Use of Tributyl Phosphate for Extracting Organic Acids from Aqueous Solution H. ARR'IIN PAGEL AND FRED W. MCLAFFERTY Avery Laboratory of Chemistry, University of Nebraska, Lincoln, Rebr. T H E authors have found that n-tributyl phosphate is a decidedly more effective agent for extracting certain organic acids from aqueous solution than ethyl ether ( I ) , isopropyl ether (S), benzene ($), toluene (d), or chloroform (a), which are commonly used. The eighteen organic acids thus far studied ehow a wide range of extraction.
This indicates that the ester is not hydrolyzed under the experimental conditions. DISCUSSION
The decrease of extraction with increased concentration (as shown for six acids) would be anticipated for the ternary systems. The distribution ratio is sufficiently constant, however, to indicate that the ester is not an associating solvent for such organic acids. Furthermore, triple extraction of 0.10 ' h succinic acid showed a total of 98.9% extraction compared to 98.2% calculated, assuming a constant ratio. Since n-tributyl phosphate is essentially insoluble in water (0.6% by volume) while water is about 7.5yO soluble in the ester a t 25" C., a calculated volume of water was added after each extraction to maintain constant aqueous volume. The relation between extraction and the structure of the organic acid is rather marked and consistent.
REAGENTS AND APPARATUS
The concentration of the various acids was determined to four significant figures by titrating 20-ml. pipetted portions with carbonate-free standard sodium hydroxide, using phenolphthalein indicator. Glass-stoppered separatory funnels (60 ml.) with the stems cut off 1 cm. below the stopcock were used for the extractions. Vaseline served as lubricant to prevent leakage. An International centrifuge (size 1, type SB) was used to produce complete phase separation. PROCEDURE
The extraction increases with the length of the carbon chain for both monobasic (except formic) and dibasic acids, as shown by the two series: acetic-propionic-butyric-valeric-oxalic and malonic-succinic. The monobasic acids are extracted more than dibasic acids containing the same number of carbon atoms. Here oxalic acid is the exception. Hydroxyl groups strongly depress extraction as shown by comparing acetic-glycolic, propionic-lactic, and succinic-malic-tartaric, and by noting the effect of five hydroxyl groups on gluconic acid. Chloro and phenyl groups strongly increase extraction, as shown by acetic-chloroacetic and glycolic-mandelic. The double bond has a depressing efEect, as shown by succinicmaleic.
Twenty milliliters of the organic acid were pipetted into the separatory funnel, followed by a 10-ml. pipetted volume, of tributyl phosphate. The mixture was shaken vigorously for 1 minute to effect extraction and then centrifuged for 3 minutes a t 500 r.p.m. The aqueous layer (lower) was then quantitatively transferred to a 100-ml. Erlenmeyer flask and titrated with 0.1 or 0.5 N standard sodium hydroxide to determine the residual . acid. Standardization of the organic acid and the extractions were done the same day to avoid possible error due to air oxidation, bacterial action, or volatilization. Blanks were deducted for the trace of free acid in the phosphoric ester. All work was done a t 25" * 2" C.
Sulfuric acid is 1.0% extracted a t concentrations of 0.10, 0.50, 1.0, and 2.0 iV, Hydrochloric acid, however, shows a marked increase with increased concentration-for example, with 0.10, 0.49, 1.0, and 1.9 S acid, the per cent extracted is 0.8, 0.8, 1.8, and 4.2, respectively. Sitric acid showed pronounced extraction, ranging from 14.47, with 0.10 N to 3l.6yGwith 2.0 K acid. A study of the separation of organic and inorganic acids by this extraction method is in progress.
Table I. Results of Single Extractions Using One l'olume . of Ester to Two Volumes of Aqueous Acid Concn.,
n.
Acid Formic -4cetic
Propionic n-Butyric n-Valeric Isovaleric Oxalic Malonic Succinic Malic Maleic Tartaric Chloroacetic Glycolic Lactic Citric Gluconic Mandelic (NaOH)
0.10 3.8 1.2 0.60 0.30 0.10 0.08 0.50 0.11 0.10 0.10 0.25 0.11 0.11 0.11 0.10 0.49 0.10 0.53 0.10 0.60 0.10
0.48
0.11 0.10 0.10 0.05 (0.10)
Extracted, 70 ('0.2) 59.2 41.2 48.1 51.6 53.7 53.9 80.7 91.9 93.1 97.8 97.5 62.5 68.1 74.0 38.7 64.1 21.2 22.4 86.4 87.5
20.4
21.6 40.0 40.7 50.0 4.0 93.8 (0.0)
Cester Cwater
2.90
1.40
1.85 2.13 2.31 2.34 8.36 22.7 27.0 88.9 78.0 3.33 4.40
LITERATURE CITED
(1) Dermer, 0. C., and Dermer, V. H., J . Am. Chem. Soc., 65, 1653 (1943). (2) International Critical Tables, 1'01. 111, p. 422, New York, McGraw-Hill Book Co., 1928.' (3) Werkman, C. H., ISD.ENG.CHEM., ANAL.ED.,2, 302 (1930).
5.69
1.26 3.57 0.54 0.58 12.i 14.0 0.51 0.55 1.33
RECEIVEDBpril 9, 1947
1.37
2.00 0.083 30.3
Standardization of Microchemical Apparatus A Committee for the standardization of Microchemical Apparatus has been appointed by the Division of Analytical and & h x o Chemistry of the AYERICABC m m i c A L SOCIETYunder the chairmanship of A1 Steyermark, Hofmann-LaRoche, Inc., Iiutley, K.J. The committee has begun its meetings, and is desirous of getting in contact with other committees throughout the world which deal with standardization of apparatus, methods, etc., with a view to possible cooperation.
VALIDlTY OF ANALYTICAL PROCEDURE
After the ester and water phases are separated, the acid in the ester phase can be quantitatively converted to salt by adding aqueous sodium hydroxide and shaking. In several different determinations the total acid found by titrating the two separated phases was in excellent agreement with the total acid taken.
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