cyberzed
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Registered: 23-7-2006
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extract a ketone from a bisulphite adduct
hi, collegue of mine needs some help doing a bisulphite adduct.
According to following procedure
1) Preparation of the bisulfite reagent
(This must be prepared just prior to use, as it will autooxidize within hours if left to it's own devices.)
Add 52g sodium bisulfite (NaHSO3, .5moles) to approximately 90mL of distilled water at room temperature with vigorous stirring (slightly more water
may be used to get it all into solution). Add a volume of denatured alcohol of about 70% of the solution's volume (ie - if you end up with 100mL of
solution, add 70mL of alcohol) then add more water to just dissolve the precipitate (~60mL).
2) Reacting with the ketone
Slowly drip .25moles of ketone(*) into a beaker containing the bisulfite solution with vigorous magnetic stirring. The 2:1 molar ratio insures that
all of the ketone will be converted. Let sit on the stirrer for an additional 30-45 minutes then filter on a vacuum Buchner funnel. Wash the crystals
with 20-50mL of denatured alcohol. Dry in a vacuum dessicator or open tray then store in a stoppered glass bottle until needed.
(*) If adding an impure reaction matrix, add as much solution as you expect to contain .25moles of ketone.
3) Recovering the ketone
Add the ~.25moles of bisulfite addition product to a separatory funnel then slowly pour in 105mL of 10% Sodium Hydroxide solution (w/w). Separate out
the aqueous layer (which may be on top or on bottom depending on the ketone), saturate with salt (NaCl), and extract with 50mL of ether (toluene or
benzene ok if the ketone is of high enough bp). Combine the extract with the ketone layer and strip off the ketone by distillation (condense and
reuse!). Distill the ketone residue, preferably under vacuum , to yield up to 90%, depending on the purity of the starting ketone, of course.
At step 3 he added the bisulphite addition product as dry crystals to the sep funnel, he then poured in the 10% sodium hydroxide solution. After a
brief shake the aqueous solution turned slightly yellow, the rest of crystals clogged up.
Then he drained off the aqueous layer, saturated the aqueous layer with a 20 ml saturated NaCl solution, extracted this with 50 ml of ether and
combined the clogged up crystals with the ether.
According to the procedure after the addition of the 10% NaOH, there should be two layers formed but he states that did not happen.
Should the bisulphite addition product had to be dissolved in solvent before adding to the sep funnel?
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Ozone
International Hazard
Posts: 1269
Registered: 28-7-2005
Location: Good Olde USA
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Yes.
Most organosulfites are soluble in water. Dissolve the product in water, some heating may be required. Cool. Then add alkali (acid will work
too)--beware of condensing your carbonyl via acid or base catalyzed aldol condensation--you will know if this happens (tar or yellow orange products).
The workup depends on the compound.
This is olde-skule chemistry, and can be referenced in almost any organic chemistry text. Wear your safety glasses and...
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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