Lillian N. Ellis ond Marjorie Fox1
Douglass College, Rutgers University New Brunswick, New Jersey
A Simple Extraction Experiment
Experience with the experiments available in the organic laboratory manuals has emphasized the need for a simple, visual experiment demonstrating the principles of extraction. The experiment to be described here was found to be satisfactory either for a laboratory exercise, using student equipment, or for a lecture demon~tration.~The amount of solute remaining after single and multiple extractions was evaluated calorimetrically, on a semiquantitative scale, by comparison with standards. The following procedures were found to give satisfactory results. A saturated solution of salicylic acid was prepared by dissolving 0.3 g of the acid in 150 ml hot, distilled water. Afresh solution of the color developer was prepared by dissolving one g of iron(II1) chloride (I"eC13.6H20,Baker, anal.) in 10 ml of water. For the first, test (T,), 15 ml of the salicylic acid solution was extracted wit.h an equal volume of the organic extractant, pure n-butyl acetate. The water layer was separated and reserved for subsequent testing. The same technique was used for a second test (T2)with the exception that 30 ml of the extractant was used. I n the third test (T3), two consecutive 15-ml portions of the extractant were used. A series of six standard solutions of salicylic acid were prepared in order t o estimate the amount of acid remaining in the water layer after extraction. The first standard (SJ was distilled water. The remaining five standards were prepared by diluting the original acid solution with distilled water in the following amounts: (&) one ml of the acid solution to 300 ml final volume; (S3) one ml to 200 ml; (SI) one ml to 100 ml; (8s) 2 ml to 100 ml; and (Ss) 3 ml to 100 ml. Stronger standards were not required when proper extraction technique was used. For the final evaluation, 10 ml of each of the extracted water solutions was placed in an appropriatelylabeled test tube. Ten ml of each of the six standard solutions was treated in a similar manner. To each tube wereadded2 drops of the freshly-prepared iron(II1) chloride solution. The tubes were shaken and the 'Present address: Junior College of Kansas City, Kansas City, Missouri. BLANK, E. W., J. CHEM. EDUC.,12, 179 (1935).
510
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Journal of Chemical Education
pink-purple color which developed in the test solut,ions was matched as closely as possible to the appropriate color in the standard solutions. I n repeated tests the following results xx.ere obtained: TIclosely matched the color of Ss; Tz that of S4; and T3fell between t,hat of Sl and S2. These result,s demonstrated, as would be expected from theory, the difference between multiple versus single extraction, i.e., that in T3the least amount of acid remained. In order to test t,he reproducibility of the experiment, the optical densky of the purple-colored solution of both the test and standard samples was determined a t 530 mfi in four separate experiments. From the closeness of the data it was evident that the experiment was reproducible and t,hat the visual comparison of the t,est with the standard solution was valid. The close matching of TI to Ss and of T? to & provided the basis for calculating the per cent of salicylic acid extracted. In addition, the coefficient of distribution, K, could be calculated and was found to be about 50. When this K was used for T3,t,he multiple extraction test, the mg of salicylic acid remaining was estimated to be less than S2. The solute and extractant were selected for stabilky in storage, safety in handling, and stability of the colored phenol-iron(II1) complex formed. The purple color lasted several hours because of the chelate formed4 and the favorable The color developed when resorcinol was tried as the solute was less stable due to inner salt formation.' A number of extractants ITere possible but, except for the pure n-butyl acetate, required prior washing until free from impurities decolorizing potassium permanganate. Technical n-butyl acetate, pure n-propyl acetate, and sec-amyl alcohol could be used under these conditions. The following extractants were found to he unsuitable: ethyl acetate because of the low solub'lity of the solute; diethyl and diisopropyl ethers because of permanganate active substances remaining after repeated washings; and lertamyl alcohol and cyclohexanol because of the formation of stable emulsions. a PANKRATZ, R. E., A N D BANDELIN, F. J., J . ilmer. Pha~m. Assoe., 41, 267-70 (195'2). SOLOU~AY, S., .4m \TILEN, S. H., Anal. Chem, 24, 9i9-83
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(1952)
