Sciencemadness Discussion Board - Manganese Mediated Electrochemical Oxidation of Ethanol

Manganese Mediated Electrochemical Oxidation of Ethanol

nlegaux - 17-2-2016 at 08:27

1. Procedure

The electrolyte is prepared by dissolving 64g MnSO₄*H₂O, 30g (NH₄)₂SO₄, and 193ml 17.5M H₂SO₄(aq) in 100ml H₂O. This electrolyte is loaded into a three necked flask which is attached to a distillation rig. The remaining 2 joints are used for attaching two lead electrodes, each with a surface area of approximately 1400mm². Next, 19V @ 4.7A is run through the electrodes and the reactor is run for 30min to ensure that all components function properly. During this time, a purple color is observed in the electrolyte. Following this, 100ml 12.0M ethanol is than added to the reactor. The reactor is run at 60*C until no more distillate condenses in the receiver. Note that these steps may be repeated as many times as desired due to the electrochemical regeneration off the oxidizing agent.

An image of the purple color observed.

An image of the apparatus. On the left is a PID used to maintain the temperature at 60*C.

2. Notes

This procedure can be greatly improved by utilizing a more efficient method of stirring. A magnetic stir bar was used in this procedure, but it quickly became useless due to the formation of a white precipitate in the bottom of the flask. A similar procedure was attempted utilizing Cerium instead of Manganese, but this reaction failed because the ethanol was over oxidized to ethanoic acid.

3. Discussion

4. References

1.Sciencemadness Forum Thread (http://www.sciencemadness.org/talk/viewthread.php?tid=6882)
2.US Patent 80895 (http://www.google.com/patents/US808095.)

[Edited on 2-19-2016 by nlegaux]

Metacelsus - 17-2-2016 at 08:58

What was the (approximate) surface area of the electrodes you used? (Also, your image links don't seem to be working.)

I would appreciate more characterization of your acetaldehyde fraction (b.p. and density). The odor of acetaldehyde is by itself not a very good indicator of purity.

Besides toluene and ethanol, I wonder if these oxidation conditions can be used on other substrates.

Having personally done this with toluene, I can agree that a strong stirring mechanism is necessary. A quite large magnetic stir bar was sufficient for me, but mechanical stirring is likely the best option.

blogfast25 - 17-2-2016 at 09:36

This doesn't belong in prepublication, IMHO.

Texium - 17-2-2016 at 13:23

Quote: Originally posted by blogfast25

This doesn't belong in prepublication, IMHO.

Comments like this don't belong in prepublication, IMHO.

It's called prepublication because it is not yet published though the intention is for it to be eventually. If you don't think it's at that level yet, why not offer some advice or constructive criticism? Or if you don't have anything to add to it, just don't say anything...

I think that it's an interesting and potentially quite useful procedure. The write-up could use some better formatting and more details in general. Also, it is necessary to undertake better characterization of the product (at least a BP), and possibly a workup procedure to purify it since it is discolored and likely also contains some unreacted ethanol.

blogfast25 - 17-2-2016 at 14:42

Quote: Originally posted by zts16

I think that it's an interesting and potentially quite useful procedure. The write-up could use some better formatting and more details in general. Also, it is necessary to undertake better characterization of the product (at least a BP), and possibly a workup procedure to purify it since it is discolored and likely also contains some unreacted ethanol.

So do I. But it adds very little to the procedure already described in the first link, which is where I do honestly believe this work would be an interesting addition. Furthermore only one in three links work and there's no product characterisation whatsoever.

So I stand by what I wrote: interesting work by all means but no need to go into prepublication.

[Edited on 17-2-2016 by blogfast25]

gsd - 17-2-2016 at 15:47

Quote: Originally posted by blogfast25

Furthermore only one in three links work....

Link No 1 & 3 worked for me.
As far as 2nd link is concerned, knowing the US patent number is enough.

For uninitiated the patent is attached.

gsd

Attachment: US808095.pdf (322kB)
This file has been downloaded 521 times

nlegaux - 17-2-2016 at 15:54

I should be able to begin work on further characterizing the product tomorrow. As far as organization goes, what is suggested? I haven't seen any clear outline of what should be done.

