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Alkene Reactions

By James Ashenhurst

Alkene Reactions: Ozonolysis

Last updated: July 9th, 2019 |

Ozonolysis of Alkenes

Today’s post represents not so much a pattern in alkene reactions, so much as it does a very common reaction that bears mentioning along with the rest. What makes this reaction special is that it does not simply break the carbon-carbon π bond, as we have been accustomed to seeing, but additionally breaks the C-C σ bond as well.

This type of reaction is known as oxidative cleavage [i.e. cleavage of bonds, occuring with oxidation] and the most prominent example of an oxidative cleavage reaction is ozonolysis. 

Table Of Contents

  1. Ozone (O3) Is A Powerful Oxidant For Cleaving Alkenes To Carbonyl Compounds
  2. Ozonolysis With “Reductive Workup” :  All C–H Bonds Are Preserved
  3. Ozonolysis Of A Ring Results In A Chain With Two Carbonyls
  4. Ozonolysis Of A Compound With Multiple Bonds Results In Several Fragments
  5. Ozonolysis With Oxidative Workup Converts Aldehydes To Carboxylic Acids
  6. Summary: Ozonolysis of Alkenes
  7. Further Reading

1. Ozone (O3) Is A Powerful Oxidant For Cleaving Alkenes To Carbonyl Compounds

As mentioned on one Reagent Friday back in the day, ozone does more than absorb UV radiation in the upper atmosphere and cause breathing problems in traffic-clogged cities. It’s a powerful oxidant, and since its discovery in the mid 1800’s by (Schönbein) has found use in the cleavage of carbon-carbon multiple bonds.

Here’s the pattern for the reaction of alkenes with ozone:

1-o3

Note that the carbon-carbon double bond is broken and we are forming a carbon-oxygen double bond on each of the two carbons that originally composed the alkene. The second step in ozonolysis is called the “workup”. There are two different types of “workup”, and the most common is referred to as “reductive workup”. In this step, we add a reducing agent (commonly zinc metal or dimethyl sulfide) that decomposes the intermediate formed at the end of the ozonolysis reaction (called an “ozonide” by the way). If you’re wondering where the third oxygen of ozone went – it’s now attached to what used to be our reducing agent (making either zinc oxide (ZnO) or dimethyl sulfoxide (DMSO). [For more details / mechanism everything is written out in this post.]

2. Ozonolysis With “Reductive Workup” – All C–H Bonds Are Preserved

Using “reductive workup” preserves all other aspects of the molecule save the double bond. So if we start with, say, a trisubstituted alkene, as in the example below, we will end up with a ketone and an aldehyde. [What happens if the alkene carbon is attached to two hydrogens? It becomes formaldehyde, which is then further converted to carbon dioxide]

2-o3

Note that although I’ve written (CH3)2S as the reductant here, it’s essentially interchangeable with Zn for our purposes.

3. Ozonolysis Of A Ring Results In A Chain With Two Carbonyls

An interesting consequence of ozonolysis is that if the alkene is within a ring, you end up with a chain containing two carbonyls:

3-o3

4. Ozonolysis Of A Compound With Multiple Bonds Results In Several Fragments

If your molecule has multiple alkenes, then you will end up with more than two fragments. For many years ozonolysis was used as a method for the structure determination of unknown molecules. By analyzing the fragments it is then possible to deduce what the original structure was, through “stitching” together the fragments. [This was particularly important in the case of unsaturated molecules known as terpenes]. Here’s one example:

4-o3

5. Ozonolysis With Oxidative Workup Converts Aldehydes To Carboxylic Acids

This isn’t the end of the story with ozonolysis. There’s a second type of workup that can be used, referred to as oxidative workup. Instead of using Zn or S(CH3)2, if we use the oxidant hydrogen peroxide [H2O2], any aldehydes that form will be oxidized to give carboxylic acids. Like in the example below – notice that the green C-H bond is oxidized to C-OH  [but all the other hydrogens remain intact ].

5-o3

6. Summary: Ozonolysis Of Alkenes

An alternative to using ozone for oxidative workup is to use the reagent KMnO, especially in the presence of hot acid; this will lead to the same result.

This is the last category of important alkene reactions we’ll cover for now in this series; in the next post we’ll wrap up the reactions of alkenes with a summary post.

