teodor
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What can cause garlic-like smell ?
I have some mixture which began to stink after few days. It didn't contain any pnictogen besides N and no sulfur compounds besides sulfate.
I just dissolved pure chromium metal in H2SO4 with some small addition of HCl to remove passivation layer. Then I kept it on a water bath to
volatilise HCl. I remember it started to smell like burned matches, I think chlorates have similar smell. Then I added (NH4)2SO4 in the hot solution.
I doubt I added any alcohol, in some experiments I tried to use methanol or ethanol to precipitate crystals. For this butch I have no such record, but
not sure 100%, so still there is a small possibility.
So, NH3, SO42-, Cr, Cl-, possible methanol/ethanol. What could be formed to produce strong garlic-like smell?
Edit: dissolving of Cr produced "nascent" hydrogen which was capable to reduce lower sulphur compounds (SO32-) to S and H2S. So, I think
the result of the reaction of Cr and H2SO4 is not pure sulfate but there are some reduced sulfur compounds also (but still not S).
[Edited on 2-12-2020 by teodor]
[Edited on 2-12-2020 by teodor]
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mackolol
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Yeah, probably and the chromium could act as a catalyst.
It's not the first thread on this forum (there were quite a few) about the weird smell present when dissolving metals in sulfate solution.
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MidLifeChemist
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I thought the concept of nascent hydrogen was disproven?
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teodor
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It is like Pluto, still there but not a planet anymore.
Edit: by the way, I am interested in collecting experiments showing the difference between nascent hydrogen and bubbling H2 at the ordinary
pressure/temperature with optional catalyser.
For example, I know that H2 bubbles can reduce permanganate but unable to reduce sulfite. But sulfate reduction is so rare with other methods that I
unable to name another reducer which capable to do this except bacteria and the disproven concept.
[Edited on 3-12-2020 by teodor]
[Edited on 3-12-2020 by teodor]
[Edited on 3-12-2020 by teodor]
[Edited on 3-12-2020 by teodor]
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TriiodideFrog
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Allicin is the chemical in garlic that causes its smell. Maybe Allicin, although I doubt it.
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teodor
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I doubt there were components in the mixture to make allicin. I would search among nitrogen-sulfur compounds.
[Edited on 3-12-2020 by teodor]
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mackolol
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If it smells like garlic it doesn't have to be allicin. Even in garlic, although allicin may be main smell component, a lot of other chemicals combine
for its smell. There are so many different chemicals that smell similar, but not the same. I doubt that he smelled freshly minced garlic from his
mixture 
The same thing with esters - ethyl butyrate may smell somewhat like a pinapple ( more or less ), but will never smell exactly like the fruit, we're
talking about, I wouldn't be surprised if it's not even in the pinapple.
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Heptylene
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Could it be a phosphorus or arsenic impurity in chromium metal? Dissolving metals are a well established way to reduce organic compounds (tin/HCl,
Fe/HCl, etc.), so perhaps phosphine/arsine can form under these conditions. They are reported to have a garlic odour at low concentrations.
Even high purity metals are typically "only" 99.99 %, which leaves room for some phosphorus or arsenic, so I wouldn't be so sure of the absence of
pnictogens
I have also noticed some garlic smells when dissolving certain metals like manganese (99.9%).
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teodor
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@Heptylene: The point is that the garlic smell has appeared not during dissolving (there were no any strong smell) but after addition of (NH4)2SO4 and
storing for week or more after that. The piece of chromium was still there but no any bubbling , so I doubt it comes from the metal. It is quite
strong now.
One of idea is some sulfate-reducing bacteria which grow was boosted by ammonium sulfate. One of the most terrible smell I had was spoiled solution of
thiosulfate due to bacteria. But it was stored for much longer time.
[Edited on 3-12-2020 by teodor]
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