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Author: Subject: OTC source of thiocyanates or ferrocyanides?
Fulmen
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[*] posted on 16-4-2018 at 15:04
OTC source of thiocyanates or ferrocyanides?


What are the most common uses for thiocyanates? Any products out there that could contain a fair amount? I suppose I could synthesize it from ferrocyanide, but again I don't know where to look for it. Ebay isn't really an option (overseas shipping and customs etc).
I need some as a rectifier for caustic black baths, thiocyanates are the only rectifier I have found so far.




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[*] posted on 16-4-2018 at 15:45


Are you blackening ferrous metals, or something else?

--------------------

Does anyone in your country still use old fashioned blueprints? Or cyanotype photographic processes?

If anyone there sells photographic chemicals, you might look there.


[Edited on 4-17-2018 by Bert]




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[*] posted on 17-4-2018 at 01:34


Yeah, it's a plain caustic black bath for steel.

Haven't found many shops selling photo-chems, and none of them had any thiocyanates. Cyanotype seems to be the best option, but it still involves import. It's still better than photo-chems, I have found a couple of cases where they tested positive for GHB. I don't need the police kicking down my door over some bogus drug charge...




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[*] posted on 17-4-2018 at 06:10


High or low temperature? I assume high (around 141 C), but just to be sure.



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[*] posted on 17-4-2018 at 06:25


Isn't K2Fe(CN)6 use as an anti-caking agent in table salt?

That would be a inconvenient source but maybe you can buy it as the additive?
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[*] posted on 17-4-2018 at 06:33


High temperature.



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[*] posted on 18-4-2018 at 01:42


Both ferrocyanides and thiocyanate can be prepared easily from Prussian blue pigment. This pigment is fairly cheap if you can find a supplier, it depends I suppose on which country you are in. Try a larger supplier of art materials or specialist pigment suppliers.

The process method has been described on SM on several threads already.
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[*] posted on 18-4-2018 at 03:04


Prussian blue is an interesting option. I do have some in the form of marking compound for metal work, but it's fairly expensive. I'll start digging through art&crafts-suppliers to see if anyone sells the pure stuff at a reasonable price.



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[*] posted on 18-4-2018 at 07:50


You can get Prussian Blue by just evaporating off the water from laundry bluing. Around here you can get an 8 oz bottle of bluing, yielding about 100 grams of pigment, for about $5.

It will have small traces of gluteraldehyde and oxalic acid additives, (at least the brand I use) but otherwise essentially pure Prussian Blue.





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[*] posted on 18-4-2018 at 08:07


I have never seen any laundry bluing products around here, and a web search didn't turn up any products either. But I have found a shop that might sell pure prussian blue pigment at a reasonable price, so I think I will try that route first.

Boffis: I couldn't find any posts on prussian blue to thio, but several using alkali salts. I assume those should work as well?




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[*] posted on 18-4-2018 at 09:39


You can easily find Mrs Stewart's bluing on eBay.

I also would like to hear of good synthetic routes to both thiocyanides and ferrocyanides.

[Edited on 4/18/18 by PirateDocBrown]




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[*] posted on 18-4-2018 at 10:23


True, it's just so painful having to pay 3xprice for shipping. I'll give the local sources a chance first.




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[*] posted on 18-4-2018 at 10:55


Quote: Originally posted by PirateDocBrown  
You can get Prussian Blue by just evaporating off the water from laundry bluing. Around here you can get an 8 oz bottle of bluing, yielding about 100 grams of pigment, for about $5.

It will have small traces of gluteraldehyde and oxalic acid additives, (at least the brand I use) but otherwise essentially pure Prussian Blue.



If you already have the pigment in suspension and want to make ferrocyanide just add a strong warm solution of KOH or NaOH until the blue colour has turned to an even dark brown, stir periodically and allow to settle for a day or so to make it easier to filter. Potassium ferrocyanide is less soluble in the cold so crystallises more easily.

@Fulmen, Thiocyanates are prepared from either dried potassium or sodium ferrocyanide and sulphur. They are simply mixed with the appropriate metal carbonate or hydroxide and sulphur and fused, the mixture turn black from the formation of iron sulphide and the appropriate thiocyanate leached out with water and crystallised by evaporation. I am sure this is mentioned in a thread somewhere on SM.

