Sciencemadness Discussion Board - Prussian Blue from Laundry Bluing

Prussian Blue from Laundry Bluing

JJay - 10-3-2016 at 17:09

Today I decided to boil down some laundry bluing to see if I could recover any ferricyanide compounds from it. I used an 8 oz (227 mL) bottle of bluing and simply heated it gently on a hot plate with stirring.

So far, I have removed about 3/4 of the water. The bluing has taken on an appearance very similar to blue ink used in pens, and there is some very fine precipitate.

One thing that I have noticed - the solution has a very weak almond odor... I'm told that cyanide smells like almonds. The MSDS for this variety of bluing says that it is nonhazardous but warns not to mix it with acids. I can't confirm it, but I believe that the ingredients are water, Prussian blue, oxalic acid, and ammonia.

Heating will likely gradually drive off the ammonia... I do have a respirator, of course, but before I evaporate to dryness, I suppose I ought to ask: Does oxalic acid react with Prussian blue to produce hydrogen cyanide?

[Edited on 11-3-2016 by JJay]

JJay - 10-3-2016 at 19:47

I ended up boiling it down and obtained a few grams of a tarry, extremely blue substance that is mostly soluble in water.

My next move is to calcine it to destroy any oxalic acid compounds.

ave369 - 11-3-2016 at 01:49

I think, hot concentrated oxalic acid could produce a small amount of hydrogen cyanide. But it's probably cyanidophobia on my part.

[Edited on 11-3-2016 by ave369]

JJay - 11-3-2016 at 08:30

I believe that is exactly what happened, but I don't believe that dangerous amounts were produced... just enough to create a noticeable odor.

Boffis - 11-3-2016 at 14:54

Laundry bluing often contains ultramarine and the reason it should not be mixed with strong acid is because it gives off hydrogen sulphide. This latter reaction allows easy distinction between the two pigments.

JJay - 11-3-2016 at 18:21

This particular brand is widely believed to contain Prussian blue... It is Mrs. Stewart's.

I suppose I could do some tests.

Daffodile - 12-3-2016 at 09:52

Could you distill with acid into huge excess of aqueous potassium Hydroxide, add Ferrous Sulfate, and collect pure Prussian blue precipitate? That way you can measure purity.

JJay - 12-3-2016 at 10:02

Quote: Originally posted by Daffodile

Could you distill with acid into huge excess of aqueous potassium Hydroxide, add Ferrous Sulfate, and collect pure Prussian blue precipitate? That way you can measure purity.

I have been thinking about doing something along those lines, bubbling gas produced with sulfuric acid and the blue compound through a hydroxide solution and reacting with ferrous sulfate... of course, that is a fairly dangerous procedure since it involves creating hydrogen cyanide as an intermediate.

As a test for hydrogen sulfide, I could try bubbling the gas through copper sulfate solution to see if a precipitate is formed. This is also pretty dangerous, not to mention smelly.

[Edited on 12-3-2016 by JJay]

JJay - 26-4-2016 at 23:41

I pulled this experiment out of the cabinet today to look at finishing it up, and I noticed that long, white needles had grown out of the blue substance. I'm not sure what these are, but they appear to be crystalline.

fluorescence - 27-4-2016 at 01:56

Interesting, depends on where you stopped your cleaning process. If you washed everything in the end most of the soluble parts should be driven off as well. Although the original post seems to be somewhat older I'd just like to mention that this particular idea that HCN smells like Almonds is kinda dangerous.

To be honest I have no idea what fresh almonds actually smell like. I worked with stuff like Benzaldehyde and they all smell completely different to what HCN actually smells. It's very characteristic, since I have to work with it quite often I do tests once every 2 weeks where I have a small bottle with a tiny amount wet KCN in there to test if I can still smell it and to remember the exact smell it has. I could probably detect it very fast by smell since as said its very characterisitc but I have never smelled anything else that would resemble it afterwards.

