Hexavalent
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Stoichiometry of Bouveault-Blanc Reduction
I would like to attempt a Bouveault-Blanc reduction of an ester using metallic sodium and dry ethanol. The ester I would use would be dry ethyl
acetate, as the only product would be ethanol; the EtOAc is also readily-available and a cheap aliphatic ester. I could then distill the mixture and
collect the ethanol from it.
However, there is one thing I just don't understand; where to begin with stoichiometry. Supposing I start with 25ml of the ester: how much of the
ethanol and sodium metal do I need? Where do I begin with these calculations?
Any help would be greatly appreciated.
[Edited on 10-9-2012 by Hexavalent]
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Lambda-Eyde
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Figure out the difference in oxidation states of the carbon atom. This is the same as the number of electrons added during the reduction. Then keep in
mind that metallic sodium is a one-electron reducing agent (Na -> Na<sup>+</sup> + e<sup>-</sup> . The rest I think you can handle yourself; molecular weights and using density to
figure out how many milliliters you need based on number of moles.
But why on earth do you want to use such a dirty reaction (with valuable sodium) to produce such a mundane product as ethanol? Get ahold of some fatty
acid ester (a pure one) and isolate a long-chain alcohol instead. I think you can get small amounts on eBay at a nice price.
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Hexavalent
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Quote: Originally posted by Lambda-Eyde  | Figure out the difference in oxidation states of the carbon atom. This is the same as the number of electrons added during the reduction. Then keep in
mind that metallic sodium is a one-electron reducing agent (Na -> Na<sup>+</sup> + e<sup>-</sup>. The rest I think you can handle yourself; molecular weights and using density to
figure out how many milliliters you need based on number of moles.
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Sorry, still don't understand
I thought I'd try running it with ethanol as the product to get a feel for the reaction, but your idea is better. Any suggestions?
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Magpie
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Bouvealt-Blanc is a bitch. I agree with Lambda-Eyde.
Have you read my trials at:
http://www.sciencemadness.org/talk/viewthread.php?tid=16306#...
Also see the procedure in OrgSyn for lauryl alcohol (1-dodecanol).
The single most important condition for a successful synthesis is good mixing - Nicodem
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Hexavalent
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I assume this is what you are referring to, Magpie?
http://www.orgsyn.org/orgsyn/default.asp?formgroup=basenp_fo...
Also, I am having second thoughts about safety; I lack a good fume cupboard like yourself and might wait until I'm older to do it when I have more
experience under my belt. The last thing I want is a sodium fire with flammable solvents in a garage at age 14.
[Edited on 10-9-2012 by Hexavalent]
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Magpie
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Yes, I guess. All that link got me was a search page in OrgSyn.
| Quote: Originally posted by Hexavalent |
Also, I am having second thoughts about safety; I lack a good fume cupboard like yourself and might wait until I'm older to do it when I have more
experience under my belt. The last thing I want is a sodium fire with flammable solvents in a garage at age 14.
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Amen.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Lambda-Eyde
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Look at the structure of a carboxylic acid/ester (they are all the same with respect to the carboxyl carbon) compared to an alcohol. As you know, if
you oxidize an alcohol you get a carboxylic acid. What you want to do is the opposite. Knowing that hydrogen has oxidation state +1, oxygen -2 and a
C-C bond is equal to a difference in oxidation state of 0, you can calculate the difference in electrons. Knowing how many electrons you need to add
to a carboxylic acid (or ester, the same thing) you know the amount of sodium to add. The carbon attached to the -OH group or containing the carboxyl
group is of course the carbon of interest.
But that's not the whole story... Organic reactions are rarely so clean and well-behaving (the Bouveault-Blanc reduction is notorious) that you can
just go with the exact number from your calculations. Reagents are used in excess to account for this, and sometimes order of addition, mixing,
heating and other conditions are important in maximizing yields and minimizing side reactions. I don't know much about the BB reduction myself (other
than it is, as Magpie describes, a bitch), but I expect there to be a lot of alkoxide formation, transesterifications and other stuff that will hamper
yields (as well as ease of workup...). A whole other world compared to e.g. making simple metal salts and complexes.
[Edited on 10-9-2012 by Lambda-Eyde]
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Hexavalent
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Sorry, wrong link. Will correct now.
[Edited on 10-9-2012 by Hexavalent]
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kristofvagyok
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| Quote: Originally posted by Hexavalent | | I would like to attempt a Bouveault-Blanc reduction of an ester using metallic sodium and dry ethanol. The ester I would use would be dry ethyl
acetate, as the only product would be ethanol;[Edited on 10-9-2012 by Hexavalent] |
I have made a reaction similar to this today accidentally... I was dissolving sodium in propanol and when just a little sodium left (few little
pieces) I added diethyl oxalate. The interesting was that it turned poison green... Anyone, any idea?
Usually in reductions performed with reagents like solid sodium and ethanol they use a large excess of both reagents, because it is a heterogeneous
reagent and just a really little part of the liquid is reacting with it.
Usually 10-15x excess of finely cut sodium or sodium pellets (they are perfect for demonstration of sodium and water rxn ) are used. Ofcourse with strong stirring....
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Magpie
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Hex, I gave you the wrong link to my B-B work. Try this instead:
http://www.sciencemadness.org/talk/viewthread.php?tid=18625#...
[Edited on 10-9-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Hexavalent
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Ah yes, thanks.
Thanks for explaining the calculations, Lambda; I've got my head around them now - much appreciated.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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