Sciencemadness Discussion Board

Carbon Disulfide from NH4SCN?

Takron - 29-10-2011 at 18:52

I've been racking my brain trying to find an easy way to create Carbon Disulfide that does not: ruin glassware, require huge temps, or some other extreme measure.

So I did some research and I found that NH4SCN is made industrially by reacting NH3 with CS2 here. Then the resulting compound of Ammonium dithiocarbamate is heated and NH4SCN is formed while giving off H2S.

So I did some more poking around and thought that heating to decompose the ammonium thiocyanate would result possibly in Carbon Disulfide since that was one of the original reactants. This is when I found the wiki entry on NH4SCN and it said that it could be possible to decompose into CS2 but I don't always trust the wiki. My first gut instinct was that it was too easy to be true or I would see that method in more use. I tried looking up this method on the forum but I didn't see it even though there were quite a few mentions of CS2 production. My question is, is it true from the wiki that "When heated at 200 °C, the dry powder decomposes to ammonia, hydrogen sulfide, and carbon disulfide, leaving a residue of guanidine thiocyanate."

Doing this I thought if that was true, with good ventilation and a good distillation setup it would be very easy to get CS2 from the ammonium thiocyante. I figure it would take 4 Moles to get 1 Mole of CS2 because of all the sulfur by-products that are formed.

I've tried to do my research on this one but I'm sure its not perfect, so if anyone has any input or constructive opinions, or I have missed a blatant elephant in the room, please let me know.

[Edited on 30-10-2011 by Takron]

[Edited on 30-10-2011 by Takron]

BromicAcid - 30-10-2011 at 08:35

It's certainly not going to be a neat decomposition, plus you'll be generating both ammonia and the CS2 at high temps so how are you going to avoid reacting them back with each other?

The best preparative decompositions are unimolecular but you cannot get CS2 from an intramolecular reaction in this case. That's why if you want CS2 via decomposition then you want to start from thiuram monosulfides and thiuram disulfides which usually decompose cleanly and with high yields to give CS2. They can be found OTC in some anti fungal preparations

Retard-3000 - 30-10-2011 at 08:57

You may need something that'll react with the ammonia but won't react with the carbon disulfide which also doesn't decompose at the temperature at which the carbon disulphide is being formed. At the moment it's not panning out well in my head.

Takron - 30-10-2011 at 18:50

Quote: Originally posted by BromicAcid  
...you'll be generating both ammonia and the CS2 at high temps so how are you going to avoid reacting them back with each other?


What about reacting them under a constant flow of HCl gas? The HCl would react with the formed ammonia and form NH4Cl and that decomposes at 338* much higher than the 200 we'll be working with. The ammonia will be pulled out and the H2S can be ventilated away?

Nicodem - 3-11-2011 at 10:29

Quote: Originally posted by Takron  
What about reacting them under a constant flow of HCl gas? The HCl would react with the formed ammonia and form NH4Cl and that decomposes at 338* much higher than the 200 we'll be working with. The ammonia will be pulled out and the H2S can be ventilated away?

And what would prevent the HCl from reacting with ammonium thiocyanate?

AndersHoveland - 3-11-2011 at 23:20

Yes, NH4SCN will decompose to CS2 when it is heated. But trying to isolate the CS2 would be like trying to isolate the SO3 from the fumes given off from boiling concentrated sulfuric acid.

(6)NH4SCN <==> (6)NH3 + (3)CS2 + (3)NH2CN

There will be an equilibrium when the ammonium thiocyanate is decomposed, but it the products are likely to condense back to ammonium thiocyanate when it cools.

Or decomposition and re-condensation might result in melamine and hydrogen sulfide:

(3)NH4SCN --> C3N3(NH2)3 + (3)H2S


Ammonia reacts with carbon disulfide:

(2)NH3 + CS2 --> NH4SCN + H2S

[Edited on 4-11-2011 by AndersHoveland]

woelen - 4-11-2011 at 02:24

Maybe you could try leading the still hot gaseous mix through dilute ice cold hydrochloric acid. NH3 will dissolve in this and H2S also to some extent. CS2 then will condense and settle at the bottom as a dense liquid.

I'm not sure whether this works, I did not try myself, but if the recombination of the gaseous products is not instantaneous, then I can imagine that this may work. Still, expect the procedure to be messy.

497 - 4-11-2011 at 03:04

These guys talk about using an autoclave at 110*C to react ammonia and CS2
http://docs.google.com/viewer?url=http%3A%2F%2Frepository.ku...
So that seems to indicate the possibility of trapping the hot decomposition products. You could insulate the bubbler tube to hopefully prevent clogging.