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Author: Subject: Acylium ion formation - schmidt rxn
haroldramis
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[*] posted on 29-3-2013 at 21:30
Acylium ion formation - schmidt rxn


Hello all-
Every example of a schmidt reaction that I have seen uses concentrated sulfuric acid, lewis acids, or concentrated phosphoric acid to form the acylium ion so that it can be attacked by hydrazoic acid. I have a few questions:
- can an acylium ion be formed under milder conditions? Conditions that would not harm ether or hydroxyl groups.
- Is there another way of replacing a carboxylic acid group with an amino group without the harsh schmidt conditions?
- If one had a carboxylic acid group on a compound that also contained hydroxyl and methoxy groups, could a schmidt be performed that would not demethylate the methoxy and/or dehydrate the hydroxyl groups?

For instance, if one wanted to make 1 amino 3 hydroxy 4 methoxy cyclo hexane, could one use a schmidt reaction from the corresponding acid?

Thanks all
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Nicodem
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30-3-2013 at 00:23
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[*] posted on 30-3-2013 at 00:49


Quote: Originally posted by haroldramis  
Hello all-
Every example of a schmidt reaction that I have seen uses concentrated sulfuric acid, lewis acids, or concentrated phosphoric acid to form the acylium ion so that it can be attacked by hydrazoic acid. I have a few questions:
- can an acylium ion be formed under milder conditions? Conditions that would not harm ether or hydroxyl groups.

Acylium cations O-acylate aliphatic alcohols, so the most likely answer is no unless esters can undergo the reaction under the same conditions.
Diaryl ethers are totally stable toward acidic cleavage. Ethers with both primary alkyl substituents, or one aryl and the the other primary alkyl are generally resistant to concentrated sulfuric acid up to not too high temperatures. Ethers with one or both secondary alkyl substituents might cleave, depending on their structure and reaction conditions. Ethers with any tertiary alkyl substituent, cleave rapidly in acidic media.
Quote:
- Is there another way of replacing a carboxylic acid group with an amino group without the harsh schmidt conditions?

Assuming you talk about RCOOH to RNH2 type of transformations (dehomologations), then there are many strategies available, of which already the related rearrangements cover the spectra from acidic to neutral to basic media:
Hofmann rearrangement
Lossen rearrangement
Curtius rearrangement

For the RCOOH to RCH2NR2 transformations (R=H, alkyls and/or aryls) the most common strategy is amidation and amide reduction.
Quote:
For instance, if one wanted to make 1 amino 3 hydroxy 4 methoxy cyclo hexane, could one use a schmidt reaction from the corresponding acid?

Cyclohexanols easily dehydrate to cyclohexenes in strongly acidic media. The cyclohexyl ethers are also prone to cleavage/elimination, being that they the cyclohexyl group is a secondary alkyl.

PS: Please open threads without any references only in the Beginnings section. See the forum guidelines for more information.




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haroldramis
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[*] posted on 30-3-2013 at 05:28


Thank you for moving it to the appropriate forum, I will remember for future reference.
Your answer to my question was excellent. Many Thanks :)
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