04-08-03 11:32
No 424805
An oxime was prepared by combining .5 mole of ketone with 1 mole of NH2OH, and bringing the contents to reflux in 800ML MeOH. The oxime was a white oil, that partialy separated upon cooling. It was isolated by stripping of the solvent in a rotorvap, but not allowed to dry up to a solid.
This oil was placed in ethanol, which was dryed with silica gel in the freezer for a couple of hours, along with 20g Raney Ni, into a hydrogenation apparatus. The pressure was brought up to 2.5 bar, and the stirrer speed was 1500 rpm.
(The Ni was washed down with a bit of water, dew to time constaints.)
After only 1.5 hours the absorbtion has completely stopped, and after 2 hours the reaction was stopped. The catalyst was fitered off, and a crystal clear oil dropped out of the solution. It was separated off, and the remainder of the alcohol was evaporated off in a rotorvap, leaving more crystal clear residue. The clear oil was combined, and represented a 92% yeild!!! It was not the target molecule
Where am I going wrong??
P.S. The ketone was tested with the bisulfate test.
(Hive Bee)
04-08-03 12:08
No 424812
Just a thought , but swim would follow Sonson's words to the T. In other words , dry the oxime as much as possible. If he used dry, powdered oxime , then swim would too. Good luck and keep the bees updated .
my guru once told me to "just be" , now I realize he meant "just bee" :)
(Old P2P Cook)
04-08-03 16:45
No 424897
After only 1.5 hours the absorbtion has completely stopped, and after 2 hours the reaction was stopped.
And is the product basic?
All those moments will be lost in time, like tears in rain.
(Synaptic Self-Mutilator)
04-08-03 19:27
No 424940
If I'm using powdered oxime, I get 80% yields with Al/Hg reduction, if I'm using the gooey oil oxime I get 20% yields.
I think you should more carefully distill your ketone and really watch the reaction conditions for the oxime formation.
(Hive Addict)
04-09-03 02:01
No 425029
If you are performing a hydrogenation with which you are unfamiliar you would do yourself a great favor by measuring the hydrogen uptake. This will make it possible to better understand what has happened inside the reactor. Was the product neutral or alkaline? Have you distilled it? Done any A/B wash? You have left out a lot of information.
Freaky
(Stranger)
04-09-03 10:47
No 425144
How much H2 was absorbed? --> 1 mole, or very close to it
And is the product basic? --> The crystal clear residue was neutral, the reaction contents were PH 6.5
Have you distilled it?Done any A/B wash? --> No, distilled off the alcohol, and attempted an A/B, a little product went into the acidic water, the clear oil left on bottom was separated off, and the acidic water washed once with toluene. Then basified, and extracted with a preweighed amount of toluene. Toluene was then separated and weighed again. It only was 1 gram heavier. And that is with sloppy lab technique. So I assume there was no product in there.
(Stranger)
04-09-03 10:53
No 425149
I believe that the ideal PH for oxime formation is 5.5
Someone correct me if I am wrong.
What was your PH at that stage?
You should definately distill the oxime to dryness in your rotorvap.
Can someone explain why that is? The properties of the oxime state that it could be an oil, or a crystalline solid, and basic or acidic. Why does it matter for further reduction purposes to specificly turn it into a solid?
________________________________________
You will never truly understand something, until you fuck it up.
(Hive Addict)
04-11-03 12:32
No 425786
Why does it matter for further reduction purposes to specificly turn it into a solid? so you know it isn't ketone or some other kind of crap. oxime that won't crystalize isn't usually very pure either.