Dylan Stiles is full of spirit
Dylan Stiles is full of spirit
I’m thinking of a liquid that’s a chemical solvent, reagent, antiseptic, beverage, alternative energy source, blessing, and curse (mostly blessing). What else could I be talking about but ethanol?
Any carbon attached to a hydroxyl group is technically an alcohol, but when you simply say ’alcohol’ everyone understands you are talking about the original and still the best - ethyl alcohol.
Ethanol has a lot going for it. As a solvent, it’s great at getting organic compounds into solution to react. Its boiling point of 78?C sits in a sweet spot where it’s volatile enough that you can easily boil it off when the reaction is done, but not so volatile that it will evaporate away prematurely.
You can also use it as a reagent. Drop a nugget of sodium metal into ethanol and when the hydrogen bubbling stops you’ll have a solution of sodium ethoxide, a lovely base that can deprotonate any number of substrates. The electrons zipping around during all that bubbling are good at reducing functional groups too, as in the Bouveault-Blanc reaction to reduce esters.
The low toxicity of ethanol is a plus. Of course, too many people die from alcohol poisoning every year. But when you’re working in a laboratory surrounded by carcinogens and asphyxiating gases, it’s nice to work with a chemical that won’t cause you to panic if you spill some on the floor. Indeed, what other chemicals in the organic lab are also key ingredients in tasty intoxicating beverages? (For those of drinking age, of course).
That’s why pure ethanol is often ’denatured’ - spiked with various other chemicals to render it unsuitable for human consumption. The laundry list of denaturants added to ethanol can include poisons such as methanol, methyl ethyl ketone, and acetaldehyde. Denatonium, known by the trade name Bitrex, is an oddball denaturant that discourages consumption by ranking amongst the world’s most bitter substances. On one occasion I tasted a fraction of a drop of Bitrex-denatured ethanol (using it as aftershave), an unpleasant experience indeed.
In the grocery store, the purest form of ethanol you’re likely to find is premium vodka. I’ve never understood why the most expensive bottles of vodka advertise their purity by proclaiming ’triple’ or even ’quadruple-distilled’. As far as I can tell, the more expensive the vodka, the closer it approaches a 40 per cent solution of pure ethanol in water. It seems to me that the thrifty shopper could make the same product simply by diluting undenatured ethanol.
Of course you should never drink ethanol from the lab, denatured or not. Older, wiser chemists than I will tell you that breaking the water-ethanol azeotrope to obtain alcohol above 95 per cent purity is accomplished by distillation with benzene, some fraction of which remains in the final product. That might be lore - in reality there are several ways that anhydrous ethanol is produced. Still, it’s a good general policy never to drink anything you find in the chemistry lab.
Ethanol might also have the power to save the world from global warming. It’s touted as a potential candidate in the quest for alternative energy sources, since ethanol can be produced by fermentation of renewable feedstocks like corn. The catch is that it takes energy to get the ethanol out of the plant, and some complex accounting is required to determine whether it’s worthwhile. With the notable exception of Brazil, which has a thriving ethanol economy based on sugar cane, no other country has yet been able to balance the equation in a way that makes clear economic or environmental sense (see ’The green fuel myth’, Chemistry World, October 2007, p48).
Without ethanol, chemists would have to make do with one of its chemical brothers, methanol or isopropanol. Every alcohol has its place in the lab, of course, but both of these are much more poisonous when ingested, making them wholly unsuitable for cocktails. If you want the undisputed champ of the alcohols, in both lab and bar, it has to be ethanol.
Dylan Stiles is a PhD student based in California, US