fluorescence
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Morland's Salt and Guanidinium formation
Hey Guys,
I need this explanation for a youtube video but I am pretty much stuck. I tried making Reinecke's salt by fusing Ammoniumthiocyanate and
Ammoniumdichromate together. According to literature Reinecke's Salt forms which is [NH4][Cr(SCN)4(NH3)2] bur also so
called Morland's salt which is the same compound but with a Guanidinium as counterion.
Now two questions arise. What is the redox-partner to reduce the Cr(VI) to Cr(III) and how the heck can a Guanidinium just form out of nowhere ?
Usually for Ammoniumdichromate the Cr(VI) and the N(-III) react to form N2 and Cr(III) but in this case the Oxygen remain as water or
Cr2O3 and here we have to get rid of them. So I thought of a redox reaction between Oxide and Cr(VI) but this seems kinda
odd....
For the Guanidinium formation I thought of treating the Ammonia for a real neutral Ammonia for a second. Maybe due to the hot temperature it might
decompose like many Ammonium salts do to form some Ammonia. Then the Ammonia could attack the slightly positive carbon in thiocyanate, the tripple
bond to the N is dissolved forming a [NH4][S-C(NH3)=N] which quickly shifts the proton to form [NH4][S-C(NH2)=NH] and then another Ammonia attacks
forming a [NH4S]- that could find another Ammonium somewhere or an extra proton to make it neutral again and the final product which is
protonated now.
I guess something like this could theoretically happen if we leave all the extra protantions and deprotonations inbetween out.
But I am still missing a redox-partner as neither the Nitrogen, nor the Sulfur or the Carbon change in their oxidation states during that reaction....
Any suggestions or ideas? It's hard to find anything on the topic. I found the old papers where both were discovered but no explanation why they
formed.
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Boffis
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Hi Fluorescence. The original method of producing guanidine as its thiocyanate salt was simply to heat ammonium thiocyanate at a higher temperature
and for a longer period than that used to produce thiourea. The mechanism is not clear to me but the replacement of the enolized -SH group by ammonia
with the liberation of H2S is probably the effective reaction. Morland's salt is simply the guanidinium salt of the tetrathiocyanatodiaminochromate
III. I have made the ammonium salt by the process you describe and it is fairly rapid giving little time for the formation of much guanidine. The
excess of ammonia in the reaction mixture or possibly the theoretical production of hydrogen sulphide during guanidine formation act as the reducing
agent for the Cr VI.
From your statement that: "neither the nitrogen nor the sulphur or the carbon change their oxidation state..." I am forced to ask:- how do you know,
did you test the reaction mixture for other valencies of these elements? The oxidation of ammonia tends to give nitrogen; did you measure the nitrogen
volume evolved?
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fluorescence
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I was referring to the elements found in the reactants and products. If a gas is evolved I didnt look for that I was focused on finding a suitable
redox partner within the known compounds. But to be honest I didn't take the time to check if anything is missing from A to B. With a proper mechanism
this would be easier as it doesnt seem to be important whether Potassium Dichromate or Ammonium Dichromate is used there could be some spare Ammonia
as well which doesn't appear in the end because it's oxidized for example.
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