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Previous by Date: Subject: Re: Questions out of my realm Date: Fri, 10 Mar 2006 14:32:31 -0500 Author: ILPI |
Next by Date: Subject: Re: Questions out of my realm Date: Fri, 10 Mar 2006 11:51:44 -0800 Author: Linda Wraxall |
>All, > >I got the following two questions from a colleague and since I work in the >art field, these are out of my area. Can I get some help? > >1. a student was boiling ether in a large open flask on a stirrer hotplate >and the fume alone caught on fire, inside the hood. . Do you have suggestions >for them to reduce the ether amount for re-crystallization in a safer manner? Yikes. They should be using a rotary evaporator or some sort of simply vacuum line system. There is no need to heat ether on a hotplate - ever! Some general references: http://www.ilpi.com/inorganic/glassware/rotavap.html http://www.ilpi.com/inorganic/glassware/vacline.html >2. a student in was quenching butyl lithium with n-propanol in an open flask >and it also caught on fire. Is there a safer way to quench the butyl lithium >w;ithout catching on fire? Usually, one lets flasks like that age quietly in an otherwise empty hood for a day or two before beginning the quench. Give the flask a swirl once in a while. If the solvent evaporates or it becomes too concentrated add some hexane or petroleum ether to dilute it. n-propanol is too reactive for safe quenching. Use isopropanol instead. *Very* small amounts to start, followed by swirling/stirring and then waiting minutes or hours between the next aliquot. The key is to quench slowly, never adding enough alcohol to raise the temperature of any part of the flask - watch out particularly for localized heating or the formation of solid chunks that may shield their core from quenching. You can keep a blanket of dry nitrogen over the system to exclude oxygen as an added precaution, but as long as you aren't being "greedy" by trying to quench too fast this shouldn't be an issue. There is always a degree of risk in a quench, so these are just typical guidelines, not hard and fast rules. If the solvent catches fire, remember that placing a watch glass over the top will snuff. Most quenching accidents I have seen come from folks panicking or trying to quench too rapidly. Rob -- ===================================================== Safety Emporium - Lab & Safety Supplies featuring brand names you know and trust. Visit us at http://www.SafetyEmporium.com esales**At_Symbol_Here**safetyemporium.com or toll-free: (866) 326-5412 Fax: (859) 523-0606, 4905 Waynes Blvd, Lexington, KY 40513-1469
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