Bubbling Chlorine gas through K Ferricyanide = HCN?

[Athiril]

Hi,

 

 

So bubbling chlorine through potassium ferrocyanide is a production method for potassium ferricyanide.

 

I use potassium ferricyanide as a bleach for films with a halide salt.

 

As it gets used, potassium ferrocyanide is formed.

 

So I can regenerate this by bubbling chlorine gas through the solution.

 

If I use Sodium Chloride (normally it's Bromide, but Chloride works fine for bleaching purposes too) I'll have less trouble, and the chlorine will also re-halogenate the solution, although perhaps I should use potassium chloride.

 

 

In any case, my question is; Once all ferrocyanide has been converted to ferricyanide is there a further reaction?

 

Potassium Ferricyanide produces nasty stuff with strong mineral acids (like HCl), so I would assume after some point HCN gas is produced, is this correct? If so, how do you know when to stop the reaction to avoid this? I want to completely avoid HCN production (Since it's a production method of ferricyanide... where is the stopping point? etc).

 

Or does the fact that chlorine gas only make dilute HCl in this case not affect it? Also if i buffer the solution very well, I can completely avoid it right? (working solution should be pH ~6.5 for best colour balance on film)

 

My solution would be a mix of potassium ferricyanide, potassium ferrocyanide, and a chloride salt.

 

 

I'd like to do this, as a) It'd be quite simple to do, I've used chlorine gas for several other experiments and am setup to do this. b) It's very cost efficient, and saves me from having to throw out spent bleach solution and keep using more potassium ferricyanide.

Edited September 2, 2011 by Athiril