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| | From:  Ceca93 (Original Message) | Sent: 10/19/2003 2:09 AM |
Hi I'm an organic I student and I had a little trouble with a distillation. I would appriciate any advice on what the problem could have been. I was doing the oxidation of Cyclohexanol to get cyclohexanone. I made several mistakes over the course of my expirement. I think the biggest was allow the temperature to get too high when I added the 10% sol. of NaOCl. When I began my distilation I at first forgot to add a boiling chip. When I did (Not long after I began my distillation--no overboiling!) a little while later I noticed a white solid forming in my round bottomed flask. What could this have been and what could have caused it? Thanks in advance! Ceca93 |
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| | | From: ·Steve· | Sent: 10/19/2003 6:09 PM |
One possibility is that the solid was NaCl, a normal product that could precipitate during the distillation as the volume decreases. But if this was the case, probably everyone should have seen this same solid during their distillations. The other possibility, since you mentioned overheating during the NaOCl addition, is that some of the cyclohexanone product oxidized further at higher temperature, forming adipic acid (hexanedioic acid), a solid with m.p. 152oC. This compound might also precipitate as the solution becomes more concentrated during the distillation. The only way to know for sure is to check the melting point of the solid - if it melts, it's probably adipic acid; if it doen't melt, it's probably NaCl. How was your percent yield of cyclohexanone? A low yield could indicate that much of the cyclohexanone was lost due to adipic acid formation. Steve |
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| | | From: ·Steve· | Sent: 10/21/2003 12:46 AM |
Just a follow up - now that I had a chance to check my lab book (Macroscale and Microscale Organic Experiments by Williamson), some other possibilities come to mind, if you used that procedure. Sodium sulfite is added after the addition of NaOCl to remove any excess hypochlorite, forming sodium sulfate, which could form as a white solid during the distillation. Then, the solution is neutralized with 6 M NaOH, which would form some sodium acetate (since acetic acid was initially present); this could also precipitate. The procedure mentions not letting the temperature get any higher than 50oC during the addition of NaOCl, but it doesn't say what will happen if does. No mention is made of adipic acid forming as a by-product using NaOCl (my theory!) so that may not happen. The adipic acid prep is in the same chapter right after the cyclohexanone prep; it is prepared by the oxidation of cyclohexanone with HNO3 or KMnO4, rather than with NaOCl. It's always interesting and necessary to analyze the results of an experiment, but the explanation is not always obvious or easy to pin down without more information, about this solid, for example. Interesting question though! We do not do this experiment at the college where I teach or I would know the ins and outs of it, so if anyone else is familiar with it I would be interested in your comments too. Who knows, we may add this experiment to our organic curriculum some day. Steve |
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