DrDevice
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Niacin Chlorochromate (NCC??) for oxidation of alcohols
I was pondering the structure of niacin (nicotinic acid or pyridine-3-carboxylic acid) and recalled that it is the nitrogen in the pyridine ring that
performs the actual oxidation. Would niacin perform the same way? It is easier to obtain than pyridine in many areas, and I recall some posts here in
SM where people talk about decomposing niacin to obtain pyridine for the purpose of PCC.
And niacin is, after all, in conjunction with the NAD enzyme, responsible for oxidation of ethanol in the human body.
I prepared the compound in question using the same molar amounts as is used in the Corey / Suggs PCC paper, but 1/10 quantity to start with:
Dissolve 0.1M (10g) CrO3, in 19ml 6M HCl, with magnetic stirring.
After 5 minutes, cool solution to 0C and slowly add 0.1M niacin = 12.31g.
The first thing I noticed was that the reaction is no where near as violent as the addition of pyridine to a CrO3 / HCl solution. It
dissolves easily, but without the drama of the pyridine reaction.
Subsequent times I tried this, I didn't cool the reaction mixture. I added the entire niacin powder pretty much in one go.
There is no immediate precipitate as is the case with pyridine.
I continued stirring at room temperature overnight. Other attempts I made included heating to 50C and stirring for 2 hours. I haven't found other
approaches yet that make much difference to the yield.
There is a period about half an hour after the start of stirring where the solution goes cloudy. I haven't looked further at this, but this may be
crystalization. However, I kept stirring, and then refrigerated the dark red solution.
After being in the fridge for a day, a mass of dark red-brown crystal had formed. A second batch I made refused to crystalize until I used a small
seed crystal from my first batch. The crystals formed are quite large and prismatic.
These crystals are filtered and dried in air, then ground to a fine powder. The product is soluble in water, very sparingly soluble in acetone,
insoluble in DCM, that's all I tried.
My yields are about 60 - 70% each time.
I don't think my product is very pure - on grinding the crystals, the resulting powder has yellow and dark brown bits.
Anyway, I tried this with butan-1-ol, again using the same ratios as the PCC paper ie a 1.5:1 ratio of NCC to butanol.
The NCC is suspended in stirred DCM, and butanol added. Immediately the solution darkens and deposits a brown gummy substance (not black as is the
case with PCC). I continued stirring for 2 hours, after which I decanted the liquid & washed the solid 3 times with a little ether. The combined
solvents were evaporated, leaving a dark, oily, odd smelling liquid. A small amount of decolourizing carbon then filtering left a very faintly
green/brown liquid.
This liquid gave a negative result to cerium ammonium nitrate reagent (ie indicating no alcohol remained), and it provided a very pleasing silver
mirror with Tollen's reagent. It was indeed an aldehyde. I didn't have enough product to doing a boiling point test.
I tried this also with propan-2-ol, but I don't think I left it stirring long enough - there was still a faint CAN reaction at the end, but there was
a distinct acetone smell.
Clean up was quite easy compared to PCC. The brown residue loosened fairly easily, and dissolved fairly readily in 6M HCl.
So, I have spent a bit of time looking for this compound in the literature, but haven't found anything? Is my "NCC" a known oxidizer of alcohols?
I haven't explored the range of alcohols, or indeed any other reactions that might occur - I don't have the skills, materials or equipment. I have no
idea what impact that carboxylic acid group would have in competing reactions...
Comments? Suggestions for other tests?
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Praxichys
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Did you calculate the aldehyde yield? I'd be concerned about losing yield to esters of the niacin forming with the alcohols. Also, the acidic nature
of the free niacin (albeit weak) could free a small equilibrium of chromic acid/chlorochromic from the PCC-COOH which would lead to some
over-oxidation of the aldehyde to carboxylic acid.
An easier way to do this (without pyridine at all) is to use alkali salts of chlorochomic acid. In many cases, sodium chlorochromate or potassium
chlorochromate works just as well as PCC.
[Edited on 18-1-2016 by Praxichys]
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DrDevice
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I didn't produce enough of the aldehyde to get a quantitative measurement - next time...
Thanks for the suggestion regarding potassium chlorochromate. I'm looking through a few references now eg the one by Woelen:
http://woelen.homescience.net/science/chem/exps/KCrO3Cl/inde...
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Dr.Bob
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Quote: Originally posted by DrDevice  | | I was pondering the structure of niacin (nicotinic acid or pyridine-3-carboxylic acid) and recalled that it is the nitrogen in the pyridine ring that
performs the actual oxidation. Would niacin perform the same way? It is easier to obtain than pyridine in many areas, and I recall some posts here in
SM where people talk about decomposing niacin to obtain pyridine for the purpose of PCC. And niacin is, after all, in conjunction with the NAD
enzyme, responsible for oxidation of ethanol in the human body. |
The pyridine does not do any of the oxidation in the PCC reaction, it complexes with the chromium complexes to both keep it easier to handle and
moderate their reactivity. I don't see any reason why the niacin could not work in place of pyridine, but not because it is involved in in-vivo
oxidations.
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Nicodem
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Thanks for sharing your experiment.
| Quote: Originally posted by DrDevice | | So, I have spent a bit of time looking for this compound in the literature, but haven't found anything? Is my "NCC" a known oxidizer of alcohols?
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3-Carboxypyridinium chlorochromate is a known compound and its use as the oxidant for various functional groups was published in several articles by
same Iranian authors. The preparation and its use for oxidative cleavage of oximes and hydrazones is described in DOI10.1080/00397919608003856. Two
articles on alcohols oxidations were also published, but they report the use of the reagent under useless conditions instead of doing a proper study.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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DJF90
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Attached are two papers detailing inorganic chlorochromates. There are more in the literature but this ought to get someone started.
Attachment: Oxidation with magnesium chlorochromate.pdf (408kB)
This file has been downloaded 429 times
Attachment: Oxidation of alcohols with potassium chlorochromate.pdf (639kB)
This file has been downloaded 419 times
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DrDevice
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OK, so my searches missed all this 
I guess it is a matter of experience in knowing where to look & what search terms to use....
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DrMethyl
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This is a known reagent used as a less rective alternative to PCC, its called 3CPCC. Try to look under this name to find the preparative steps.
Edit : Sorry, I didn't see the answer of nicodem
[Edited on 28-1-2016 by DrMethyl]
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