Reduction of carboxylic acids to alcohols Watch

Lifeisnice
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Supposedly, Lithium Aluminum Hydride \mathrm{LiAlH_4} can reduce carboxylic acids to alcohols. http://www.chem.ucalgary.ca/courses/.../ch15-2-8.html However, I can't seem to find any book or site documenting how this happens. Is the leaving group a hydroxide ion \mathrm{OH^{-1}}? That would be pretty strange, as \mathrm{OH^{-1}} is usually a poor leaving group, especially in the ether solvent the reaction is carried out in?

Also, does anyone know the mechanism for the borane reduction of carboxylic acids? Clayden has the mechanism for the amide, but the one for the carboxylic acid isn't given in detail, and I'm not sure how it works.
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najeezy
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what board are u doing? if you have an official book by the board such as salters ocr and its not in the book forget about it, double check the spec, if it is just learn it from the site, no harm done.
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Lifeisnice
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(Original post by najeezy)
what board are u doing? if you have an official book by the board such as salters ocr and its not in the book forget about it, double check the spec, if it is just learn it from the site, no harm done.
I'm studying chemistry in university. =X
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EierVonSatan
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You might get some some kind of metallic species attached to the oxygen to make it a better leaving group; I doubt the -COOH group would remain intact upon contact with LAH considering what LAH does to water :p:

Have a look at this for the borane reduction: http://www-oc.chemie.uni-regensburg....actions-08.pdf
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Lifeisnice
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(Original post by EierVonSatan)
You might get some some kind of metallic species attached to the oxygen to make it a better leaving group; I doubt the -COOH group would remain intact upon contact with LAH considering what LAH does to water :p:
Do you know the mechanism of this or the one involving borane in THF? =X It seems that lots of the oxidation reduction mechanisms regarding inorganic compounds such as Borane and Lithium Aluminum Hydride aren't particularly known or simple. For example, the combustion of methane has more than 20 radical steps ZOMG.
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EierVonSatan
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(Original post by Lifeisnice)
Do you know the mechanism of this or the one involving borane in THF? =X It seems that lots of the oxidation reduction mechanisms regarding inorganic compounds such as Borane and Lithium Aluminum Hydride aren't particularly known or simple. For example, the combustion of methane has more than 20 radical steps ZOMG.
I just added a link to a pdf that goes through many reducing agents including B2H6 in my previous post. You're right though about these as not being particularly well understood, but there are accepted mechanisms around - but it's not really of much interest tbh :p:
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najeezy
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(Original post by Lifeisnice)
I'm studying chemistry in university. =X
, rofl then learn w/e u find. soz.
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badboy1
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sure its got something to do with the hydirde ion
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Lifeisnice
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(Original post by EierVonSatan)
I just added a link to a pdf that goes through many reducing agents including B2H6 in my previous post. You're right though about these as not being particularly well understood, but there are accepted mechanisms around - but it's not really of much interest tbh :p:
I only understand the borane mechanism up to the part where there's the formation of the double carbonyl compound. Then were does the hydrogen gas come from, and how does it interact?

I think the oxidation of an alkane to a ketone by potassium permanganate is quite interesting. Unfortunately, it seems to involve SETs, and I can't find a decent mechanism anywhere :s
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Lifeisnice
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http://www.chemgapedia.de/vsengine/v...oli.vscml.html
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EierVonSatan
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(Original post by Lifeisnice)
I only understand the borane mechanism up to the part where there's the formation of the double carbonyl compound. Then were does the hydrogen gas come from, and how does it interact?
The hydrogen comes from the formation of the B-O bonds via protonolysis. I found a paper with the mechanism: http://pubs.acs.org/doi/abs/10.1021/jo00956a011.
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mattx10
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(Original post by Lifeisnice)
Supposedly, Lithium Aluminum Hydride \mathrm{LiAlH_4} can reduce carboxylic acids to alcohols. http://www.chem.ucalgary.ca/courses/.../ch15-2-8.html However, I can't seem to find any book or site documenting how this happens. Is the leaving group a hydroxide ion \mathrm{OH^{-1}}? That would be pretty strange, as \mathrm{OH^{-1}} is usually a poor leaving group, especially in the ether solvent the reaction is carried out in?

Also, does anyone know the mechanism for the borane reduction of carboxylic acids? Clayden has the mechanism for the amide, but the one for the carboxylic acid isn't given in detail, and I'm not sure how it works.
Here is a mechanism for the reduction of propanal which might help?
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Lifeisnice
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After a year, I have finally managed to locate an excellent mechanism for the reduction of carboxylic acids by borane. It is found here: http://www.ch.imperial.ac.uk/rzepa/blog/?p=2902 http://www.ch.ic.ac.uk/rzepa/blog/wp...loxyborane.jpg

There is a paper here which describes it in more detail: http://pubs.acs.org/doi/pdf/10.1021/ja00467a016

The mechanism also explains why esters are not reduced by borane
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