Semicarbazide preparation from urea
first prepare urea nitrate: urea dissolved in twice the amount of hot water, add 48 ml conc. nitric acid and warming until the urea is dissolved. Cooling is excreted urea nitrate crystals. After draining and drying is obtained about 57 g (93%).
urea nitrate and finely pulverized with vigorous stirring and cooling (ice + salt) we bring 200 ml conc. sulfuric acid. Maintaining the temperature below 0 ° C. Finally, mix the mixture for about 30 minutes.
The flask pour in small portions to 400 g of ice-cooled externally ledema salts. Excluded nitrourea sucked through a glass frit or double filter paper on a Buchner funnel, washed with glacial water and squeezing rid of mother liquor.
2. Reduction of nitrourea
Nitrourea suspended in 320 ml conc. hydrochloric acid, well rozmělníme and is cooled (ice + salt). The suspension then pouring over very small portions with good stirring to the slurry 135 g of Zn-powder and 150 g of ice. Chladíme container (ice + salt) so that the temperature did not exceed 10 ° C. Adding takes a very long time. After adding nitrourea mix with 30 minutes to feed the liquid chloride sodnýma filtered through a Buchner funnel. To the filtrate add sodium acetate to dulling mineral acid (indicator of Congo) then another 30 grams. After about 30 minutes the precipitate with suction, the filtrate add 35 ml of acetone and left to stand overnight.
The solution of the precipitate with acetone semicarbazone zinc chloride. That sucked and get rid of zinc chloride, stirring several times with conc. ammonia solution and re-suction. Finally, we get pure acetone semicarbazone with a melting point of 187 ° C.
The spread heat the same amount of conc. hydrochloric acid. The solution is distilled acetone and part of the water in vacuo. Once they begin to secrete needles semicarbazide hydrochloride, is cooled residue in the flask and crystals aspirated. From the mother liquor obtained by diluting the product with 4 volumes of ethanol and precipitating with 1 volume of ether.