Hexavalent - 25-6-2012 at 11:33
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.
Any ideas? Thanks in advance.
[Edited on 25-6-2012 by Hexavalent]
DJF90 - 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?
UKnowNotWatUDo - 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.
barley81 - 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.
smaerd - 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]
mr.crow - 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.
mnick12 - 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.
Hexavalent - 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