11-29-03 03:36
No 473749
A bromination of 2C-H was attempted as described in ../rhodium /2cb.bro
The reaction was run at 1/10th scale of that described in the aforementioned document.
The 2C-H was prepared by Zn/HCOOH reduction of 1-(2,5-dimethoxyphenyl)-2-nitroethane. This reduction was incomplete, leaving some of the starting material in the reaction product. To solve this, the reaction product was washed with 10% NaOH, which resulted in the yellow colour of the contaminated organic product disappearing as the sodium salt of the nitro compound was formed, drawing it out of the organic layer. The organic product was extracted with ether, dried with MgSO4 and evaporated to leave 2C-H as an almost white (v. slight brown tinge) oil that was rubbery smelling.
The bromination reaction was run as described in the document linked above. The reaction certainly created a significant amount of HBr, that fumed in air if the foil lid was left off the container (also ate through the tinfoil).
One day later no crystals have formed, in spite of putting the finished reaction in the fridge (not even any crystals of GAA).
Can anyone enlighten me as to possible reasons this reaction has not run as described?
Has anyone else had a similar experience?
What should be done with the post-reaction mixture. Is it possible to isolate any product do you think?
What work-up would you suggest?
Many thanks for your help.
(Chief Bee)
11-29-03 05:08
No 473755
You didn't distill the intermediate 2C-H freebase? If so, the contained impurities might trap the product. I suggest you perform an acid-base extraction and then crystallize the hydrochloride salt and then purify it by recrystallization (I have posted suitable recrystallization solvents before).
(Hive Addict)
11-29-03 06:00
No 473763
The 2C-H was prepared by Zn/HCOOH reduction of 1-(2,5-dimethoxyphenyl)-2-nitroethane.
I have performed exactly the same reaction not that long ago; I submitted the 2C-H to a bromination reaction as well (Br2 in AcOH).
My 2C-H was not purified and contained some high MW impurities (but not more then 5% according to GC), tentatively identified as dimers originating from the NaBH4 reduction of the nitroethene. However, these impurities did not interfere with the bromination. It took a while before the 2C-B.HBr precipitated though, but not longer then 1h. I'd have to take a look in my labnotes to give you the exact reaction conditions.
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(Hive Bee)
11-29-03 09:08
No 473783
Thanks for your advice. Wanted to distill the freebase, but only had 2.5g and distilling this small amount would likely be a way to end up with nothing.
I imagine the freebase was too impure as you suggest Rhodium.
Your advice on A/B extraction, crystallization and recrystallization will be followed.
Will report back in 2-3 days.
(Hive Bee)
11-30-03 05:45
No 473891
after being kept in the fridge for a further 24hr, there is definitely some crystallization and the mixture is now a dark brown sludge. Warming the mixture to room temperature does not get rid of the (tiny) crystals, so they are unlikely to be acetic acid.
Strange think is the mixture is still evolving noticable quantities of HBr. There are misty strands coming out the top of the beaker when the foil is removed. Blowing across the top of the beaker makes the HBr gas really obvious.
Do you think that the bromination is progressing really slowly for some reason (possibly water contamination or something) and the mixture should be left longer?
I also don't really understand why HBr is being evolved. Doesn't all the HBr created from the bromination reaction react with the freebase brominated product to create the HBr salt?
(Hive Bee)
12-06-03 01:37
No 474974
Reaction mixture was made alkaline with 10% NaOH and extracted with toluene. Toluene extracts were combined and shaken with a bit of conc. HCl, which led to a black gooey mess falling out at the bottom of the flask - prouduct with a hell of a lot of contamination.
The black gooey mess was stirred in boiling ether which broke it up somewhat and made the ether somewhat brown. Ether was decanted to leave a still gooey, black mess.
Acetone was added to the mess and stirred. The mess went into solution and then began to crystallize within 30 seconds (this was complete in 10 minutes).
The acetone was filtered from the crystals and the crystals were recrystallized twice from propan-2-ol and ether.
The result was a poor yield of bright white crystals (0.5g from 2.5g of impure 2C-H). But I'm somewhat surprised to get anything worthhwhile out of that sticky black mess.
Guess this shows that it can be important to purify your 2C-H before bromination. This way you could end up with tan crystals rather than black goo.
Bioassay of 5mg insufflated provided a very positive effect - more tests to be done later! Even though the yield is a failure, it has been nice to try a new product.
Thanks to rhodium for this last bit of advice, bandil for advice on the nitrostyrene condensation and barium for advice on the C=C reduction.
It will be possible to do much better from here, but for the moment I am happy that I can experience this new (to me) compound.
In the end I left the bromination going for about 5 days. I dont know if this may have produced some of the black mess.
(Chief Bee)
12-06-03 07:18
No 475019
In the end I left the bromination going for about 5 days. I dont know if this may have produced some of the black mess.
Yup, a lot of side-reactions can happen during that time - the desired reaction happens in a few hours, after that only detrimental effects set in.
(Stranger)
12-10-03 08:00
No 475938
Bee a maniac of the purity distil under vac 2CH freebase, Xtalise and reXtalise it (HCl salt).
Because the 2CH resulting from this route ( Zn/HCOOH reduction of 1-(2,5-dimethoxyphenyl)-2-nitroethane.)
can contain a lot of impurities notably dimeric impurity.
Have you protected your 2CH freebase from the CO2?
I do not advise you to absorb your product because it can contain toxic impurity (5 days?!) and particulary bromine.
Excuse my bad english