Mephobarbital

(mef'' oh bar' bi tal).

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

—

USP Mephobarbital RS

Identification—

A: Infrared Absorption

197M

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.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Hariram Ramanathan, M.S. Associate Scientific Liaison 1-301-816-8313	(SM42010) Monographs - Small Molecules 4
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org

USP35–NF30 Page 3804

Pharmacopeial Forum: Volume No. 30(5) Page 1634