Author Topic: 3,4,5-trimethoxynitrosyrene rdxn trouble  (Read 3564 times)

0 Members and 1 Guest are viewing this topic.

Vaaguh

  • Guest
3,4,5-trimethoxynitrosyrene rdxn trouble
« on: March 23, 2004, 05:18:00 PM »
Hi,

After performing the NaBH4/IPA/H2O reduction of recrystalized 3,4,5-trimethoxynitrostyrene the nice white solution always turns to a deep yellow color after adding dilute acetic acid to quench the excees borohydride, deduced from bariums trials the 3,4,5-trimethoxynitroethane is supposed to be a white solid. A yellowish oil however is always recovered. As for the details a 1,3 molar excess of NaBH4 was used and from the fizzing it definately shows that there is some excess borohydride in the post reaction mixture.

Does anybody know what could be the cause of this spontaneous color transformation?


Barium

  • Guest
Have you given the oil time to crystallise?
« Reply #1 on: March 23, 2004, 09:26:00 PM »
Have you given the oil time to crystallise? Right now I can't remember if I have gotten the nitroalkane as an oil which later solidified. But it would not seem too strange since there is a lot of alcohol present which can prevent immediate crystallisation. Isolate the oil and store it overnight at room temp and see what happens. I know that 1-(2,4,5-trimethoxyphenyl)-2-nitropropane falls out as an oil first if there is too much alcoholic solvent present. It has taken up to five-six hours for it to solidify completely on occasions.

Vaaguh

  • Guest
will try!
« Reply #2 on: March 23, 2004, 10:40:00 PM »
Thanks for the information, the alcohol was stripped but the oil was not given time to solidify. Yesterday a new reduction was started but there was no time to work it up, i will post the details in a few days.


Barium

  • Guest
Ouch! I would not leave such a reaction ...
« Reply #3 on: March 24, 2004, 12:57:00 AM »
Ouch! I would not leave such a reaction mixture for a couple of days and expect a good yield of nitroalkane.

Vaaguh

  • Guest
as a side note
« Reply #4 on: March 24, 2004, 12:58:00 AM »
After a quick peek there seems to be a lot of white solids in the now yellow NaBH4 post reaction mixture (could be all borate salts ofcourse but that is doubtfull). The mixture shouldnt have left sitting there like that  :-[



The starting 3,4,5-trimethoxynitrostyrene that was used had been recrystalized twice and gave a sharp mp of 118-119 °C.
One hour after the addition of the nitrostyrene the alcohol/water solution was milky white.

The yellow oil obtained from previous NaBH4 reductions of 3,4,5-trimethoxynitrostyrene (10 mmol runs) gave upon reduction of the nitro group using zinc/formic acid or zinc/potassium formate a wide variety of yields ranging from excellent to none.

Would anyone know what a good TLC solvent system would bee for 3,4,5-trimethoxynitrostyrene/3,4,5-trimethoxyphenylnitroethane?


Sunlight

  • Guest
CH2Cl2
« Reply #5 on: March 26, 2004, 06:20:00 PM »
There's a scientific paper in wich they reduce nitrostyrenes with IPA:CH3Cl3 and silica gel with NaBH4. In his example, may be 3,4 DMNS or similar, they use CH2Cl2 as TLC solvent, the nitroethane was at about 0.8 and the dimeric imputity at about 0.6. Unfortunately I don't have the paper at hand. I made it and I believe to remember that for 2,5 DMNS the nitrostyrene and nitroethene were in the same place (test it) and the impurities were lower. I hope it can help.

Rhodium

  • Guest
silica-gel assisted reduction
« Reply #6 on: March 26, 2004, 07:31:00 PM »
Sunlight: The article you are thinking of has been posted here:

Post 492478

(Rhodium: "Not novel, but a classic reference", Novel Discourse)



Panoramix

  • Guest
The best
« Reply #7 on: March 27, 2004, 03:45:00 AM »
You are the best, rhodium.