Thank you,
nlegaux

gsd - 17-2-2016 at 16:25

@nlegaux

AFAIK there are no clear cut written guidelines for Pre-pub, nor is the format specified.

However I would suggest that you take a look at posts made in that section. All well written posts follow a certain format and syntax which makes them extremely readable.

I would especially recommend any post made there by magpie as a template to follow.

You are working on a very interesting project and it would be very nice to see it is presented in structured and organised way.

gsd

[Edited on 18-2-2016 by gsd]

UC235 - 17-2-2016 at 16:46

This is a cool project given the obnoxiousness of preparing acetaldehyde by other means (jones oxidation for example). I think you need to fractionate the distillate to remove any ethanol that co-distilled and then give us a weight of pure acetaldehyde obtained.

blogfast25 - 17-2-2016 at 16:53

@nlegaux:

Assuming you have these photos on your HD you can upload them to SM and show them directly in your post. In Preview Post mode, choose the file from your HD, then click Preview Post again. The file will appear at the bottom as 'file ####', cut and paste this into the body of your post, where you want the picture to appear. No need for imgur.

nlegaux - 17-2-2016 at 17:07

Thank you for the advice blogfast! I updated the procedure with embedded photos. I will take a closer look at the formatting of some of the other posts in prepublication and update this one ASAP.

I went ahead and began a workup. I recorded the boiling point at 23.4*C (lit. 20.2*C), but the amount of product that distilled is too small for me to accurately obtain a density for. I will probably rerun this procedure this weekend. I believe adding the ethanol dropwise rather than in batches may increase yields by giving the oxidant more time to regenerate (now just to find a way to add an addition funnel and still have the apparatus fit into my small fumehood

).

nlegaux

blogfast25 - 17-2-2016 at 17:13

@nlegaux:

Much better already.

Do you have any idea what the white precipitate is? Lead sulphate seems like a reasonable guess, in which case a different electrode material may be worth considering. I see nothing in the Patent that explains lead is mandatory...

nlegaux - 17-2-2016 at 17:37

I'm not sure, but when I rerun it this weekend I will collect some and attempt some characterization. If it does turn out to be a lead salt, I will investigate alternative electrode materials.

nlegaux

blogfast25 - 18-2-2016 at 08:33

I think the ability of Mn(+3) to oxidise alcohols to aldehydes (but not to carboxylic acids):

R-CH₂-OH + 2H₂O ===> R-CHO + 2 H₃O+ + 2 e

2 x [Mn3+ + e ===> Mn2+]

... might also be used without any electrolysis.

In this rather long thread, woelen, me and Xenoid established that Mn(+3) can also be prepared via another method:

http://www.sciencemadness.org/talk/viewthread.php?tid=11309&...

MnO₂ is reacted with 98 % H₂SO₄ to form a green and insoluble mangani - sulfato complex. On dilution with water the complex dissolves and forms a solution of Mn₂(SO₄)₃. Excess acid used in the first step stabilises it.

Adding the equivalent amount of alcohol should then result in its oxidation to aldehyde and would be distilled off.

The manganous sulphate could be recovered by precipitation as Mn(OH)₂ and re-oxidised by air to MnO₂.

blogfast25 - 19-2-2016 at 08:55

Another quite interesting possibility was explored by ChemPlayer: the oxidation of benzyl alcohol with 'fresh' MnO₂ in DCM solvent:

https://www.youtube.com/watch?v=HrZAMlj0kPM

Starts at about 4:31 (first part is preparation of MnO₂).

Presumed reactions:

Ph-CH₂-OH ===> Ph-CHO + 2 H+ + 2 e

2 MnO₂ + 2 H+ + 2 e ===> Mn₂O₃ + H₂O

I wonder if such a reaction would work for EtOH, perhaps even w/o DCM and with bit of conc. H₂SO₄ thrown in as presumed catalyst.

[Edited on 19-2-2016 by blogfast25]

nlegaux - 19-2-2016 at 09:07

That is quite interesting. I once attempted using MnO₂ to oxidize 4-aminophenol (from hydrolyzed Pararcetamol) to benzoquinone (similarly to the prepchem procedure found here http://www.prepchem.com/synthesis-of-p-benzoquinone/). Instead of benzoquinone, however, all I got was a terrible sticky black residue to clean out of my flask.

