chloroform and you

Last week one of the techs here dropped a bottle of chloroform on the floor. She's a ditz and asked me if she should do anything. I told her it was quite volatile and would disappear on its own quite well but that she might want to stand somewhere else--she was standing in the puddle of chloroform--or she might find herself passing out soon.

I'm not sure why she was juggling the bottle in the first place. It's true that chloroform used to be a standard molecule in the molecular biologist's toolset but easy to use kits have largely replaced chloroform. We used to use it all the time to do DNA extractions.

If you're interested, a DNA extraction is when you take a bunch of cells (from tissue culture flasks, blood, ground up tissue, etc), disrupt the cell membranes so that the DNA is released, and then collect the DNA. The problem is that DNA is a very long molecule and very sticky so you tend to get a ball of "gunk" which isn't usable. That's where the Phenol/chloroform Extraction of DNA comes in.

What you do is add equal volumes of buffer-saturated phenol and chloroform to the DNA solution. Mix well. Then you vortex the DNA solutions for 10 sec or gently rock in the case of high molecular weight DNA. After that you spin in a microfuge for 3 min and then remove the aqueous layer to a new tube, being careful to avoid the interface.

Uh-uh. You're not done. Usually we have to repeat this a bunch of times before the interface is clear. It's a long tedious and smelly procedure. Which is why I'm quite happy to no longer have to use chloroform all the time.

Here's something to think about regarding chloroform: the chemical formula is CHCl3. So there's one carbon atom, one hydrogen--so far all is nice--and 3 chlorines. Not so nice! You attach a chlorine to a sodium atom and you have sodium chloride, table salt. But you put two chlorines together and you have chlorine gas and that's VERY nasty. Death on wings.

Chloroform was first prepared in 1831 by the chemist Dr Samuel Guthrie. His rudimentary synthesis involved mixing whiskey with chlorinated lime. He was attempting to discover an inexpensive way to make a pesticide known as Dutch Liquid (C2H4Cl2). Although the product of his investigation possessed properties in common with Dutch liquid it is now believed that Guthrie had formed an alcoholic solution of chloroform. This mysterious chemical became locally known as "Guthrie's sweet whiskey".

Today chloroform is usually produced by direct heating of methyl chloride with chlorine to 500 celcius. This heating process spontaneously produces a series of chloromethanes (chloromethane, dichloromethane, chloroform, and tetrachloromethane) which are then separated by distillation. There are a number of other ways to manufacture chloroform and the one used will depend on local conditions and laws.

Considering how volatile and explosive the gases used in this process are, as well as often poisonous, it's amazing that any of the chemists of yesteryear using and/or synthesizing chloroform survived.