11-04-03 04:45
No 468608
hi,
is there any bee who has more experience with the recrystalization of 5-bromovanillin and could tell
me more about this,do i have to use methanol or ethanol,
and so yes how much solvent per how much crude 5-bromo-
vanillin.
i would be very greatfull for this help!
(Hive Adickt)
11-04-03 09:40
No 468656
../rhodium /345-tmb
(Chief Bee)
11-04-03 10:19
No 468663
Simply add boiling ethanol to a stirred slurry of the bromovanillin in a small amount of boiling ethanol on a hotplate until all of it has dissolved. Allow to cool slowly and then filter.
(Newbee)
11-04-03 23:36
No 468789
(Rated as: excellent)
Hereby I want to give some general guidelines to find a good solvent for recrystallization:
1.Find a solvent that will dissolve the solid while hot
2.The same solvent should not dissolve the solid while cold
3.The cold solvent must keep the impurities dissolved in it forever or longer (of course if the impurities don't dissolve you can just get rid of them by simple filtration)
Finding a good solvent
If you cannot find solubility data for your compound you can use the following experimental way to find a good solvent:
1)Place 0.10 g of your solid in a test tube
2)Add 3 ml of solvent and shake vigorously. If all the solid dissolves at room temperature, then your solid is soluble. Do not use this solvent as a recrystallization solvent. (make a note of this in your notebook)
3)If none (or very little) of the solid dissolves at room temperature, increase the temperature and shake now and then to promote dissolving. If it does not dissolve at all, then do not use this as a recrystallization solvent.
4)If the sample dissolved when hot, and did not dissolve at room temperature, you're on a trail for a good recrystallization solvent. One last test is needed though.
5)Place the no longer hot test tube in an ice-water bath, and cool it to about 5°C. If lots of crystals come out, this is good, and this a recrystallization solvent.
6)Suppose your crystals don't come back when you cool the solution. Get a glass rod into the test tube, stir the solution, rub inside of the tube with the glass rod, and agitate the solution. If crystals still don't come back, you probably should look for another solvent.
7)Suppose, after all this, you still haven't found a solvent. Look again. Perhaps your compound completely dissolved in ethanol at room temperature and would not dissolve in water. Aha! Ethanol and water are miscible. You will have to perform a mixed solvent recrystallization.
The above is taken out of the recrystallization chapter of The Organic Chem Lab Survival Manual by James W. Zubrick.
In the recrystallization chapter of this excellent book you can find more about
-gravity filtration
-the use of activated charcoal in purification
-working with a mixed-solvent system
Finding the ideal solvent is often art over science...
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