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ALDEHYDES AND KETONES

ALDEHYDES AND KETONES. CARBONYL COMPOUNDS. ALDEHYDES. KETONES. EXAMPLES. Formaldehyde. Acetaldehyde. Acetone. MOLECULAR MODELS. Formaldehyde. Acetaldehyde. Acetone. INDUSTRIAL PRODUCTION. Catalytic dehydrogenation (oxidation) of alcohols. Common names of simple carbonyl compounds.

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ALDEHYDES AND KETONES

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  1. ALDEHYDES AND KETONES

  2. CARBONYL COMPOUNDS ALDEHYDES KETONES

  3. EXAMPLES Formaldehyde Acetaldehyde Acetone

  4. MOLECULAR MODELS Formaldehyde Acetaldehyde Acetone

  5. INDUSTRIAL PRODUCTION Catalytic dehydrogenation (oxidation) of alcohols

  6. Common names of simple carbonyl compounds

  7. Physical properties of aldehydes and ketones • More polar than alkanes, higher melting and boiling points • No hydrogen bonds formation – lower boiling points than alcohols • Solubility in water – only formaldehyde, • acetaldehyde and acetone

  8. Physical properties of carbonyl compounds

  9. Preparation of aldehydes Oxidation of primary alcohols Aldehyde which boils at lower temperature than alcohol is distilled off the reaction mixture immediately after formation

  10. Preparation of aldehydes Ozonolysis of di- or trisubstituted alkenes

  11. Preparation of aldehydes Reduction of carboxylic acids esters DIBAH – diisobutylaluminum hydride (aldehyde is not reduced further to primary alcohol)

  12. Preparation of aldehydes Reduction of carboxylic acids chlorides Tri-tert-butoxylithiumaluminum hydride

  13. Preparation of aldehydes Oxidation of methylarenes

  14. Preparation of ketones Oxidation of secondary alcohols 90% yield

  15. Preparation of ketones Ozonolysis of alkenes

  16. Preparation of ketones Friedel-Crafts acylation of arenes (electrophilic aromatic substitution) 95% yield

  17. Preparation of ketones Hydration of alkynes (terminal or symmetric) 78% yield

  18. Preparation of ketones Reaction of acid chloride and diorganocopper reagent 81% yield

  19. Oxidation of aldehydes and ketones

  20. Oxidation of aldehydes and ketones Tollens oxidation Reaction used as laboratory test to distinguish aldehyde and ketone

  21. Oxidation of ketones Reaction limited to symmetric cyclic ketones

  22. Nucleophilic addition reactions of aldehydes and ketones Alcohol Alcohol Cyanohydrin Alkene Imine Alkane Acetal Enamine

  23. Aldehydes are more reactive than ketones Nu Formaldehyde Acetaldehyde Acetone Steric factor Access of nuclephile to carbonyl carbon is less hindered in aldehyde (hydrogen is smaller than any alkyl substituent)

  24. Aldehydes are more reactive than ketones Electronic factor Positive charge on carbon is stronger stabilized by inductive effect of two alkyl groups Ketones are more stable – less reactive

  25. Nucleophilic addition of H2O (hydration) A gem-diol A gem-diol

  26. Base-catalyzed addition of H2O Hydroxide anion is more reactive nucleophile than neutral water

  27. Acid-catalyzed addition of H2O Protonated carbonyl is more electrophilic and more reactive

  28. Nucleophilic addition of HCN (cyanohydrins) In practice HCN is generated during reaction by adding acid (like H2SO4) to a mixture of carbonyl compound and NaCN (or KCN). Cyanide anion is nucleophile

  29. Reactions of cyanohydrins Cyanohydrin formation from ketone or aldehyde provides compounds with new functional groups while lenghtening the carbon chain by one unit

  30. Nucleophilic addition of Grignard reagents (alcohol formation) New alcohol with larger hydrocarbon framework is obtained

  31. Nucleophilic addition of hydride (reduction) Alcohol with the same hydrocarbon framework as starting ketone or aldehyde is formed

  32. Nucleophilic addition of amines to carbonyl group

  33. Water elimination from carbinolamine

  34. Crystalline imines

  35. Crystalline imines m. p. 126°C

  36. Nucleophilic addition of hydrazine (Wolff-Kishner reaction)

  37. Nucleophilic addition of alcohols (acetal formation) Protonated carbonyl group is strongly electrophilic and highly reactive towards nucleophiles

  38. Nucleophilic addition of alcohols (acetal formation)

  39. Mechanism of acetal formation

  40. Acetal as carbonyl protective group How to reduce ester carbonyl without reducing ketone carbonyl?

  41. Acetal as carbonyl protective group

  42. Nucleophilic addition of thiols (thioacetal formation) Conversion of carbonyl to thioacetal and subsequent desulfurization is a method for reducing C=O to CH2

  43. Nucleophilic addition of phosphorus ylides (The Wittig reaction) New molecule containing C=C bond instead of carbonyl group is synthesized

  44. Conjugate nucleophilic addition to ,-unsaturated carbonyl ,-unsaturated carbonyl compounds possess 2 electrophilic carbons Conjugate addition product

  45. Conjugate nucleophilic addition to ,-unsaturated carbonyl

  46. Some biological nucleophilic additions Synthesis of -amino acid from -ketoacid in living cells

  47. Biological reaction reverse to nucleophilic addition Millipede Apheloria corrugata and itspredator – an ant

  48. The Cannizzaro reaction The only example when hydride ion is expelled from aldehyde as leaving group (like in nucleophilic acyl substitution) Nucleophilic acyl substitution

  49. The Cannizzaro reaction (disproportionation) Only aldehydes without protons at -carbon react this way in the presence of base

  50. The Cannizzaro reaction as model for biological reductions NADPH functions as hydride donor in biological reductions

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