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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: gimlipig on January 31, 2005, 10:00:27 PM

Title: NaBH4 Vanillin Mechanism
Post by: gimlipig on January 31, 2005, 10:00:27 PM

I'm trying to figure out the mechanism for this reaction

NaBH4 + Vanillin + in NaOH + EtOH (solvent) ---> Vanillyl Alcohol

We never went over NaBH4 mechanisms in class. I've found two possible ones, one is simply where a hydrogen on the NaBH4 attacks the carbonyl group of vanillin, leaving RCH2O-. Ethanol then comes in, donating a proton to the negatively charged oxygen to get vanillyl alcohol.

The other mechanism just completely confuses me. It's basically a bit different from the mechanism I described above (ie. carbonyl group attacks proton on ethanol, NaBH4 attacks carbonyl group, and another EtOH attacks the NaBH4) all at the same time.

Can someone help me figure out which one I'm susposed to use?

Thanks so much

Title: Re:NaBH4 Vanillin Mechanism
Post by: AWK on February 01, 2005, 01:25:06 AM

http://www.wiu.edu/users/mftkv/CHEM330/REDUCTIONEXPERIMENT.html
http://www.wiu.edu/users/mftkv/CHEM330/carbonylreductions.html
http://chemistry2.csudh.edu/rpendarvis/OxRed.html

Title: Re:NaBH4 Vanillin Mechanism
Post by: movies on February 01, 2005, 01:08:18 PM

The second one is better!  In general, you always want to have something to activate the carbonyl group towards addition.  In this case, coordination of the carbonyl to the somewhat acidic alcohol hydrogen or perhaps to some Lewis acidic boron species is the best way to show this activation.

It appears that the sodium cation doesn't really play a role in the mechanism since it isn't a very good Lewis acid.