With HCN it's like with H2S, you can smell actually quite tiny traces of it already although H2S can be detect in like 10.000 times lower conc. Still you will smell the difference between a tiny conc. and a larger one. I had the unpleasant experience, more than once actually, to smell a larger amount of HCN and then it's like HCl or HF, a larger amount is really irritant to your nose. Its really like breathing above a bottle of HCl. So yeah I don't have oxalic acid to test it for you but as long as you work under a fume hood or outside you should be fine I guess, no guarantees!

[Edited on 27-4-2016 by fluorescence]

JJay - 27-4-2016 at 02:36

The almond smell is a bit hard to describe... it smelled like a watery artificial almond smell rather than like almonds. Unlike bitter almond flavoring (which doesn't smell like almonds but does smell delicious), it didn't smell like anything that would be particularly good to eat, although the smell was similar.

fluorescence - 27-4-2016 at 02:48

Mhm okay. I'd have to smell it. I once tried some artifical bitter almond oil and the smell was different as well.
We had that topic quite often what to do to actuall help people identify it. I thought of a wet q-tip that you hold for a short period of time into some HCN vapour and that can be send to other members but it didn't really work out.

Best would be to avoid such experiments. Like Prussian blue can be easily made and just washing it multiple times should clean it enough. What would you need a perfectly clean sample for ?

JJay - 27-4-2016 at 02:53

I can easily make Prussian Blue, but in this case I am trying to isolate it from OTC compounds. I am very curious about what the white needle-like crystals I am seeing are. My cell phone camera doesn't really do them justice....

fluorescence - 27-4-2016 at 03:13

Have you checked them under a microscope to see how many different compounds there could be ?
I don't know what other compounds were in that OTC product you used.

I boiled Prussian Blue once in nitric acid. There is a very old paper on so called Prussian Green or Berlin Green a compound that should form when PB is boiled in Nitr. Acd. or Chlorine. I tried it and it became really green but in the end blue particles formed and it became all blue again, seems to be pretty reversible so I think some boilin will actually reduce the particle size. So not all acids seem to react with it I guess. Not really a fan of this compound anyway. I work a lot with d-Metal Cyanides but I avoid Iron for many reasons.

Artemus Gordon - 2-5-2016 at 16:05

Quote: Originally posted by JJay

I can easily make Prussian Blue, but in this case I am trying to isolate it from OTC compounds. I am very curious about what the white needle-like crystals I am seeing are. My cell phone camera doesn't really do them justice....

The Mrs. Stewart's site doesn't make it easy, but if you poke around long enough they tell you MSB is a colloidal suspension of ferric hexacyanoferrate in water with a small amount of a biocide/algaecide and a "pH buffering agent".

My guess is your crystals are of this pH buffer, and I suspect it is sodium carbonate. Have you tried to find the pH of these crystals?

JJay - 2-5-2016 at 23:42

Quote: Originally posted by Artemus Gordon

Quote: Originally posted by JJay

Where do they say that it is a colloidal suspension of ferric hexacyanoferrate?

JJay - 2-5-2016 at 23:45

Quote: Originally posted by fluorescence

Have you checked them under a microscope to see how many different compounds there could be ?
I don't know what other compounds were in that OTC product you used.

I boiled Prussian Blue once in nitric acid. There is a very old paper on so called Prussian Green or Berlin Green a compound that should form when PB is boiled in Nitr. Acd. or Chlorine. I tried it and it became really green but in the end blue particles formed and it became all blue again, seems to be pretty reversible so I think some boilin will actually reduce the particle size. So not all acids seem to react with it I guess. Not really a fan of this compound anyway. I work a lot with d-Metal Cyanides but I avoid Iron for many reasons.

No... I have not checked them under a microscope.

Artemus Gordon - 3-5-2016 at 15:03

Quote: Originally posted by JJay

Quote: Originally posted by Artemus Gordon

Quote: Originally posted by JJay

Where do they say that it is a colloidal suspension of ferric hexacyanoferrate?

