How Safe Is Potassium Ferricyanide?

[Kirk Keyes]

I just put a pinch of potassium ferricyanide into some glacial acetic acid - No visible reaction. One of these days, I'll test that mix and see how much cyanide is released when it is boiled.

 

[CRhymer]

Or just set a match to the acid - less set-up time

Cheers,
Clarence

Don't try this at home.

 

[Alexander Ghaffari]

Okay...I do not know where the confusion lies but potassium ferricyanide (Prussian blue) does not form HCN when mixed with HCl...ah, perhaps there is confusion with potassium ferrocyanide, which I believe will react with HCl, causing the formation of HCN?

Anyway...I worked with potassium ferricyanide and concentrated HCl...I assure you that no poisonous gas was liberated; however, working with KCN and concentrated HCl...oh yeah, you bet there was deadly gas released.

The CN bonds on the iron in potassium ferricyanide is essentially irreversible, just like when it attaches to the heme group in red blood cells (the bond is so strong it cannot be easily reversed); however, that's the least of a person's problems when poisoned with cyanide (like KCN or the classic NaCN) because the Krebs cycle shuts down long before a person dies of suffocation.

Yeah, I like science, I could go on about cyanide poisoning, but I have more fun drawing diagrams and what not. Eekk, do not ask me to draw out the entire Krebs cycle though...*flashbacks of that organic chemistry exam (it was just a blank sheet of paper and we had to draw out the entire cycle)* Happy photoging!

 

[Photo Engineer]

Potassium Ferricyanide is NOT Prussian Blue! That is a common misconception. Go here:

http://en.wikipedia.org/wiki/Prussian_blue For an explanation.

Actually, we studied the Krebs cycle in Biochemistry 601.

And, our studies at Kodak along with what has been said here, indicates that the bond of CN with Ferric ion can be broken by strong acid and heat or UV from sunlight! A Rochester photofinisher was shut down when free cyanide was detected in downstream effluent due to excess ferricyanide from the Ektaprint C process. They were the first company to trade trial the Ektaprint 3 process due to that shutdown event.

PE

 

[Kirk Keyes]

I'd modify what Alexander wrote and say that the ferricyanide complex is a strong bond, and not "essentially irreversable" as I do it all the time boiling it with sulfuric acid all the time. But it is complexed, and not easily broken.

Update, the potassium ferricyanide in the glacial acetic acid now has a slight yellow-green tinge to it. This tells me that some of it is now in solution (it's the same color as when you have a fresh solution of potassium ferricyanide in water) so there's still not a fast breakdown of the complex with the acetic acid.

Dan - also make small batches of potassium ferricyanide solutions so that you use them up fairly quickly. They color will change as the ferricyanide breaksdown. You can notice it in a week or so in dilute solutions.

 

[Photo Engineer]

Actually, as the ferricyanide is used up in bleaches, it forms the ferrocyanide. If prussian blue does not form, then the ferrocyanide is most likely the source of cyanide as it is more prone to decomposition wiht UV or heat + acid.

Therefore, the users of ferricyanide should be aware that the reduced ferrocyanide is potentially more apt to produce hydrogen cyanide. And, this is what happens in farmers reducer. Ferro -> Ferri with use.

PE

 

[gainer]

When I was teaching Organic Chem Lab 301, a young gal was shaving sodium metal under benzene. She decided to pour the scraps down the sink and wash it away with water. I was running towards her screaming NONONONONONONO, when she turned the tap on. Boom! The flame reached the ceiling.

We have all sorts of these things in the lab. I could spend a day just relating lab and AF stories here for APUG.

whicever is applicable.

PE

In one chem lab class, I forget which one, there was a large container of glacial acetic acid with the blow tube arrangement. The blow tube is supposed to be over the level of acid in the jug and the collecting tube below. The lab assistant had just filled the jug and had left both tubes below the acid level. I went to get a little acid and got a lot...right in the mouth, when I let up on the pressure. OUCH!

