Random
International Hazard
Posts: 1120
Registered: 7-5-2010
Location: In ur closet
Member Is Offline
Mood: Energetic
|
|
Hoffman degradation
I finally got eberything what I need for hoffman degradation of benzamide and I have like 4 grams of mostly benzamide with urea, biuret and ammonium
carbonate impurities. I won't recrystalize that or even try to purify it because I want just to see from that how to make aniline until I will make
bigger quantity.
I looking at some hoffman degradations using bleach and it produces toxic benzyl isocyanate that hydrolyses into aniline. I read about methyl
isocyanate and saw it is very toxic so I want to be sure if this is safe to do.
I have 5% bleach, sodium hydroxide solution made from Ca(OH)2 and Na2CO3 and of course water.
I would add like 50mL of that bleach (maybe it would even be too much) then add like 50mL of that hydroxide solution to that. then I would add like 30
grams of crushed ice into that and make an ice bath around the jar to cool it even more. Finally, I would add all of that benzamide into the solution.
Aniline should form after some time and it's solubility is 3grams in 100mL of water, but I could salt it out by concentrating a solution with NaCl,
then aniline layer should form which I could separate.
Is this procedure good and safe? Maybe I missed something.
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
Since this is third time you have asked about isocyanates, in the curtius, lossen or hofmann degradation, there will always be isocyanate formation.
This however is an extremely transient species in a strongly basic solution.
About the hofmann, I will not spoonfeed you because, every post I have read by you has been, "I have X and Y can I make Z? How?"
Balance the hofmann rearangement, figure out how many equivalents of base you need. Titrate your NaOCl, figure out how many mL's you need to use say
1.2eq. Run the reaction.
Of course, you could just run the reaction as I posted and avoid all of that.
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
Random
International Hazard
Posts: 1120
Registered: 7-5-2010
Location: In ur closet
Member Is Offline
Mood: Energetic
|
|
Not every post, but it was a lot of them I agree 
I will do it as you say, using 1.2eq, but I didn't saw that you posted a reaction about it, or maybe I already forgot it?
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
*facepalm*
You posted in the thread. Twice! http://www.sciencemadness.org/talk/viewthread.php?tid=4201&a...
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
Ephoton
Hazard to Others
Posts: 463
Registered: 21-7-2005
Member Is Offline
Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.
|
|
smuv you legend I missed that.
ive always used alcohol as my solvent for that and then stripped it all off.
your doing all of that in straight water very very nice.
would it not be better though to form the chloroamide before adding caustic
there for lessening side reactions.
TCCA should convert an amide near quantitive to chloroamide.
but caustic can covert amides too acids as can bee seen from phenylacetamide to PAA.
maby if one was to add the TCCA in cold water to the amide at around 0 too 5 C
then stirr till milky then add the caustic and bring it to temp it might have a higher
yeild.
still I am kicking my self for not seeing that thread.
[Edited on 12-4-2011 by Ephoton]
e3500 console login: root
bash-2.05#
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
Thanks, I'm glad you like it!
Nah, amides take a lot of work to hydrolize, I am not too worried. Also, benzamide is almost totally insoluble in cold water.
Also, IDK if the amide will be quantitatively converted to the chloramide under the conditions; in methanol yes, because the reaction is driven to
completion due to the fact TCCA is very soluble in methanol but cyanuric acid is totally insoluble; in water I think this is less of a driving
force...but maybe.
Anyways, I think I proposed it somewhere in the thread, for larger scale, I would produce the chloramide in methanol and then add it dropwise to a
solution of caustic. The reason being, you can greatly reduce solvent volumes this way. It is also more friendly to very water insoluble substrates
as the chloramide formation is done in an organic solvent, where the degradation of the now water soluble (in alkaline solutions) chloramide can be
done without using tons of water or having to deal with carbamate formation (in methanol).
Lol, legend?
BTW what are you doing your hofmanns on? How heat sensitive have you found the chloramides to be, I am thinking about isolating one for something.
[Edited on 4-12-2011 by smuv]
[Edited on 4-12-2011 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
Ephoton
Hazard to Others
Posts: 463
Registered: 21-7-2005
Member Is Offline
Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.
|
|
the problem is that the more carbon on the amide the lower the yeild from hypochlorite based
hoffman.
but if one forms chloroamide first this is not a problem.
looking into this I see that the cyanuric acid is even more soluble than TCCA in water.
this may just hinder the reaction as you just mentioned.
using alcohol is truly a pain if one uses the idea of dripping the chloroamide in alcohol into a caustic
solution they still have to deal with seperating the alcohol from the finished amine.
also I have never had success from a mixture of alcohol and water when trying to rearrange the
chloroamide.
the chloroamide that comes from this reaction in alcohol is very clean compared to what
comes out of the other end of a hypohalide hoffman that is for sure.
post edit.
still your yeild says much.
you have a comparable if not better yeild than what is expected from nitrobenzamide.
that says a lot I belive as benzamide should yeild lower than the nitro subst.
you were also a little high on the temp when doing the rearrangement
and left it over night wow.
I would expect that to make a lot of difference as it would in a normal rearrangement.
[Edited on 12-4-2011 by Ephoton]
e3500 console login: root
bash-2.05#
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
I think that is due to solubility though.
See my edits.
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
Ephoton
Hazard to Others
Posts: 463
Registered: 21-7-2005
Member Is Offline
Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.
|
|
chloroamides I think can blow up when distilling 
hoffmans were on alphatic amides attached too aromatic rings.
I think after 8 carbons I started to loose yeilds.
was some time ago that I played with this but finding this was very interesting.
post edit
I always stripped under vac no pritty for methanol.
but lit leads us towards rotovap.
[Edited on 12-4-2011 by Ephoton]
e3500 console login: root
bash-2.05#
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
Yeah, I heard that . I just want to strip off the methanol.
Anyways, another option for the amides you speak of is to form the amide in methanol and filter the TCCA, then treat that solution with an excess of
sodium hydroxide in methanol. You will primarily get the carbamate, which can be hydrolzed by either acid or base in water. Edit:but I suspect youve
seen that route.
But I agree, it is interesting stuff. I like the acid -> amide -> amine sequence because carboxylic acids are so common OTC.
[Edited on 4-12-2011 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
