I remembered an old experiment today. If you light a sugar cube, it does not burn, but if you put some cigarette ash on the sugar cube, it burns, because cigarette ash acts as a catalyst. So I made use of it for my hexamine/alkali metal nitrates problem. A mixture of 1/3 hexamine, 2/3 KNO₃ and some cigarette ash burns in fact much better than hexamine and KNO₃ alone and leaves a brownish-black diffluent lump. A strong odor of highly toxic HCN can be noticed during combustion. The residue is completely soluble in water, the solution highly basic. Treated with HCl, some small gas bubbles can be observed and a strong odor of HCN can be noticed again. It really seems that the combustion of hexamine and KNO₃ leads to KOH and some KCN. Potentially following reaction take place:
HCN + KOH → KCN + H₂O
Next step will be to test the brownish-black lump for cyanide. This can be done relatively easily with iron(II) sulfate and iron(III) chloride. The formation of Prussian blue is a positive result for cyanide.

*****Update 2010.12.28*****

Today I tested the brownish-black lump for cyanide. A piece of the lump was dissolved in distilled water and filtered off. A fresh 10% iron(II) sulfate solution was added in shortfall. The solution turned already green. Then some iron(III) chloride solution was added and the solution turned into deep blue.

Fe²⁺ + 6 CN → [Fe(CN)₆]^4-

Fe³⁺ + K₄[Fe(CN)₆] → K[Fe^IIFe^III(CN)₆] + 3 K⁺

Pictures below show the brownish-black combustion residue and the cyanide test:

At least I have found an unusual synthesis of potassium cyanide.

Author: M. Bindhammer, Team Selene