Sciencemadness Discussion Board

Does anyone have a prefered method for synthesis of acetaldehyde?

Tkuze - 29-6-2019 at 17:12

I'm familiar with several methods to synthesize acetaldehyde, but each has its downside. Can anyone offer their prefered method and some insight into the results and procedure? Thanks

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Assured Fish - 30-6-2019 at 00:21

Well, what methods have you personally tried?
I unfortunately have only tried a few ways that don't work so great, like oxidation of ethanol using hypochlorite or dichromate, or trying to dehydrogenate ethanol with copper metal in a very crude apparatus (this method needs work on my part).

I know of a method that nobody has tried yet which involves oxidation of ethanol with H2O2 and a catalytic amount of bismuth tribromide.
This might work well as the reaction proceeds at 70*C so the distillate could be directly caught in dilute ammonia.

Is that the ammonia trimer you have there? If so then it looks like you have managed to get together a reasonable amount, do you know what the discoloration is?

rockyit98 - 30-6-2019 at 01:25

acetylene hydration using HgSO4 and H2SO4
HC≡CH + H2O + HgSO4 & H2SO4 ——> [ H2C=CHOH ] ——> H3C-CH=O

unionised - 30-6-2019 at 01:40

"Does anyone have a prefered method for synthesis of acetaldehyde?"
Over the years I have synthesised a lot of acetaldehyde by enzymatic oxidation of ethanol- typically on Friday nights.
It's my favourite method but it's impractical to extract the product.

clearly_not_atara - 30-6-2019 at 08:42

It’s not really synthesizing acetaldehyde that’s hard, it’s capturing and purifying it. It has a low bp, a strong odor, and it polymerizes easily. Inconvenient, to say the least.

Tkuze - 30-6-2019 at 13:55

Thanks for the imput. The bismuth tribromide seems very interesting. For some reason that picture was accidentally included when I posted this topic. It does seem that making the timer is the most stable way, as you can store it and depolymerize it on demand.

Assured Fish - 30-6-2019 at 16:27
8th post up from the bottom, you will find the bismuth tribromide reference there.

karlos³ - 1-7-2019 at 07:07

So far, I have only used the dichromate oxidation of ethanol.
That works fine and is easy, yields are ok as well.
Works for my purpose.

But since I have some ethyl iodide, I want to try the sommelet reaction on it using hexamine too.
Found a paper on that and it seems feasible, first they form the adduct in chloroform just like it is done in the delepine reaction, and then the isolated adduct is hydrolysed with acid.
I am planning to isolate the acetaldehyde by distilling it off directly from the reaction mixture.

I must admit, that for general purposes I rather buy it, while preparing it myself is just for fun.

Tkuze - 1-7-2019 at 15:19

Assured fish: thanks so much for the link.
Karlos: would you be willing to share your notes in a private message or email? Also, I have not been able to find a commercial source of ethanal. Could you share the source?
Any other imput or procedures/notes would be very helpful to me! Thanks
Heres a picture of german lab grown bismuth from my element collection for fun!
Let me know if I can offer any advice or help for your research in exchange for your advice.

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VSEPR_VOID - 1-7-2019 at 17:57

Copper wire and acetone, its a classic

If you were to do this in a proper reaction vessel with a reflux condenser and inert atmosphere it may work

I think you can also use acidified dichromate for this as well

Tkuze - 1-7-2019 at 19:55

Thanks. Using the copper cat. Is the reaction im trying to avoid, but I may end up having to do it.

DrScrabs - 2-7-2019 at 16:36

Quote: Originally posted by rockyit98  
acetylene hydration using HgSO4 and H2SO4
HC≡CH + H2O + HgSO4 & H2SO4 ——> [ H2C=CHOH ] ——> H3C-CH=O

There can be side products like dimethyl mercury (I read somewhere I don´t remember but the possibility is enough to not do it).

I like the method using fenton´s reagent if I can get H2O2 cheap. The FeSo4 can be present in low concentrations and produces no heavy metal waste. The high acetic acid "side product" may be a downside but I neutralized it as the sodium salt, purified by recrystallisation and store it for further use. It was a fun project anyway.

The following is from my self written data book. All I write down for me is not fulltext style as I tend to shorten text, so I give no guerantee but I try to post it as accurate as I can.

