10-20-03 17:36
No 465769
Cub has some oxime that needs to be reduced in near future.He already has ordered some sodium metal but now found out that anhydrous ethanol is completely out of reach for him.However 99,5% methanol and IPA of at least same purity are both available.Cub remebers someone saying that IPA should work.Cub understands that reaction between sodium and alcohol goes as follows:
Na + R-OH --> R-ONa + H+
Does IPA react with sodium as sodium does with ethanol and at same rate?Should he extend reaction times?What is indication of completed reaction?No more sodium floating around as it has already been converted to isopropoxide and is soluted in IPA?Cub is no organic chemist by any means that's why he asks dumb question like that.
Thanks for yer time,
Cub
(Chief Bee)
10-20-03 22:27
No 465817
Does IPA react with sodium as sodium does with ethanol
Yes.
and at same rate?
No, slower. The reaction rate for sodium with hydroxylic compounds is as follows:
Water >> Primary alcohol > Secondary alcohol > tertiary alcohol
Should he extend reaction times?
Yes.
What is indication of completed reaction? No more sodium floating around as it has already been converted to isopropoxide and is soluted in IPA?
Yes, and then some, also see the second prep in ../rhodium /nitrile
(Stranger)
10-20-03 23:13
No 465825
Since the topic of oxime reduction has been brought up here, SWIM would like to ask a question about the catalytic hydrogenation of oximes/nitriles.
Using a nickel catalyst in EtOH saturated with NH3, oximes/nitriles are reduced to primary amines in good yields (JACS vol 66., pp. 876 (1944)). However, there is always going to be some amount of secondary amine in there. Ni catalyst is easier and cheaper than Pd/Pt which are used as you Rhodium describe in post Post 450229 (Rhodium: "Catalytic Reduction of Nitriles and Oximes", Methods Discourse).
So is there a facile way of isolating the secondary amines from the primary, or is vacuum distillation of the base the only way to go? What about the solubility of secondary amine salts? - is fractional crystallization viable?
OH!!, what about enamine formation!? Primary amines recrystalllize just fine from acetone, but secondary amines react to form enamines. But SWIM doesn't know the solubility of these compounds either.
SWIM finds the oxime reduction in this post: Post 360373 (Barium: "TMA-2 by low-pressure catalytic hydrogenation.", Methods Discourse), sort of hard to accept. No TLC was done on the final product to see how much secondary amine was in there, and an excess of base in the reaction was not used (just the base absorbed on the Ra-Ni).
Any thoughts on purifying without using vacuum distillation are welcome.
(Chief Bee)
10-20-03 23:44
No 465831
Read the document linked from Post 465743 (Rhodium: "NaBH4/NiCl2/Boc2O: Nitriles to N-Boc-Amines", Novel Discourse) - they cleverly use Boc2O to prevent the formation of any secondary amines. Boc2O is apparently not affected by the reduction system, but as soon as a primary amine is formed, it is acylated to the N-Boc carbamate, preventing any further dimerization. The N-Boc is then cleaved in nearly quantitative yield using HCl.
(Stranger)
10-21-03 00:15
No 465839
Very clever indeed!
But di-tert-butyl dicarbonate isn't a reagent often encountered by this bee.
Perhaps just using acetic anhydride as the 'trapping' agent will also work well? The Rylander book at your webpage (thank you!) implies so for nitriles and oximes... SWIM will dig up the refs relating to it. Oh, are nickel catalysts suitable with an acetic anhydride solvent? SWIM really must go to the library to read these articles!
. Thank you for your input Rhodium (you've been busy today, no?).
(Newbee)
10-21-03 05:56
No 465876
IPA should be primary alcohol aswell.Cub thinks he will give it a try.First he tries how fast sodium reacts with boiling IPA then decides how small pieces of sodium must be made(more pieces more surface and more surface means faster reaction).Thanks for pointing out that document.These guys don't use stirring raf thinks he should.Cub ordered sodium from Fluka and it was dirt cheap,anyone seen how they pack that stuff(ie vacuum or under oil or something else?)Cub has to cut that sodium into pieces and keep under hexane like Sonson did.Some hexane gets into the rx but it shouldn't matter(hexane should be soluble in IPA,anyway, it should be completely inert in this reaction).Thanks for help,cub will surely pioneer this stuff and post results.If anyone has something potentially useful to say,please do,all comments are welcome,
Cub
(Chief Bee)
10-22-03 22:11
No 466171
IPA should be primary alcohol aswell.
No, IPA is a secondary alcohol, and it takes several minutes at room temp for a one gram chunk to dissolve (but it's faster when an oxime or nitrile is dissolved in the IPA).
Sodium is always shipped under mineral oil.
Stirring is highly recommended in the Na/alcohol reduction.