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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: PRIYA1022 on April 19, 2007, 09:35:55 PM

Title: wolf-kishner reduction
Post by: PRIYA1022 on April 19, 2007, 09:35:55 PM

 I am trying to synthesize 2-methylpyrrole from pyrrole-2-carbaldehyde using Na/EtOH and hydrazine hydrate,( heat for 1-4 hrs) and I get a mixture of the three substances, as per the NMR.. I think they are perhaps the aldehyde, hydrazone and  the product.Can anyone offer a suggestion to get a better yield of 2-methylpyrrole/have the complete reduction of the hydrazine?
I have also tried going through the semicarbazone pathway and heating with KOH(aq).I get very little of 2-methylpyrrole ,and there is a lot of the semicarbazone in the reaction mixture.Would a nitrogen atmosphere make a difference?
Thanks.

Title: Re: wolf-kishner reduction
Post by: sjb on April 30, 2007, 07:56:31 AM

Quote from: PRIYA1022 on April 19, 2007, 09:35:55 PM

I am trying to synthesize 2-methylpyrrole from pyrrole-2-carbaldehyde using Na/EtOH and hydrazine hydrate,( heat for 1-4 hrs) and I get a mixture of the three substances, as per the NMR.. I think they are perhaps the aldehyde, hydrazone and  the product.Can anyone offer a suggestion to get a better yield of 2-methylpyrrole/have the complete reduction of the hydrazine?
I have also tried going through the semicarbazone pathway and heating with KOH(aq).I get very little of 2-methylpyrrole ,and there is a lot of the semicarbazone in the reaction mixture.Would a nitrogen atmosphere make a difference?
Thanks.

I'd certainly consider a nitrogen (or argon) atmosphere. Do you have a procedure you're following, or adapting? My limited understanding of the wolff kishner (have not carried out one myself) is that you use KOH, hydrazine and heat. Maybe you just need to make sure all the aldehyde is consumed before adding the strong base.

Other ways around this may be to do a Clemmensen see eg http://www.organic-chemistry.org/namedreactions/clemmensen-reduction.shtm or via the thioacetal and raney hydrogenation. You may need to protect your free NH in some cases as well...

I'd be surprised if 2-methylpyrrole wasn't commercial though - could be wrong.

S

Title: Re: wolf-kishner reduction
Post by: PRIYA1022 on April 30, 2007, 07:07:26 PM

Hi,
  Yes,I have a literature procedure, and I did carry it in a nitrogen atmosphere. I have also tried Huang Minlon modification,(Jacs 2002,page 4572-73) .
 I have isolated the hydrazone. I want let it dry and then heat with KOH pellets and collect the distillate. I know that wolff kishner reduction is a single step process where the hydrazone is not isolated....just giving a try..
I am also trying with 1-methyl-pyrrole-2-carbaldehyde..
2-methylpyrrole is available commercially ,but  in small quantities.

Title: Re: wolf-kishner reduction
Post by: kiwi on May 01, 2007, 04:08:35 AM

i wonder if that aldehyde is activated enough for lewis acid/Et3SiH reduction? conditions might also cook your pyrrole though, not very up to speed on my practical pyrrole chemistry