A STUDY O F T H E TERNARI SYSTEM METHYL BEKZOATE, METHANOL, WATER* BY E. C. GILBERT AND B. E. LAVER
During the course of an investigation along other lines it became necessary to know the solubility relationships of the three liquids represented by this system and accordingly a careful study was made at three different temperatures to ascertain particularly the effect of rising temperature. Materials Methyl Benzoate-Chemically pure methyl benzoate, obtained from Eastman Kodak Company, was redistilled under reduced pressure, a fraction boiling between 88°C. and 9 1 T . a t a pressure of 17 mm. being collected. Methanol--"C. P. Special" dry methanol was redistilled, and a fraction collected which boiled between 64.7'C. and 64.8'C. a t a pressure of 760 mm. Water-Freshly distilled water was used throughout. Apparatus and Method The apparatus and method used were similar to those of Walton and Jenkins'. Starting with a measured quantity of one component in a large test tube in a transparent constant-temperature bath, the other two components were alternately added dropwise from calibrated burettes. which were provided with long extension tips running down into the test tube through the stopper. The mixture was stirred rapidly with a motor stirrer and the equilibrium end-point taken at the instant the solution became clear (with a lamp on the opposite side.) The end-points were sharp and easily duplicated for the most part. The temperature of the burettes was recorded, and from the density of the materials the weight was computed. The temperature varied very little during any run. The solutions were carefully protected from moisture. Several runs were made at zs0, IS', and 3 5 T . Overlapping portions of the curves obtained in different runs coincided exactly. The solubility of water in methyl benzoate and vice versa was determined a t each temperature from the densities of the respective saturated solutions by assuming the mixture law to hold at the low concentrations involved. The density of all materials was determined with a Sprengel-type picnometer. Results A few representative results obtained are given in Table I, and the solubility isotherms for I ~ T and . 3 5 T . are plotted in Fig. I . The isotherm at 25%. falls between these two and is omitted for the sake of clarity in the drawing. *Contribution from the Department of Chemistry, Oregon State College. Walton and Jenkins: J. Am. Chem. SOC., 45, z j j j - j g (1923).
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'METHYL BENZOATE, METHANOL AND WATER
MET~IYL BENZOATE FIG. I
TABLE I Weight percentage of one-phase equilibrium mixtures along the solubility isotherms At 15°C. Ester % Alcohol
99.8 79.4 75.0 60.0 44.0
34.5 29.9 23. I 17.3 14.5 IO. 7 0. I
0.0
16.1 19.4 29.3 39.3 45.1 47.4 50.6 52.6 52.4 j 2 . 0 0.0
.It 25'C. Y0Ester yo Alcohol
99.4 83.8
0.0
1.1
12.4 19.2 24.5 31.7 39.4 45.4 48.0 49.8 50.6 50.6 50.3 46.5 43.6 39.9
0.4
0.0
74.1
65.8 54.4 41.3 30.0 23.9 17.8 14.0 11.7 9.5 4.4 2.2
At 35°C.
% Ester 70Alcohol 98.8 68.3 62.4 59.9
0.0
20.9 25.0
11.3 8.9
26.9 32.3 35.7 39.1 42 7 44.9 47.8 48.6 49.2 48.3 47.0
0.5
0.0
51.7
45.8 39.8 32.7 28.0 21.7
18.0 15.2
'
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E. C. GILBERT AUD B. E. LAUER
Discussion Methyl benzoate and water are almost immiscible at ordinary temperatures and a considerable proportion of the alcohol is necessary to produce a one-phase mixture. The solubility surface rises abruptly and a twenty degree rise in temperature causes but little decrease in the amount of alcohol which must be used. Bancroft and others' found in a number of similar systems that if the quantity of one component is kept fixed, an equation of the type, X/Y" = constant represents quite well the resulting curve, where X is the amount of the second component, Y the amount of the third, and 1~ is a constant. This being the case log X plotted against log Y should give a straight line, since X - n log Y = log K, but when the equation was tested for the system here investigated an interesting fact was observed. If the weight of methanol is taken as Y and that of water as X for a fixed weight of methyl benzoate, the plot of log Y against log X is practically a straight line at IsOC., but at zs°C.the curve has become concave toward the X axis, and at 35OC. the concavity is quite pronounced. Agreement with the simple equation is therefore apparently dependent on the temperature. &
S-WV
The solubility isotherms of the ternary system methyl benzoate, 2j°C., 35OC. methanol, water are given for 15"C., 2. The equation X/Y" = K, fits the system very well at the lower temperature, but the divergence increases considerably with increasing temperatures. I.
Corvallzs, Oregon. Bancroft: J. Phys. Chem., 3,217 (1899); Bonner: 14, 738 (1910j; Lincoln: 8 , 248 (1904).