I did a bit of work with the cell yesterday, and in the process I corroded one of my electrodes to a point that it is no longer useful. I think I will make a few more lead electrodes for experimentation in the immediate future, but I will definitely need to investigate more corrosion-resistant electrode materials (perhaps platinated titanium?).

Also, would it be more appropriate to move this thread to organic chemistry or technochemistry until I have created a finalized procedure?

nlegaux

[Edited on 2-19-2016 by nlegaux]

Magpie - 19-2-2016 at 09:23

Quote: Originally posted by nlegaux

Also, would it be more appropriate to move this thread to organic chemistry or technochemistry until I have created a finalized procedure?

I think that is a good idea until you can verify your target product and quantify a yield.

blogfast25 - 19-2-2016 at 09:31

Quote: Originally posted by nlegaux

I did a bit of work with the cell yesterday, and in the process I corroded one of my electrodes to a point that it is no longer useful. I think I will make a few more lead electrodes for experimentation in the immediate future, but I will definitely need to investigate more corrosion-resistant electrode materials (perhaps platinated titanium?).

Also, would it be more appropriate to move this thread to organic chemistry or technochemistry until I have created a finalized procedure?

You're probably anode oxidising lead to lead sulphate. Not a big problem but better avoided nonetheless.

PtTi sounds expensive and may not even be that effective, unless the coating is very good. Ti is corroded easily to purple/blue Ti3+ (a strong reducing agent) by warm dilute H₂SO₄.

Why not consider good old graphite, for anode?

Re. your last point, that's a moderator's responsibility (contact Bert or zts16 or Nicodem) but I'd favour splicing this thread onto the first link in your post. It would revive an old but interesting thread, until your method's teething problems have been sorted out.

[Edited on 19-2-2016 by blogfast25]

gsd - 19-2-2016 at 09:58

Quote: Originally posted by blogfast25

The manganous sulphate could be recovered by precipitation as Mn(OH)2 and re-oxidised by air to MnO2.

Mn(OH)2 to MnO2 by air oxidation sounds interesting!

Could you please site a reference or an experimental procedure showing how to do it?

gsd

blogfast25 - 19-2-2016 at 11:36

Quote: Originally posted by gsd

Quote: Originally posted by blogfast25

The manganous sulphate could be recovered by precipitation as Mn(OH)2 and re-oxidised by air to MnO2.

Mn(OH)2 to MnO2 by air oxidation sounds interesting!

Could you please site a reference or an experimental procedure showing how to do it?

gsd

Simply dry the Mn(OH)₂ slurry (moist filter cake), preferably with some alkali in it, on a hot plate: it oxidises to MnO₂ almost as quickly as Fe(OH)₂ to Fe₂O₃.

Keep stirring and turning until it's all brown/black, wash out the (optional) alkali and dry and semi-calcine.

Of course it's almost instantaneous if you use bleach (hypochlorite).
<hr>
And then there's this, from a google book:

It's the reference to:

MnO₂ + Mn2+ + 4 H+ <===> 2 Mn3+ + 2 H₂O

... claimed to be fast from left to right that I find interesting.

[Edited on 20-2-2016 by blogfast25]

Texium - 19-2-2016 at 17:18

I moved the thread to Organic Chemistry since it was requested by the OP.

PHILOU Zrealone - 23-2-2016 at 11:46

For the characterization of acetaldehyde...
-acetaldehyde imine trimer (2,4,6-trimethyl-1,3,5-perhydrotriazine) should be cristaline
-acetaldehyde cyclic trimer (paraldehyde)
-acetaldehyde cyclic tetramer (metaldehyde)

And here pertinent pages 44,45 and 67 from
"Spectral & Chemical Characterization of Organic Compounds - by W.J.Criddle and G.P.Ellis - A Laboratory Handbook - 3rd edition - WILEY"

Making of the following derivatives
1°) 2,4-dinitrophenylhydrazone
2°) Semicarbazone
3°) Oxime
4°) 4-nitrophenylhydrazone and phenylhydrazone
5°) Dimethone

nlegaux - 24-2-2016 at 15:37

My graphite electrodes finally came in the mail. They seem to be working quite well; after running for a few hours I see little corrosion. On this run of the cell rather than maintaining the cell at 70*C using heating, I have placed it into a bowl of water and it maintains its own temperature at around 50*C.

