Paulo - 2-10-2003 at 06:18
When studying the benzene nitration products, an idea cross my mind.
If I purify the mixed acid (nitric acid + sulphuric acid) with urea, will the benzene by-products decrease? Apparently the urea should react with the
nitrous acid and maybe this will reduce the oxidation of benzene into phenol. This way I should be able to produce less nitrophenols, namely di- and
tri-nitrophenols.
I don’t have any other information on this, so please any suggestion would be appreciated.
Please remember that I use temperatures between 80 and 100 ºC, will this be any problem? What amount of urea should be used? Will be dangerous if I
use too much?
My mixed acid uses the following composition:
400 ml Sulphuric acid at 68% (wt)
50 ml nitric acid at 60% (wt)
Thanks!
Paulo
KABOOOM(pyrojustforfun) - 4-10-2003 at 19:40
urea works in "sulfuric free" nitric acid. with sulfuric acid present you get nitrous oxide (but if kept under 5°C nitro/dininitrourea
forms)
which acid do you think is responsible for oxidation?
edit: just found I had written acid instead of oxide
[Edited on 8-10-2003 by KABOOOM(pyrojustforfun)]
Paulo - 6-10-2003 at 05:00
Sulphuric acid is present because is the catalyst of the main nitration reaction.
I think that the nitric acid undissociated or the nitrous acid formed is the oxidiser of the benzene into phenol. If I can remove the nitrous acid
formed from the mixed acid, maybe I can decrease the nitrophenols (NP’s) formed, because maybe the mechanism of formation of this NP’s passes
through the nitrous acid present, and if I can removed it by the introduction of urea, maybe I can decrease the NP’s formed.
However I must use temperatures near the 90 ºC and acid concentrations as referred.
Thanks.
Paulo
KABOOOM(pyrojustforfun) - 7-10-2003 at 20:10
it can't be nitrous acid . HNO3 is a quite stronger oxidiser than HNO2.
anyway why didn't you post it under the previous thread?
Marvin - 8-10-2003 at 19:36
Nitrous acid, and the products its associated with, like nitrogen dioxide are frequently the cause of nitrating mixtures going oxidising. More
usually though with ester formation from alcohols.
A furthur cause tends to be when the nitric acid concentration in the nitrating mixture drops to a low value. If this turns out to be part of the
problem using excess nitric acid industrially would probably not be economical.
vulture - 9-10-2003 at 00:49
Nitration in DCM significantly reduces, sometimes totally inhibits, the formation of byproducts according to the patent.
I guess the reason why, in my experience, is that NOx does not dissolve in DCM.
[Edited on 9-10-2003 by vulture]