Rhodanide
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Hydrazine soln. + Time = ... Maple Syrup?!
Hi all, a bit over a year ago, I got my order of 250g of Hydrazine Sufate from Ukraine. (I still have a good 200g still unused) I used about 50 grams
to make a solution of Hydrazine in Ethanol. Over time, it darkened, and continued to get more and more syrupy. Now it looks identical to Grade-A dark
amber maple syrup. Now, what the hell would cause it to do this? The container it's in is plastic, and shows absolutely no signs of
compromisation, or corrosion of any kind. The only impurities that were in there would be excess NaOH (I used too much in the reaction), and that's
about it.
It's quite strange, and I'll add a picture when I can find one.
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Rhodanide
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Here it is after 3 months.
https://postimg.org/image/wdxiggmvp/
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chemplayer...
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Could this be slow oxidation of the alcohol to acetaldehyde (via air) and then subsequent condensation with the hydrazine? In addition if the alcohol
also oxidises to aldehyde slowly, could the alkali conditions cause aldehyde self-condensation to form other ketones and then condensation with
hydrazine etc.?
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Tdep
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Is the plastic PET or HDPE? Because if it is PET it may be pulling out some of the terephthalic acid (as strong bases tend to do) and that could be
making some new polymers in the solution.
I do like chemplayers idea though, the colour does look like the aldehyde condensation reaction I've seen, they seem to go a red
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Rhodanide
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Quote: Originally posted by chemplayer...  | | Could this be slow oxidation of the alcohol to acetaldehyde (via air) and then subsequent condensation with the hydrazine? In addition if the alcohol
also oxidises to aldehyde slowly, could the alkali conditions cause aldehyde self-condensation to form other ketones and then condensation with
hydrazine etc.? |
Hey man, good to see you're still here.
I'll look to see what type of plastic the container is. It's an old 29% NH3 bottle, and I'll check to see whether it's PET or HDPE.
I also noticed that there's a negative pressure inside the container, because the sides are being gently sucked in. I'm currently busy, but will be
back to see what material it is later. I'll let you know.
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Rhodanide
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| Quote: Originally posted by Tdep | Is the plastic PET or HDPE? Because if it is PET it may be pulling out some of the terephthalic acid (as strong bases tend to do) and that could be
making some new polymers in the solution.
I do like chemplayers idea though, the colour does look like the aldehyde condensation reaction I've seen, they seem to go a red
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It's probably HDPE, because of the consistency of the bottle.
There's also a strange smell, aside the N2H4 and denat. Alcohol. I can't quite put my finger on it, but it's there. Probably acetaldehyde like you and
CP were saying.
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Darkstar
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Not only that, but if excess NaOH really is present, then it may even be the hydrazine itself that's causing the ethanol to be slowly oxidized to
acetaldehyde. Hydrazine is already far more susceptible to autoxidation than ethanol is due to its much lower bond-dissociation energies. Ethanol's
alpha-carbon C-H bonds require around 88 kcal/mol of energy to cleave homolytically, while hydrazine's N-H bonds only require around 77 kcal/mol. And
then there's also the fact that alkali hydroxides are known to significantly accelerate the oxidation of hydrazines by free O2 in general.
So it could be that the excess NaOH in solution is inadvertently accelerating the oxidation of ethanol to acetaldehyde by first accelerating the
autoxidation of hydrazine to diazene. This would inevitably lead to the generation of radical hydrazine intermediates that could then react with the
nearby ethanol molecules to give the corresponding ethanol radicals, which, in turn, could then go on to react with other nearby radicals to give
acetaldehyde through radical disproportionation. (either via direct disproportionation to acetaldehyde, or through a vinyl alcohol intermediate that
then tautomerizes to acetaldehyde)
Edit: In addition to radical disproportionation, I suppose the ethanol radicals could also be oxidized by combining with the initial hydroperoxyl
radicals generated by the abstraction of hydrogen from hydrazine, forming an organic hydroperoxide that gives acetaldehyde on elimination of hydrogen
peroxide. And since the oxidation of hydrazine to diazene likely also produces hydrogen peroxide, the ethanol radicals could also react with any
hydroxyl radicals around to form a geminal diol that then gives acetaldehyde on elimination of water.
[Edited on 10-16-2016 by Darkstar]
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