NOVEMBER 15, 1935
ANALYTICAL EDITION
399
CRYSTALLOGRAPHIC DATAFOR DERIVATIVES OF BARBITAL AND PHENOBARBITAL TABLE11. OPTICAL Derivative
Optical Characteristic (Sign)
o-Bromobenzvl m-Bromobeniyl p-Bromobenzyl o-Chlorobenzyl m-Chlorobenzyl p-Chlorobenayl p-Iodobenayl~ m-Nitrobenayl
-Refractive Alpha Barbital 1.556 1.577 1.556 1.548 1.538 1.545 1.531 1.487
~i~~treoyqenl;YI
*-
p-Bromophenacyl
-
++ +
o-Bromobenzyl
+
f
1.599 Phenobarbital 1.605
+--
1.599 1.563 1 h8n is0 1.
rn-Bromobenzyl p-Brom p-Bromobenzyl rn-Chlornhanxvl rn-Chlorobenayl p-ChloI p-Chlorobenayl A B p-Iodobenz yl P
-a a
+-
-
(All monoclinic) Sign of Elongation
*I
1.510 1.587
1.585 1.580
Indices at 25' Beta Gamma
1.640 1.679 1.577 1.649 1.640 1.563 1.642 1.626
1.663 1.693 1.698 1.696 1.690 1.664 >CHzIz 1.715
1.606 1.626
1.706 1.634
1.642
1.649
1.620
1.720
l.!68
1.6D8 >CHh 1.681 = CH& 1.730 >CH&
a
1.660 1.568 1.568 1.593 1.730
+ +
1.538
1.652
1.715
p-Nitrobenz yl
1.534
1.666
= CH21r
p-Bromophenacyl
-
1.599
1.656
1.703
m-Nitrobenzyl
Rhombic Dispersions None None None None None None None Strong V > P
Strong Moderate
Extinction Angle, Degrees 16 30 4 20 23 33 34 7
14 42
P > V
None
32
Moderate
36
V > P
None Nye
None Moderate
7
9 5 8 15 34
V > P
Moderate
25
U > P
Strong
17
V > P
Strong
36
V > P
Since no optio axis interference figure could be seen, these values could not be determined.
Eleven derivatives of barbital and nine derivatives of phenobarbital were prepared, purified, and analyzed. The results are presented in Table I. OPTICAL CRYSTALLOGRAPHIC DATA. The optical properties of each compound listed in Table I were determined by methods used in a similar study for compounds of strychnine (4) and cinchonine ( 5 ) ,and are presented in Table 11. The optical properties of the derivatives of barbital differ sufficiently from those of phenobarbital to allow the use of the optical data in the identification of the original barbituric acid.
Summary Ten new derivatives of barbital and eight new derivatives of phenobarbital have been prepared and described. The optical crystallographic data for twenty benzyl and phenacyl
compounds of barbital and phenobarbital have been determined.
Acknowledgment The authors wish to thank the Winthrop Chemical Company, Inc., New York, N. Y., for kindly furnishing the barbital and phenobarbital.
Literature Cited (1) Hargreaves and Nixon, J . Am. Phamn. Assoc., 22,1250 (1933). (2) Jesperson and Larsen, Dunsk. Ti&. Furm., 8,212 (1934). (3) Lyons and Dox, J . Am. Chem. SOC.,51,288 (1929). (4) Poe and Sellers.Ibid., 54,249 (1932). (5) Poe and Swisher, Ibid., 57,748 (1935).
RECEIVED July 8, 1935.
Surface Tension between Aqueous and Isopropyl Ether Solutions of Acetic Acid F. M. BROWNING AND J. C. ELGIN Department of Chemical Engineering, Princeton University, Princeton, N. J.
THE
factors determining the rate of extraction of acetic acid from aqueous solution by isopropyl ether and the efficiencies of types of equipment applicable to the extraction operation are under investigation in this laboratory. These form one phase of an investigative program directed toward the development of methods and data for the rational design of liquid-liquid extraction systems. Results thus far obtained show that the rate of extraction and, consequently, the efficiency of liquid-liquid contact equipment in which one solvent phase i s dispersed may be primarily influenced by the interfacial surface tension between the two solvents. It is apparent that this result is logically explained by the fact that for a given volume of liquid the degree of dispersion and droplet size (hence contact area) are determined primarily by interfacial surface tension. Since the concentration of the soluble
component distributing itself between two immiscible solvents in contact may exert a very considerable influence on their interfacial surface tension, the extent or efficiency of extraction in a given equipment is a function of the respective solute concentrations in the two phases, operating conditions and concentration gradient being otherwise fixed. Thus, in the extraction of acetic acid from water solution by isopropyl ether, the capacity coefficients in a tower of the spray type and the plate efficiencies of a bubble plate column are dependent upon the respective acid concentration of the two phases. A similar result for other types of contacting devices is also to be expected. To permit a correlation of the results on this system the surface tension of different concentrations of aqueous acetic acid against isopropyl ether of varying acetic acid concentra-
INDUSTRIAL AND ENGINEERING CHEMISTRY
400
VOL. 7, NO. 6
mostat a t 20" C. before making measurements. The solutions were removed from the thermostat into a room a t approximately 20" C. immediately prior to each determination. With solutions of different concentrations the drop weight method is superior to the ring method. The latter requires a large surface and consequently allows variation in the respective solution concentrations during measurement due to diffusion across the interface. Use of the drop weight method greatly reduces this effect. Reproducible results were readily obtained by permitting fresh drops to form continuously in a large volume of solution.
