Argox (Hive Bee)
01-27-02 03:55
No 261343
      Can imine be isolated?  Bookmark   

SWIA respectfully asks for some help:

An amount of PMK (MDP2P) was subjected to red amin with NaBH4.  Molar ratio of PMK to MeNH2 = 1:1.2 (cutting it close, SWIA knows).  Reaction seems to be a complete failure.  Everything same as in successful operations except for two  things:

1.  Dessicant was not added to MeOH/MeNH2 solution either before, during or after ketone addition, although MeNH2 gas was passed over MgSO4 before dissolution in MeOH.

2.  MeOH was not fresh, but had some MeNH2 dissolved in it (about 0,5% w/w) and had been stored at room temp for 2 months.  Does MeNH2 react with MeOH?  What is product?  H2O?


The characteristic color change upon NaBH4 addition did not occur.  Solution remained same greenish lemonade color during entire 30 hours, not the brownish orange that is normally seen.

An oil can be obtained from the solution, but this oil is clear, not brown.  It does not smell like base, nor does it smell like ketone.  Subjecting a dry aliquot of this oil to normal hydrochloride precipitation nothing happens.

SWIA postulates this oil to be the intermediate imine (Please, God!) due to fact that NaBH4 was rendered ineffective by too much water in solution--(1 mol ketone yields 1 mole H2O, if additional H2O were present, perhaps NaBH4 was destroyed by water--the foaming upon NaBH4 addition was quite a bit more than is normally seen and temp did not rise as much as normal).  If this is the case, then perhaps SWIA can isolate the imine and subject it to new reduction in anhydrous MeOH.

How will SWIA know this is the imine and not secondary alcohol or other reaction product?  Analytical instruments are not available.

Is the imine stable enough to subject to high-vacuum distillation.  Will it decompose?  At what temp?

One last thing--ketone is commercial PMK, but nine months old.  Mostly stored in freezer, but for last 45 days at room temp.  Recooled right before red amin.  Does commercial PMK go bad?  (Please, say no.)

Before SWIA jumps in front of the train, perhaps the experienced bees could tell him what might have happened and how to remedy.

(Master Searcher)
01-27-02 04:35
No 261369
      Re: Can imine be isolated?  Bookmark   

I have these patents numbers in my notes.  They might help.

(Old P2P Cook)
01-27-02 08:11
No 261412
      Re: Can imine be isolated?  Bookmark   

So what was the molar ratio of NaBH4? Did you get hydrogen gas evolution from the excess NaBH4 when you acidified for workup? When you mixed the methylamine solution with the ketone did you get a mild exotherm. If all of the chemicals were what you thought they were then this is a reaction that is very difficult to screw up.

If you think you still have imine (which seems unlikely), don't try to isolate it just add more borohydride.

You have done this reaction before? What is the difference this time?
(Hive Bee)
01-27-02 17:52
No 261513
      Re: Can imine be isolated?  Bookmark   

Imines have been isolated by distillation, but it's rather unlikely that you have the imine, since imines also form hydrochloride salts frown

01-28-02 01:37
No 261570
      Re: Can imine be isolated?  Bookmark   

You got alcohol. PM LT/