However, I have found an issue. I have not been able to collect any distillate on this run of the cell. As a test, I removed a small amount of electrolyte and added it to a test tube. It is a brown/black clear color (see photos below) with a small immiscible layer on top. I than took about 1ml of the collected electrolyte and added about 1ml of Fehling's solution. After heating, the test was negative (which is to be expected because of the lack of distillate). Next, I added a small amount of ethanol and repeated the test. It indicated again that no aldehydes were present.

The collected electrolyte. My apologies about the poor photo quality, I couldn't get my phone camera to focus on the test tube. The immiscible layer is too small to be clearly visible in this photo.

Because of this information, I believe I may know what is going on. I think the ethanol is being over-oxidized to ethanoic acid which is forming an ester in the highly acidic environment with the unreacted ethanol forming ethyl acetate (hence the immiscible layer). This ethyl acetate would not boil off at the apparatus's operating temperature of 50*C, causing it to remain in the reactor and possibly consume the oxidant (that last part is purely a guess. I have not been able to find any references to oxidizing ethyl acetate to carbon dioxide and water, but it certainly seems plausible. Also, this would fall in line with the test indicating that the electrolyte was unable to oxidize the ethanol). I will attempt to distill this immiscible liquid off in order to better characterize it. In previous runs of the cell, I was probably distilling mostly ethyl acetate with a small amount of acetaldehyde dissolved into it, which would fall in line with my observations on the original product work up (a small amount of material boiling at 23.4*C with the majority of the liquid left in the boiling flask). In the mean time, are there any ideas on how to remedy this issue, assuming it is ethyl acetate formation?

nlegaux

blogfast25 - 24-2-2016 at 16:07

@nlegaux:

Ouch.

I'm now beginning to think the method may only be suitable for certain aldehydes, like benzaldehyde. The latter is of course poorly soluble in water, while ethanal is totally miscible with it. That makes the further oxidation of the latter to ethanoic acid much easier. The Mn(+3)/Mn(2+) system is a very strong oxidiser.

The formation of the ester is of course plausible, considering the high concentration of H₂SO₄ in the mix.

The formation of EtOAc may even promote the further oxidation of ethanal to ethanoic acid by Le Chatelier.

[Edited on 25-2-2016 by blogfast25]

nlegaux - 24-2-2016 at 16:52

Could this problem possibly be fixed by introducing an immiscible organic phase to dissolve the ethanol/ethanal?

The distillate is coming over at approximately 70*C (lit for ethyl acetate is 77.1*C, but the barometric pressure here today is about 750mmHg). It is a slight yellow color and immiscible with water. Its odor is the same as that of a known sample of ethyl acetate I have on hand. I found the density to be 0.954g/ml, which is similar to the reported value for a ternary azeotrope of ethyl acetate, ethanol, and water (lit. 0.901g/ml).

Worst case scenario I may be able to make an ethyl acetate producing cell :cool:

nlegaux

[Edited on 2-25-2016 by nlegaux]

blogfast25 - 24-2-2016 at 17:16

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]

PHILOU Zrealone - 25-2-2016 at 10:53

Also to worry in the acidic environment...acetal formation.
CH3-CH=O + 2 CH3-CH2-OH -H(+)-> CH3-CH(-O-CH2-CH3)2 + H2O

clearly_not_atara - 25-2-2016 at 12:50

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.

blogfast25 - 25-2-2016 at 12:54

Quote: Originally posted by clearly_not_atara

My first guess is that you need to run the reaction hotter so that acetaldehyde boils away as it's formed.

Higher temperature also favours aldehyde oxidation rate.

nlegaux - 25-2-2016 at 17:58

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]

blogfast25 - 25-2-2016 at 18:50

@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/

clearly_not_atara - 26-2-2016 at 01:39

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?

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]

nlegaux - 5-4-2016 at 17:42

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

nlegaux - 8-4-2016 at 15:11

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

blogfast25 - 8-4-2016 at 16:41

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.