Author Topic: Hofmann Rearrangement Yields  (Read 3632 times)

reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #80 on: August 18, 2011, 02:56:07 PM »
No, I fucked that up. I will be trying again, though. Like an idiot I tried what came out, but not enough, thought it to be mostly inactive and dumped it :( Makes me sick because when I did that was the first time I got anything crystalline from the hoffman and I fucking chunked it. Part of the problem is my living situation, working in a kitchen. I need a dedicated lab area and I would hang on to things longer. I'm looking for a crib with a garage or work shed now, then the serious shit can start!
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #81 on: August 23, 2011, 04:08:31 AM »
Okay, what's up with this? I have had several people vehemently insist that heat in the Hoffman is what is killing the yield. I've also had several people vehemently insist that you must have heat to effect the rearrangement. I have no idea, as I am but a lowly uneducated hick who does what smart people do and hope I have the same or atleast favorable results.

What some guys on Mattlock did
20gms of amide were placed in 250ml of -2C bleach and stirred until a uniform consistency was achieved. This was stirred in an ice/acetone bath for about 2 hours as the idiot doing it forgot all about the lye. Finally a solution of 200ml of water and 20gms of lye were added. The ice bath was replenished as needed for 24 hours to maintain 0-2C and stirring set as high as it could go without slinging the stir bar loose. The progression of colors in this reaction has thus far been very consistent, being loosely tied to temperature and time. As expected the color never changed during it's time in the ice, it never does. Usually upon hitting room temperature it will get white, then brown/tan and with heat it will go into darker brown and finally to red. None of this happened. Upon letting the solution warm up to room temperature on it's on it stayed the exact same color. After 18 hours or so it turned yellow and a brown precipitate began to show. After another full 24 hours (three days from start to finish) heat was added to bring it up to 60-63C and was held there for 30 minutes. After the 30 minutes it was allowed to cool on it's on. Then the yellow liquid was decanted off of the waxy brown chunk in the bottom of the flask. 150-200ml of fresh xylene were added to the solid and it was stirred vigorously for an hour. The resultant xylene was filtered and washed with HCl water as usual.

Now, what's weird.

6.18gms of unreacted amide were recovered, this has never happened. That means only 13.82gms of the amide participated in the reaction. The recovered amide was as white as the day it was born, and apparently unaltered. Sparkly, soft and white (like Sedit's girlfriend)
The xylene then shat out 4.3gms of amine for a total yield of 31.11%

I'm inclined to believe that the heat is definitely an issue, especially considering that blahblahblah's monkey is obviously a pro and he didn't use heat. I have also came to another conclusion, to hell with bleach. TCICA to get the chloramide before hand from now on.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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dingbow

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Re: Hofmann Rearrangement Yields
« Reply #82 on: August 23, 2011, 10:18:52 AM »
I have yet to come across anyone posting an actual write up of this 'cold method' you speak of which doesnt use any heat, nor have I seen any patents or literature to state it either. Am I missing something here, who are these pros your referring to and where are their experiences noted?!

By the way when calculating yield, generally its calculated based on the amount of initial reactants used, regardless of whether you recovered any unreacted material at the end. Thus, your yield calculation should be based on 20g of starting amide, not 13.8. If you do this, the yield you achieved is lower then the 25% I achieved (I never measured the amount of amide I recovered in this run) with the well known method which involves heat. It took 6hrs to run my reaction, compared to your 3 days, this along with your current yield has me questioning this so called cold method.

I have acquired some TCCA to play with, i'll be removing the copper sulfate impurity shortly to give it a go. I just finished monomethylation which I'll post about shortly too.

reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #83 on: August 23, 2011, 07:45:33 PM »
One person in particular who has chose to not join this conversation, so I'm not sayin' names, claims steady 70% yields using no heat over two days sometimes more.

What else can I say?

There it is.

ETA: as for yieid calculation- at the end of the day I got 6.18gms of amide back, so......

Edit2: Dnigbow, I have less than zero interest in a pissing contest. If you get better yields in 6 hours, then I commend you, well done. I am an experimenter, plain and simple. I change things and note what happens. You won't see people posting write ups about the 'cold method' because it's anti to the info in the patent. Heat is generally just an accelerant for a reaction, not always, but usually. I've said numerous times that I don't understand the mechanism here, what do you want me to say to justify my not using heat? The people who have taken me under their wing are not people who blow these boards up and participate in these conversations, therefore I won't be saying so and so told me this or that. If you'd like me to keep my results to myself you can always ignore me. But, I'm hoping someone sees something in my procedure and makes a connection of some sort and says 'AHA, the XXX, that seems to be using a greater percentage of your amide and shitting out what it doesn't use" I dunno, this is fun to me, 4.3 grams of amine is more than I need for a year, so I don't give two fucks. I'm here to figure out a mystery, now where's my dog????
« Last Edit: August 23, 2011, 08:03:12 PM by reDEEMed »
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #84 on: August 25, 2011, 11:18:42 AM »
One person in particular who has chose to not join this conversation, so I'm not sayin' names, claims steady 70% yields using no heat over two days sometimes more.
hmm have they actually posted their procedure on a forum or have they only passed on this information to you in private?

