[sambasivarao]

Dear Friends

    I am doing reduction of 3,4-dihydroxy banzaldehyde with NaBH4. The reaction is monitiring with TLC total reactent is completed it showing required compound with two mixtures.
   
   Then we went for column chromatography to we got single compound in(showing in TLC) then we go for distill out the solvent in rotovapour. It is not forming any solid and it becoming a black mass with coluour change. After this i check the TLC it is showing two to three spots.


   Is there any another method to reduct the benzaldehyde and to get single compound. Can i do that one with NaH.

[alphahydroxy]

not sure i'm following...

sounds like - you perform the reduction, which doesn't go to completion - hence you see 2 spots... is one of the spots from the starting material?

You may need to use a rather large excess of NaBH₄ because the boron may coordinate to the hydroxyl groups - I'm not sure though as I don't really do much of this sort of thing.

Are you quenching the reaction properly in order to get the actual alcohol - something like 1M HCl would probably be appropriate...

So if you're doing these things and you column out the alcohol, and it's one spot off the column, then the problem doesn't lie with the actual reaction - it lies in the isolation. i.e. if the compound you are removing the solvent from is one spot on TLC, then once you've removed the solvent it becomes 3 spots - your problem is not in the use of NaBH₄ !

You could try keeping the temperature low when using the rotary evaporater - don't heat it or maybe even use an ice bath...

Finally, NaH is not reducing agent, it's a strong base so it won't work for this reduction.

[sambasivarao]

thank you for your valuble suggestion.

when we are monitiring the tlc in reaction time,  we are giving the refflux up to the starting material  to  be complete.

[alphahydroxy]

You might also want to try performing the reaction at room temperature (20-30^oC) as I'm pretty sure reducing the aldehyde won't need high temperature.