<a href="http://mrsstewart.com/wp/wp-content/uploads/2013/02/Salt-Crystal-Garden.pdf">Salt Crystal Garden pdf</a> page 2.

JJay - 3-5-2016 at 21:04

Ok, so it is definitely largely Prussian Blue.

Here is what I got after I boiled down one bottle of it and allowed the moist solids to air dry. There are some long needle-like crystals that look almost like white hairs.

[Edited on 5-5-2016 by JJay]

Artemus Gordon - 4-5-2016 at 11:03

Nice picture!
Those crystals are much thinner than I'd assumed. Maybe they are CaCO3. I would try touching a pH strip dampened with distilled water to one or two of them. That would both tell you the pH and it would give you an idea of the solubilty. Did the crystals start to form early or late in the dehydrating process?

JJay - 4-5-2016 at 20:42

Quote: Originally posted by Artemus Gordon

Nice picture!
Those crystals are much thinner than I'd assumed. Maybe they are CaCO3. I would try touching a pH strip dampened with distilled water to one or two of them. That would both tell you the pH and it would give you an idea of the solubilty. Did the crystals start to form early or late in the dehydrating process?

I think they formed late... they are very soluble and very acidic... as acidic as they are, I think they must be oxalic acid or perhaps sodium hydrogen oxylate.

[Edited on 5-5-2016 by JJay]

Artemus Gordon - 8-5-2016 at 11:46

That's interesting. I assumed the biocide would need an alkaline environment. What pH did you measure?

JJay - 8-5-2016 at 11:48

I measured pH 1, touching the paper directly to the crystals. This does indicate strong acidity, if nothing else.

PirateDocBrown - 6-2-2017 at 15:40

I'm going to try this as well. I did a bit of digging, and one of the MSDS's on Mrs. Stewarts listed the ingredients (but not the proportions):

Water
Gluteraldehyde
Oxalic Acid
"pigment"

Other things I found said the gluteraldehyde replaced formaldehyde, so that they could continue to say they were "non-toxic". How oxalic acid jibes with that, I don't know.

JJay - 6-2-2017 at 15:48

I never got around to actually calcining it (at least I haven't yet), but I have the Prussian Blue sitting in a vial close at hand.

I'm pretty sure that heating it above a few hundred degrees will drive off the impurities.

Edit: A pharmacist I know who has a master's degree in chemistry thought that was a dangerous idea, so I held off on it, but I'm really not seeing how that would be dangerous. I mean, if you allow yourself to get a faceful of hot oxalic acid vapor, you'll wish you hadn't, but really, how dangerous is it to boil down some laundry bluing and heat it in a crucible....

[Edited on 7-2-2017 by JJay]

PirateDocBrown - 6-2-2017 at 19:37

The gluteraldehyde is likely a few ppt, as a biocide.

The oxalic acid is likely there, just to keep it near pH 7.

I would imagine the stuff to be over 95% of the dry mass the ferric ferrocyanide.

JJay - 7-2-2017 at 04:04

I'm going to try heating part of it to 300 C on a hotplate and see if it is still water soluble and acidic.

JJay - 10-2-2017 at 02:35

... doing some reading, it looks like 300 C will actually scorch Prussian Blue... http://adsabs.harvard.edu/abs/1989HyInt..46..723I

I'm not seeing a lot of clear information on the temperature for boiling/subliming oxalic acid, but every source I am seeing suggests a temperature under 200 C.

I can easily reach a temperature of 225 C in my oven.

JJay - 10-2-2017 at 04:08

Reading over that paper (as opposed to just glancing at the abstract), it looks as though temperatures up to 300 C mainly affect the electron configuration of the iron, changing the electrical conductivity of Prussian blue, and have little to no effect on the bound cyanide of pure Prussian blue. I suspect that high temperatures might affect the solubility too.

I checked, and a sample of the dried bluing is soluble in water prior to any heat treatment. So I dried a clean 50 mL beaker in an oven and weighed it at 35.46 grams and then added 0.19 grams of dried Mrs. Smith's bluing. There is an unknown amount of water in the mix, and with such a small sample, it is not really feasible to accurately assay the impurities with a cheap pocket scale, but I'd like to retain most of the bluing for future experiments such as checking the effect of different temperatures on the bluing's properties.

