mycotheologist
Hazard to Others
Posts: 154
Registered: 16-3-2012
Member Is Offline
Mood: No Mood
|
|
Paracetamol + NaOH
I added some USP grade acetaminophen to a few mLs of saturated NaOH solution. After about 20 minutes I noticed it had turned this dark red colour:
What is this red compound? I would assume 4-aminophenol produced via base catalysed hydrolysis of the amide group but all the pictures I've seen of
4-aminophenol show a white powder. Its odourless so I'm guessing its not too volatile, I'll evaporate the water and see whats left behind tomorrow.
|
|
|
mnick12
Hazard to Others
Posts: 404
Registered: 30-12-2009
Location: In the lab w/ Dr. Evil
Member Is Offline
Mood: devious
|
|
Excess NaOH would deprotonate the phenol, and the resulting phenoxide is susceptible to atmospheric oxidation. Hard to say exactly what it is, most
likely a mixture of oxidation product. If you want to isolate the pure phenol your best bet is to conduct a hydrolysis using stoichiometric amounts of
base (maybe a slight excess), then neutralize the solution with HCl or acetic acid. This is something I plan on doing in the future as part of another
synthesis, if you are interested I can let you know how things go when I get around to it.
|
|
|
mycotheologist
Hazard to Others
Posts: 154
Registered: 16-3-2012
Member Is Offline
Mood: No Mood
|
|
Cool, keep me updated on that synthesis.
|
|
|
Nicodem
|
Thread Moved
22-4-2012 at 04:10 |
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
If you want to prepare 4-aminophenol, then the base hydrolysis is pointless, because you can not avoid oxidation unless you degas the solvent and use
inert atmosphere. Acidic hydrolysis bypass this problem.
Check the literature and use a verified procedure.
PS: Please open referenceless threads only in the appropriate forum section. Read the forum guidelines for more info.
|
|
|
kristofvagyok
National Hazard
Posts: 659
Registered: 6-4-2012
Location: Europe
Member Is Offline
Mood: No Mood
|
|
Dark red color of the acetaminophen could be the result of a lot reaction, but mainly the decomposition of the phenol.
There is a commercial reagent, named pyrogallol. Long ago, (50-100year), it was a common reaction to make pyrogallol sodium or potassium salt to check
that is there any oxygen left in the atmosphere, because if any oxygen remained there the pyrogallol-Na/K salt in solution immediately turned black,
it just simply decomposed.
In this case, it could be a similar thing what results this color. If the acetyl group hydrolises down from the amine, it will yield paraaminophenol
what is a sensitive compound and could easily yield a red/black tar.
I have a blog where I post my pictures from my work: http://labphoto.tumblr.com/
-Pictures from chemistry, check it out(:
"You can’t become a chemist and expect to live forever." |
|
|
AndersHoveland
Hazard to Other Members, due to repeated speculation and posting of untested highly dangerous procedures!
Posts: 1986
Registered: 2-3-2011
Member Is Offline
Mood: No Mood
|
|
The base is first going to hydrolyse off the acetyl group. Because the amino and hydroxy groups are in the para- position respectively with eachother,
the 4-aminophenol is going to be susceptible to oxidation from the air, especially under alkaline conditions:
http://www.sciencemadness.org/talk/viewthread.php?tid=13514
Paradiaminobenzene is also know to be able to polymerise to a black compound, as it is an ingredient in some hair dyes.
Read about p-Phenylenediamine: http://en.wikipedia.org/wiki/Hair_coloring
|
|
|
BlackDragon2712
Hazard to Others
Posts: 124
Registered: 22-12-2012
Location: Everywhere
Member Is Offline
Mood: Sleepy
|
|
The patent WO 1998027931 A2 states that salts of acetaminophen can be form by reacting it with an hydroxide in an organic solvent. they say that the
products are salts of p-hydroxyacetanilide... so wouldn't it be the same as p‐acetamidobenzenolate? and why does it take so long (more than 24h) to
get hydrolysed to p-aminophenolate?
The reactions seems quite simple... would the product be useful for performing williamson ether synthesis? considering that the acetyl head protects
the amino group this has potential for making some very interesting molecules.
Link to the patent: http://www.google.co.in/patents/WO1998027931A2?hl=es&cl=...
Sorry if I woke up an old post but I was very curious about this.
Thanks in advance.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
