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Carbonyl chemistry

Carbonyl chemistry. -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions. Formation of carbonyl compounds. Starting with an alcohol, react with an oxidising agent (such as acidified potassium dichromate) Propan-1-ol + [O]  Propan al +water.

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Carbonyl chemistry

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  1. Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions.

  2. Formation of carbonyl compounds • Starting with an alcohol, react with an oxidising agent (such as acidified potassium dichromate) • Propan-1-ol + [O]  Propanal +water

  3. The carbonyl functional group ORBITAL OVERLAP The bond is polar due to the difference in electronegativity. PLANAR WITH BOND ANGLES OF 120° NEW ORBITAL

  4. CH3 CH3 C2H5 H C = O C = O C = O C = O CH3 H CH3 H Aldehydes vs. Ketones • Aldehydes have the carbonyl group at the end of a carbon chain (joined to only one carbon) • Ketones have the carbonyl group bonded to two carbons.

  5. Naming aldehydes/ketones AldehydesC2H5CHO propanal KetonesCH3COCH3 propanone CH3CH2COCH3 butanone CH3COCH2CH2CH3 pentan-2-one CH3CH2COCH2CH3 pentan-3-one C6H5COCH3 phenylethanone

  6. Identification of carbonyls • IR spectroscopy shows a strong peak around 1400-1600 cm-1

  7. Oxidation of carbonyl • Reacting an aldehyde with an oxidising agent (acidified dichromate ions) produces a carboxylic acid. • Propanal + [O]  Propanoic acid +water

  8. Reduction of carbonyls • Carbonyl groups can also be reduced. • Reduction agent used is Sodium tetrahydroborate(III) (also called Sodium Borohydride) • This is classed as a weak reducing agent.

  9. Reduction of carbonyls • Propanal is reduced to a primary alcohol by sodium borohydride. • Propanal + 2[H]  Propan-1-ol

  10. Reduction continued • NaBH4 reacts with ketones also. • Propanone + 2[H]  propan-2-ol

  11. Reduction explained • The BH4 ion is acting as a source of hydride ions (:H-) • Hydride ions being a negatively charged hydrogen ion containing a lone pair of electrons • The mechanism is an example of nucleophilic addition. • H- ion is attracted to the δ+C of the carbonyl, forming a new C-H bond • The resulting O- ion forms a dative covalent bond using the H+ from a water molecule

  12. Reduction reaction mechanism • Propanal + 2[H]  propan-1-ol

  13. Carbonyl questions • Write equations + mechanisms for the reduction of: • Butanal • 2-methylhexan-3-one • Define the term nucleophile • Show the mechanism for the reaction between butanone and NaBH4

  14. Carbonyl chemistry 2chemical tests on carbonyls -How to detect a carbonyl group -Aldehyde or ketone?

  15. ILPAC experiment 8.4 • Using the instruction sheets, follow the method for experiment 8.4 A and 8.4 B • DO NOT DO EXPERIMENT C • Make full and detailed notes on what you observe during the reactions.

  16. Condensation reactions • We can detect the presence of a carbonyl group using 2,4-dinitrophenylhydrazine (abbreviated to 2,4-DNP or 2,4-DNPH). • 2,4-DNPH is also called Brady’s reagent when prepared with methanol and sulfuric acid.

  17. Using 2,4-DNPH • When Brady’s reagent is added to an aldehyde or ketone, a yellow or orange precipitate is formed. • The precipitate, called a 2,4-dinitrophenylhydrazone derivative confirms the presence of a carbonyl functional group.

  18. Aldehyde or ketone • Aldehydes and ketones can be distinguished from each other by using Tollen’s reagent • Tollen’s reagent is a weak oxidising agent, the carbonyl group is oxidised to form a carboxylic acid. Ammoniacal silver nitrate

  19. Tollen’s reagent. • Silver ions are reduced to silver metal • Ag+(aq) + e- Ag(s) • Aldehyde + [O]  Carboxylic acid

  20. Carbonyl questions 2 • The carbonyl compounds CH3COCH3 and CH3CH2CHO are structural isomers. • Name these compounds • State the reagents used and observations made to prove the presence of a carbonyl group in these compounds • State the reagents and observations made to distinguish between the two chemicals.

  21. Carbonyl chemistry 3Identifying a carbonyl compound -Determining experimentally an unknown carbonyl compound

  22. ILPAC 8.5 • Using the instruction sheets given last lesson, carry out experiment 8.5, parts A and B • Complete a detailed method for identifying a carbonyl compound • Purifying by recrystallisation -> melting point determination -> compare melting point to known values.

  23. Carbonyl questions 3 • Explain how you would use the solid obtained from the reaction of an aldehyde with 2,4-DNPH to prove the original aldehyde was butanal. • The reaction of 2,4-DNPH with ethanal gives water as a product. Suggest the type of reaction taking place.

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