Sciencemadness Discussion Board

Hydrogenation of esters

Mike - 18-1-2004 at 08:09

Hi!

Like you know NaBH4 doesn’t hydrogenate esters to alcohols.

What’s my problem? I want to reduce esters (aliphatic and aromatic) to alcohols without using LiAlH4.

Will NaBH4 at least reduce the ester to a aldehyde and alcohol? Like when we use DIBAH? Then the aldehyde can be turn to alcohol by reacting with NaBH4 and H3O(-).

I heard about activating NaBH4 by adding NiCl2. Apparently using this method the –CN group is quickly reduce to –NH2. Normally NaBH4 doesn’t reduce –CN. I wonder if it works for the esters.

Maybe someone has more certain information about hydrogenation of esters without LiAlH4?

guaguanco - 18-1-2004 at 22:56

Quote:
Originally posted by Mike
Will NaBH4 at least reduce the ester to a aldehyde and alcohol? Like when we use DIBAH? Then the aldehyde can be turn to alcohol by reacting with NaBH4 and H3O(-).

I don't think so; Esters are stable little suckers.
A google search revealed some catalytic techniques that are out of reach of the home chemist. An old-school route would be:
ester -> acid -> acid chloride -> aldehyde -> alcohol, but I know you're looking for something easier.
What ester are you trying to reduce?

Mike - 19-1-2004 at 00:42

Actually I want to: benzoic acide =>methyl benzoate=>benzyl alkohol
Any ideas?
To make an acid chloride I will need SOCl2 wich I can't get. :( The only hope is in that NaBH4/NiCl2 way.

guaguanco - 19-1-2004 at 13:48

Then again, some esters can be reduced with NaBH4
http://www.albmolecular.com/features/tekreps/vol07/no51/

Everything you wanted to know about NaBH4
http://www.rohmhaas.com/hydride/pdf/finaldigest.pdf

It appears that under the right conditions, BH4- is a much stronger reducing agent that has been traditionally thought!

[Edited on 20-1-2004 by guaguanco]

Mike - 21-1-2004 at 11:08

Quote:
http://www.rohmhaas.com/hydride/pdf/finaldigest.pdf


Thanx a lot! This is just what I was looking for.