Dont take it the wrong way, im not interested in any pissing contest. The reason I started this thread was to try and get some help to increase yields in this reaction. I merely made the point around your yield calculation, so that when comparing yields amongst ourselves we are comparing apples with apples, otherwise determining the best reaction parameters becomes rather confusing.

Its akin to comparing molar/molar yields to weight/weight yields and hence why in the hive people would stipulate either m/m or w/w to avoid confusion.

Coming back again, im open minded to the cold method (or any method proposed), but given the lack of info its a bit hard to understand whats going on.

reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #85 on: August 25, 2011, 04:09:58 PM »
It was passed on in private by more than one person and I have gotten the overwhelming impression that's how it should stay. I don't know why, but that's what I take away from it.

I think mostly anything that is gonna spoonfeed people these guys don't want it on their boards. I'm just guessing, but there again, that's my take away. I think talking about how the mechanism can run better cold would be okay.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna

fries

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Re: Hofmann Rearrangement Yields
« Reply #86 on: August 25, 2011, 05:00:59 PM »
Here's my take on the cold method. I am no chemist, so i know this writeup is shit etc. This is just how i got it to work with very limited experience and equipment. I don't even have a thermometer  that goes up higher than 40c.

Into a coke bottle is placed:
1. 20g Amide
2. 223ml of 4.7% NaOCl pre-cooled
3. 10g NaOH (15g monohydrate) in 200ml H2O pre-cooled

Shake the coke bottle like your life depends on it for about 5 minutes and place it in the freezer/fridge to get it nice and cold again. Shake it every 30 minutes or so, making sure never to let the temperature get too hot that the second part of the reaction starts happening. Keep doing this for a few hours, then leave the bottle in the fridge over night.

I usually lay the coke bottle on its side for the entire Hoffman, I think this allows greater surface area between the two phases.

Continue for a couple of shakes the next morning and then allow the mixture to rise to room temperature. Make sure your room isn't too cold, above 23c should be ok - otherwise it takes ages. I try to shake it as often as possible, every hour for a few minutes should be good.

Leave it at RT for about 24 hours. By this time all of the precipitate has turned into a dark brown oily mush that flows around the inside of the coke bottle (First picture). Add another 5g of NaOH and shake which instantly warms the mixture to about 30c. Leave it for another 2 hours and shake a few times (2nd and 3rd picture).

Extract with 3x100ml toluene, first extract is dark brown, almost black (4th picture), the combined extract is also almost black. Titrate with dilute HCl to get your orangish water layer (5th and 6th picture), wash with toluene, evap to get some reddish yellowy orange amine crystals, clean to get 4.5g purely white glimmering amine.

I know the yield isn't great, but you wanted a writeup on the cold method...

« Last Edit: August 25, 2011, 05:07:05 PM by fries »

reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #87 on: August 25, 2011, 05:20:18 PM »
I usually get some nasty looking shit too, but one wash in acetone usually brightens it up quite a bit. What's weird about that last time when it gave back all the unreacted amide, the amine that came out was WHITE AS FUCK. This pic is as it came out, no wash.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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fries

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Re: Hofmann Rearrangement Yields
« Reply #88 on: August 26, 2011, 12:43:08 PM »
I find a simple acetone wash to be inadequate. Dissolve in ABSOLUTE MINIMUM volume of boiling alcohol, dump in 3/4 volumes of acetone and put in the fridge for a while. Then filter off your beautiful clean crystals. If you didn't use too much alcohol, the whole lot should turn into a crystal soup as soon as you dump in the acetone.

jon

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Re: Hofmann Rearrangement Yields
« Reply #89 on: August 26, 2011, 08:25:18 PM »
thanks for the fries that's what i been saying for a long time.
that method seems to yeild no better than say 70-80 c.
« Last Edit: August 26, 2011, 08:27:39 PM by jon »

reDEEMed

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Re: Hofmann Rearrangement Yields
« Reply #90 on: August 26, 2011, 10:34:48 PM »
Well, I'm thankful mine has been very clean thus far and scary potent, so I hear on tv ;D
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna

