gdflp
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Sodium Nitroprusside Synthesis
I am trying to make sodium nitroprusside for use in Simon's Reagent. I've seen different methods for making this, but most involve an intermediate of
hydrogen cyanide which I don't want to and can't safely deal with. I found one method of reacting potassium ferrocyanide and nitric acid, then
neutralizing the product with sodium carbonate. Will this work and if so, how toxic are the intermediates?
[Edited on 14-2-2014 by gdflp]
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bfesser
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Thread Moved
14-2-2014 at 07:59 |
Boffis
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The answers to your questions are 1) Yes and 2) only very slightly! Check out the detailed preparation in Brauer's Handbook of Preparative Inorganic
Chemistry on the SM site library. I have carried out this preparation on a couple of occasions in the past and it works but careful control of the
temperature is essential or nitrogen oxides are evolved. I have a more detailed preparation somewhere and I'll try and dig it out and post it if I can
find it. However, I seem to remember that the best temperature for the nitric acid oxidation is about 65-70 C and I am sure I didn't leave it to stand
for a couple of days, just until it cooled to room temperature.
Their is another method using CN- displacement in which sodium nitrite and a ferrocyanide are treated with a barium salt (Hydroxide if I recall) I
will try and find this method too because in my hands it was simpler but required sodium ferrocyanide to get the best yield (I have described the
preparation of sodium ferrocyanide on this web site somewhere). I'll dig out and post this prep too but I am pretty sure I have seen it in one of the
books in the SM library.
Yep! both preparations are presented in Schlessinger's Inorganic preparation which s available for download from the SM library. Page 105 for the
nitric acid method and pages 106-107 for the nitrite/barium method and he even includes the preparation of sodium ferrocyanide from the potassium
salt. The latter method requires barium chloride I see (my memory failed me) and this is modestly poisonous. Schlessinger says both methods give of
cyanic fumes and require a fume hood but my experience is that the former gives off little fumes in reality though the latter definitely gives of HCN
though my attempted to recovery it were not very successful.
Schlessinger's book is not the source I originally used and the details were slightly different so there are other preparations out there.
[Edited on 16-2-2014 by Boffis]
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gdflp
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Thanks for your answer. I've read on some MSDS's that sodium nitroprusside is metabolized into cyanide ions in the body. Would this give it a
toxicity similar to that of sodium cyanide, or is this just MSDS's exaggerating as usual?
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byko3y
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Guys, I suck. Every time I try to prepare nitroprusside, and it was at least 3 times, I get some reeeeeeally low yields. My potassium ferrocyanide
crystals looks good and must be of high purity, nitric acid solution in a demineralized water mixed with excess of NaOH solution in the same water
gives a completely clear solution meaning no iron or other metal ions contamination present.
When I mix the reagents, solution turns green in a matter of minutes. All the manuals tell about cofee color, which is dark-red-brown, while can't see
in no way this color. Next, the solution becomes darker and darker, until I can barely see its color, which is greenish-blue. Precipitate is formed,
either completely black or white, depending on conditions (white is probably a ferrous ferrocyanide). On worksup the black compound appears to be
really dark even in dilluted form, heavily coloring everything. I think the black compound could be a mixture of some compounds, like prussian blue
and ferric ferricyanide, which have blue and orange color, thus becoming black on mixing.
This black precipitate is also insoluble in alcohol, after neutralization and filtration only slightly red solution remains, which contains less than
10% of theoretical amount of nitriprusside. In one of my attempts I managed to get no yield at all, only clear yellow solution with traces of
nitroprusside.
It is well known that the result of the reaction strongly depends on reaction conditions. I initially heat the mixture at 60-70 C on a water bath for
approx 2 hours - that's what is usually recommended. Still I don't understand what's wrong.
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PHILOU Zrealone
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Are you sure it is ferrOcyanide that you have and not ferrIcyanide?
Ferrocyanide is Fe(CN)6(4-) so a Fe(2+) core and yellow...
Ferricyanide is Fe(CN)6(3-) so a Fe(3+) core and orange-red...
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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byko3y
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It's ferrocyanide, it is yellow.
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byko3y
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From my last attempt I can say that the most probable cause of my failure is incomplete digestion of initial ferrocyanide. after neutralization with
sodium carbonate, the solution gives prussian blue reaction with ferrous sulfate. That's despite the fact I performed the initial reaction for as long
as 3 hours at 60 C. I think the required conditions are something like 80-90 C for 2 hours.
So I've got a resulting solution, which is of yellow-orange color, and i'm pretty sure it is a mixture of ferrocyanide plus traces of nitroprusside. I
don't really get why I have so much black precipitate (at least 1 g), that becomes green after addition of sodium carbonate, or blue on mixing with
solution of ferrous salt (or maybe it's residual liquid that contains some ferro/ferricyanide). Probably, nitric acid is sopposed to initially reacts
with ferrocyanide, leaving decomposition products, and then the actualy reaction producing nitroprusside commences.
I can't precipitate nitroprusside with copper to measure its amount, because ferrocyanide is also precipitated with copper.
I'm not sure whether low purity of my ferrous salt is acutlly a problem. AFAIK, the only side reaction of prussian blue formation from Fe2(SO4)3 +
ferrocyanide, which is not a problem, beause ferrocyanide is supposed to be completely converted.
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Velzee
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Quote: Originally posted by Boffis  | The answers to your questions are 1) Yes and 2) only very slightly! Check out the detailed preparation in Brauer's Handbook of Preparative Inorganic
Chemistry on the SM site library. I have carried out this preparation on a couple of occasions in the past and it works but careful control of the
temperature is essential or nitrogen oxides are evolved. I have a more detailed preparation somewhere and I'll try and dig it out and post it if I can
find it. However, I seem to remember that the best temperature for the nitric acid oxidation is about 65-70 C and I am sure I didn't leave it to stand
for a couple of days, just until it cooled to room temperature.
Their is another method using CN- displacement in which sodium nitrite and a ferrocyanide are treated with a barium salt (Hydroxide if I recall) I
will try and find this method too because in my hands it was simpler but required sodium ferrocyanide to get the best yield (I have described the
preparation of sodium ferrocyanide on this web site somewhere). I'll dig out and post this prep too but I am pretty sure I have seen it in one of the
books in the SM library.
Yep! both preparations are presented in Schlessinger's Inorganic preparation which s available for download from the SM library. Page 105 for the
nitric acid method and pages 106-107 for the nitrite/barium method and he even includes the preparation of sodium ferrocyanide from the potassium
salt. The latter method requires barium chloride I see (my memory failed me) and this is modestly poisonous. Schlessinger says both methods give of
cyanic fumes and require a fume hood but my experience is that the former gives off little fumes in reality though the latter definitely gives of HCN
though my attempted to recovery it were not very successful.
Schlessinger's book is not the source I originally used and the details were slightly different so there are other preparations out there.
[Edited on 16-2-2014 by Boffis] |
What was your original source?
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Boffis
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Woohoo, that's a while back but most probably either:
Cyanogen Compounds, Their chemistry, detection and estimation by Herbert Williams (1948). This is my standard starting point for all things cyanidy.
or Thorpe's Dictionary of applied chemistry (I think my set is about 1953).
But of course you can simply download the two references I gave above Brauer and Schlessinger from the SM library
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Velzee
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Thank you 
Check out the ScienceMadness Wiki: http://www.sciencemadness.org/smwiki/index.php/Main_Page
"All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident."
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"¡Vivá Cristo Rey!"
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