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#Post#: 974--------------------------------------------------
dehydrating primary alkanols?
DIR By: Chris
Date: October 24, 2012, 10:26 am
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Is it possible to dehydrate primary alkanols? If yes, how? And
what products formed?
Plz reply fast
#Post#: 976--------------------------------------------------
Re: dehydrating primary alkanols?
DIR By: Potla
Date: October 24, 2012, 12:01 pm
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Primary alcohols get dehydrated by Concentrated H2SO4 at 170
degrees celsius (at lower temperatures of about 140 degrees they
give ethers).
The mechanism for primary alcohols is a E2 (bimolecular
elimination) mechanism. (Of course, it does not proceed through
carbocation formation because 1o C+ is not stable)
But there are some tricky stuff with a 1o C-OH next to a 3o one,
for example consider (CH3)3C-CH2-OH ; in which case the
carbocation formed gets rearranged via a methyl shift, through
which it forms a very stable 3o C+.
Else it's simply extraction of water: CH3CH2OH gives CH2=CH2
etc.
Ah, and 1-cyclopropyl methanol should also undergo E1 mechanism
as an exception, 'cause the carbocation formed is stable by some
orbital overlapping etc.
Hope it was useful. :)
#Post#: 1031--------------------------------------------------
Re: dehydrating primary alkanols?
DIR By: Chris
Date: November 1, 2012, 9:00 am
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Ohh! Sorry i meant dehydrogenating not dehydrating! :O
#Post#: 1037--------------------------------------------------
Re: dehydrating primary alkanols?
DIR By: Michel
Date: November 2, 2012, 9:15 am
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--- Quote from: Chris link ---
>
> Ohh! Sorry i meant dehydrogenating not dehydrating! :O
>
--- End Quote ---
there is no way of removing hydrogen atoms from an unsubstituted
primary alkanol except by dehydrating it, at least as far as I
know.
#Post#: 2173--------------------------------------------------
Re: dehydrating primary alkanols?
DIR By: etvsharma
Date: February 24, 2013, 12:18 am
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Dear
Primary alcohols can be dehydrogenated..
Ethanol vapours when passed over heated Cu at 300degree celcius
undergo catalytic dehydrogenation to give acetaldehyde.
Alcohol gives alcohol-dehydrogenation product..
Infact for aldehydes the name has come from this reaction.
S.N.Sharma
#Post#: 2214--------------------------------------------------
Re: dehydrating primary alkanols?
DIR By: Potla
Date: February 26, 2013, 12:57 pm
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If dehydrogenation is just another name of oxidation to
carbonyls, then there are loads of reagents other than Cu/heat,
like PCC or CrO3/Acetone, etc. This can only be done for primary
and secondary alcohols. For 3o alcohols, however, Cu/heat causes
elimination and an alkene is formed.
Thanks etvsharma, I did not know that the name aldehyde has come
from this reaction only. :)
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