Sciencemadness Discussion Board

NaBH4 substitute

Triflic Acid - 16-11-2020 at 12:10

Would a Hunsdiecker reaction followed by hydrolysis reduce a carboxylic acid to an alcohols. Using iodine as the halogen has two benefits, it's easy to make iodine, and the waste product is hydroiodic acid. The silver could be recycled as well. Is this a good NaBH4 substitute? https://en.wikipedia.org/wiki/Hunsdiecker_reaction

DraconicAcid - 16-11-2020 at 12:17

It's not the same reaction. A carboxylic acid RCO2H could be reduced to an alcohol RCH2OH with LiAlH4 (I don't think sodium borohydride would work), whereas your suggestion would result in the formation of ROH.

Triflic Acid - 16-11-2020 at 12:58

Oh, I don't know how I didn't notice that CO2 coming out of that reaction :P.

ArbuzToWoda - 16-11-2020 at 13:10

Quote: Originally posted by DraconicAcid  
It's not the same reaction. A carboxylic acid RCO2H could be reduced to an alcohol RCH2OH with LiAlH4 (I don't think sodium borohydride would work), whereas your suggestion would result in the formation of ROH.


The nice thing is... that you CAN use NaBH4! But not alone :(
Add iodine or sulfuric acid to produce diborane in situ, and that guy can reduce most things. Carboxylic acids included!

Triflic Acid - 16-11-2020 at 13:11

But NaBH4 is a pain to get:(

Corrosive Joeseph - 16-11-2020 at 13:16

What exactly are you trying to do......? The must be 3 or 4 or 5 members selling borohydride on here right now!

Carboxlic acids are reduced to alcohols with ZnCl2-NaBH4 in refluxing THF..... And also NaBH4-I2 in THF at RT.
https://tinyurl.com/y32nhymk

I have also seen amino acid to amino alcohol reduction with a huge excess of NaBH4-NiCl2 in alcohol, if I remeber correctly, excess was 10 or 15 equivalents.

Shit, Arbuz beat me too it....



/CJ


Attachment: enhancing.nabh4.reactivity.and.selectivity.pdf (333kB)
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NaK - 16-11-2020 at 13:23

Quote: Originally posted by Triflic Acid  
NaBH4 substitute



There is none. At least no good one. NaBH4 is awesome on small scales - very versatile, easy to use, high yielding and clean. For some reductions you might find alternative ways like hydrogenation over Pd/C , Al/Hg, Zn/HCl, dithionite, etc. but for the most part they are more labor intensive / dangerous / expensive / messy.

I would advise spending the time you are researching NaBH4 substitutes on researching NaBH4 suppliers. I think that will get you further in most cases

Triflic Acid - 16-11-2020 at 13:32

I don't actually need NaBH4 right now, I just came across this reaction while looking for a synthesis route for haloalkanes and thought that it might be useful

Corrosive Joeseph - 19-11-2020 at 11:41

More carboxylic acid to alcohol with NaBH4.....
Quote:


2-(3-Hydroxyphenyl)ethanol

2-(3-Hydroxyphenyl)acetic acid (0.5 g) was dissolved in anhydrous methanol (50 mL) and two drops of concentrated H2SO4 were added. After 2 h, the reaction was concentrated in vacuo, diluted with ethyl acetate, washed with brine until the pH was neutral, dried with anhydrous sodium sulfate, and the solvent evaporated under reduced pressure. The methyl ester (0.45 g; 82%) was obtained and immediately treated with an aqueous solution of excess NaBH4. After 2 h, the solution was acidified with 2 N HCl, extracted with ethyl acetate, and worked up as reported above. The residue obtained was purified by silica gel column chromatography, eluting with CHCl3/MeOH (9:1), gave pure 25 (0.37 g; 98%).



Reference: Eur. J. Org. Chem. 17, 3407-3411 (2003)



/CJ