I need to take exception with the statement =91benzene =85 is a solvent that simply should not be used under any circumstances=92. Research involving very reactive organometallic 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).

In regards to the original question about using dichloromethane as an extraction solvent - the sad reality is that the alternative solvents don=92t work as well as does dichloromethane for this experiment. A few weeks ago, we performed the extraction of caffeine from 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 =91water insoluble phase=92.

This discussion reminds me of why there often is an adversarial relationship between faculty and EHS staff.

Dr. John Nail

Professor of Chemistry

Oklahoma City University

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=92m being extreme here, not intending to imply Ernest wouldn=92t agree) is benzene.  I=92m sure we=92d all agree that this is a solvent that simply should not be used under any circumstances.

But Ernest=92s point is spot-on.  If all we do is =91dumb down=92 the content of labs and remove all possible hint 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 whether a given situation is really a problem or not.  Heck, if this is going to be our response (i.e. let=92s remove all danger from the lab), we might as well discontinue =91real=92 labs and just do the whole thing as an online & virtual experience.  Take a video of the experiment and let 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 world does not operate this way (ambulance-chasing, TV ad-trolling trial lawyers notwithstanding).  Far better to teach them what the real issues are and 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 proper handling, care and understanding, chemicals can and do perform wonderful things for us.

I=92ll get off my soapbox now.

Brad

Dr. Bradley K. Norwood

Laboratory Director

Arista Laboratories

1941 Reymet Road

Richmond, VA  23237

(804) 271-5572 ext. 307

(804) 641-4641 (cell)

brad.norwood**At_Symbol_Here**aristalabs.com