The Partially Miscible System Water-Normal Amyl Alcohol JOSEPH J. JASPER, LOREN G. FARRELL, and MILTON MADOFF Wayne Uniaersity, Detroit, Michigan
I.
N A previous description of the laborato~yprocedure
increasing quantities of normal amyl alcohol were .' involnng the construction of the temperature-com- measured into successive small flasks in incremeqts of position diagram of the partially miscible system 0.5 ml. for the first 19 solutions and of 0.2-ml. increwater-isobutyl alcohol,' it was shown that a number ments for the remainder of the series. Sufficient of difficulties are encountered in obtaining the data water was then added to make a total volume of 10 ml. necessary for the construction of such a diagram. The In most of the flasks two-phase liquid systems were obmost important of these arises from the tendency of tained which were reducedto the desired homogeneity the distillate samples, which are collected a t their boil- by the addition of 95 per cent ethyl alcohol. Various ing points, to resolve themselves into two saturated other solvents were first tried, but the least quantity was fiven by the layers a t the relatively low temperatures where their needed to produce homogeneity . compositions are most conveniently determined. Un- ethyl alcohoi. Previous trials indicated that a minimum of 7 ml. of der these conditions, i t is clearly impossible to determine, by the usual methods employed for zeotropic the ethvl alcohol was renuired to brinp about homoand azeotropic systems, the total composition of the geneity in the 10-ml. samples of the two-phase systems. various vapor phases (the distillates) which are in ther- Therefore, to every prepared sample, 7 ml. of ethyl mal equilibrium with the cerresponding residues. To alcobol were added, thus bringing the total volume to insure homogeneity, it was found necessary to employ 17 ml. To all distillation samples subsequently cola third liquid, one in which both saturated phases were lected, sufficientethyl alcobol was added to maintain this completely miscible. Since this solvent was used volume ratio of 10 parts of the sample to 7 parts of ethyl both in preparing the samples for the refractive index- alcohol. Smaller quantities of the mutual solvent procomposition reference curve and for holding the subse- duced turbidity. The refractive indexes of the prequent distillation samples homogeneous, its effect was pared solutions were determined a t 25'C. with an canceled and did not enter into composition determina- Abbe refractomer. tions. The purpose of this investigation was to further demTABLE 1 onstrate the simplicity and practicability of the method DATA POI( RBPBRBNCE CVEYB previously described by applying it to a different parVolume Mol Mdcs Volrma Amy1 tially miscible binary system, the characteristic propFrar1ion Alcohol, Amy1 Amy1 Water, Indr. of Solulion erties of which necessitated the use of considerably Akohol Alcohol Refrnrlion No. MI. MI. greater proportions of the mutual solvent in order to OOOW 0.0046 induce homogeneity. The resulting solutions were 0.0093 relatively dilute in the active components as compared 0.0139 0.0186 with those previously employed. An Abbe refrac0.0232 tometer was used to determine the composition of the 0.0279 0.0325 samples, and, regardless of their dilution, the precision 0.0372 of the instrument was found to be sufficient for this 0.0418 0.0465 purpose. From the data so obtained, the temperature0.0511 0.0558 composition diagram was constructed.
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THE REFERENCE CURVE
In accordance with the procedure previously described,' i t was found both convenient and instructive to construct the reference curve as the initial step. This was accomplished by preparing a series of 24 solutions containing constantly varying proportions of the components over the whole composition range between the pure components. With the use of a microbnret
0.0605 0.0652 0.0698 0.0745 0.0791 0.0838 0.0857 0.0876 0.0895 0.0914 0.0933
The mol fraction of the normal amyl alcohol in each solution was calculated on the basis of a total volume of 10 ml. The presence of the ethyl alcohol was dis-
regarded, since this factor is automatically canceled when the refractive indexes are applied to the reference curve for the determination of their compositions. The amyl alcohol used had a boiling point of 136 to 137'C. a t 748.6 mm. pressure and a density of 0.8199 a t 25'C. The data obtained for the reference curve are shown in Table 1. , The refractive indexes were plotted on a very large scale as ordinates against the mol fraction of normal amyl alcohol as abscissas. This gave a smooth, continuous curve, which was not too flat a t the higher mol fractions for readings of good precision. By referring the indexes of refraction of the various distillation samples to this curve, their corresponding compositions were determined. THE DISTILLATION APPARATUS
