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Reagent Friday: Sodium Periodate

In a blatant plug for the Reagent Guide and the Reagents App for iPhone, each Friday  I profile a different reagent that is commonly encountered in Org 1/ Org 2. 

In organic chemistry, sometimes you need to build molecules up. Other times, you need to break molecules down. Ozone, which we talked about earlier, is a really useful reagent for that. Here’s another one, although it’s a little more obscure : Sodium periodate (NaIO4) breaks apart 1,2-diols (vicinal diols) to form aldehydes and ketones. In this respect it’s the same as periodic acid (HIO4) and lead tetra-acetate [Pb(OAc)4].

Notice what’s happening to NaIO4 here – it’s becoming reduced from iodine(VII) to iodine(V). In the process we’re cleaving a C-C bond and forming two C-O π bonds. Comes in handy sometimes, when you want to break apart an alkene and form aldehydes and ketones.

How it works: 

NaIO4 works by forming bonds with alcohols to the iodine. In the second step, what happens is a kind of reverse cycloaddition (similar to what happens when an ozonide breaks down). This is a somewhat simplified version of the mechanism (skipping over the proton transfer). The key part here is the third diagram, where the cyclic iodate ester breaks down to give the ketone and aldehyde.

And there you go: aldehydes or ketones, depending on whether you’re breaking down secondary or tertiary alcohols (primary alcohols become formaldehyde). So this actually gives you a second way to cleave double bonds to alkenes/ketones besides ozone. You can take an alkene, treat it with osmium tetroxide (OsO4) first to make the diol, and then NaIO4 it. This is, incidentally, sometimes called “Johnson-Lemieux cleavage“. Obscure organic chemistry named reaction of the day!

P.S. You can read about the chemistry of NaIO4 and more than 80 other reagents in undergraduate organic chemistry in the “Organic Chemistry Reagent Guide”, available here as a downloadable PDF. The Reagents App is also available for iPhone, click on the icon below!


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