What a difference an isomer makes

Last week we did the Williamson Ether Synthesis lab, reacting o-cresol with chloroacetic acid in refluxing aqueous KOH. The product, 2-methylphenoxyacetic acid, is easily purified by digesting the acid-workup slurry, then slow cooling. Very ordinary and routine “recipe” procedure. So why post about it? Because (a) I haven’t put anything up for a couple weeks, and (b), this one is worth remembering:

Ortho-cresol smells much less than para-cresol. 

In 2012, I did this same lab using p-cresol, and the whole lab smelled like a horse barn for weeks afterward. That’s an odd event,  considering “fresh” p-cresol has a typical phenol/medicinal smell. It’s only after aging (air oxidation? dilution below a threshold?) that the horse smell comes in. It’s not a horribly unpleasant smell, but it’s very lingering and it does get everywhere. The products don’t have much odor, unless they aren’t pure.

So I put this out there for the wide world of Google-searchers who are thinking about the smell of para-cresol and how to avoid it.


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