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Topic: Reduction of ketone to form an alkene  (Read 15901 times)

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Offline CHEKAL

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Reduction of ketone to form an alkene
« on: January 02, 2013, 08:28:35 AM »
right, ive done an alternative reaction to the wolff-kishner reduction because it contains hydrazine.

ive reacted a ketone with lithium aluminium hydride and aluminium chloride to remove the carbonyl group and convert it into a methylene group, im really suck of where to even start a mechanism for the reaction.

does anyone have any idea of what the mechanism would be like?

thanks and happy new year

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #1 on: January 02, 2013, 09:27:58 AM »
Do you not mean alkane?
Or is it actually alkene?

Have a look here:
http://en.wikipedia.org/wiki/Wolff–Kishner_reduction

p.s. there is nothing wrong with hydrazine as long as you take the relevant precautions. It is probably safer than LiAlH4/AlCl3.
« Last Edit: January 02, 2013, 09:49:41 AM by discodermolide »
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Offline CHEKAL

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Re: Reduction of ketone to form an alkene
« Reply #2 on: January 02, 2013, 09:59:18 AM »
yes i mean alkane sorry! ive already done the reaction, i need a mechanism for it, ive not used the wolff-kishner, how would the carbonyl be removed?

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #3 on: January 02, 2013, 10:01:09 AM »
Why don't you suggest a mechanism?
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Offline CHEKAL

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Re: Reduction of ketone to form an alkene
« Reply #4 on: January 03, 2013, 05:02:29 AM »
i have no idea where to begin, hence why im on here  :-\

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #5 on: January 03, 2013, 06:11:12 AM »
i have no idea where to begin, hence why im on here  :-\

No need to show an attempt. Hint what do you get when LAH reacts with AlCl3?
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Offline CHEKAL

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Re: Reduction of ketone to form an alkene
« Reply #6 on: January 03, 2013, 01:55:14 PM »
you get AlH3 + LiCl correct?

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #8 on: January 03, 2013, 05:13:15 PM »
yes, a solution of aluminium trichloride and  diethyl ether was made, this was then added dropwise to a LAH/THF solution.

just another additional question to go with it: if i changed the amount of aluminium trichloride, what effect would this have on the reduction reaction? would it change the power of the reduction?

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #9 on: January 03, 2013, 05:17:02 PM »
Yes, it says that in the link I sent you.
It modifies the reductive strength of LAH making it more selective.
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Re: Reduction of ketone to form an alkene
« Reply #10 on: January 06, 2013, 04:58:38 AM »
So if I added more aluminium chloride to change the stoichiometry, would it make the reduction less powerful as to only reduce to a secondary alcohol? Would it have an effect at all if I'm wrong?

Offline CHEKAL

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Re: Reduction of ketone to form an alkene
« Reply #11 on: January 06, 2013, 04:26:17 PM »
would this have an effect?

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #12 on: January 06, 2013, 04:42:52 PM »
Yes t would probably have an effect.
You usually do this with t-Butanol. By doing this you modify the reactivity and hence the selectivity of the LAH reduction.
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Re: Reduction of ketone to form an alkene
« Reply #13 on: January 06, 2013, 04:48:04 PM »
would this mean dibenzosuberenone would be reduced to an alcohol if i added more AlCl3? as the stoichiometry i used in my procedure reduced the ketone to a methylene group.

Offline discodermolide

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Re: Reduction of ketone to form an alkene
« Reply #14 on: January 06, 2013, 04:51:29 PM »
A methylene group is a CH2 do you mean it got reduced to a Methyl group?
Having looked up the structure of your compound, which you finally supplied, yes it got reduced to a methylene group.

Just a suggestion: If you can supply the structure or a part of it it makes the answering and understanding of the question much easier, instead of trying to fathom out vague questions, which leads to mis-understanding.
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