05-07-03 20:20
No 431959
Here is the Oxime by Chromic:
Typical run forming anethole ketoxime from PMP2P
In this example anethole ketone was used to form anethole ketoxime, but the amount of MDP2P is the given and in the end it will give a similar yield. Detailed notes on using isosafrole ketone aren't in my lab book as the procedure is straight forward and I never thought it necessary to take notes.
Added a 1" magnetic stirbar, 14ml dH2O and 6.7g Na2CO3 (126mmol base, 1.35 equiv) to a 250ml round bottom flask. Start stirring and add 9.6g (NH2OH)2.H2SO4 (116mmol hydroxylamine in the salt, 1.25 eq). Allow this to stir until uniform and add 72ml MeOH and 15.3g PMP2P (93mmol phenylacetone, 1 eq - or 16.6g MDP2P). Refluxed for 60 mins then added 37ml cold water. A white sludge settles to the bottom of the flask. This is not the oxime. Move this to the freezer for one hour. Remove and shake. Crunchy crystals of ketoxime should form. Do not confuse this with a thick sludge that always forms. Suction filter the solution and wash the crystals with 186ml of cold water. If you go to filter before the crystals form, you will see an oil form in the filter flask, this is your oxime that failed to crystallize. The yield of white anethole ketoxime in this example was 14.6g (87% yield). Expect a higher yield! I accidentally spilled some oil in transferring it... Isosafrole ketoxime has always been prepared in just as good yields, but has always turned out an off-white color. No purification was ever used before proceeding to the reduction. Make sure the oxime is bone dry--this can take days--before you take the yield and progress to the reduction. Also note that other substitutions for the hydroxylamine source, other alcohol solvents and other bases (baking soda, sodium acetate, etc) have worked just as well when in equimolar amounts.
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Swim tryed this with MDP2P, and his ketone was not soluted.
And it did not work. Swim got a ton of that precipitate that Chromic warns about, which upon shaking did not dissolve. So swim filtered it off, looked like Na2SO4, washed it with some water. Most dissolved, some did not.
Refiltered, these crunchy looking rocks were not the oxime, but had a distinct hydroxylamine smell to them.
Were completely insoluble in MeOH, hot or cold, but soluted in water completely, with stirring. Swim layed them out on a piece of aluminum foil. Warmed up the oven for 5 minutes, turned the heat off, and put the foil in the oven. Within a minute these crunchy rocks were completely liquid, swim took the foil out of the oven right away and within another 5 minutes this stuff recrystallized at RT.
What do you think these crystals are?
Once the precipitate was filtered oil was left sitting at the bottom of the jar, this oil distilled out at ketone temp. and was completely clear after distillation.
Swim is starting to suspect that his ketone is not good, even though it passes the bisulfite test with near quntitave yield. This tone does not get viscous in the freezer. And did not form an oxime upon several attempts.
Can this be? Any input would really be appreciated.
It's starting to feel like there is a new generation of bad sass out there.
if at first you don't succeed...BzZz at the-hive
(Synaptic Self-Mutilator)
05-08-03 00:46
No 431990
Those crystals are more like a sludge, they are very fine, right? They are not the ketoxime. The ketoxime is often off-colored, melts easily, etc. Just try melting those crystals on some aluminum foil under a flame, if a small 50mg bunch isn't nearly in flames in seconds, then it's not ketoxime.
Well, if you're positive you've got pure ketone, then add a ton of water to crash out your ketoxime. Extract with DCM and boil off the DCM, you should get crystals if you started with pure ketone and all your other reagents, reaction times, etc were good. (you might need to seed it, or wait a bit)
Keep in mind, you MUST wait for those ketoxime crystals to form after the rxn. They often take time to form... sometimes even overnight.