There's even a chemplayer video https://www.youtube.com/watch?v=CKNBKCnnwLY

If not it is certainly covered in several practical inorganic chemistry books

Here's a link to an ebay supplier in the UK, I have bought this brand so I can vouch for the quality:
https://www.ebay.co.uk/itm/Cornelissen-Dry-Pigment-Prussian-...

[Edited on 18-4-2018 by Boffis]
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[*] posted on 18-4-2018 at 11:30


Thanks, Boffin. I was searching for a direct route, but converting it to the sodium salt isn't much work.

I have found a shop selling Paris Blue PB27. It's listed as ferriammonium ferrocyanide, but I doubt if that matters.




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[*] posted on 18-4-2018 at 22:36


@Fulmen, There is also this thread on SM

http://www.sciencemadness.org/talk/viewthread.php?tid=21329#...

but I have to say the OP's "recipe" is a bit off the mark as Blogfast pointed out. It need a source of nitrogen. Now a days cyanuric acid left over from making chlorine from TCCA tablets is probably a better source of nitrogen, or perhaps calcium cyanamide if you want to try making the ferrocyanide yourself without Prussian blue.

There are numerous variations on the basic Prussian blue including so called "soluble" Prussian blue which is actually a colloidal preparation but all work; a little ammonia may be evolved though.

It might be possible to convert Prussian blue directly to thiocyanate but I can't find a description of such a process but maybe heating the pigment with potassium polysulphide (liver of sulphur which is sold as a patinized for bronze and other copper alloys) or just fused sodium sulphide might work.
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[*] posted on 18-4-2018 at 23:12


Well, since polysulfide is made by heating sodium carbonate and sulfur the original reaction should work as well. But I don't mind one extra step to avoid any possible problems. Synthesizing it from scratch sounds like a fun challenge, I might just give it a try. I do believe I have some cast iron turnings, and I can just dig plain steel turnings out of the lathe. Any idea what temperature is needed?



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[*] posted on 19-4-2018 at 04:07


If you are going to try from scratch here are a couple of references that you might find useful. They are both old and out of copy write, both cover the preparation of ferrocyanide from scratch and can be downloaded from the internet. The files are too large to attach to this post.

The Cyanide Industry, Robine & Lenglen, 1906

and

The Chemistry of Cyanogen Compounds an the manufacture and estimation, H E Williams, 1915

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[*] posted on 19-4-2018 at 05:03


Thanks, I love those old books. Downloading as I type.



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[*] posted on 19-4-2018 at 07:35


Robine & Lenglen only lists one interesting direct route: "Igniting nitrogenous substance with potassium sulfate, or with sulfur and potassium carbonate". No further details are given, so I question the feasibility of this route. The others require either cyanide, carbon disulfide or other toxic or hard to get precursors. Williams did not list anything useful.



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[*] posted on 19-4-2018 at 14:49


Seems like the same holds true for ferrocyanides, either Na/k+Fe+C+N at high temperature or cyanides in some shape or form. Using atmospheric N sounds like a recipe for poor yields, and N-bearing organics would probably make for a very smelly afternoon. Neither sounds appealing.



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[*] posted on 20-4-2018 at 00:18


What are my options for safe, non-stinking sources of nitrogen (no proper ventilation for the furnace)? Cyanuric acid has been mentioned, but I can't find it anywhere local. I can get TCCA, but converting it in any real amount would mean handling a lot of chlorine.



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[*] posted on 20-4-2018 at 01:02


Cyanuric acid forms when you heat urea to about 200˚C, giving off huge amounts of ammonia gas in the process. Surely you can obtain urea somehow? In the presence of alkali metals, you get cyanate salts.



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[*] posted on 20-4-2018 at 01:43


*facepalm*
I only found coldpacks (expensive and unknown) and 600kg big bags. But AdBlue exhaust additive should be pure urea, and it's not that expensive either.
I assume sodium cyanate would be the best choice, seems like CA decomposes at 400°C while the cyanate is listed with a mp of 550°C. The cyanate could also be used for nitrocarburizing, something I could have a real use for.




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