Acetaldehyde - Ammonia trimer preparation [The practical methods of organic chemistry, by C. Gattermann, 135, 1909]

Bubble dry ammonia through a etheral soloution of acetaldehyde until the liquid is saturated. Filter the precipitate after an hour or more(cool on a salt ice bath). Wash the filtrate with ice cold ether.
Back to acetaldehyde:
dissolve 10g of the trimer in 10ml of water, treat it with 15 ml of cold H2So4 and 20ml of water and distill the fraction coming over at 21°C.

Paraldehyde preparation [Organinc medical chemicals, by M. Barowliff 15-16, 1921]

500g of acetaldehyde are placed in a round bottom flask with mechanical stirring and an efficient reflux condenser. 1ml of conc. HCl (d=1.18) is added. The polymerization reaction begins depending of the initial tremperature and a vigorous reaction sets in. The acetaldehyde begins to boils and begins to reflux. On slowdown 1ml of HCl is added and this procedure is repeated until no further heat is evolved. when the maximum degree of polymerization is reached the reaction mixture is neutralized with aqueous NaHCO3 soloution. To obtain pure paraldehyde, the reaction mixture is fractionally destillied with a very efficient column. Unchanged acetaldehyde passes over first, then the fraction wich consits of a mixture of acetaldehyde and paraldehyde*. The fraction distilliling at 123-125°C consists of pure paraldehyde yielding a colourless mobile liquid.
Paraldehyde melts at 10°C. Depolymerization with 0.5ml conc. H2SO4 for 50ml paraldehyde.

* paraldehyde : acetaldehyde 46.6 : 53.4% constant boiling mixture @ 42°C , unkown source

[Edited on 3-7-2019 by DrScrabs]

Tkuze - 3-7-2019 at 11:05

Thanks! I will incorporate this. I really appreciate your help. This is probably the more important part of the procedure because it allows the careful storage of the product.

Tkuze - 3-7-2019 at 18:26

I ordered ferrous sulfate heptahydrate(couldnt find anhydrous), potassium dichromate, and potassium dichromate. Does anyone know the best way to make the ferrous sulfate anhydrous without oxidizing it to pesky Fe(III) species? Or is it even neccesary since i will be using an aqueous solution of 40% H202 in ethanol in a 14/20 distillation setup?

DrScrabs - 4-7-2019 at 00:59

You answered your question on your own, use the hydrate.
Be careful as the reaction tends to runaway.

Fenton's oxidation of ethanol to ethanal part 1:

Tkuze - 5-7-2019 at 13:31

Thanks DrScrabs! This was the video I settled upon as my plan for the reaction i will carry out. Since we independently came to the same conclusion, then its a game plan. Thanks

DrScrabs - 5-7-2019 at 14:47

Great, I am really interested in your results!
Take care of the H2O2 concentration you want use. In the video he uses 20vol (6%) H2O2 if I understood it right. I used 10% but better start at 6% to get a feeling for the reaction.
If you use your 40% H2O2 you will probably have a rocket.

Tkuze - 5-7-2019 at 15:52

Wow! Thanks for the head up. I will carefully document the procedure and post here probably next week when my reagents arrive.

j_sum1 - 5-7-2019 at 17:10

Make sure you check out the sticky on acetaldehyde. Lots of good stuff in there, including some recently-posted references to H2O2 oxidation of ethanol.

Tkuze - 8-7-2019 at 11:55

I found a few exact procedures from your link wirh exactly what I need. I CAN'T thank you enough!

markx - 9-7-2019 at 03:27

Ozonation of ethyl alcohol also yields acetaldehyde....just a curious discovery I made while playing around with ozone generation process. Probably not too good of a method for generating bulk quantities, but as a sidenote it is perhaps an interesting piece of trivia.

Tkuze - 9-7-2019 at 06:51

Really? Interesting. One would think of undergrad orgo and forsure 2-butene would yield acetaldehyde. Can you elaborate on the mechanism and experimental?

Picture of ozonolysis

Tkuze - 9-7-2019 at 07:01

Ozonolysis of an oxysterol derivative in MeOH followed by NaBH4 reduction

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Interesting ozonide mechanism

Tkuze - 9-7-2019 at 10:19

Markx- thanks for the comment. I found this to be an interesting read. It might serve as a good way to make an alcoholic acetaldehyde solution, which you could add water to and store for long periods with good stability similar to 37% formaldehyde solutions.