EXPERIMENT C
PREPARATION AND IDENTIFICATION OF AN
UNKNOWN KETONE 2,4-DNP DERIVATIVE
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A: Absolutely not - acetone is one of our possible unknowns, so you would run the risk of contamination. You could rinse with a small portion of 95% ethanol - this is our reaction solvent.
Q: Do I need to dry the crude derivative? A: No, you can proceed on and do the mixed-solvent recrystallization the same day if you have enough time.
Q: Does it matter is some solid passes though the filter paper upon vacuum filtration? A: Not in this experiment - we are emphasizing purity rather than yield.
Q: What is the best way to get the yellow DNP derivative out of the Buchner funnel when cleaning the funnel. A: Using acetone to remove the DNP residue works well - rinse into the waste jar.
Q: How can I keep the funnel warm during hot gravity filtration? A: One trick is to add a couple of mL of ethanol to the receiving flask prior to the filtration. Heat the receiving flask on the steam cone - at which temperature the ethanol will boil and condense on the wide-stem funnel ("reflux"), heating the funnel.
Q: When I gravity filtered some crystalline solid was left behind on the filter paper - does this matter? A: Not really. We're keeping the apparatus hot to minimize this loss, but in this experiment we're not too concerned with yield, and it doesn't take much for melting point and TLC analysis. If you wish you could wash with some hot ethanol to dissolve the solid, but it is really not necessary.
Q: Why do we use a wide-stem funnel for gravity filtration? A: A narrow-stem funnel might plug up with crystallizing solid.
Q: Do we need to chill the suspension before the vacuum filtration? A: No, because in this reaction we're interested in maximizing purity and not yield.
Q: How long does it take to develop these plates? A: About 15 minutes?
Q: Can we develop all three plates at the same time? A: Yes. ©2001,2002 Daniel A. Straus |
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