Sciencemadness Discussion Board

Benzyl alcohol oxidation with iron trinitrate --> benzaldehyde

organometallic - 8-3-2008 at 09:02

During the course of the reaction from benzyl alcohol to benzaldehyde, the substrate loses 2 hydrogen atoms. Where do they go? I don't think they are released as H2 gas because no bubbling is seen in the microwave.

It is observed that a sludgy orange-red precipitate forms. Is this somehow iron oxide?

Also, upon microwaving the rxn mixture, allowing it to cool, and adding bisulphite, how would i then separate the adduct from the benzyl alcohol? Any thoughts?

H2 + Fe(NO3)3 --> ??

Ref is :

[Edited on 8-3-2008 by organometallic]

Attachment: DisplayHTMLArticleforfree.htm (50kB)
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not_important - 8-3-2008 at 09:27

You've got ferric nitrate in there, it's an oxidation, and likely a messy one with no simple equation. The hydrogens don't just pop off the substrate, they're getting removed by reaction with the oxidiser, and end up as water or Fe(OH)3.

And ferric nitrate is Fe(NO3)3, in this case Fe(NO3)3.9H2O

Klute - 8-3-2008 at 14:46

Have you tried out this reaction yourself? I'd been very interested as how it worked out as I did simialr work with various oxydants a few months ago. I remember people mentionnning Fe(NO3)3.xH2O a few times, but as I neevr found a tangible ref, I neevr tried it out.

The fe III would be reduced to Fe II, wich could be reoxydized back to Fe III by atmospheric O2. Couldn't HNO3 be produced, aswell as H2O?
It's true Fe(OH)3 precipitaes at a very acidic pH (for a hydroxyde), so that's surely your red/brown precipitate.

EDIT: Am I the only one that can't read the attached paper correectly? I see it in HTML code or somehting similar...

[Edited on 8-3-2008 by Klute]

smuv - 8-3-2008 at 15:06

You can just save what you download and add .html to the end of the file and then open it with your favorite web browser. The quality is bad though as there are no pictures. I have attached a pdf of the article.

[Edited on 8-3-2008 by smuv]

Attachment: Benzyl_alcohol_oxidation_FeIII.pdf (395kB)
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Klute - 8-3-2008 at 15:08

Thanks a million. I'm not much of a computer guy! :)

evil_lurker - 8-3-2008 at 18:57

Very interesting indeed.

Heck they are getting 40% yields just by letting it sit for 6 hours at 50ºC.

I'd like to do a 100ml batch in a PTFE bottle myself just to see how it'd turn out.

not_important - 9-3-2008 at 06:09

Quote:
Originally posted by Klute
...
The fe III would be reduced to Fe II, wich could be reoxydized back to Fe III by atmospheric O2. Couldn't HNO3 be produced, aswell as H2O?
It's true Fe(OH)3 precipitaes at a very acidic pH (for a hydroxyde), so that's surely your red/brown precipitate.
...


Fe(II) is not stable around NO3(-) if in an acid environment, or if warm; it gets oxidised to Fe(III) and the nitrate reduced to NO and NO2.

So the reaction should be producing Fe(III) as the hydroxided or hydrated oxide, water, and NOx. The NOx could react with O2 and water to make HNO3, but if that reaches any concentration it will react with the ferric (hyd)oxide to give Fe(NO3)3.

It's possible this could give a semi-catalytic process where Fe(NO3)3 is use to oxidise alcohol to aldehyde using atmospheric oxygen, but I'll bet that it is not very effective, that there is enough loss of NOx to require an appreciable if sub-stoichiometric amount of ferric nitrate.

Klute - 9-3-2008 at 08:52

Of course, how stupid of me... Thanks for clarifying.

So is Fe(NO3)2 stable? Obviously it can't be made by adding Fe turnings to dilute HNO3... maybe by some kind of metathesis (sp?)? Just curious.

not_important - 9-3-2008 at 22:47

Quote:
Originally posted by Klute
So is Fe(NO3)2 stable? Obviously it can't be made by adding Fe turnings to dilute HNO3... maybe by some kind of metathesis (sp?)? Just curious.


Stable if cool, if in weakly to moderately acid solution less stable at lower temperatures than the pure salt.

Made by FeSO4 + Pb(NO3)2, FeCl2 + AgNO3, or by dissolving iron in cold dilute nitric acid keeping an excess of iron. Crystallised by slow evaporation without any heating, reduced pressure to speed it up.

organometallic - 10-3-2008 at 10:01

Klute: Yeah, i've tied the reaction myself, but got lowwwwww yeilds, although I was unable to locate any azeotrope data about benzyl alcohol and benzaldehyde for the separation (by distillation.) So i'm unsure how pure my product was. Next run, i'm going to use 10ml benzyl alcohol, and add quite a bit of iron nitrate (3g.) This will more than saturate the solution. Afterwards, I will separate the aldehyde with bisulphite. PS I believe my low yeilds were due to either: not enough microwaving, or:

One strange thing, the paper seems to say that the pre-reaction fluid was simply Fe(NO3)3.9H20 saturated benzyl alcohol, however i doubt that a saturated solution would contain enough ferric nitrate to react fully..(just a hunch, and as i lack the stochiometry i was unable to calculate it hence this thread.)

Anyway, on a previous run i distilled the reaction fluid without filtering first, and i noted a small evolution of NO2, the smell of which was disguised most worryingly by the almond scent.

Anyway, how would i separate a bisulphite adduct from benzyl alcohol solution? Filtration, then washing with what? Acetone?

Thanks for the thoughts guys, i do appreciate it. Pics on my next run!!
OM

[Edited on 10-3-2008 by organometallic]

smuv - 10-3-2008 at 10:52

@ Organometallic, I have not been able to find any benzaldehyde, benzyl alcohol azeotrope. I would expect that during the distillation benzaldehyde would be oxidized by any remaining Fe(III) to benzoic acid.

For the bisulphite...

'The distillate [benzaldehyde] is mixed with a concentrated solution of sodium bisulphite until after prolonged shaking the greater part of the oil has gone into solution. The additive compound of benzaldehyde with sodium bisulphite is formed; should crystals separate out, water is added until they are again dissolved. The solution is then separated from any oil remaining undissolved, and treated with solid sodium carbonate until it shows a strongly alkaline reaction [I assume this means benzaldehyde will separate out as an oil]. '

Pracitcal Organic Chemistry, by Sudborough & James

Klute - 10-3-2008 at 11:12

You can rinse the adduct with a minimum amount of cold EtOH, cleans it very well but can dissolve some if too much is used, then with ether or pet ether to hasten drying. Don't sue acetone! It will react with excess bisulfite....

Have a look at the thread I started on various benzyl alcohol oxidations for the workup I used. With a good column, seperation of BnOH and BnO isn't problematic at all, just go slowly.

The best results I obtained were with calcium hypochlorite/DCM, and TCCA/SiO2/DCM for unsubstitued benzyl alcohol, a strange product was obtained with subs. benzyl alcohols (surely the chloride).

Here is the thread:
Benzylic alcohols oxidation with various oxidants

Good luck!

[Edited on 10-3-2008 by Klute]