I need to take exception with the statement ‘benzene … is a solvent that simply should not be use d under any circumstances’. Research involving very reactive organometa llic molecules uses hexadeuterated benzene (C6D6) as a solvent for NMR samples. The alternatives solvents either react with the sample molecule (example: CDCl3 ) or are prohibitively expensive (example: D12-cyclohexane). font>
In regards to the original question ab out using dichloromethane as an extraction solvent – the sad reality is t hat the alternative solvents don’t work as well as does dichloromethane f or this experiment. A few weeks ago, we performed the extraction of caffeine f rom tea using diethyl ether – the results were very disappointing. Ethyl acetate and 2-propanol have also been proposed for this experiment – both of these are water-soluble. Pedagogical reasons prevent me from using water-soluble solvents for this experiment. Students find the concept of solvent-solvent extraction sufficiently confusing before we make it more complex by using even moderately water-soluble solvents as the ‘water insoluble phase’.
This discussion reminds me of why ther e often is an adversarial relationship between faculty and EHS staff.
Dr. John Nail
Professor of Chemistry
Sent: Saturday, October 09, 2010 7:01 AM
Subject: Re: [DCHAS-L] Scien ce Education & Safety
While I agree (mainly) in principle with Ernest, there are some things that really should come off of the list. An obvious example (and I’m being extreme here, not intending to imply Ernest wouldn’t agree) is benzene. I’m sure we’d all agree that this is a solvent that simply shou ld not be used under any circumstances.
But ErnestR 17;s point is spot-on. If a ll we do is ‘dumb down’ the content of labs and remove all possible h int of danger, we exacerbate the problem of a society full of chemophobic individuals who simply do not know how to handle any chemical, much less make a rational decision as to whe ther a given situation is really a problem or not. Heck, if this is going to be our response (i.e. let’s remove all danger from the lab), we might as well discontinue ‘real’ labs and just do the whole thing as an online & virtual experience. Take a video of the experiment and l et the kiddies watch it.
I think we do our students (and, ultimately, society itself) a disservice when we immediately presume that we must be the nanny-protector from all harm. The real w orld does not operate this way (ambulance-chasing, TV ad-trolling trial lawyers notwithstanding). Far better to teach them what the real issues are a nd how to think critically through a situation to assess it, and to actually perform, hands-on, real chemical reactions with real chemicals and reagents – some of which can harm them – to demonstrate that, with prope r handling, care and understanding, chemicals can and do perform wonderful th ings for us.
I’ll get off my soapbox now.
Dr. Bradley K. Norwood
Laboratory Dir ector
Arista Laborat ories
(804) 271-5572 ext. 307
(804) 641-4641 (cell)
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I guess I am "Old School" but it is hardly possible to te ach (or practice) chemistry without some exposure to more or less dangerous chemicals. What needs to be taught is how to handle chemicals safely, not how to handle only safe chemicals. We must be careful not to occupationally regulate ourselves out of existence.
On Fri, Oct 8, 2010 at 3:51 PM, Russell Vernon <russell.vernon**At_Symbol_Here**ucr.edu> wrote :
I found out today that one of our teaching labs is conducted an extraction experiment with dichloromethane (caffeine from coffee)
I would like to provide them a reasonable alternative extraction experiment with an occupationally regulated carcinogen…
If you h ave a recommendation to look at, would you please contact me? font>
Russell Vernon, Ph.D.
Environmental Health & Safety p>
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