Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

SEMICARBAZIDE HYDROCHLORIDE 161

123. Semicarbazide Hydrochloride.

From ammonia and cyanic acid urea can be obtained, with the interme-

diate formation of ammonium cyanate. From hydrazine, which is an amino

substituted ammonia, semicarbazide

C= 0

an analogous substituted urea is obtained. Semicarbazide, like free hydra-

zine, condenses with carbonyl groups (cf. Introduction to No. 121), and the

semicarbazones thus formed being difficultly soluble, serve for the detection

and isolation of carbonyl-containing compounds.

Dissolve 130 g. hydrazine sulphate and 54 g. anhydrous sodium

carbonate in 50 c.c. of water, warm the solution to 50°-60°, and

then add a solution of 86 g. potassium cyanate in 500 c.c. water.

The next day filter off the few grams of secondary product which

have separated, treat the filtrate with 120 g. of acetone and allow
the mixture to stand in a flask, with frequent shaking, for another

24 hours. Drain the precipitated salt, and evaporate the mother-

liquor to dryness on the water-bath, stirring towards the end.

Place the entire amount of the salt in an automatic extraction
apparatus, and extract it thoroughly with alcohol, in which the

acetone-semicarbazone is more soluble than in acetone; a few

cubic centimeters of acetone should be mixed with the alcohol.

The acetone-semicarbazone crystallizes in the distilling flask of
the extraction apparatus. After it is drained and washed with a

little alcohol and ether, it melts at 186°-187°. Crystallize the

remainder of the salt by evaporating the alcoholic mother-liquor

somewhat and adding a little ether. Yield, 80%.

The above product can be transformed quantitatively into

semicarbazide hydrochloride, as follows: Warm the acetone-

semicarbazone gently with concentrated hydrochloric acid in the
proportion of 11.5 g. of the former to 10 g. of the latter until the

solid is just dissolved. On cooling, the solution solidifies to a

thick paste of colorless, well-formed needles. Drain the product

with suction and wash it with a little alcohol and ether; it melts at
173° with decomposition. To the mother-liquor, add double its

volume of alcohol, and bring the rest of the salt to crystallization

by adding ether.