Author Topic: Bleach + EtOH --> Acetaldehyde  (Read 1948 times)

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ning

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Bleach + EtOH --> Acetaldehyde
« on: June 16, 2004, 01:31:00 AM »
Or it's diethyl acetal, at least.

Here is an Idea, and a request for comments.

Basically, the usual problem with producing acetaldehyde is twofold. One, normal oxidizing agents tend to overoxidize the aldehyde to acetic acid, which is not what we want. This can bee partially overcome by continuous distillation of the formed aldehyde. Two, acetaldehyde has a very annoyingly low boiling point, which requires it to be stored in some other form, like paraldehyde, an ammonia adduct, etc.

My proposal attempts to solve both problems at once, with no distillation.

The idea is basically this. Into a room-temperature solution of HCl in ethanol is introduced dropwise 1/4 equivalent bleach or strong NaOCl or Ca(OCl)2 solution. The after the addition ends, the solution is stirred for 30 minutes, then diluted with cold water, and the top layer of acetaldehyde diethyl acetal removed.

When the acetaldehyde is desired, it can be hydrolyzed from this acetal form, or, more likely, used as it is.

The following reactions should occur:

Acidic bleach equilibrium tends to the right:
NaOCl + HCl <--> NaCl + HOCl, + HCl <--> H2O + Cl2

Oxidation of alcohol to aldehyde regenerates the 2 HCl
CH3CH2OH + Cl2 --> CH3CH=O + 2 HCl

The aldehyde, in the presence of HCl and excess ethanol, forms an acetal immediately, which is resistant to further oxidation.

CH3CH=O + 2 CH3CH2OH --> CH3CH(OEt)2 + 2 H2O

If need be, a drying agent can be used to remove water from the alcohol layer, but I suspect the NaCl generated by the oxidation is going to pull out the water (salting out) from the alcohol layer as is. More salt could always be added to begin with.
(1 NaCl is generated for every 3 H2O)

By adding the oxidizing agent slowly, we ensure that the formed aldehyde immediately meets more ethanol, to prevent the other two undesireable reactions from happening:

1. acid catalyzed alpha-chlorination

CH3CH=O + Cl2 --> ClCH2CH=O + HCl

2. oxidation of hemiacetal or hydrate form.

CH3CH(OH)OR + Cl2 --> CH3CH(=O)OR

By means of this careful operation, I expect high yields.

The extraction takes advantage of the fact that while we could distill the alcohol off the acetal, it shouldn't be necessary, due to the widely differing solubilities of the two compounds in water. AFAIK, acetal is not soluble in water much, like ether. That being the case, simply diluting the product should cause the acetal to separate, if it hasn't already.

This seems to be the easiest, simplest, least apparatus-intensive way to get decent yields of acetaldehyde.

A THEORETICAL EXPERIMENT

75 g commercial Ca(OCl)2 is slowly added with stirring to 150 ml 95% ethanol acidified to pH 1 with concentrated HCl. The mixture is stirred for an hour as addition progresses, and for 30 minutes after it is completed. At this point, the mixure may have separated into two layers, or not. The mixture is filtered and poured into 100 ml ice-cold water, and the water layer stripped off in a separatory funnel. The acetal may be dried over CaCl2 or left as-is.


Thoughts?


longimanus

  • Guest
Should work
« Reply #1 on: June 16, 2004, 09:11:00 AM »
I saw that reaction in my textbook when I was at high school and it was said to be one of the main characteristics of alcohols. Works for primary and secondary alcohols and the product is respectively aldehyde and ketone. The mechanism:



 There are maybe two difficulties with that reaction:
1. Preventing the Cl2 from flying off and preventing us from the chlorine.(this one`s easy)
2. At the end of the reaction the medium may become not enough acidic resulting in production of let`s say chloroform.(easily solved when controling the pH)

 Great idea! 8)  Now to concentrate on the practice.

Organikum

  • Guest
Bleach + EtOH = Ethylacetate
« Reply #2 on: June 16, 2004, 12:44:00 PM »
Yes, thats it.

Use an large excess of water anyways, HCl has to be added. There is a ref. on this in the "wanted references 1" thread, just dont have my stuff by hand sorry....

BUT: BzOH + HCl + bleach + LARGE excess of water = benzaldehyde in 98% yields.
same ref., water excess about 18-fold as far as I remember.


ning

  • Guest
Ok
« Reply #3 on: June 16, 2004, 08:04:00 PM »
first, the pH should not need control. Reason is, if you analyze above eqations, you will see that the basic NaOCl consumes 2 HCl to become Cl2, but the two HCl are regenerated when the Cl2 dehydrogenates the ethanol.

This being the case, pH buffering shouldn't be necessary.

Now, bleach + ethanol can produce several things depending on pH. The alkaline mixture can produce haloform reaction, neutral or HOCl mixture could probably result in ethyl acetate or other fully oxidized form. But as far as I know, without water, there will be not full oxidation. If the hemiacetal formed is allowed to react with HCl and EtOH before it encounters another Cl2, then the full acetal will be formed, rather than an ester or acid. This is my thought.

