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ALDEHYDES AND KETONES.

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Presentation on theme: "ALDEHYDES AND KETONES."— Presentation transcript:

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
Formula Common name Systematic name HCHO CH3CHO CH3CH2CHO CH3CH2CH2CHO CH3CH2CH2CH2CHO H2C=CHCHO PhCHO CH3COCH3 CH3COCH2CH3 CH3CH2COCH2CH3 Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Acrolein Benzaldehyde Acetone Methyl ethyl ketone Ethyl ketone Methanal Ethanal Propanal Butanal Pentanal 2-Propenal Benzenecarbaldehyde Propan-2-one Butan-2-one Pentan-3-one

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
M.p (°C) B.p (°C) Formaldehyde Acetaldehyde Propanal Butanal Pentanal Benzaldehyde Acetone 2-Butanone 2-Pentanone 3-Pentanone Cyclohexanone -92 -121 -81 -99 -26 -95 -86 -78 -40 -16 -21 21 49 76 103 178 56 80 102 156

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 8 October 2018 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 Reaction limited to symmetric cyclic ketones
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 its predator – 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) -carbon react this way
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

51 The Cannizzaro reaction as model for biological reductions
NADPH reduction of carbonyl to hydroxyl – one of the key steps during fatty acid biosynthesis

52 -Substitution reactions of aldehydes or ketones

53 Keto-enol tautomerism Concentration of enol form at equilibrium

54 Enol formation is catalyzed by base or acid
Acid-catalyzed enol formation

55 Enol formation is catalyzed by base or acid
Base-catalyzed enol formation

56 Only the protons on the  position are acidic
Not acidic Not acidic acidic Not acidic

57 Mechanism of -substitution in aldehydes or ketones
Net effect – substitution of -hydrogen by group E

58 -Substitution in aldehydes or ketones
Examples: -halogenation

59 -Substitution in aldehydes or ketones
-Halogenation of enolate ions (iodoform reaction) Bromine and chlorine react in the same way

60 Two modes of enolate ion reactivity
An enol derivative An -substituted carbonyl compound More commonly followed path

61 Condensation of aldehydes and ketones
(aldol condensation) Nucleophilic donor Mechanism Electrophilic acceptor Aldol - -hydroxyaldehyde

62 Condensation of aldehydes
Examples:

63 Condensation of ketones
Examples:

64 Mixed aldol reactions (useless)
Symmetrical products Mixed products

65 Mixed aldol reactions (useful)

66 Brief summary Aldol self-condensation cannot occur for aldehydes or ketones without -hydrogens Aldehydes containing -hydrogens are more reactive than ketones Aldol equilibrium is favorable for aldehydes without branching at -carbon Aldol equilibrium is not favorable for -branched aldehydes Mixed aldol reaction between two different carbonyl partners with -hydrogens leads to a mixture of products (useless as synthetic method) Mixed aldol reaction is very efficient when one partner is an unusally good nucleophilic donor or is a good electrophilic acceptor 29 October 2018

67 1,3-Dicarbonyl compounds are excellent nucleophilic donors
Enolate ion stabilized by three resonance structures

68 Acidity constants for some organic compounds
Compound type Formula pKa Carboxylic acid 1,3-Diketone 1,3-Ketoester 1,3-Dinitrile 1,3-Diester WATER Primary alcohol Acid chloride Aldehyde Ketone Ester Nitrile Dialkylamide AMMONIA Dialkylamine CH3COOH CH2(COCH3)2 CH3COCH2CO2C2H5 CH2(CN)2 CH2(CO2C2H5)2 H2O CH3CH2OH CH3COCl CH3CHO CH3COCH3 CH3CO2C2H5 CH3CN CH3CON(CH3)2 NH3 HN(i-C3H7)2 5 9 11 13 16 17 19 25 30 35 40

69 Dehydration of aldol products
NOT FORMED

70 Dehydration of aldol products

71 Recognizing aldol products (Retrosynthetic analysis)

72 Intramolecular aldol reactions

73 Intramolecular aldol reactions


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