Results
06
la
/4-
PO
l)b
JD
SJ
CO/CENTRAFUNL/N WATER
FIGURE 1. SURFACE TENSION BETWEEN WATERAND IsoPROPYL ETHERPHASES CONTAINING ACETIC ACID Concentrations in gram molecules per liter.
tion has been measured. Inasmuch as this system is the basis of an industrial process for the recovery of acetic acid and no previous data on its surface tension appear to be available, it was thought that the present measurements would be of industrial as well as scientific interest.
Experimental Method The "drop weight'' method of determining surface tension was employed. The procedure followed was based on suggestions advanced by Harkins and Brown (8). This method combines simplicity (1) with a degree of accuracy commensurate with that to be expected from any usual applications of the results. The apparatus consisted of a 5-cc. buret attached through a * suitable sto cock to a IO-cm. length of 7-mm. capillary tubing. The tip of tEis was carefully ground, and its diameter accurately determined ta be 0.377 mm. The denser phase was placed in the buret and permitted t o drop through the less dense at the rate of approximately one drop every 3 minutes. From accurate measurements of the volume of the drops, the densities, and the size of the tip surface tensions were calculated from the usual relation as given in the International Critical Tables. The accuracy yielded by the apparatus as constructed was checked by comparing values of the surface tensions of water, benzene, and benzene-water obtained with it with the corresponding values reported in the literature. That substantial agreement was obtained may be seen from Table I. TABLEI. SURFACE TENSIONCOMPARISON (Temperature 20' C.) System Water-air Ben~ene-air Benzene-water
Drop Volume cc. 0.1070 0,0485 0.4500
Density G./cc. 0.9972 p%ft.9968 CsHa-O. 8738
Surface Tension Accepted Obeerved value ( 5 ) DUnes/cm. Dynes/cm. 73.46 72.75 28.49 28.80 34.50
35.00
I n making the measurements presented herein aqueous acetic acid of different concentrations was placed in the buret and drops were permitted to form in isopropyl ether solutions of various concentrations. Purified isopropyl ether from the Eastman Kodak Company, distilled water, and U. 8. P. acetic acid were employed. Each phase was mutually saturated with the other by agitation for a prolonged period in a ther-
The surface tension results obtained are recorded in Table 11. Corresponding densities of the aqueous and isopropyl ether solutions of acetic acid employed, each solvent mutually saturated by the other, were also determined since their knowledge was necessary for the calculation of surface tension values. (As reported by the Carbide and Carbon Chemicals Corporation commercial isopropyl ether a t 25" C. is soluble in water to the extent 0.65 per cent by volume, water being soluble in the ether to the extent of 0.025 per cent by volume. Pure isopropyl ether is undoubtedly considerably less soluble.) Inasmuch as no previous data on these have been reported the authors' values are also included in the table. TABLE11. VALUESOF SURFACE TENSIONBETWEEN AQUEOUS ISOPROPYL ETHERSOLUTIONS OF ACETIC ACID AT 20" C .
AND
Ether Water ConoenConoentration tration Ci. moles/l. G . moles/l. 0.0044 0.0001 0.0583 0.0001 0.1718 0.0001 0.5239 0.0001 0.0060 0.2519 0.0581 0.2519 0.1710 0.2519 0.5134 0.2519 0.0092 0.6234 0.0584 0.6234 0,1709 0.6234 0.5009 0,6234 1.5368 0.0140 0.0623 1.5368 0,1716 1.5368 0.4976 1.5368 0.0212 3.2513 0,0679 3.2513 0.1724 3.2513 0.4982 3.2513
Density Ether Water G./cc. U./cc. 0.7246 0.9951 0.7262 0.9951 0.7296 0.9951 0.7399 0.9951 0.7247 0,9977 0.9977 0.7262 0.7295 0.9977 0.7396 0.9977 0.7247 1.0008 0.7262 1.0008 0,7295 1.0008 0.7392 1.0008 0.7249 1.0074 0.7263 1.0074 0.7296 1.0074 0,7392 1.0074 0.7250 1,0199 0.7265 1.0199 0.7296 1,0199 0.7391 1.0199
Drop Volume Cc. 0.0940 0.0914 0.0843 0.0624 0.0900 0.0882 0.0825 0.0604 0.0836 0.0825 0.0776 0.0594 0.0761 0,0751 0.0712 0.0573 0.0676 0.0664 0.0637 0.0539
Surface Tension Dgnes/cm. 17.56 17.08 15.66 10.90 16.97 16.54 15.28 10.65 15.95 15.65 14.55 10.60
14.84 14.57 13.73 10.46 13.69 13.39 12.69 10.26
By plotting the surface tension exerted between solutions of various concentrations with acid concentration in the ether as ordinates and in water as abscissas as in Figure 1, lines of constant surface tension are obtained. From this graph the surface tension exerted between the two phases for varying acid concentrations may be readily obtained by interpolation. It is evident that the surface tension between these two immiscible solvents is markedly dependent upon their respective acetic acid concentrations. Consequently, the dispersion of either phase in the other will vary greatly with their respective acid concentrations. These data are of value for predicting qualitatively where other variables are fixed, the area of contact and, consequently, the influence of acid concentration on the extraction efficiency to be expected for the various stages of extraction equipment operating this process.
Literature Cited (1) Dorsey, Bur. Standards Sci. Paper 540, 563-95 (1926). (2) Harkins and Brown, J. Am. Chem. Soc., 41, 499 (1919).
(3) International Critical Tables, Vol. IV, p. 435 (1928). RECEIVEDMarch 21, 1936.