 

[Vaughn]

Vaughn,

Was this an accident or are you conducting experiments based on what you read in the APUG posts? :confused:

Steve

It was accidental a few years back. It is part of my spiel I give all our new lab assistants.

PE -- it might have been just the dye, but I'll keep my "warning tale" the same for the new recruits. (Actually the red came on slowly over 20 minutes or so, so I am not sure one way or the other...dye or "sunburn".)

The other story I tell the new lab assistants is the time someone spilled Fixer Part B on the counter and did not clean it up. I lean against it both front and back -- and when I washed my Levis, the cloth disintergrated...fortunately in the washer and not while I was wearing them. Part Be has sulphuric acid in it, I believe.

Vaughn

 

[Photo Engineer]

Vaughn;

Yes, Sulfuric acid and Aluminum Sulfate.

A young lady in one of my classes spilled sulfuric acid down the front of her lab coat and clothing. She was too ashamed to admit it after all of our admonitions to be careful. When she began to hurt, about 1/2 way through the 4 hour lab we found her clothing dissolving and we had to place her in a sink with running water and call for medical attention.

Fortunately, we were a "teaching" campus with a hospital right there! And, IIRC, she and most of her classmates were prenursing.

She was OK, more embarassed than hurt after they treated her.

PE

 

[Alexander Ghaffari]

Potassium Ferricyanide is NOT Prussian Blue! That is a common misconception. Go here:

http://en.wikipedia.org/wiki/Prussian_blue For an explanation.

Actually, we studied the Krebs cycle in Biochemistry 601.

And, our studies at Kodak along with what has been said here, indicates that the bond of CN with Ferric ion can be broken by strong acid and heat or UV from sunlight! A Rochester photofinisher was shut down when free cyanide was detected in downstream effluent due to excess ferricyanide from the Ektaprint C process. They were the first company to trade trial the Ektaprint 3 process due to that shutdown event.

PE

This is why I hate Sigma-Aldrich (I love the original Aldrich)...their chemical labeling sucks...tremendously. The potassium ferricyanide container is labeled "Prussian blue" in parenthesizes. And I meant to say that we had to know the entire Krebs cycle in Biochemistry...we "learned" (not the entire thing like in BioChem) it in three classes prior (including OChem...you think after learning it four times, I would have it memorized, but I sure do not).

Again to clarify, concentrated HCl could not liberate HCN (g) from potassium ferricyanide at room temperature in my research (lest I be poisoned). The bond, as I say, is "essentially irreversible" because the only way to free CN from heme that I know of consists of sodium thiosulfate (yay, photo fixer!)...and you need your ATP to live (I do not recall the exact mechanism)...so, to get the heme back to snuff before the Krebs cycle shuts down...yeah, good luck with that. Yes, I could see the reaction to light causing that (considering Fe being as sensitive as it is to light *remembers needing to store solutions containing potassium ferricyanide away from light*).

 

[Kirk Keyes]

Prussian blue is generated by the reaction of K3[Fe(CN)6] with ferrous (Fe2+) ions. To detect ferric (Fe3+) iron, potassium ferrocyanide is used and the stain and pigment produced are commonly known as Prussian blue.

The color of the old ferricyanide solutions I mentioned above is bluish, so the ferricyanide is most likely reducing to ferrocyanide. The ion still has 6 CN groups attached, and it's the iron that's changing valence as it sits.

PE is right, ferricyanide does liberate CN gas with time and exposure to UV light. Not generally a concern in the lab, but it is in the environment.

 

[Larry Bullis]

This is why I hate Sigma-Aldrich (I love the original Aldrich)...their chemical labeling sucks...tremendously.

But I keep getting their catalogs just for the great covers.

 

[dancqu]

Actually, as the ferricyanide is used up in bleaches,
it forms the ferrocyanide.

And, this is what happens in farmers reducer.
Ferro -> Ferri with use. PE

Working on an image's elemental silver it forms an
insoluble silver ferrocyanide complex. How convenient!
The image stays in place. If some halide, a chloride, bromide
or iodide is present then an immediate conversion to that
halide takes place. How convenient again. The light
sensitive silver halides are once again restored.