Two distillations were made, one with an excess of the amyl alcohol and the other with an excess of water. The procedure was the same in both cases. The distillation system is shown in Figure 1. It consists of a 500-ml. distilling flask a equipped with a 45-cm. side arm d of 5-mm. bore. This long side arm, which functioned as an air condenser, was bent sharply downward at an angle of about 45' to facilitate rapid passage of the distillate. The neck and upper portion of the bulb of the flask were covered with a thick layer of asbestos. Small narrow slits cut diagonally opposite in the jacket provided for inspection of the contents of the flask. These openings were closed with strips of asbestos during most of the distillation process. In order to obtain smooth curves bounding the various areas of the temperature-composition diagram, it is necessary to obtain samples of distillate and residue as nearly simultaneously as possible. The distillation system, therefore, had to be so constructed that small quantities of the liquid could be readily removed from the flask without interrupting the boiling. To accomplish this a capillary delivery tube b for obtaining residue samples was inserted through the stopper, with the lower opening a t a level near the center of the liquid contents. The upper end was bent downward in an arc, as shown in the figure. Two receiving containers, e and f, were constructed, one for the residue and the other for the distillate, respectively. These consisted of small lengths of 7-mm. pyrex tubing, closed a t one end and carefully calibrated to 1 ml. The residue-receiving container was equipped with a short side ann. A small rubber gasket c, which fitted into the neck of e, was drawn over the end of the residue delivery tube. T o obtain a sample of the liquid within the flask, the upper end of tube b was inserted into the container e with the gasket closing the neck. Liquid from within the flask was readily obtained by suction on the side arm. To insure that the residue samples were representative of the liquid within the flask, the residue delivery tube was each time blown free of trapped liquid and the samples immediately withdrawn, as described. A thermometer with 0.2' scale divisions was used.
THE DISTILLATION PROCESS
About 250 ml. of the amyl alcohol were placed in thc distilling flask and enough water added until, after vigorous shaking for about 10 minutes, a double liquid layer was just noticeable. The flask was then heated slowly in an oil bath until the liquid just started to boil. The boiling rate was so regulated that the vapor front, which was clearly observed, was held to a point between 15 and 20 cm. from the lower opening of delivery tubed. After discarding the first few milliliters of distillate, but with a double layer still existing in the JEask, exactly 1 ml. of distillate was collected. As quickly as possible a l-ml. sample of the residue was collected from the alcohol layer, as previously described. Upon cooling to room temperature, two liquid layers appeared in the distillate sample, hut after the addition of 0.7 ml. of 95 per cent ethyl alcohol the sample became homogeneous. The same volume of ethyl alcohol was added, likewise, to the residue sample. The samples were placed in respective test tubes, tightly stoppered, labeled, and reserved for the refractive index measurements.
During the initial stages of the distillation process, the temperature remained constant until the water layer disappeared from the flask. At this point the temperature started to increase. The temperature was then gradually raised, and other samples of the distillate and the residue were collected over the remaining temperature range up to the boiling point of the pure amyl alcohol. The process described was duplicated for a system containing an excess of water. This time 250 ml. of water were added to the flask. To this enough of the amyl alcohol was added until, after shaking for several minutes, a double layer was again observed. As before, a number of distillate and residue samples were collected, one set at the temperature of coexistence of the two saturated liquid phases and others over the remaining temperature range up to the boiling point of water. As before, ethyl alcohol was added to every sample in the volume proportions of 7 parts of ethyl alcohol to 10 parts of the sample. The refraction indexes of the various samples were measured a t 25' and their compositions determined by applying to the reference curve. The data are assembled in Table 2. The miscibility of the components in each other a t 25' was determined by shaking them together a t room temperature and then suspending the resulting two-phase system in a thermostat bath a t 25'. Samples from each layer were obtained and the proper proportions of ethyl alcohol added. Their compositions were then determined as described. The mol fractions of the normal amyl alcohol in the various samples of the distillate and the residue were plotted against the corresponding boiling points. The boiling points were corrected to 760 mm. of mercury. The temperature-composition diagram obtained is shown in Figure 2. TABLE 2 D A T A FOR TEMPBRATORB-COllPOSInON
Obrclvcd Pressure, Mm.
Tmmpnolurc, ' C . Obxerctacd Corrcdrd lo 760 M m .
Di-itillationwith
750.5 750.5 750.8
132.0 134.8 136.6
*Interpolated from the referenee curve.
95.3 101.7 119.3 126.9 132.4 135.2 137.0
DIAGRAM
Refrecli~eInddz at 25' Dirlillolc Rcridu~ excess water
Distillation with excess amyl alcohol 1.3738 1.3867 1.3818 1.3875 1.3882 1.3896 1.3895 1.3902 1.3902 1.3905 1.3905 1.3907 1.3908 ....
Mol Frodion of Normal A m r l Alohol* Dislillolc
Residue
