Sciencemadness Discussion Board

Knoevenvagel Condensation Applications

Azane - 23-8-2014 at 21:33

So for those of you who know about and/or have experience with the Knoevenvagel condensation, I have a question: could it be carried out in aqueous solution to synthesize potassium tricyanomethanide from potassium cyanate and malononitrile...

KNCO + H2C(CN)2 --> KC(CN)3 + H2O

...or would the reaction just result in the formation of carbon dioxide, ammonia, and potassium dicyanomethanide?

KNCO + H2C(CN)2 + H2O --> KHC(CN)2 + H3N + CO2

Would changing the solvent to something like acetonitrile make the first reaction more favorable? Could the reaction even be performed without a solvent (i.e. just mixing the reactants in the solid state, and heating them)?

Dan Vizine - 1-9-2014 at 17:08

The cyanidation of malononitrile (MN) was first described by Schmidtmann in Ber. Dtsch. Chem. Ges. 1896, 29, 1168. In Chem. Ber. 1929, 62B, 153, Birckenbach et al. have disclosed the cyanidation of MN by means of cyanogen bromide.

These rely on strong bases and anhydrous conditions, unlike your route.

I don't think you have much chance of effectively deprotonating the MN with weak bases in aqueous media.



[Edited on 2-9-2014 by Dan Vizine]

Azane - 10-10-2014 at 12:35

Quote: Originally posted by Dan Vizine  
The cyanidation of malononitrile (MN) was first described by Schmidtmann in Ber. Dtsch. Chem. Ges. 1896, 29, 1168. In Chem. Ber. 1929, 62B, 153, Birckenbach et al. have disclosed the cyanidation of MN by means of cyanogen bromide.

These rely on strong bases and anhydrous conditions, unlike your route.


Yeah, I've read the description of using cyanogen halides, and so I thought of using potassium isocyanate instead, considering its properties in comparison to cyanogen halides.

KNCO:
-stable
-solid at STP
-easily prepared by heating K2CO3 and urea, both of which are stable solids at STP, as well as cheap and readily available

NCCl:
-prone to polymerization
-gaseous at above -6.55ºC, thus requires refrigeration or pressurization to handle
-preparation requires the use of HCN/cyanides and chlorine, the latter of which also requires either refrigeration or pressurization to handle (while Br2 and I2 don't necessarily require either refrigeration or pressurization, with I2 being the safest among them, their cyanogen halides are even less stable than that of chlorine, and I'd also like to avoid working with Br2)

Not to say that KNCO's described benefits make it a viable reactant for this process, just that it'd be a bit more practical.
However, I'm still wondering if the reaction could be performed in an aprotic solvent, and also if it could be carried out by heating the reactants in the solid state.

[Edited on 10-10-2014 by Azane]

Azane - 10-10-2014 at 14:31

Alright, I've thought of an alternative using KCN and HCI3.

4KCN + HCI3 --> 3KI + KC4N3 + HCN

I'm basing my assumption that the cyanide ions will displace HCI3's iodine atoms (via SN2 reactions) off of the fact that cyanide is a stronger base than iodide, and will thus have a higher affinity for the central carbon atom than the iodide ions released.

Again, I'm wondering if this could take place in an aprotic solvent.

Metacelsus - 10-10-2014 at 18:03

What about sterics?

AvBaeyer - 10-10-2014 at 18:05

Azane,
I think you need to get a better grasp of organic reaction fundamentals. You seem to be throwing stuff at the wall to see what sticks. I do not want to be snarky, but you really need to do some library research.

AvB

Azane - 12-10-2014 at 09:35

Yes, I am throwing stuff at the wall to see what sticks, mainly because you guys are being unyielding in whatever precious knowledge you seem to have that would refute what I'm asking you about.