Cyclic malonyl urea structure of parent barbituric acid (common part)

substituent part

The mother core cyclic structure contains a 1,3-dimide group Its molecules can undergo keto-enol tautomerism and undergo secondary ionization in aqueous solution.

Slightly acidic Can react with strong bases to form water-soluble salts, usually sodium salts

Barbiturate sodium salt formed by weak acid and strong base, its aqueous solution is alkaline After acidification, crystalline free barbiturates are precipitated, which can be extracted with organic solvents.

Contains imide structure It is hydrolyzed by azeotrope with alkali solution, releasing ammonia gas, which can turn red litmus paper blue.

Used to identify amobarbital and barbital

The sodium salt of this type of drug can also undergo hydrolysis under hygroscopic conditions. In general, hydrolysis is slow at room temperature and below pH 10; above pH 11, hydrolysis speeds up as the alkalinity increases.

Contains malonyl urea (-CONHCONHCO-) ​​or imide group

The hydrogen in its malonyl urea group is relatively active and can undergo a condensation reaction with vanillin in the presence of concentrated sulfuric acid to produce a brown-red product.

BP2009Amobarbital

The UV absorption spectrum changes significantly with its ionization series.

In acidic solutions, 5,5-disubstituted and 1,5,5-trisubstituted barbiturates do not ionize and have no obvious UV absorption peaks.

In an alkaline solution of pH 10, first-order ionization occurs, forming a conjugated system structure with a maximum absorption peak at a wavelength of 240nm.

In a strong alkaline solution of pH 13, 5,5-disubstituted barbiturates undergo secondary ionization, causing the conjugated system to prolong, causing the absorption peak to red-shift to 255nm.

1,5,5-trisubstituted barbiturates do not undergo secondary ionization due to the presence of the 1-position substituent, and the maximum absorption wavelength is still at 240nm.

The UV absorption spectrum of thiobarbiturates is different

Commonly used thin layer chromatography

Alprazolam hydrochloric acid solution bismuth potassium iodide → orange-red precipitate

Alprazolam hydrochloric acid solution Silicotungstic acid solution → white precipitate

Diazepam – yellow-green

Chlorazepam - yellow

Diazepam – Yellow

Chlorazepam – Purple

Estazolam – blue