WazOne

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Re: Hofmann Rearrangement Yields
« Reply #91 on: August 27, 2011, 12:09:22 AM »
Run it cold over night. Work up is a bitch. So thats why heat was added. But it is not needed. 50+ % w/ consistent and thorough work up. Off white, a tone wash brings out the white.

akcom

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Re: Hofmann Rearrangement Yields
« Reply #92 on: August 27, 2011, 02:22:15 AM »
As an aside, aldehyde was opened, left at RT in a closed container for 24hr, then transferred to a fridge.  TLC 3 months later shows a major spot and a less polar very minor spot.  NMR confirmed aldehyde is the major spot, minor spot unknown.  Seems pretty stable.
« Last Edit: August 27, 2011, 02:31:56 AM by akcom »

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #93 on: August 27, 2011, 09:51:43 AM »
Thanks fries, appreciate the write up. I might try and mish mash your method with mine, say run it in a bottle in the fridge with shaking overnight then heat it as per the 'usual' method.

Im going to try the TCCA method first though, should be done in a few days. If that works out, it could turn out better then the 'cold' or 'hot' method. Hopefully it works, I need more amine to try the monomethylation again...

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #94 on: August 27, 2011, 09:53:03 AM »
As an aside, aldehyde was opened, left at RT in a closed container for 24hr, then transferred to a fridge.  TLC 3 months later shows a major spot and a less polar very minor spot.  NMR confirmed aldehyde is the major spot, minor spot unknown.  Seems pretty stable.
Interesting, did you have a control TLC result? My aldehyde has been sitting in dark RT conditions for months, hope it stays good!

fries

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Re: Hofmann Rearrangement Yields
« Reply #95 on: August 27, 2011, 06:00:41 PM »
that method seems to yeild no better than say 70-80 c.
Yeah i know that, but its pretty simple and doesn't need any fancy schmancy stuff like decadent hot plates and thermometers :D

I don't find workup difficult, my only sep funnel is 100ml, so i'm separating layers more manually from beaker to beaker... just clean the result as i mentioned.

I'd love to know what Waz is doing right to get those 50% + w/w yields... running 200g batches or something?
« Last Edit: August 27, 2011, 06:05:04 PM by fries »

akcom

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Re: Hofmann Rearrangement Yields
« Reply #96 on: August 27, 2011, 10:24:14 PM »
As an aside, aldehyde was opened, left at RT in a closed container for 24hr, then transferred to a fridge.  TLC 3 months later shows a major spot and a less polar very minor spot.  NMR confirmed aldehyde is the major spot, minor spot unknown.  Seems pretty stable.
Interesting, did you have a control TLC result? My aldehyde has been sitting in dark RT conditions for months, hope it stays good!
Not sure what you mean by a control?  A known authentic sample of aldehyde?  The TLC was confirmed via NMR.  Aldehyde was the major spot.

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #97 on: August 28, 2011, 01:36:14 AM »
No I meant did you TLC your aldehyde as soon as you received it, to obtain its original purity for comparison to the aged sample? Or did you purify it then store it?

akcom

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Re: Hofmann Rearrangement Yields
« Reply #98 on: August 28, 2011, 05:37:48 AM »
The aldehyde was stored as is.  Its very possible the minor contamination was in the sample originally.

edit: should mention that the contamination was definitely not the carboxylic acid as it was less polar
« Last Edit: August 29, 2011, 03:53:54 AM by akcom »

dingbow

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Re: Hofmann Rearrangement Yields
« Reply #99 on: August 28, 2011, 05:38:26 AM »
Alice just ran the TCCA method for prep of N-Chloroamides:

-Fully dissolved 10g amide into 100ml MeOH (took tiny bit of heat to speed things up)
-Added 4.1g TCCA, stirred for an hour (some evolution of heat occurred)
-Solid precipitate formed fairly quickly after addition of TCCA, assuming this precipitate is CYA
-CYA filtered
-Instead of boiling off solvent (pita to setup and timely) to obtain N-Chloroamide solid, I precipitated it by addition of H20, seemed to work great.

Few things work mentioning, my TCCA was a solid block that had copper sulfate mixed in. This was removed by powdering the block and stirring in H20, which dissolved the copper sulfate, then filtered and dried it as much as I could be bothered. MeOH was not dried. The final product obtained is a very clean white powder with no smell what so ever. Currently drying, so when thats done I will post yield.

I'll get a MP test for this substance too. Im pretty excited to see how this stuff goes in the rearrangement.
« Last Edit: August 28, 2011, 05:46:56 AM by dingbow »