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| | From:  88672 (Original Message) | Sent: 3/15/2005 6:59 PM |
I have a few questions to ask concerning a lab experiement. 1. What color would the final solution be if 9-fluorenol were oxidized to 9-fluorenone in methanol, assumming all other reactants and products are colorless? I said yellow b/c thats the color of 9-fluorenone when you start from it and reduce it...but since all the other reactants/products are colorless is it colorless too. 2.Why do you get crytals or a solid on cooling the solution after hydrolysis? I understand taht the crystals are non polar and the water added is polar and only dissolves other polar compounds but why does it hae to be cold water? 3.Give 2 reasons why you would wash out an erlenmeyer flask with 50% aquesous ethanol. why does this wash have to be cold. I know why the wash has to be cold but I'm not sure about the 2 reasons. Is it so that more precipitate forms in the polar ethanol and so we get a max. yiled?? Thanks a bunch, Nicole:D:D:D |
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| | | From: MikeKL5 | Sent: 3/15/2005 11:20 PM |
Nicole, 1. I would assume that if you put pure 9-fluorenone in methanol, and the solution is yellow, then you could expect to get a yellow solution if you synthesize 9-fluorenone in methanol. In real life this question would be difficult to answer, because the final crude product of a synthesis doesn't always fit the description of the pure product. 2. Solubility of a solid in any solvent is directly proportional to the temperature. Solubility of a gas in any solvent in indirectly proportional to the temperature. Translation= As temp goes up, the solubility of a solid increases. As temp goes down, solubility of a solid decreases, but the solubility of a gas increases. 3. This part of your question is confusing. Are you asking about rinsing out a flask with nothing in it, or with crude product in it? If you were asking this question in regard to a flask with crude product in it, then the answer to your question is the same as the answer to question 2. The solubility of a solid decreases as temp decreases. Thus, you will get more ppt at a lower temp then you will at a higher temp. Hope this helps, MikeKL5 |
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| | | From: ·Steve· | Sent: 3/16/2005 5:26 AM |
9-Fluorenone has a "light yellow colour" according to the description in a chromatography experiment here. BTW, the site, from McMaster University, has a nice outline of chromatography here. Given the high conjugation in 9-fluorenone, this is not surprising (see the structure here; in this exp they are reducing 9-fluorenone to 9-fluorenol).
On question 3, I agree with Mike also - this looks like a washing step where the solid is swirled with cold 50% ethanol/water. This is often done in the Buchner funnel rather than in the flask. After the solid is collected in the funnel, the suction is disconnected and the washing solvent or solvent mixture is added and the solid is stirred gently in the funnel. Then the suction is re-applied to remove the liquid. If the solid has a slight solubility in the washing solvent, it is important to limit the number of washings and to use cold solvent to avoid dissolving a significant amount of solid. I've seen this happen in the lab every now and then - a lab group has a good amount of solid product in the funnel ("Aww-w-r-i-i-igghht!!") which they then wash repeatedly to get it nice and clean, after which I hear, "A-r-rrrrgghhh!! What happened to our beautiful solid???!!!"
Steve
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