Dibutyl Phthalate
(dye bue' til thal' ate).
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C16H22O4 278.34

1,2-Benzenedicarboxylic acid, dibutyl ester [84-74-2].
» Dibutyl Phthalate contains not less than 99.0 percent and not more than 101.0 percent of C16H22O4.
Packaging and storage— Preserve in tight containers. No storage requirements specified.
USP Reference standards 11
USP Dibutyl Phthalate RS Click to View Structure
Appearance— The substance is clear and not more intensely colored than a solution prepared immediately before use by mixing 2.4 mL of ferric chloride CS and 0.6 mL of cobaltous chloride CS with dilute hydrochloric acid (10 g per L) to make 10 mL, and diluting 5 mL of this solution with dilute hydrochloric acid (10 g per L) to make 100 mL. Make the comparison by viewing the substance and the solution downward in matched color-comparison tubes against a white surface (see Color and Achromicity 631).
Identification—
A: Infrared Absorption 197F, on undried specimen.
B: It meets the requirements of the test for Refractive index.
Specific gravity 841: between 1.043 and 1.048, at 20.
Refractive index 831: between 1.490 and 1.495, at 20.
Acidity— Mix 20.0 g of Dibutyl Phthalate with 50 mL of alcohol that previously has been neutralized to a phenolphthalein endpoint, add 0.2 mL of phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS: not more than 0.50 mL is required to change the color of the indicator.
Water, Method I 921: not more than 0.2%.
Residue on ignition 281: not more than 0.1%, determined on 1.0 g.
Related compounds—
Internal standard solution— Transfer 30 mg of dibenzyl to a 10-mL volumetric flask, and dissolve in and dilute with methylene chloride to volume.
Test stock solution— Transfer about 5.0 g of Dibutyl Phthalate to a 50-mL volumetric flask, and dissolve in and dilute with methylene chloride to volume.
Test solution 1— Transfer 5.0 mL of Test stock solution to a 10-mL volumetric flask, and dilute with methylene chloride to volume.
Test solution 2— Transfer 5.0 mL of Test stock solution to a 10-mL volumetric flask, add 1.0 mL of Internal standard solution, and dilute with methylene chloride to volume.
Standard solution— Transfer 1.0 mL of Test solution 1 to a 100-mL volumetric flask, add 10.0 mL of the Internal standard solution, and dilute with methylene chloride to volume.
Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and contains a 4-mm × 1.5-m column packed with 3% liquid phase G3 on support S1A. The carrier gas is nitrogen, flowing at a rate of about 30 mL per minute. The column temperature is maintained at 190, and the injection port temperature and the detector temperature are maintained at 225. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the elution order is the internal standard peak followed by the dibutyl phthalate peak; and the resolution, R, between these peaks is not less than 12. Chromatograph Test solution 1, and verify that there is no peak with the same retention time as the internal standard. If a peak observed in the chromatogram for Test solution 1 has the same retention time as that for the internal standard, make any necessary correction for factors of dilution, and then determine the area due to the interfering component that must be subtracted from the area of the internal standard peak appearing in the chromatogram recorded for Test solution 2, as directed for Procedure.
Procedure— Inject 1-µL portions of Test solution 2 and the Standard solution successively into the gas chromatograph, record the chromatograms for three times the retention time of dibutyl phthalate, and measure the responses of the peaks. From the chromatogram of the Standard solution, calculate the peak area ratio of dibutyl phthalate to the internal standard, A. From the chromatogram of Test solution 2, calculate the peak area ratio of the sum of all peaks, excluding the main peak, the solvent peak, and the internal standard peak, to the internal standard peak: this ratio is not greater than A (1.0%).
Assay— Transfer about 0.75 g of Dibutyl Phthalate, accurately weighed, to a flask, add 25.0 mL of 0.5 N alcoholic potassium hydroxide VS, attach a reflux condenser to the flask, and boil in a water bath for 1 hour. Add 1 mL of phenolphthalein TS, and titrate immediately with 0.5 N hydrochloric acid VS. Perform a blank determination (see Residual Titrations under Titrimetry 541). Each mL of 0.5 N potassium hydroxide is equivalent to 69.59 mg of C16H22O4.
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