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Ketones

Ketones. William, Nanda, Hafiz & Mio. Introduction. Alcohols are found in two forms: Primary: -OH group attached at the end of the chain. Secondary: -OH group attached to a carbon atom not located at the end of the chain. Formation of ketones.

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Ketones

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  1. Ketones William, Nanda, Hafiz & Mio

  2. Introduction • Alcohols are found in two forms: • Primary: -OH group attached at the end of the chain. • Secondary: -OH group attached to a carbon atom not located at the end of the chain.

  3. Formation of ketones • When a secondary alcohol is heated with the oxidising agent potassium dichromate (VI), it oxidises into a ketone. CH3CH(OH)CH3 + [O]  CH3COCH3 + H2O propan-2-ol potassium dichromate propanone water • Ketones cannot be oxidisedany further.

  4. So what is a ketone? • A ketone is a carbonyl compound where one of the carbon atoms along the chain (not at the ends) is double-bonded to an oxygen atom.

  5. Naming convention

  6. Applications • Polymer precursor • Pharmaceuticals • Solvents • e.g.: • acetone • methylethyl ketone • cyclohexanone

  7. Reduction of ketones • When a ketone is warmed with the reducing agent NaBH4 (sodium tetrahydridoborate), it reverts into a secondary alcohol. CH3COCH3 + 2[H]  CH3CH(OH)CH3 propanonereducing agent propan-2-ol • We can think of it as a nucleophilic addition, where H-ions from the reducing agent act as the nucleophile.

  8. Testing for ketones • Testing for ketones and aldehydes in a solution may be done with 2,4-dinitrophenylhydrazine (2,4-DNPH). • If the solution contains either, an orange precipitate will be formed. • This is an example of condensation reaction between 2,4-DNPH and the ketone.

  9. Testing with Tollens’ reagent • Both aldehydes and ketones form an orange precipitate with 2,4-DNPH. • To differentiate, we may react the solution with Tollens’ reagent – a solution of silver nitrate in excess ammonia. • When it is warmed with an aldehyde, a silver precipitate builds up. • Ketones, however, will remain colourless.

  10. Fehling’s solution • is an alkaline solution containing copper (II) ions. • It oxidises and turns from clear blue to an opaque red/orange when heated with an aldehyde. • Ketones cannot be oxidised any further,so the solution remains blue.

  11. Nucleophilicaddition with HCN • The carbonyl group C=O is highly polarised, as the oxygen atom has more electron pairs (and therefore more negative). • The carbon atom, being more positive, is open to addition reactions* from nucleophilic ions (i.e. negative ones). *”nucleophilic attack” is a proper term and sounds cooler. - - - - O C - - - - - -

  12. Mechanism • Addition, as you’ll recall, involves the breakdown of a double bond into a single bond. • An example of a nucleophile is the CN- ion in HCN, hydrogen cyanide. - - - - O C O- C - - - - - CN H+ H CN

  13. H - - O C CN- - - - CN

  14. Thank You

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