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The use of benzene and all of the other chemicals talked about needs to be given a closer look. Sure, most all chemicals have a risk due to being toxic to the human body if the exposure is sufficiently high. I believe that benzene is a chemical that is somewhat maligned because it can cause a blood disease. If all of us who are older remember that we often used benzene as a hand washing agent to remove tar and other water insoluble stuff. We should be dead by now if it is a really bad guy. I am not advocating its indiscriminant use, just a safe use with proper PPE and a good operating fume hood.
Now with hexane, I believe that it should never be used due its inherent toxicity that leads to peripheral neuropathy and its absorbent properties into the skin and easy inhalation. If it is to be used, the safety issue is paramount with the proper gloves, etc. The proper respirator is also needed.
Dichloromethane is a problem in that respirators, except SCBA, cannot be used because dichloromethane breaks through in moments and is not absorbed. The other safety issues would be the absorbency of gloves and breakthrough.
I am somewhat concerned by many of the comments below that seem to say that we should not be using any “dangerous” chemicals in our experiments. If used properly, hopefully in small amounts, with the proper PPE and hoods, almost any chemical can be used safely. We cannot shield the students from all dangers, but teach them about the care to be taken to prevent exposure. The world out there is not a generally nice place if they do not understand the problems and how to keep themselves healthy in the workplace.
My take is as a retired chemist and a retired 20 year Cal/OSHA CIH. Schools were some of the worst places for safety that I inspected and there has to be an effort to fix the problem.
From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**list.uvm.edu] On Behalf Of DAVID KATZ
Sent: Saturday, October 09, 2010 7:42 AM
Subject: Re: [DCHAS-L] Science Education & Safety
I did a quick and dirty web search for a caffeine extraction that does not use dichloromethane. I found this https://teach.lanecc.edu/thompsonj/CH241/laborato ry/Caffeine%20Extraction.pdf It is by John Thomson at Lane Community College, Eugene, Oregon
I have not tried this procedure and I would be curious to know how well it works.
I do not know the scale at which the class at your university performs this experiment, macroscale, small scale, semi-micro, or micro. That will also affect the extraction solvent used. For semi-micro scale or microscale procedures, I agree with Ernie Lippert that students must learn how to work with chemicals such as dichloromethane safely. That includes the generation of only small quantities of waste product.
In another experiment, I have my class extracting the fat from potato chips and French fries. Starting with 5 g of chips or 10 g of French fries in a 125-mL flask, I have switched the solvent from dichloromethane to hexane and use several rinsings of 10 mL or less. The solvent is disposed of in a waste bottle and the chips or fries which are only slightly damp with solvent, in the flask, are dried in a water bath under the hood. The fat content is determined by the loss in mass. We get good results.
David A. Katz
Chemist, Educator, Expert Demonstrator, Science Communicator, and Consultant
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