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Author Topic: Hofmann Rearrangement Yields  (Read 3632 times)

Tsjanga

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Re: Hofmann Rearrangement Yields
« Reply #160 on: August 23, 2012, 11:41:30 AM »
Hmmm I allready fucked it up by step 1.....
Would love to try the TCCA route but I have to get to the amide first....  :-[
Used 2 different sources of hydroxylamine and Soda but still it isn't solidify just being a greenish blobbish layer and 1 watery layer.

WazOne

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Re: Hofmann Rearrangement Yields
« Reply #161 on: August 23, 2012, 09:18:28 PM »
This doesnt relate to the hofmann. Try extra hydroxylamine and half again carbonate stir some more. Is the ph neutral?
Or decant water layer add 3 times the volume in ICE cold H2O and stir as quick as possible. The oxime should crash out.. Carry on from there.

The answers you seek or should I say the solution to your problem/s have been published already.
Hope none of the previous experiments were chucked out as its an easy Fix.

Cheers

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #162 on: September 01, 2012, 10:58:43 AM »
As has been mentioned, you do not need a solid oxime to continue. I have never obtained a solid oxime. Just extract the non aqueous and proceed, there have been posts made about this already, I described my procedure on PN.

Sneak

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Re: Hofmann Rearrangement Yields
« Reply #163 on: September 02, 2012, 12:06:56 AM »
After reading this thread i heard local wild life are quite excited to defrost some shit soon and report some results. They mentioned they need to create the oxime and amide first still. The method posted by fries in the coke bottle ran cold looks straight forward for a first time run for the rearrangement , the arrangement of animal's went on to explain then they are going to try a few other heated methods later depending on yields. 45% would be good enough for them. 3g street mda allows for many visually enhanced nights in the forrest. And lasts a good while.  :)

It also beats fucking around with mercury they said.

This had made a lot of sense. Hope we can contribute!... They said, whilst merrily disappearing back into from whereth they cometh.

Thank you.
« Last Edit: September 02, 2012, 12:10:36 AM by Sneak »
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Tsjanga

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Re: Hofmann Rearrangement Yields
« Reply #164 on: September 02, 2012, 12:45:11 PM »
Quote from: dingbow on September 01, 2012, 10:58:43 AM
As has been mentioned, you do not need a solid oxime to continue. I have never obtained a solid oxime. Just extract the non aqueous and proceed, there have been posts made about this already, I described my procedure on PN.

Allright!
Thank you dingbow, heard that the neighbors dog has a friend who told him that it worked.

letters

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Re: Hofmann Rearrangement Yields
« Reply #165 on: September 04, 2012, 10:46:31 PM »
oxime can be made to generate small seed crystals when put under at least 4000 rpm for 5 minutes. These can then be used to crystallize large batches of oxime. With a seed crystal, the oximes crystallizes in minutes. Make sure to keep efficient stirring while adding the seed and while letting it crystalize, or it will make a brick that will be very hard to break.

regarding the hofmann/tcca - with a co-solvent yields are much better then 45%...

Sneak

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Re: Hofmann Rearrangement Yields
« Reply #166 on: September 04, 2012, 11:32:00 PM »
How much better?
If you really want to enjoy a pure, clean product the only way... is to make it yourself...

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Tsjanga

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Re: Hofmann Rearrangement Yields
« Reply #167 on: September 05, 2012, 09:43:55 AM »
Quote from: letters on September 04, 2012, 10:46:31 PM

regarding the hofmann/tcca - with a co-solvent yields are much better then 45%...

Can you explain it a bit more please?

German

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Re: Hofmann Rearrangement Yields
« Reply #168 on: September 05, 2012, 09:25:43 PM »
The oxime can be solid or liquid it doesn't matter. Usually just washing with a bunch of water then cooling will turn from liquid to solid but I personally would pour it out before it had a chance to solidify because liquid is a hell of a lot easier to get out of a flask then a solid.

You're not getting a %45 yeild on the hoffman no matter what your solvent. Aint happening. I don't care about theory and I don't care about how much you got your unclean product to finally weigh in at, %45 isn't happening. As cheap and as few as all reagents are who cares anyways. If yeild is that big of deal get your %98 yeild with sodium azide in a few hours and hope you don't blow yourself up or poison yourself, otherwise I wouldn't get caught up in dramatically increasing yeild because it's futile.

DopeBee

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Re: Hofmann Rearrangement Yields
« Reply #169 on: September 06, 2012, 03:09:09 AM »
Quote from: German on September 05, 2012, 09:25:43 PM
You're not getting a %45 yeild on the hoffman no matter what your solvent. Aint happening. I don't care about theory and I don't care about how much you got your unclean product to finally weigh in at, %45 isn't happening.

