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How can you tell if a compound is a Secondary alcohol or Ketone?

How can you tell if a compound is a Secondary alcohol or Ketone?

Thanks
the_wizzz
How can you tell if a compound is a Secondary alcohol or Ketone?

Thanks



A secondary alcohol will have an -OH group attached to a carbon atom that has only on H attached to it. Eg propan-2-ol CH3CHOHCH3

A ketone has a C=O bond, where the C bond is not attached to any hydrogen atoms, but to ethyl groups. Eg propanone CH3C=OCH3
Reply 2
Avatar for the_wizzz
the_wizzz
OP
thanks

how can you test/tell the difference between them?
the_wizzz
How can you tell if a compound is a Secondary alcohol or Ketone?

Thanks

Test for the presence of a carbonyl group (C=O)
Add 2,4-dinotrophenylhydrazine
It will give an orange crystaline percipitate with a characteristic melting point.
If you add acidified potassium/sodium dichromate to each of them, the alcohol will reduce the chromium ions and the solution will go from orange to green. The ketone won't react.
I think.
hitchhiker_13
If you add acidified potassium/sodium dichromate to each of them, the alcohol will reduce the chromium ions and the solution will go from orange to green. The ketone won't react.
I think.

The alchol will not react with the acidified potassium dichromate because he specified a secondary alcohol.
these_apples
The alchol will not react with the acidified potassium dichromate because he specified a secondary alcohol.


Secondary alcohols form ketones don't they?
And primary ones form carboxylic acids?
hitchhiker_13
And primary ones form carboxylic acids?

Sorry, my mistake :redface: .
Ketones are oxidised, and do show a colour change from orange to green with acidified potassium dichromate
Reply 9
Avatar for hihihihi
hihihihi
these_apples
Sorry, my mistake :redface: .
Ketones are oxidised, and do show a colour change from orange to green with acidified potassium dichromate

No!

Oxidising aldehydes with potassium dichromate will turn the orange solution to green.

Ketones do not.
Reply 10
Avatar for Helenia
Helenia
20
hihihihi
No!

Oxidising aldehydes with potassium dichromate will turn the orange solution to green.

Ketones do not.


But the 2ry alcohol will be.
Reply 11
Avatar for mullally87
mullally87
In the presence of excess acidified potassium dichromate, an aldehyde will be oxidised to form a carboxylic acid. When reacted with acidified potassium dichromate a secondary alcohol will also be oxidised, but to a ketone. Both of the reactions turn the mixture from the orange of K2O7- to the green of chromium (III) ions Cr3+. If you want to distinguish between the two compunds you can use 2,4 dinitrohydrazine. The aldehyde will turn it result in the formation of an orange hydrazone precipiatate and there will be no reaction in the case of the secondary alcohol.

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