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Carbonyl Compounds


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Revision of carbonyl compounds

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Carbonyl Compounds

  1. 1. Carbonyl Compounds Aldehydes and Ketones
  2. 2. Contents <ul><li>Aldehydes vs. Ketones </li></ul><ul><li>Testing for Carbonyl Compounds </li></ul><ul><li>Distinguishing Between Aldehydes and Ketones  Mild Oxidation </li></ul><ul><li>Oxidation of Aldehydes (Primary Alcohols) </li></ul><ul><li>Oxidation of Ketones (Secondary Alcohols) </li></ul><ul><li>Neucleophilic Addition Reaction </li></ul><ul><li>Definitions </li></ul><ul><li>Summary </li></ul>
  3. 3. Aldehydes vs. Ketones <ul><li>The functional group is: >C=O </li></ul><ul><li>Polar bond </li></ul><ul><li>The aldehyde has the functional group attached to one carbon </li></ul><ul><li>Suffix = -al </li></ul><ul><li>Oxidation of primary alcohols </li></ul><ul><li>Has a low boiling point </li></ul><ul><li>Soluble in water </li></ul><ul><li>The functional group is: </li></ul><ul><li> >C=O </li></ul><ul><li>Polar bond </li></ul><ul><li>The ketone has the functional group attached to two carbon </li></ul><ul><li>Suffix = -one </li></ul><ul><li>Oxidation of secondary alcohols </li></ul><ul><li>Has a low boiling point </li></ul><ul><li>Soluble in water </li></ul>Back to Contents
  4. 4. Testing for Carbonyl Compounds <ul><li>Brady’s reagent or a 2,4-DNPH solution </li></ul><ul><li>When added to a carbonyl compound it produces a yellow-orange precipitate </li></ul><ul><li>Works with ketones and aldehydes </li></ul><ul><li>Does not work with carboxylic acids, esters, esters, acid clorides and amides which contains the >C=O group </li></ul><ul><li>Find the boiling point of the precipitate and the identity of the carbonyl compound can be found </li></ul>Back to Contents
  5. 5. Distinguishing Between Aldehydes and Ketones  Mild Oxidation <ul><li>Tollen's Reagent </li></ul><ul><li>Involves a ammoniacal silver nitrate solution </li></ul><ul><li>A aldehyde or ketone is shaken with the ammoniacal silver nitrate solution </li></ul><ul><li>If there is an aldehyde then the test tube will form a “silver mirror”  silver precipitate </li></ul><ul><li>This is due to the silver ion being reduced </li></ul><ul><li>The silver may be formed as a black precipitate </li></ul><ul><li>This works with all aldehydes </li></ul><ul><li>Fehling's Reagent </li></ul><ul><li>Involving copper (II) ions </li></ul><ul><li>When added to a aldehyde and placed into a water bath, it will form a red precipitate </li></ul><ul><li>The red precipitate is Cu₂O </li></ul><ul><li>But it only works with aliphatic aldehydes </li></ul>In both tests the aldehyde is oxidised to a carboxylate salt Tollen’s Reagent is better because it works with all aldehydes. Both don’t work with ketones but vigorous oxidation will work Back to Contents
  6. 6. Oxidation of Aldehydes (Primary Alcohols) <ul><li>Mild oxidation </li></ul><ul><li>CH₃CH₂OH (l) [O]  CH₃CHO (l) + H₂O(l) </li></ul><ul><li>This is done by distillation </li></ul><ul><li>CH₃CHO (l) + [O]  CH₃COOH (l) </li></ul><ul><li>This is done by refluxing </li></ul><ul><li>Easily oxidised to acids unlike ketones </li></ul>Back to Contents
  7. 7. Oxidation of Ketones (Secondary Alcohols) <ul><li>CH₃CHOHCH₃ (l) + [O]  CH₃OCOCH₃ (l) + H₂O </li></ul><ul><li>C₂HCOCH₂CH₃ (l) + 3[O]  C₂HCOOH (l) + CH₃COOH (l) </li></ul><ul><li>Only oxidised under vigorous conditions to acids </li></ul>Back to Contents
  8. 8. Neucleophilic Addition Reaction <ul><li>Occurs with both aldehydes and ketones </li></ul><ul><li>Reagent: NaBH₄ </li></ul><ul><li>Conditions: Aqueous/ alcoholic solution </li></ul><ul><li>Nucleophile: H⁻ </li></ul><ul><li>CH₃CHO + 2[H]  CH₃CH₂OH </li></ul><ul><li>CH₃COCH₃ + 2[H]  CH₃CHOHCH </li></ul><ul><li>Mechanism: </li></ul>Primary alcohol Secondary alcohol Back to Contents
  9. 9. Definitions <ul><li>Redox reaction – both reduction and oxidation take place </li></ul><ul><li>Reflux – continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry </li></ul><ul><li>Neucleophile – an atom or group of atoms attracted to an electron-deficient centre, where it donates a pair of electrons to form a new covalent bond </li></ul><ul><li>Functional group – the part of an organic molecule responsible for its chemical reactions </li></ul><ul><li>Electronegativity – a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond </li></ul><ul><li>Stem – the longest carbon chain present in an organic molecule </li></ul><ul><li>Suffix – the part of the name added after the stem </li></ul>Back to Contents
  10. 10. Summary Back to Contents Aldehyde Reacts with 2,4-DNP(H) Yellow/orange precipitate Reduced to Primary alcohol Oxidised to Carboxylic acid Ketones Reacts with 2,4-DNP(H) Yellow/orange precipitate Reduced to Secondary alcohol Not oxidised