Sciencemadness Discussion Board - semicarbazide

semicarbazide

neeraj - 22-1-2003 at 00:49

hey
i tried to produce semicarbazide by reacting chlorine urea caustic soda and ammonia but could not get it.
can someone suggest me the proper way of producing it.

KABOOOM(pyrojustforfun) - 1-2-2003 at 18:57

it had been discussed before. to me the best method is reduction of nitrourea. I think an alternative method could be heating hydrazinium carbamate
N₂H₅CO₂NH₂ => H₂NCONHNH₂

Magpie - 23-12-2010 at 21:44

I am taking a crack at making semicarbazide using Gattermann's method at 1/2 scale. This employs hydrazine sulfate, Na2CO3, and KOCN. When adding my dirty homemade KOCN I used a filter so that a nearly clear solution was added. The product was filtered then acetone was added to form acetonesemicarbazone, a white crystaline solid. This can be seen in the flask in the picture below with the salmon colored supernate. When the supernate was evaporated to dryness this color disappeared.

Tommorrow I'm planning to extract the solids from the Buchner filtration cake, and the evaporation solids of the supernate, in separate runs, using denatured alcohol. I could use a Soxhlet extractor. I don't know if there is a simpler way to do the extraction. Perhaps I could just use a separatory funnel?

Magpie - 25-12-2010 at 11:08

re: my Gattermann synthesis of semicarbazide, 12/23/10 post

The solids from the supernate evaporation didn't look all that great so I extracted them with denatured alcohol using a Soxhlet extractor. The extractate is evaporating now and some decent looking crystals of putative acetonesemicarbazone are starting to form. I'll put it on the steam bath to hurry it along.

The cake crystals of acetonesemicarbazone, on the other hand, looked so good that I felt extraction might be a waste of time. So I took a melting point: the result was sharp at 190C, same as my literature value. So I'm not going to extract this fraction.

[Edited on 26-12-2010 by Magpie]

Magpie - 27-12-2010 at 10:05

My yield of acetonesemicarbazone was 2.1g from the supernate and 16.2g from the filter cake. The mp of the product from the supernate would only come up to 185C (vs 190C) despite careful crystallization/washing, so it was discarded.

Below is a picture of the final product semicarbazide.HCl. The yield was only 3.7g, or 16.6% based on the hydrazine sulfate charged. Expected yield per Gattermann was ~12g. Contributors to the low yield are assumed to be:
1. Discard of the supernate fraction
2. Decomposition during heating of the final product solution
3. Excessive washing of the final product

I'm satisfied, however, as I only wanted a small amount of pure product for preparation of derivatives for confirmation of identity of aldehydes and ketones.

This synthesis also confirms the identity of my homemade KOCN.

If I ever repeat this experiment I will not again waste time on trying to extract product from the supernate.

Magpie - 1-1-2011 at 09:04

My synthesized semicarbazide.HCl was tested with some homemade benzaldehyde. The reaction was immediate even at lab winter temperature. After a careful recrystallization with alcohol a sharp mp of 222C was obtained, in agreement with the literature.

I'm also attempting to get a semicarbazone and mp using some butyraldehyde I made some years ago. This is proving more difficult and may be just a verification of what I've always suspected: my "butyraldehyde" isn't any good.

AndersHoveland - 29-3-2013 at 01:39

The german wikipedia article states that semicarbazide can be created by the reaction of "hydrazine or hydrazine hydrate with urea" and that " Hydrazine and urea react to form semicarbazide and ammonia."

"The reactions of urea with hydrazine and hydrazine hydrate for different molar ratios from 1:2.4 to 3:1 were investigated. For a ratio of 1:2 to 1:2.4 they result in carbohydrazide, for a ratio of 1:1 in semicarbazide, which reacts further with urea to biurea..."
"Untersuchungen ueber die Reaktion von Harnstoff mit Hydrazin", W. Engel, 1971, Institut Fuer Chemie Der Treibstoffe

I am not completely sure, getting urea to condense with hydrazine might require heating...

Quote: Originally posted by Axt

<b>Biurea from urea & hydrazine</b>
Six grams (0.1 mole) of urea was heated with 2.5g (0.05 mole) of hydrazine hydrate in a closed tube at 130° for 1 hr. The residue was recrystallized from hot water. The yield of biurea was about 20% based upon the amount of urea employed.

[Edited on 29-3-2013 by AndersHoveland]