Author Topic: A modification of Beaker´s method for 2C-H  (Read 10755 times)

0 Members and 1 Guest are viewing this topic.

Barium

  • Guest
I am not worthy...
« Reply #40 on: July 17, 2002, 01:13:00 PM »
The inventor himself. Great to see you here again!!

The nitronate comes out when toluene is used, this can happen when ethylacetate is used as well. In those cases I usually add a little more EtOH to bring it into solution again. If all of the nitronate is allowed to fall out the volumes of solvent needed becomes quite high. Otherwise stirring becomes very difficult. 1,4-Dioxane is a good cosolvent if one wants to isolate the nitronate. I originally used dioxane, but since this solvent is really nasty I quickly decided to find another solvent.

The better yield, stated for the potassium formate was when I compared the yield from the NaBH4/Pd-C reduction which only gave a 29% yield. I´m very curious to see the results of CTH with 2,5%Rh/2,5%Pd/C and various hydrogen donors.

Sadly my access to NMR is no more  :( . I have not looked at the dimer content yet. I´ll try when I have time and proper equipment.

What are you up to nowdays?

It was truly great to hear from you.
Pls keep in touch

Sunlight

  • Guest
Glad to see you again
« Reply #41 on: July 18, 2002, 12:57:00 AM »
Your 70-80 % matches with my 65 overall yield. I had bad luck with your procedure and this was the only run that finished without any accident, I had some hazards, one time the flask fall from my hands to the floor, and other time the refluxer was stoppered  with crystallized ammonium bicarbonate, so the methanol was boiling under pressure, when my friend removed the refluxer... well, I still have the roof stained, but no more serious consequences. This is a important question to considere in CTH with ammonium formate under reflux, it is formed ammonium carbonate in the refluxer and it must be watch over.
The reaction seems anyway a bit capricious, and yields seem to vary considerably, for example a friend has recently performed it and reported about a 40 % overall yield.

Barium

  • Guest
Improvement
« Reply #42 on: March 02, 2003, 06:02:00 PM »
It´s time to bring this old thread back to life again.

100 mmol (18,1 g) 1-(2-fluorophenyl)-2-nitropropene, or any other phenyl-2-nitropropene
100 mmol (3,8 g) Sodium borohydride
50 ml EtOAc
20 ml EtOH
About 5 ml Glacial acetic acid
100 ml Water
60 ml DCM

To a 500 ml rb-flask, placed in a cooling bath and equipped with a magnetic stirbar and a thermometer, the nitrostyrene was added in one portion followed by the EtOH and EtOAc. Sodium borohydride was now added in portions of 1 g every five minutes while keeping the temperature between 20-30°C. When all the borohydride was added the reaction mixture was allowed to stir for another 30 minutes.

Glacial acetic acid was now added in 0.5 ml portions while the temperature was kept at 20°C. Before the acetic acid addition the color of the reaction mixture had changed from the initial bright yellow to a very pale yellow. When approximately 4-5 ml acetic acid had been added the last remaining yellow coloration faded away leaving a very thick practically colorless suspension, at this point the temperature tended to rise a bit due to stirring problems.

100 ml ice-cold water was now added in one portion and mixture was stirred vigorously for a couple of minutes. The liquids were decanted from some insolubles remaining on the bottom and transferred to a rotovap. The EtOAc was removed by distillation at reduced pressure. The nitroalkane was extracted with 2x30 ml DCM, the combined extracts dried over MgSO4, filtered and the solvent evaporated leaving a slightly yellow, fruity smelling oil.

Yield 16,3 g  1-(2-fluorophenyl)-2-nitropropane (89%).


SpicyBrown

  • Guest
Sounds nice.
« Reply #43 on: March 02, 2003, 09:12:00 PM »
Barium, when Beaker originally proposed his method, he used 4 molar equivalents of NaBH4 to avoid the formation of a dimer by-product. Have you checked for such a by-product by TLC or other means? Or is the dimer by-product not an issue for some reason with nitropropenes as opposed to nitroethenes?

-SpicyBrown

Rhodium

  • Guest
Only the nitroethenes dimerize uncontrollably.
« Reply #44 on: March 02, 2003, 10:11:00 PM »
Only the nitroethenes dimerize uncontrollably.

SpicyBrown

  • Guest
Nice.
« Reply #45 on: March 03, 2003, 01:06:00 AM »

Only the nitroethenes dimerize uncontrollably.



Excellent, thank you!

-SpicyBrown