I then heated it in an oven at 260 C for 30 minutes in a ventilated area. Upon removing it from the oven, the blue sample had disappeared and been replaced by a slightly alkaline orangish brown powder that was virtually insoluble in water, with no blue color visible anywhere. This is assumed to be iron oxide with a small amount of potassium carbonate. The beaker weighed 35.55 grams.

[Edited on 10-2-2017 by JJay]

chemplayer... - 10-2-2017 at 19:09

Those needle crystals do indeed look like an oxalate salt.

HCN is famous for having a variety of odors depending on the individual. We dropped a little (VERY little - like about 30mg) alkali CN salt into dilute sulfuric acid just to see. We figured that is would be worth knowing what it smelt like just in case we ever encountered a lot of it accidentally!

The salt bubbles on contact with the acid (not super-vigorously like a carbonate, but more gently with bubbles also coming out of the acid around). Two of us cautiously wafted some of the air-diluted vapours and had a sniff to see, and compared notes.

Our perceptions were the same - it is distinctive, but weird and hard to describe. Musty, dusty, mouldy, very slightly bitter, not very acrid/acid at all. You get a strong weird feeling of something on the top of your mouth and throat - and here there is 'something' which is almond-like but it's difficult to describe. Definitely not sweet and nothing like benzaldehyde or your stereotypical almond flavouring aroma. You'll know if it's there, but if you're not used to it you're not going to obviously identify it (perhaps unless you're genetically predisposed to smelling something stronger).

So worth being a bit careful, but yields of HCN from heating even strong mineral acids with cyanoferrate compounds are normally that good due to side-reactions, and the conditions seem to be quite sensitive to the formation.

JJay - 10-2-2017 at 20:50

I just ran across this entry on Prussian blue. If true, it seems to clear up a lot of questions that I've had about its soluble form: https://books.google.com/books?id=vEwj1WZKThEC&pg=PA1444...

I wonder if perhaps there may have been some alkali cyanide and ferric cyanide in the mix. I actually didn't smell any cyanide at all while the compound was heating in the oven, but I left it mostly unattended. It is surely not a good idea to breath the gaseous byproducts from strong heating of bluing solution.

I think I might try adding some iron salts to a concentrated solution of bluing and see if there is a precipitate. I'm also curious as to the effects of lower temperatures--and was there actually a small amount of alkali cyanide present? I wouldn't ordinarily expect the temperatures to be high enough to produce any, but alkali cyanide does have an elevated pH.

Velzee - 29-4-2018 at 20:12

Using Fe salts would be a good idea to test if they are present, although I doubt if any are. As chemplayer said, it is extremely difficult to describe the scent of HCN; I personally think it is akin to a metallic, old musty odor. Quite weird, frankly.

I look forward to seeing the test results and the dried Prussian blue!

Velzee - 3-5-2018 at 18:00

Quote: Originally posted by JJay

... doing some reading, it looks like 300 C will actually scorch Prussian Blue... http://adsabs.harvard.edu/abs/1989HyInt..46..723I

I'm not seeing a lot of clear information on the temperature for boiling/subliming oxalic acid, but every source I am seeing suggests a temperature under 200 C.

I can easily reach a temperature of 225 C in my oven.

I don't think 225°C would scorch the salt

JJay - 3-5-2018 at 19:21

I don't think so either, but I'm not 100% sure... 260 C was too hot.

Oh, and as far as the scent goes, I thought the bluing smelled like kind of like watery almonds when I was boiling it down, but I took care not to smell it more than once. At the time, I attributed the watery aspect to water vapor, and in retrospect, I'm not sure what to think about that. I'm not about to try smelling boiling laundry bluing again, but I will pull this experiment out at some point and try further purification steps.

[Edited on 4-5-2018 by JJay]