Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Selective Amination of Benzoic Acid
Hexavalent
International Hazard
*****




Posts: 1564
Registered: 29-12-2011
Location: Wales, UK
Member Is Offline

Mood: Pericyclic

[*] posted on 25-6-2012 at 11:33
Selective Amination of Benzoic Acid


How would one go about selectively aminating benzoic acid to para-aminobenzoic acid (PABA)? I know the latter is sold in health food stores and online as a nutritional supplement, but I would like to have a go at synthesising it myself.


benzoic aicd.gif - 2kB


Any ideas? Thanks in advance.

[Edited on 25-6-2012 by Hexavalent]




"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
View user's profile View All Posts By User
DJF90
International Hazard
*****




Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline

Mood: No Mood

[*] posted on 25-6-2012 at 13:51


What makes you think its possible in a direct manner, and that benzoic acid would be a reasonable starting material for this preparation?
View user's profile View All Posts By User
UKnowNotWatUDo
Hazard to Self
**




Posts: 96
Registered: 30-6-2010
Member Is Offline

Mood: No Mood

[*] posted on 25-6-2012 at 15:24


A general method for addition of an amino group to an aromatic compound would be to nitrate and then reduce the nitro group to an amine by using something like stannous chloride. However in the case of benzoic acid you would not see addition of the nitro group to the para position. This is because the carboxylic acid is electron withdrawing and so it is meta directing.
View user's profile View All Posts By User
barley81
National Hazard
****




Posts: 481
Registered: 9-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 25-6-2012 at 16:01


You could reduce it to benzyl alcohol with some reducing agent (lithium aluminum hydride for example), nitrate it, separate the para and ortho isomers, oxidize back to the carboxylic acid, and finally reduce the nitro group to an amine.
View user's profile View All Posts By User
smaerd
International Hazard
*****




Posts: 1262
Registered: 23-1-2010
Member Is Offline

Mood: hmm...

[*] posted on 25-6-2012 at 18:58


Maybe start from a cheaper more practical feed-stock such as toluene. Mono-nitrate, oxidize the methyl(acidic dichromate?), then reduce the nitro group using say Sn/H+ or Fe/H+. Pretty sure that'd work.

Edit - look into electrophillic aromatic substitutions, directive effects(electron withdrawing or donating groups), and play with a couple mechanisms and resonance structures. It will quickly come to light why a direct way is just not practical.

[Edited on 26-6-2012 by smaerd]




View user's profile View All Posts By User
mr.crow
International Hazard
*****




Posts: 884
Registered: 9-9-2009
Location: Canada
Member Is Offline

Mood: 0xFF

[*] posted on 25-6-2012 at 19:23


Hexavalent: Since this is something you are interested in, now is a great time to learn about aromatic reactions! My textbook has several chapters on these sorts of reactions and ortho/meta/para directors.

methyl benzoate gets nitrated at the meta position.

I believe there are several threads already too.




Double, double toil and trouble; Fire burn, and caldron bubble
View user's profile View All Posts By User
mnick12
National Hazard
****




Posts: 404
Registered: 30-12-2009
Location: In the lab w/ Dr. Evil
Member Is Offline

Mood: devious

[*] posted on 26-6-2012 at 00:27


Hmmm more armchair chemistry!

This topic has been discussed quite a few times in the past, I suggest one should UTFSE before creating new topics.

http://www.sciencemadness.org/talk/viewthread.php?tid=13361#...

http://www.sciencemadness.org/talk/viewthread.php?tid=14713#...

http://www.sciencemadness.org/talk/viewthread.php?tid=11751#...

Quite a bit of info already out there waiting just waiting to exit the theoretical realm.
View user's profile View All Posts By User
Hexavalent
International Hazard
*****




Posts: 1564
Registered: 29-12-2011
Location: Wales, UK
Member Is Offline

Mood: Pericyclic

[*] posted on 26-6-2012 at 07:43


Thanks mnick12, I did do some Googling about the subject and tried the forum search engine using a variety of keywords and related words and got no results - thus I posted this thread. I admit to failing to find these ones you list though:)





"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
View user's profile View All Posts By User

  Go To Top