The Ozone Zone

I chose my favorite chemical reaction based purely on aesthetics. Ozonolysis, wherein ozone—that tricky triumvirate of oxygen atoms—slashes its way through double bonds to make aldehydes, ketones, and carboxylic acids. Most synthetic organic chemists make things, but ozonolysis has a certain destructive appeal. Plus, there’s the pretty blue color that the solution takes on when the alkene is consumed, a sight not common to the largely colorless reactions of organic chemistry.

My graduate work involved making analogs of Vitamin D to fight, among other things, cancer. We started the synthesis of our analogs by taking commercially available Vitamin D2, and using ozonolysis to break it into its components like so:

I was after the molecule’s fused ring system. I’ll never forget when the senior graduate student teaching me how to use the ozonolysis setup placed a latex glove in front of the O3 stream to show me the potential hazards of not paying attention to her instructions. The air stream ripped the glove to shreds in a matter of moments.

The reaction also features a nifty mechanism bound to show up on O-Chem exams:


There’s the 1,3-dipolar cycloaddition (love to draw those leaping arrows), which leads to molozonide. Wikipedia shows this intermediate breaking into a carbonyl and a carbonyl oxide, which then undergo another 1,3-dipolar cycloaddition to produce a trioxolane (Or is it an ozonide? Nomenclature was never my strong suit). I, however, prefer the drawing that appeared in my O-Chem text (Morrison & Boyd), where an oxygen atom appears to shimmy its way through the C-C bond:

 

As an aside, you should know that “What’s your favorite chemical reaction?” is not a great conversation starter. I tried it last weekend with my husband and was met with ridicule.

Author: Bethany Halford

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5 Comments

  1. Bethany – you could have made more of the absolute best thing about ozonolysis reactions – the blue colour they go while you’re pumping ozone through the reaction is awesome! Always brightened up my day.
    Plus if you use an indicator like nile red to prevent over-oxidation of sensitive functionality you get a pretty colour change from deep red to a kind of peach colour.

  2. I LOVE the mechanism for the ozonolysis :)

  3. Phillip,

    Do you have a picture of an ozonolysis reaction? They don’t let us set up reactions at C&EN.

  4. Hi Bethany,

    Sorry, I gave up life ‘in the hood’ a little while ago. Google seems remarkably short on ozonolysis images too – shame!

    I think the idea of a fumehood in the corner of the C&EN office is one you should press for some funding for – think of all the fun (and useful stock photos) you could get out of it…