(mef'' oh bar' bi tal).
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C13H14N2O3 246.26

2,4,6(1H,3H,5H)-Pyrimidinetrione, 5-ethyl-1-methyl-5-phenyl-.
5-Ethyl-1-methyl-5-phenylbarbituric acid [115-38-8].
» Mephobarbital contains not less than 98.0 percent and not more than 100.5 percent of C13H14N2O3, calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers.
USP Reference standards 11
USP Mephobarbital RS Click to View Structure
B: Boil about 200 mg with 10 mL of 1 N sodium hydroxide: ammonia is evolved.
C: Shake about 60 mg with 5 mL of sodium hydroxide solution (1 in 500), and filter. To a 1-mL portion of the filtrate add 3 drops of mercuric nitrate TS: a white precipitate is formed, and it is soluble in 6 N ammonium hydroxide. To another 1-mL portion of the filtrate add silver nitrate TS, dropwise: a white precipitate is formed, and it dissolves readily in 6 N ammonium hydroxide.
Melting range, Class I 741: between 176 and 181.
Loss on drying 731 Dry it at 105 for 4 hours: it loses not more than 1.0% of its weight.
Residue on ignition 281: not more than 0.1%.
Assay— Dissolve about 500 mg of Mephobarbital, accurately weighed, in 50 mL of dimethylformamide in a 200-mL flask. Add 4 drops of thymolphthalein TS, and titrate with 0.1 N lithium methoxide in toluene VS, using a magnetic stirrer and a cover for the flask to protect against atmospheric carbon dioxide. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N lithium methoxide is equivalent to 24.63 mg of C13H14N2O3.
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