Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

136 UEBA AND UEIC ACID FKOM UEINE
gradually in small portions until the liquid is neutral (addition of
excess of the carbonate is to be avoided). When this stage is reached
the liquid is boiled with a little animal charcoal (a few portions from
the point of a knife) filtered with suction while hot, and, after the
material on the funnel has been washed once with hot water, the
filtrate is evaporated to dryness. Urea, which is readily soluble in
hot alcohol, is completely extracted from the residue with this
solvent and is crystallised after concentration of the alcoholic solution.
Yield 20-25 g.
The amount of urea excreted daily by an adult is 25 to 30 g.
(in an average of 1-5 1. of urine).
Further Experiments.—A solution of urea is made alkaline with
sodium hydroxide solution and is then shaken with a few drops of
bromine. Nitrogen is evolved. Compare, in this connexion, the
Hofmann reaction (p. 155).
Nitrite solution is added to an acidified urea solution. Use of
urea for the removal of nitrous acid, e.g. in the preparation of ethyl
nitrate (p. 148).
Urea is but slowly hydrolysed. A solution is boiled with
barium hydroxide solution. How can hydrolysis be detected ?
Uric Acid.—The residue from which the urea was first extracted
with alcohol is freed from the solvent by heating on the water bath
and 50 c.c. of concentrated hydrochloric acid are added to it. When
the resulting mixture has been allowed to stand for a day or two,
0-3-0-5 g. of uric acid will be found to have separated and can be
purified by dissolving in 150 c.c. of hot iV-sodium carbonate solution,
adding 0 -4 g. of animal charcoal, filtering, and adding to the boiling
filtrate drop by drop from a funnel, with shaking, 150 c.c. of Nhydrochloric
acid. The uric acid separates as a beautiful crystalline
powder from the hot liquid.
Murexide Reaction.—A few centigrams of uric acid are evaporated
to dryness in a small porcelain basin on the water bath with some
drops of slightly diluted nitric acid. When ammonia is added to
the residue an intense purple colour is produced.
Uric acid is a normal product of metabolism. The chemistry of
the purines, the uric acid syntheses of Baeyer and Fischer, Behrend
and Roosen, and W. Traube, the chemistry of adenine, guanine, caffeine,
and their relationships to uric acid, should be studied.