I hope the method can be tested. I think water is fairly important to this method, and should bee carefully controlled.


longimanus

  • Guest
pH control
« Reply #4 on: June 16, 2004, 08:56:00 PM »
What you say, ning, is true - in theory. But in practice not all of the Cl2 reacts with the ethanol (some of it just flies off), so not all of the HCl is regenerated. And that is difficulty #1 I mentioned above.

ning

  • Guest
I don't see why it would
« Reply #5 on: June 16, 2004, 10:19:00 PM »
You can dissolve a fair bit of chlorine in ethanol, I bet. And are supposed to add the hypochlorite slowly, to avoid exceeding the carrying capacity of the ethanol.

I'd not be worried about that. Unless you did some tests and it came to be a problem?

Besides, I said to acidify the solution to pH 1 or below. That's lots of extra HCl to pick up the slack.


longimanus

  • Guest
Test results
« Reply #6 on: June 17, 2004, 11:51:00 AM »
Experiment #1: 5 ml 70% alcohol were acidified with hydrochloric acid to pH=1. After that just one little drop (~0.025 ml) of 5% aqueous NaOCl was added while stirring the mixture. At the bottom of the vessel appeared several bubbles with total volume of ~0.1 ml (the volume of the produced chlorine should be ~0.4 ml). Sharp smell of chlorine was felt at the distance of 50 cm.

 The results showed that chlorine is not very soluble in such kind of medium - since there were produced ~0.017 mmols of chlorine and the overall volume of the medium was 7 ml, the carying capacity of the medium is >0.0025 mol/l.

 Of course, that doesn`t mean nothing
 
 Experiment #2: 30 ml of 40% ethanol were acidified to pH=2,5-3. One drop (0.025 ml) of the same NaOCl solution was added. No smell of chlorine. Then were added another 0.5 ml of the NaOCl solution. The intensity of the smell was the same as in the first experiment.

 So, it appears that there sould be a lot of water in the mixture. And that means that pH should be more than 1. I think that pH lower than 4 should do it.

Organikum

  • Guest
From the "wanted references 1" ...
« Reply #7 on: June 17, 2004, 01:44:00 PM »
From the "wanted references 1" thread in Novel:

Post 436354

(Rhodium: "Archive of  "Wanted References" Volume 1", Novel Discourse)


The Oxidation of Alcohols and Ethers Using Calcium Hypochlorite

https://www.thevespiary.org/rhodium/Rhodium/pdf/roh-ror2esters.pdf



Everybody interested in the topic of this thread should read this please!


Also somehow related:
Direct Conversions of Ethers to Esters by Trichloroisocyanuric Acid

https://www.thevespiary.org/rhodium/Rhodium/pdf/ethers2esters.trichloroisocyanuric.pdf




ORG


naoh3000

  • Guest
KMnO4 as a substitute for bleach
« Reply #8 on: June 18, 2004, 11:07:00 PM »
I was wondering if anyone could tell me if potassium permangate could be substituted for the sodium hypochlorite in this reaction for acetaldehyde. I have seen some synths for other compounds where the two were interchangable. If anyone has tried this please give an opinion. Thanxs


Organikum

  • Guest
You dont get acetaldehyde from bleach and...
« Reply #9 on: June 19, 2004, 04:01:00 PM »
You dont get acetaldehyde from bleach and ethylalcohol and you dont get it from KMnO4 and EtOH either.

There is an article called:
"Reactions of Ethylalcohol" posted by Rhodium I believe somewhere.

UTFSE for it.


naoh3000

  • Guest
sorry.... not acetaldehyde but nings diethyl aceta
« Reply #10 on: June 19, 2004, 07:05:00 PM »
i couldnt find your previously mentioned article on tfse. But according to nings reaction i dont see why it would be possible with NaOCl and not potassium permanganate to make diethyl acetal which as he said could be hydrolyzed into acetaldehyde.


Nicodem

  • Guest
Acetals hydrolyse very fast in the given ...
« Reply #11 on: June 20, 2004, 10:34:00 AM »
Acetals hydrolyse very fast in the given conditions: aqueous strong acid. I see no possibilities of any acetal formation here.
The way to make acetals is to continously remove water: a common method is to use a catalytic amount of acid that also bind water (HCl gas, TsOH...) or a mild Lewis acid that also binds water (anhydrous CuSO4). Besides acetals don't give much protection against alpha chlorination. Even if the oxidation would not go toward the acetic acid there would still remain the problem of alpha chlorination of acetaldehide (or its acetal).


Organikum

  • Guest
?????
« Reply #12 on: June 20, 2004, 04:32:00 PM »

i couldnt find your previously mentioned article on tfse



What about clicking on the link to the pdf on Rhodiums page in my post before?