(misinformation)
I get 70% yields.
« Last Edit: September 08, 2012, 09:04:21 AM by java »

German

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Re: Hofmann Rearrangement Yields
« Reply #170 on: September 06, 2012, 04:22:47 AM »
Bullshit.

Sneak

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Re: Hofmann Rearrangement Yields
« Reply #171 on: September 06, 2012, 04:44:47 AM »
70%? That's a nice figure. How are you running that..?
If you really want to enjoy a pure, clean product the only way... is to make it yourself...

You miss 100% of the shots you don't take...

DopeBee

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Re: Hofmann Rearrangement Yields
« Reply #172 on: September 06, 2012, 06:17:42 AM »
(misinformation)


Right sorry I should've been clearer.
If I get 10% amine I'll get back 80% of my amide.
If I get 20% amine then I'll get back 70% amide.
So each reaction I only lose 10% of total weight which comes out to 70% total yield.
And since we're taking off a Carbon atom anyways, that's responsible for like 9% of the loss.
« Last Edit: September 08, 2012, 09:04:49 AM by java »

Quantum Dude

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Re: Hofmann Rearrangement Yields
« Reply #173 on: September 06, 2012, 04:41:08 PM »
Quote from: DopeBee on September 06, 2012, 06:17:42 AM
Right sorry I should've been clearer.
If I get 10% amine I'll get back 80% of my amide.
If I get 20% amine then I'll get back 70% amide.
So each reaction I only lose 10% of total weight which comes out to 70% total yield.
And since we're taking off a Carbon atom anyways, that's responsible for like 9% of the loss.
For the record, the sludge you end up with during workup is FAR from being pure unreacted amide. You should do your math again because there is no way you have 70 % (w/w)  MDA*HCl there.

German

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Re: Hofmann Rearrangement Yields
« Reply #174 on: September 08, 2012, 04:39:09 AM »
^^^ Yep what he said. You are making big assumptions about that sludge. Have you ever ran that "unreacted amide" through again? I have. A bunch. And you know what I've gotten back? ZERO. Thats not unreacted amide, it's reacted byproducts. The reason the yeild is for a fact so low and isn't increasing is because of all the side reactions going on. Who cares anyways,  I'll take %25 on an easy OTC shake and bake over a %85 schedule 1 precusor route ending with heavy metals.

Sneak

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Re: Hofmann Rearrangement Yields
« Reply #175 on: September 08, 2012, 11:24:32 AM »
Yeh man exactly!!! 25%...Then make some more!
If you really want to enjoy a pure, clean product the only way... is to make it yourself...

You miss 100% of the shots you don't take...

Tsjanga

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Re: Hofmann Rearrangement Yields
« Reply #176 on: September 08, 2012, 03:32:37 PM »
So that means dingbow is wrong about his percentages?

java

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Re: Hofmann Rearrangement Yields
« Reply #177 on: September 08, 2012, 03:38:39 PM »
.....dingbow never made such claims his comments can be found on this thread....his results are from a single run for which he states its been repeated with similar yields....java
« Last Edit: September 09, 2012, 01:32:42 PM by java »
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Quantum Dude

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Re: Hofmann Rearrangement Yields
« Reply #178 on: September 08, 2012, 04:00:53 PM »
For the sake of bringing back some actual CHEMISTRY in this thread I would like to point out that molar yields above 60 % are indeed feasible with the Hofmann rearrangement on Helionamide but one needs to understand the actual mechanism and kinetics of the reaction. There are some crucial steps that one needs to control experimentally in order to drive the reaction to the desired product. Its sure as hell more complicated than simply freezing and baking the amide in bleach Ill tell you that.

All that information is provided in this thread, one just needs to pick up some papers on the theory and dig through most of the crap within this thread.
« Last Edit: September 08, 2012, 05:04:12 PM by Quantum Dude »

poisoninthestain

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Re: Hofmann Rearrangement Yields
« Reply #179 on: September 16, 2012, 09:31:15 PM »
All mp.'s below were taken on a melting block apparatus and observed over several runs:

arylamide post Beckmann rearrangement crude mp. 107-110C (usually brown is the most common impurity)
after recryst. from a EtOH:H2O system amide mp. approx. 117-126 as white crystals.

...and yes, as QD stated yields can exceed 60% molar but kinetics of the overall reaction rate are critical with enthalpy changes probably the most crucial.
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