Laboratory Synthesis Of Barbital

BARBITAL SYNTHESIS

IUPAC NAME OF Barbital : 5 ,5- di ethyl- 2 ,4 ,6 (1 H ,3 H ,5 H)- pyrimidine trione

Use: hypnotic

Barbital MW: 184.20

Barbital MF: C8H12N2O3
Barbital LD50: 600 mg/kg (M, p.o.)

A white crystalline powder. A solution in water slowly decomposes. M.p. about 190°.

Soluble 1 in 5 of water (1 in 2.5 of boiling water) and 1 in 400 of ethanol; practically insoluble in chloroform and ether.

Dissociation Constant.

pK_a8.0 (25°).

Partition Coefficient.

Log P(octanol/water), 0.7.

Colour Tests.

Koppanyi–Zwikker Test—violet; Mercurous Nitrate—black.

Thin–layer Chromatography.

System TD—Rf 41; system TE—Rf 32; system TF—Rf 61; system TH—Rf 51; system TAD—Rf 57; system TAE—Rf 84. (Mercuric chloride–diphenylcarbazone reagent, positive; mercurous nitrate spray, black; Zwikker's reagent, pink.)

Gas Chromatography.

System GA—barbital RI 1489, barbital-Me₂ RI 1420, barbital-Me (metharbital) RI 1470, barbituric acid-Me₃ RI 1645; system GF—RI 2230; system GAJ—RRT 0.612 (relative to methylphenobarbital).

High Performance Liquid Chromatography.

System HG—k 1.11; system HH—k 0.63; system HX—RI 308; system HY—RI 258; system HZ—retention time 2.2 min; system HAA—retention time 10.4 min; system HAL—retention time 1.4 min.

Ultraviolet Spectrum.

Borax buffer 0.05 M (pH 9.2)—239 nm (A¹₁=549a); M sodium hydroxide (pH 13)—254 nm (A¹₁=427b).

Reference(s):
Clarke's Analysis of Drugs and Poisons
Fischer; Dilthey: Justus Liebigs Ann. Chem. (JLACBF) 335, 338 (1904).