Joe A. Vinson' and Edward K. Hocker Shippensburg State College Shippensburg, Pennsylvania
Saponification of Aspirin in Dimethyl Sulfoxide
M a n y direct methods have been published for the determination of the acid content of aspirin (1-7) using a variety of methods. The saponification of esters in dimethyl sulfoxide (DMSO) is a very rapid reaction (8). This indirect method is used in the following experiment to determine aspirin. The stoichiometry is the following
excess base is titrated with standard 0.1 N HC1 with cresol red as the indicator. The color change is sharp from purple to yellow. A blank is then run under the same conditions. Work with recrystallized Merck U.S.P. acetyl salicylic acid gave 99.97y0 recovery for five titrations with a standard deviation of 0.23%. The table shows the results with five different brands of aspirin. Literature Cited
Five tablets of commercial aspirin are ground into a fine powder with a mortar, accurately weighed, dissolved in DMS02, and made up to volume in a 100-ml volumetric flask. The starch binder dissolves completely in this medium. A 10-ml aliquot is taken and added to a 125-ml erlenmeyer flask. To the erlenmeyer is added approximately 20 ml of DMSO and 5 ml aliquot of 0.5 N NaOH or KOH. The stoppered flask is stirred briefly and let stand for 5 min at room temperature. To the erlenmeyer is added 70 ml of distilled water. The 'Present address: Department of Chemistry, Washington and Jefferson College, Washington, Pa. 15301. sWe gratefully seknowledge the gift of a sample of DMSO from the Crown Zellerbach Corp.
(1) JENKINS, G. L., CHRISTIAN, J . E., A N D HAGER,G. P., "Quantitative Pharmaceutical Chemistry," (4th ed.), MeGrrtwHill Book Co., New York, 1953, p. 139. (2) PROCTOR, J. S., AND ROBERTS,J. E., J. CHEM.EDUC.,38, 471 11961). , , (3) Moss, M. L., ELLIOTT,J. H., AND HALL,R. T., Anal. Chem., 20, 784 (1948). (4) FRITZ,J . S., AND LIBICKI,N. M., Anal. Chem., 23,589 (1951). P. C., AND RIDDICK,J . A,, Anal. Chem., 23, (5) MARKUNAS, 337 (1951). (6) WOLLISH,E. G., el al., Anal. Chem., 26, 1753 (1954). A. J., J. CHEM.EDUC.,42, 540 (7) SHEN,S. Y., A N D GILMAN, (1965). . , (8) VINBON, J. A., FRITZ,J . S., AND KINGSBURY, C. A,, Talanla, 13, 1673 (1966).
Determination of Acetyl Salicylic Acid in Aspirin Brand of Acetyl Salicylic Standard Deviation (%) Acid found (%) Aspirin A 78.65 0.48 B 90.72 0.41 C 43.55 0.33 D 88.88 0.42 E 87.55 0.12
Volume 46, Number 4, April 1969
/
245