NEXT POST: Summary of Alkene Addition Reactions


Further Reading

  1. Ueber die Einwirkung des Ozons auf organische Verbindungen
    Harries
    Just. Lieb. Ann. Chem. 1905, 343 (2-3), 311-344
    DOI: 10.1002/jlac.19053430209
    The first paper describing the oxidative cleavage of unsaturated compounds with ozone in solution.
  2. OZONE
    I. Smith, F. L. Greenwood, and O. Hudrlik
    Org. Synth. 1946 26, 63
    DOI:
    10.15227/orgsyn.026.0063
    This procedure from Organic Syntheses, a source of reliable, reproducible and independently tested organic chemistry laboratory experimental procedures, provides a detailed explanation of how to build a laboratory ozonizer.
  3. The Preparation of Aldehydes, Ketones, and Acids by Ozone Oxidation
    Albert L. Henne and Philip Hill
    Journal of the American Chemical Society 1943 65 (5), 752-754
    DOI:
    1021/ja01245a003
    This paper shows that carboxylic acids are formed in good yields from aldehydes when the ozonolysis reaction mixture is worked up in the presence of excess hydrogen peroxide.
  4. Notes- A Convenient Method for Reduction of Hydroperoxide Ozonation Products
    Knowles and Q. Thompson
    The Journal of Organic Chemistry 1960 25 (6), 1031-1033
    DOI: 10.1021/jo01076a044
    Although the current practice is to use dimethyl sulfide in a reductive ozonolysis workup, trimethyl phosphite can also be used, as this paper from Nobel Laureate W. S. Knowles demonstrates.
  5. OZONOLYTIC CLEAVAGE OF CYCLOHEXENE TO TERMINALLY DIFFERENTIATED PRODUCTS: METHYL 6-OXOHEXANOATE, 6,6-DIMETHOXYHEXANAL, METHYL 6,6-DIMETHOXYHEXANOATE
    Ronald E. Claus and Stuart L. Schreiber
    Synth. 1986, 64, 150
    DOI: 10.15227/orgsyn.064.0150
    This procedure in Organic Syntheses demonstrates how ozonolysis can be used to quickly generate differentiated bifunctional compounds.
  6. Mechanism of Ozonolysis
    Dr. Rudolf Criegee
    Angew. Chem. Int. Ed. 1975, 14 (11), 745-752
    DOI:
    10.1002/anie.197507451
    This is an account by Prof. Rudolf Criegee on work done towards determining the mechanism of ozonolysis. Criegee himself carried out extensive work in this area – the ‘Criegee intermediate’ in ozonolysis is named after him.

    The following papers are further mechanistic studies on ozonolysis:

  7. New evidence in the mechanism of ozonolysis of olefins
    Klopman and C. M. Joiner
    Journal of the American Chemical Society 1975 97 (18), 5287-5288
    DOI:
    10.1021/ja00851a049
  8. Mechanism of ozonolysis. (a) Microwave spectra, structures, and dipole moments of propylene and trans-2-butene ozonides. (b) Orbital symmetry analysis
    Robert P. Lattimer, Robert L. Kuczkowski, and Charles W. Gillies
    Journal of the American Chemical Society 1974 96 (2), 348-358
    DOI:1021/ja00809a006
  9. Microwave and mass spectral studies of the ozonolyses of ethylene, propylene, and cis- and trans-2-butene with added oxygen-18 formaldehyde and acetaldehyde
    Charles W. Gillies, Robert P. Lattimer, and Robert L. Kuczkowski
    Journal of the American Chemical Society 1974 96 (5), 1536-1542
    DOI:1021/ja00812a043

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Comments

Comment section

43 thoughts on “Alkene Reactions: Ozonolysis

  1. I had a question where it was a reaction map for turning a generic terminal alkyne into a generic aldehyde. I was going for using hydrogenization in the presence of Lindlar’s and ozonolysis.

    In the answer provided (one of many ways), the alkyne underwent ozonolysis with ozone followed by zinc in acid (h3O+) what would the purpose of the acid be?

    1. The acid helps to break up the intermediate ozonide – it protonates one of the oxygens and makes it a better leaving group, in a way similar to how acid helps to cleave acetals.

  2. I believe there is a typo- in the last mechanism, it is described c=o,-oh to be an “aldehyde” where it should be a carboxylic acid? (In oxidative workup, where the H is replaced with OH).

  3. when there is a cyclopentene attached to benzene ring, and ozonolysis is carried out then will the reaction take place only on pentene…? why does that happen..?

  4. If there are multiple alkenes within the original molecule but there is only one equivalent of O3, how do you determine which alkene to cleave and which to leave as is? Thanks!

    1. Hi – good question!
      Generally, the more highly substituted the alkene, the more electron rich it is, and the more reactive it will be towards O3 (sterics are not a significant factor in most cases).

      It’s possible to selectively ozonize an alkene assuming there is a significant difference in substitution pattern.

      For instance it’s possible to selectively ozonize a tetrasubstituted alkene in the presence of a disubstituted alkene. The trick is to use a dye as an indicator (an example is Sudan Red) that is intermediate in reactivity between the alkene you are trying to ozonize and the less reactive alkene. When the dye starts getting chewed up you will notice a color change and you can stop the reaction.

  5. when comparing the ozonolysis reaction to the KMnO4 (hot) reaction, why is it that ozonolysis doesn’t form carboxylic acids on alkenes but will on alkynes? KMnO4 will form carboxylic acids on both alkynes and alkenes.

    1. Ozonolysis cleaves all C-C bonds and converts to C-O bonds. In an alkyne three bonds are cleaved, and instead of forming C(triple bond)O, which would have a positive formal charge at oxygen, one forms a carboxylic acid instead.

    1. Pros: works well at gram-scale, and ease of workup. Basically add reductant at -78 and let warm, followed by concentration. Cons: poor at explorative scale (e.g. 100 mg and less) where it’s more convenient to use OsO4/NaIO4 (Johnson-Lemieux cleavage).

  6. What is the difference between oxidative ozonolysis and reductive ozonolysis
    And does their products area same or different

  7. What happens if a compound containing both double and triple bond is introduced to ozonolysis?which one will get reduced and why?

  8. hi i am in 11th grade and i got a question where i was given the final products that were obtained whilst the reactants underwent ozonolysis. how do i find out the reactant(IUPAC name) if the product is given. Pls help

  9. I aspire to reach your level of orgo proficiency. Like for real, reading your answers to these questions is awesome. Orgo 2 final coming up for me

  10. What about Ozonolysis on O-xylene? I assume the reaction would take place at all of the alkenes? If this is the case, would it require 3 equivalents?

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