{"id":8939,"date":"2015-05-21T08:51:32","date_gmt":"2015-05-21T13:51:32","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=8939"},"modified":"2026-04-11T05:55:14","modified_gmt":"2026-04-11T10:55:14","slug":"demystifying-alcohol-oxidations","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2015\/05\/21\/demystifying-alcohol-oxidations\/","title":{"rendered":"Demystifying The Mechanisms of Alcohol Oxidations"},"content":{"rendered":"

Alcohol Oxidation Mechanisms, Demystified<\/strong><\/p>\n

\u2022 The mechanisms for the oxidation of alcohols generally involve putting a good leaving group\u00a0<\/strong>on oxygen, followed by deprotonation of an adjacent C-H bond that results in elimination to give a new C-O pi bond.<\/p>\n

\u2022 In this sense it greatly resembles an E2<\/strong> mechanism.<\/p>\n

\u2022 Oxidation of aldehydes to carboxylic acids usually involves addition of water to the aldehyde first (formation of a hydrate<\/strong>) which then undergoes elimination with base.<\/p>\n

\"mechanisms<\/p>\n

Table of Contents<\/strong><\/p>\n

    \n
  1. E2: The Familiar Key Step At The Heart of (Almost) All Oxidation Reactions<\/a><\/li>\n
  2. Oxidants Are Essentially Fancy Reagents For Attaching Leaving Groups To Oxygen<\/a><\/li>\n
  3. What About Oxidation of Aldehydes\u00a0 To Carboxylic Acids? (Spoiler: Yes, that too<\/em>)<\/a><\/li>\n
  4. Why Don’t Ketones Oxidize Further?<\/a><\/li>\n
  5. Summary:\u00a0 Alcohol Oxidation Mechanisms<\/a><\/li>\n
  6. Notes<\/a><\/li>\n
  7. Quiz Yourself!\u00a0<\/a><\/li>\n
  8. (Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n
    \n

    <\/a>1. E2: The Familiar Key Step At The Heart Of (Almost) All Alcohol Oxidation Reactions<\/h2>\n

    When I was learning organic chemistry I remember the reagents for oxidation reactions completely coming out of left field.<\/p>\n

    KMnO4<\/sub>, K2<\/sub>Cr2<\/sub>O7<\/sub>, PCC, CrO3<\/sub>, Swern, Dess\u2014Martin ? Hold on. Where did these reagents come from? How do they work? Why chromium? What\u2019s the mechanism?<\/p>\n

    \"unfamiliar<\/p>\n

    In my course, the details of these reactions were completely glossed over. \u201c Don\u2019t worry about the mechanism!\u00a0No time to go through this!<\/em> \u201c the instructor said. I was left with the impression that there was something deeply mysterious about alcohol oxidation.<\/p>\n

    Only later did I learn that it\u2019s not mysterious at all. In fact the key mechanism is very familiar.<\/strong><\/p>\n

    Let me show you what I mean.<\/p>\n

    Here\u2019s a reaction we\u2019ve seen before. Elimination of alkyl halides to give alkenes through an E2 mechanism<\/a>. Base removes hydrogen, we break C-H, form C-C (\u03c0) and break C-LG. The result is an alkene.<\/p>\n

    \"familiar<\/p>\n

    Now imagine a slightly different E2 reaction, except one where the good leaving group is on oxygen.<\/strong> We\u2019ll leave it vague, as \u201cLG\u201d for now.<\/p>\n

    Watch!<\/p>\n

    \"imagine<\/p>\n

    See how we \u00a0break C-H, form C-O (\u03c0), and break O-LG, forming a new C-O \u03c0 bond in the process. Since we’ve formed a new C-O bond at the expense of a\u00a0C-H bond, an oxidation has occurred.<\/p>\n

    Believe it or not, most oxidation reactions of alcohols proceed exactly this way!\u00a0<\/strong>[Note 1<\/a>]<\/p>\n

    <\/a>I wish I\u2019d known this when I was learning organic chemistry because it would have made alcohol oxidation seem a lot less mysterious.<\/p>\n

    <\/a>2. Oxidants Are Essentially Just Fancy Reagents For Attaching Good “Leaving Groups” Directly To Oxygen<\/h2>\n

    Hold on, you might say. It can\u2019t possibly be that simple. Why do we have so many different types of oxidizing agents? And why do the mechanisms (like the Jones oxidation\u00a0here<\/a> for example) seem so\u00a0complicated?<\/p>\n

    Yes, there are a lot of steps in a typical oxidation reaction. However, most of these steps consist of:<\/p>\n