tendency to form foam. Ad
vantage was taken of this phenomenon in the present investiga
tion in establishing the water side of the solubility curve. An aqueous solution of acetic acid has a slight tendency to foam when shaken in a flask. As ether is added, the foaming tendency increases markedly until the ether phase begins to separate out.
At tins point, when ether is present in very slight excess, the mix
ture has little tendency to form foam.
The procedure which was finally used in obtaining data for the water side of the mutual solubility curve was as follows: A preliminary run was first made to establish an approximate end point. This was done by measuring definite quantities of acetic acid and water into a flask and adding ether until the mixture be
came turbid. Since the exact point at which turbidity persisted was not well defined, the above procedure yielded only an approxi
mate end point. Four separate solutions were then prepared, each of which contained the same amounts of water and acetic acid as did the trial run, but contained various amounts of ether.
The solutions were stepped in such a manner that the first one was known to have been in the homogeneous region while the last was definitely in the heterogeneous region. After the proper
Ta b l e III. D e n s i t y Da t a
Figure 5. Log Plot of ci against c2 determined by preparing several other solutions over shorter intervals of ether concentration.
T I E L I N E D A T A
The tie lino data were obtained by preparing various mixtures of the three components and analyzing the ether and water layers for acetic acid. The mixtures were placed in 12o-cc. glass-stop- pered Erlenmeyer flasks and shaken vigorously. The flasks were kept for several hours in a constant temperature bath.
Samples of the light and heavy layers were pipetted from the flasks into another set of glass-stoppered flasks and weighed.
Each layer was then diluted with water and titrated with stand
ard alkali and phenolphthalein as indicator. applicability of the method to the acetic acid-ethyl ether-wat.er system. Ci/ai is plotted against log c2/b 2, where Ci is the fraction of solute in the solvent phase, c2 is the fraction of solute in the diluent phase, ai is the fraction of solvent in the solvent phase, and b2 is the fraction of diluent in the diluent phase. The applicability of his method to the present system is substantiated by the straight-line correlations of Figure 4.
Campbell (2) demonstrated that tie line data for a large num
ber of systems are successfully correlated by plotting log ci against log c2. Figure 5 shows that this method of tie line correla
tion is likewise applicable to the present system.
The writers found that a straight line results from a plot of log (1 — ci)/ci against log (1 — ci)/c2, as Figure 6 shows. This method of tie line correlation is not applicable to all ternary sys
tems but does apply to a large number of them.
For clarity the points representing the tie line data for com
mercial ether at 20 ° C. were omitted from Figures 3, 4, 5, and 6.
These points fall in a substantially straight line, however, when plotted by each of the four methods described.
b2+ c 2
Figure 7. Effective Concentration Curves for System Acetic Acid-
Ethyl Ethcr-Water
Othmer el al. (14) showed that relative efficiencies of solvents may be ascertained by plotting (fraction solute)/(fraction solute + fraction water) in the solvent phase against the same quantity in the water phase. In such a plot the best solvent would have the highest solute concentration in the solvent phase for a given solute, concentration in the water phase. Figure 7 shows that, weight for weight, reagent-grade ether is a more efficient solvent for acetic acid than the commercial grade.
N O M E N C L A T U R E
weight fraction of solvent (ether) weight fraction of diluent (water) weight fraction of solute (acetic acid) subscript referring to solvent (ether) phase subscript referring to diluent (water) phase
L I T E R A T U R E C I T E D