Ferro -> Ferri with use? Dan

 

[gainer]

Working on an image's elemental silver it forms an
insoluble silver ferrocyanide complex. How convenient!
The image stays in place. If some halide, a chloride, bromide
or iodide is present then an immediate conversion to that
halide takes place. How convenient again. The light
sensitive silver halides are once again restored.

Ferro -> Ferri with use? Dan

The restored silver halide may then be redeveloped. If you wonder how a certain negative would have looked if you had developed it in a staining developer, now's your chance. However, you can't go back because the bleach does not remove the newly formed stain image. OTH, that means you can see what a stain-only negative would look like.

 

[gainer]

Furthermore, one can intensify the stain of a PMK or Pyrocat developed negative by bleaching the silver back to the halide and redeveloping in the staining developer.

 

[Photo Engineer]

Working on an image's elemental silver it forms an
insoluble silver ferrocyanide complex. How convenient!
The image stays in place. If some halide, a chloride, bromide
or iodide is present then an immediate conversion to that
halide takes place. How convenient again. The light
sensitive silver halides are once again restored.

Ferro -> Ferri with use? Dan

Ferro to Ferri does not take place in ordinary photographic usage.

PE

 

[wogster]

Actually, as the ferricyanide is used up in bleaches, it forms the ferrocyanide. If prussian blue does not form, then the ferrocyanide is most likely the source of cyanide as it is more prone to decomposition wiht UV or heat + acid.

Therefore, the users of ferricyanide should be aware that the reduced ferrocyanide is potentially more apt to produce hydrogen cyanide. And, this is what happens in farmers reducer. Ferro -> Ferri with use.

PE

To sum this all up then, one should take the normal precautions when working with this, as with any photo chemicals, wear chemical resistant gloves and work in a well ventilated area, make sure to work in a clean area that is not potentially contaminated with other chemicals. Wear protective eye wear to prevent splashes. When mixing chemicals following a formula or recipe, always add in the order specified. Clean up any and all spills, make sure to keep all containers properly labelled, and keep all food items away from chemicals. Avoid strong sunlight and all heat sources.

 

[Photo Engineer]

Yep.

My DVD and Book both start with a safety section!

PE

 

[Markus Röhling]

Ferro to Ferri does not take place in ordinary photographic usage.

PE

But this is what you wrote earlier: (there was a url link here which no longer exists)

Markus

 

[Philippe-Georges]

Is this the same Postassium ferricyanide (III?)as used in Anna Atkins Cyanotype process?

Philippe

 

[Ian Grant]

There's only one type of Potassium Ferricyanide.

Ian

 

[Photo Engineer]

But this is what you wrote earlier: (there was a url link here which no longer exists)

Markus

Markus;

Good catch. That reference is a typo. A blatant goof on my part.

Ferro -> Ferri is not common unless you add a strong oxidizing agent to the bleach that is stronger than Ferricyanide.

Thanks. I'm sorry I cannot edit it, but in the context, you can see I wrote it backwards.

PE

 

[Photo Engineer]

Actually, as the ferricyanide is used up in bleaches, it forms the ferrocyanide. If prussian blue does not form, then the ferrocyanide is most likely the source of cyanide as it is more prone to decomposition wiht UV or heat + acid.

Therefore, the users of ferricyanide should be aware that the reduced ferrocyanide is potentially more apt to produce hydrogen cyanide. And, this is what happens in farmers reducer. Ferro -> Ferri with use.

PE

The above should read Ferri -> Ferro during use. Ferricyanide is reduced while silver metal is oxidized.

The equation quoted above is a typo. Sorry.

PE

 

[Philippe-Georges]

There's only one type of Potassium Ferricyanide.

Ian

There is Potassium hexacyanoferrate(II) = K4Fe(CN)6 [14459-95-1] and Potassium hexanocyanoferrate(III) = K3Fe(CN)6 [13746-66-2].
I think that Potassium Ferricyanide is one of the two.

Philippe

 

[Ian Grant]

Potassium Ferricyanide is K3Fe(CN)6

Ian