B. ~ r r e g u i n J. , Padilla, and J. Herran
lnstituto d e Quimica Universidod Nocionol Aut6noma d e MQxico
II
A Laboratory Experiment with Dyer to Illustrate Countercurrent Distribution
A n experimeutal example of the Craig countercurrent di~trihution'.~ can be shown, by using a set of six separatory funnels, n-butanol and 0.1 N aqueous sodium carbonate as solvents and phenol red and bromcresol green as a mixture of substances to be separated. When the appropriate amount of each dye (0.4 mg. of phenol red and 0.5 mg of bromcresol green) is passed successively through the separatory funnels containing 20 ml of each of the two solvents, previously equilibrated with each other by shaking, a good separation is obtained; and, a t the end of the experiment, the funnels represent different stages of a countercurrent distribution. This visual experiment shows that, while the red dye has migrat,ed preferentially to the lower phases of the last funnels, the bromcresol green stayed in the upper phases of the first ones. A more elaborate experiment using the same suhstances and solvent~s,in a quantitative way, and using 29 separatory funnels, can be followed by means of a spectrophotometer, by measuring the intensities at the wave length of each maximum, as shown in the table. When making the theoretical calculations, one has to consider that t,he lower phase is the one that migrates, and, instead of the partition coefficientK , the reciprocal, 1/K, must he used. The position of the maximum in the distribution curve for each dye can he calculated from the formula: CEAIG,L. C., AND POST,0. W., Ind. Eng. Chem., Anal. Ed., 16,413 (1944). WEISSBERGER, A,, Editor, "Techniques in Organic Chemistry," Interscience Publishers, Inc., New York, 1950, Vol. 3, p. 171.
N is the funnel a t which the maximum amount of dye is present. 1/K is the reciprocal of the partition coefficient,n is the total number of transfers, and r is the ratio of the two phases. The theoretical amount present in each funnel can be obtained from the formula: logy
=
+ - 2.303 sP(l/K + X 2n/K
(1/K 1) (2wn/K)"9
In which ?/ is the amount of substance in a given funnel, n the number of transfers and x the distance in units or stages from the funnel where the maximum amount N was calculated to he present, to the funnel in question. This equation reduces to: log y = log y, =
-0 -0
6855 5941
- 0 05802 r2 for bromcresol green and - 0.0884 zVor phenol red.
Plotting the experimental values given in Table 1 and the theoretical values results in Figure 1, which shows that very similar curves are obtained. A complete description of the experimental details will he supplied to interested readers on request. Countercurrent Distribution with 29 Funnels ~Butanol phase (20 ml)
-Brom-. Funnel 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Aqueous Na&03 phase (20 ml)
cresol green present (mg)
Phenol red present (mg)
Bromcresol green present ( 4
0.017 0.058 0.114 0.163 0.160 0.132 0.093 0.058 0 . 0'28 0 0'24
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o:o%
0.0'30 0.026 0.020 0.015 ... ...
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Phenol red present (mg)
...
...
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... ... ... ... ... ...
... ...
...
Both phases (mg) 0.017 0.058 0.136 0.193 0.186 0.152 0.108 0.058 0.028 0.0'24
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F U N N E L NUMBER
Figure 1. Countercurrent distribution% 0, theoretical points; X , expeemental points.
Volume 39, Number 10, October 1962 / 539
