(Hive Bee)
01-21-04 14:42
No 483879
(Rated as: good read)
After performing a reduction with LiAlH4 the excess of reagent is usually destroyed by ice water, aqueous alkaline solution (KOH or NaOH), wet THF or ether, ethylacetate or any similiar reagent.
Lego wants to propose an OTC quenching reagent which might bee superior to other reagents: sodium sulfate decahydrate (NaSO4·10H2O).
Lego has seen this reagent in action and was really surprised as it works really good.
In this reaction a ketone was reduced with a 5fold excess (don't ask) of LAH in ether. After the reaction was over the mixture was cooled to -10°C and NaSO4·10H2O was added in several portions until no more hydrogen evolved. As with every other reagent the addition has to been done carefully and in small portions but unlike other reagents the reaction is less vigorous, the temperature increase was only about a few °C even after a too large amount of NaSO4·10H2O was added. To ensure that all LAH was destroyed a drop of water was added, no more hydrogen evolved. The ether phase was decanted, the residue washed with ether and the pooled organic phases were evaporated. The corresponding alcohol was isolated in near quantitative yield.
After Lego has seen this reaction TFSE was used and only two relevant hits were found (flame Lego if this old stuff):
Post 430820 (GC_MS: "A look on the patented world of tryptamines", Tryptamine Chemistry)
Post 210367 (Ghost_Of_BT: "Re: Substitution for NaCNBH3 in Krz's DMT synth", Tryptamine Chemistry)
Google gave this hit (just to prove that it works for amines, too):
http://www.rsc.org/suppdata/ob/b3/b30841
Nomenclature overkill
Lithium aluminium hydride (3.35 g, 83.9 mmol) was added in one portion to a stirred solution of lactam 44 (3.36 g, 13.3 mmol) in THF (52 cm3) at 0 °C under nitrogen. The resulting suspension was heated at reflux for 16 h. After cooling to 0 °C, Et2O (20 cm3) was added followed by the portionwise addition (CARE) of solid hydrated sodium sulfate until effervescence ceased. The solids were removed by filtration through Celite and the filter cake was washed with 9:1 CH2Cl2-MeOH (150 cm3). The filtrate was dried (Na2SO4) and evaporated under reduced pressure to give the crude product as a brown oil. Purification by Kugelrohr distillation gave diamine (+)-24 (2.27 g, 88%) as a colourless oil, identical spectroscopically to rac-24, bp 110-120 °C/0.5 mmHg.
None of the bees Lego asked has heard about this method before. Perhaps somewhen a bee will try this method.
The tendency is to push it as far as you can
(Heavyweight Chempion(eer))
01-22-04 06:36
No 484011
If the Na2SO4*10 H2O is mixed with celice prior to the addtion to the reaction mixture the aluminum gel is trapped inside the celite. This renders the filtration even easier, beside the fact that the destruction of excess LAH is less violent when compared to the destruction with aqueous solutions.