Why does oxidized ethanol form ethanoic acid, not other acids?

[xunxine]

What happens when alcoholic beverages are left exposed to air?
i read that they are oxidised to ethanoic acid. Strictly only ethanoic acid? Why not say, propanoic acid? Or a mixture of acids possible to be present? Is it because only ethanol is present in alcoholic drinks? If so, only ethanol then?

 

[Borek]

If there are other alcohols they can be oxidized to other acids/aldehydes, but ethanol is usually the most important component (after water), and it is present in concentration tens if not hundreds times higher than those other alcohols.

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methods

 

[chemisttree]

Ethyl alcohol contains 2 carbon atoms. Ethanoic acid contains 2 carbon atoms as well. The oxidation is straightforward. The production of propanoic acid (3 carbons here!) from ethyl alcohol would require the addition of an additional carbon atom... not as straightforward you see.

 

[pzona]

I have a somewhat related question. I know that the liver converts the ethanol into acetaldehyde dehydrogenase, and aldehydes are usually the precursors to carboxylic acids. Is there an intermediate step in the oxidation of ethanol in air, where it is first turned to ethanal (acetaldehyde) and then to ethanoic acid? I'm not claiming to have a comprehensive knowledge of organic chemistry, but I'm curious to know the mechanism behind this.

 

[Borek]

Acetaldehyde dehydrogenase is an enzyme responsible for oxidation of acetaldehyde to acetic acid, not product of ethanol metabolism.

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[pzona]

Alright, that makes sense. But from the reading I've done (given it wasn't exactly unbiased scientific research), acetaldehyde dehydrogenase is highly toxic and is produced in larger amounts when ethanol is consumed, thus the (one of many) reason drinking is harmful. However, I read your post to mean that it isn't produced as a direct result of ethanol consumption, but rather that it is present in constant amounts. I feel like I'm missing something.

 

[lisab]

Alright, that makes sense. But from the reading I've done (given it wasn't exactly unbiased scientific research), acetaldehyde dehydrogenase is highly toxic and is produced in larger amounts when ethanol is consumed, thus the (one of many) reason drinking is harmful. However, I read your post to mean that it isn't produced as a direct result of ethanol consumption, but rather that it is present in constant amounts. I feel like I'm missing something.

Perhaps you're thinking of http://en.wikipedia.org/wiki/Acetaldehyde" ?

 

[pzona]

That's what I thought at first. I checked my source (a pamphlet on responsible drinking, published by a volunteer group at Penn State) and it said that acetaldehyde dehydrogenase is produced. I'm guessing this is just a mistake made by people trying to sound scientific.

 

[Borek]

Acetaldehyde dehydrogenase is produced in cell as an answer to the ethanol presence, it doesn't sit there for ever waiting; but it is acetaldehyde it produces that is toxic.

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methods

 

[pzona]

Alright, that makes more sense. Thanks for the replies!

 

[chemisttree]

Acetaldehyde dehydrogenase is produced in cell as an answer to the ethanol presence, it doesn't sit there for ever waiting; but it is acetaldehyde it produces that is toxic.

Perhaps in a round about way this is so. Acetaldehyde dehydrogenase works on acetaldehyde, converting it to acetic acid. But of course the presence of acetaldehyde can be correlated to alcohol consumption.

Alcohol dehydrogenase converts ethanol to acetaldehyde.

 

[Borek]

Yep, my mistake

 

[xunxine]

thanks all, for the replies for the alcohol question!
thanks pzona, I'm learning something new too.