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Further oxidation of ethanol

Hey everyone!

So, ethanol is oxidized twice after dichromate ion solution is introduced

CH₃CH₂OH + [O] --> CH₃COH + H₂O

and after that

CH₃COH + [O] --> CH₃COOH

So, the question is, how would I stop (or limit) the oxidation process after the first oxidation?
Is the temperature crucial? (As far as I know, you need to cool it down to 20ºC, am I right?)

Thank you everyone!

Reply 1

illusionz

Original post by ioffer007

In practice, you can't very easily. But I think A level specs teach differently... Not sure what they say though.

Reply 2

EierVonSatan

The boiling point of the aldehyde is lower than the carboxylic acid, so it's possible to distil out the aldehyde before further oxidation occurs.

Reply 3

Mario_leufft

AQA book, Unit 2, Chapter 16 discusses this topic

Posted from TSR Mobile

Reply 4

username23423

Original post by ioffer007

I was taught using dilute H₂SO₄ and dilute dichromate without reflux would only oxidise it to aldehyde.

Reply 5

Secret.

Original post by ioffer007

If you have the Nelson Thornes chemistry textbook, it's explained on page 217 at the top. If not I'll try and summarise. They distil it by reducing the temperature of the condenser and is put in the distillation position (rather than reflux) as shown below:

So as soon as the aldehyde (ethanal) is formed it vaporises and then distils off to stop it from being further oxidised.
Hope this helped!

Reply 6

ioffer007

Original post by Secret.

So as soon as the aldehyde (ethanal) is formed it vaporises and then distils off to stop it from being further oxidised

So, what is being distilled off is aldehyde and not the ethanoic acid?

Reply 7

Libby18

Original post by ioffer007

So, what is being distilled off is aldehyde and not the ethanoic acid?

yes thats right, if you leave it to oxidise further, then you get ethanoic acid :smile:

Reply 8

ioffer007

Original post by Hormonal

I was taught using dilute H₂SO₄ and dilute dichromate without reflux would only oxidise it to aldehyde.

Isn't it if you have an excess of ethanol, then it would be further oxidized?

Reply 9

ioffer007

Original post by Libby18

yes thats right, if you leave it to oxidise further, then you get ethanoic acid :smile:

But ethanoic acid will never be distilled? (even if I reach the boiling point?)
So, if I manipulate the temperature of the solution (by, say, placing the original in a water bath), then the only difference would be an increasing (or later decreasing) amount of aldehyde vapour, that is distilled off?

Reply 10

Libby18

Original post by ioffer007

I meant if you dont distil it, you'll get ethanoic acid. Sorry if I wasn't clear.

Reply 11

ioffer007

Original post by Libby18

I meant if you dont distil it, you'll get ethanoic acid. Sorry if I wasn't clear.

No problem, I might be a dumb person in chemistry :smile:

So, if I add ethanol to dicromate solution, and heat it up to 45º then will the distillate only be aldehyde?
And if I will heat the solution up to 65º (still below the boiling point for ethanoic acid) will I get more distillate? (if I do two different distillation increments)