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blogfast25
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Quote: Originally posted by nlegaux  | Could this problem possibly be fixed by introducing an immiscible organic phase to dissolve the ethanol/ethanal?
nlegaux |
Almost impossible: ethanol/ethanol are far too soluble in water. The partitioning coefficient will work against you.
Maybe try a higher alcohol, like 1-hexanol? Not sure about 1-hexanal's solubility in water, though...
[Edited on 25-2-2016 by blogfast25]
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PHILOU Zrealone
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Also to worry in the acidic environment...acetal formation.
CH3-CH=O + 2 CH3-CH2-OH -H(+)-> CH3-CH(-O-CH2-CH3)2 + H2O
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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clearly_not_atara
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Can you verify the oxidation by making acetone from isopropanol? Assuming that's not too much wotk; there is the iodoform test for acetone but most
peole recognize even a tiny whiff of the smell.
My first guess is that you need to run the reaction hotter so that acetaldehyde boils away as it's formed. IIRC the activation energy for aldehyde
oxidation is lower than for alcohol oxidation so it's impossible to prevent unless the conditions disallow it (DMSO mediated or Oppenauer), which is
why the Tischenko reaction is favorable. Acetaldehyde's boiling point is 23 C but it will remain in solution well above that if it likes the solvent
(and it likes water and it definitely likes water that contains ammonia).
I also thought about trying to make acetaldehyde form a complex with something as it's formed, but most such reagents (eg hydroxylamine) are labile
under the conditions of reaction. N-acetylglycine might work by forming the adduct 2-methyl-3-acetyl-5-(2H)-oxazolidinone. I know this works with
formaldehyde but I don't know about higher aldehydes.
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blogfast25
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Higher temperature also favours aldehyde oxidation rate.
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nlegaux
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I would try a higher primary alcohol, but I do not own any 
Forming a complex of the acetaldehyde as it's created isn't a bad idea. Do you have any ideas for complexing agents besides N-acetylglycine?
On most preparations of ethanal I have been able to find online, H₂CrO₄ is used as the oxidant (see http://www.prepchem.com/synthesis-of-acetaldehyde/). Is there a possibility that this oxidant can be regenerated electrochemically?
nlegaux
[Edited on 2-26-2016 by nlegaux]
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blogfast25
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@nleqaux:
As a first port of call, look at the Standard Reduction Potentials of Mn(+2)/Mn(+3) and compare to Cr(+3)/Cr(+6). Or look at the Pourbaix diagrams
that J_sum1 linked too in the recent Ni/Cr separation thread?
https://www.materialsproject.org/
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clearly_not_atara
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| Quote: Originally posted by nlegaux | I would try a higher primary alcohol, but I do not own any
Forming a complex of the acetaldehyde as it's created isn't a bad idea. Do you have any ideas for complexing agents besides N-acetylglycine?
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http://chemistry.mdma.ch/hiveboard/rhodium/pdf/n-cbz-aminoac...
The complexing agents I know for aldehydes are: 1,2-diols, 1,3-thiols, hydroxylamine, monoacyl hydrazines, N-heterocyclic carbenes, bisulfite,
cyanide, resorcinol and N-acyl amino acids. All of these except for resorcinol and N-acyl amino acids will be oxidized by the reaction conditions,
methinks (I could certainly be wrong), and resorcinol's adducts can't be so easily broken: it makes a polymer.
N-formylation of amino acids is particularly easy to achieve thanks to the ease and versatility of the formic acid/toluene system. I don't think that
works with other carboxylic acids. Hippuric acid also works and can be synthesized by ingesting sodium benzoate (but seriously don't do that).
[Edited on 26-2-2016 by clearly_not_atara]
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nlegaux
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Recently I have been synthesizing methanoic acid for trying my hand at the eschweiler-clarke and leukart reactions. Dissatisfied with the classical
method (glycerol and oxalic acid) I attempted using this electrochemical cell to oxidize methanol. Preliminary it seems that I have generated methyl
methanoate, and I will be posting a proper product characterization (b.p, density, etc...) in the next few days.
Assuming I can get this reaction to work properly, would it be possible to prune this thread and post a cleaned-up procedure (perhaps something along
the lines of "Mn(III) Mediated Electrochemical Oxidation of Primary Alcohols to Esters")?
Thank you,
nlegaux
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nlegaux
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The density of the crude product was found to be about 0.9078g/ml. This indicates that the product, assuming it contains methyl methanoate, is
probably contaminated with a fair amount of methanol. Next I will attempt to hydrolyze it using ammonia and measure the melting point of any solid
isolated.
nlegaux
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blogfast25
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| Quote: Originally posted by nlegaux | Next I will attempt to hydrolyze it using ammonia and measure the melting point of any solid isolated.
nlegaux |
Even strong ammonia is too weak an alkali to de-esterify most esters at an appreciable rate, I think.
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