Date: Sat, 9 Oct 2010 14:32:28 -0500
Reply-To: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: Robert Pertuit <papatweet**At_Symbol_Here**MSN.COM>
Subject: Re: Science Education & Safety
In-Reply-To: <-3903285660578643011**At_Symbol_Here**unknownmsgid>


Perchloroethylene is a surprisingly passive and stable solvent. It reacts only very slowly with bromine in the dark. Used as dry cleaning fluid and vapor degreaseing solvent gives it a low incident safety reputation. It is subject to air oxidation to aldehydes, oxides and acids, but this is controllable with inert gas padding. See patent 5731482.
Hexane with a little dichloromethane makes a good mix for water extraction because it is less dense than water and practically everything else in the universe. Starting with the methylene chloride to break up any resins in the sample followed by addition of the hexane to flip the density can be done on an extremely small scale where the organic phase is separated by centrifuge and removed from the aqueous meniscus with a pasteur pipette for analysis by gas chromatography (e.g., GC/MS).

From: Nail, John
Sent: Saturday, October 09, 2010 11:06 AM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L] Science Education & Safety

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

From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**LIST.UVM.EDU] On Behalf Of Norwood, Brad
Sent: Saturday, October 09, 2010 7:01 AM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L] Science 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=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.


Dr. Bradley K. Norwood

Laboratory Director

Arista Laboratories

1941 Reymet Road

Richmond, VA  23237

(804) 271-5572 ext. 307

(804) 641-4641 (cell)


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From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**] On Behalf Of Ernest Lippert
Sent: Friday, October 08, 2010 11:51 PM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L] Science Education & Safety

I guess I am "Old School" but it is hardly possible to teach (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.


Ernest Lippert

On Fri, Oct 8, 2010 at 3:51 PM, Russell Vernon <russell.vernon**At_Symbol_Here**> 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=85


If you have a recommendation to look at, would you please contact me?




Russell Vernon, Ph.D.

Research Safety

Environmental Health & Safety

University of California, Riverside

900 University Ave

Riverside, CA 92521



Direct (951) 827-5119

Admin (951) 827-5528

Fax (951) 827-5122


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