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Aldehydes & Ketones

Aldehydes & Ketones. The Carbonyl Group. Compounds containing the carbonyl group, C=O aldehydes and ketones carboxylic acids , Carboxylic acid derivatives : Acid halides, acid anhydrides, esters, amides. Structure.

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Aldehydes & Ketones

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  1. Aldehydes& Ketones

  2. The Carbonyl Group • Compounds containing the carbonyl group, C=O • aldehydes and ketones • carboxylic acids , • Carboxylic acid derivatives : Acid halides, acid anhydrides, esters, amides.

  3. Structure • The functional group of an aldehyde is a carbonyl group bonded to a H atom and a carbon atom • The functional group of a ketone is a carbonyl group bonded to two carbon atoms

  4. Nomenclature • IUPAC names: • the parent chain is the longest chain that contains the functional group • for an aldehyde, change the suffix from -e to –al

  5. Position of substituents or side chains for aliphatic aldehydes is indicated by numbers.

  6. When –CHO (aldehydic group) is a substituent: –CHO group (as a terminal group) in IUPAC and Common names is given the name formyl . N.B: Priority of functional groups: COOH, SO3H, acid derivatives (esters, acid halides, amides, nitriles), CHO, C=O, OH, SH, NH2, OR, X.

  7. Nomenclature: Ketones • IUPAC names: • select as the parent alkane the longest chain that contains the carbonyl group • indicate its presence by changing the suffix -eto -one • number the chain to give C=O the smaller number

  8. when the carbonyl group is a substituent: • The =O is given the name oxo; its position is indicated by a number.

  9. Common Names1) Aldehydes • for an aldehyde, the common name is derived from the common name of the corresponding carboxylic acid . The ending ic or oic of the acid is dropped, and the suffix aldehyde is added.

  10. •Position of substituents or side chains for aliphatic aldehydes is indicated by Greek letters (∝,β,γ,δ……ω), α-carbon is the carbon attached to CHO group.

  11. 2) Ketones • for a ketone, name the two alkyl or aryl groups bonded to the carbonyl carbon and add the word ketone

  12. • Position of substituents on side chains for aliphatic ketones is indicated by Greek letters, the α-carbon being the one adjacent to the carbon of the carbonyl group.

  13. Aromatic ketones are named phenone and the second group is named as the corresponding acid • Ex ; CH3COph is named acetophenone . • phCOph is named benzophenone . • Position of substituents for aromatic Ketones is indicated by • o,m and p.

  14. Synthesis of Aldehydes and Ketones I. From alcohols: A-Oxidation of alcohols: • Oxidation of primary alcohols

  15. The oxidation of aldehydes to carboxylic acids usually takes place with milder oxidizing agents than those required to oxidize alcohols to aldehydes, so it is difficult to stop the oxidation at the aldehyde stage. To avoid this problem, the aldehyde as soon as it is formed is removed by distillation, but poor yields are obtained with aldehydesb.p >100 C0. Higher yields (93%) are obtained by using pyridiniumchlorochromate (PCC) at room temperature

  16. 2) Oxidation of secondary alcohols:

  17. B. Dehydrogenation of alcohols:

  18. II. From Acid Derivatives: 1) From Acid Chlorides: •Aldehydes from acid chlorides: Rosenmund Reduction: The catalyst is poisoned with quinoline and sulfur to stop the reaction at the aldehyde stage.

  19. •Ketones from acid chlorides: Reaction with organocadmium compounds • We don’t use Grignard reagent, as it reacts with the formed ketone and gives 3◦ alcohol. • Dialkylcadmium R2Cd act as Grignard reagent but it is less reactive

  20. 2) From Esters: • Aldehyde From Esters: i) Reduction of Carboxylic acid esters using DIBAL-H ( Diisobutyl Aluminium Hydride ) ii) Reaction of orthoformic esters with Grignard reagent:

  21. Can’t be prepared by reaction with RMgX which can react with ketone produced to give 3ry alcohol So we use orthoesters but orthoacetate to give the ketone Ketones From Esters (RCOOR):

  22. 3) From Nitriles: •Aldehyde from Alkyl or aryl cyanides “nitriles”: Stephen’s reaction:

  23. • Ketones from Alkyl or Aryl Nitriles: Reaction with Grignard reagent

  24. III. From alkenes a ) Ozonolysis of alkenes:

  25. b) Hydration of alkynes All alkynes give ketones except acetylene gives aldehyde

  26. C ) From geminal dihalides: 1) Aldehydes from terminal geminal dihalides: 2) Ketones from non terminal geminal dihalides:

  27. Special Methods for Synthesis of Aromatic Aldehydes • A. Oxidation of methyl group: • CrO3/Ac2O is specific reagent to stop reaction at the formation of aldehyde & not acid.

  28. Special Methods for Synthesis of Aromatic Ketones •Friedel Crafts Acylation:

  29. Physical Properties • Oxygen is more electronegative than carbon (3.5 vs 2.5) and, therefore, a C=O group is polar • aldehydesand ketones are polar compounds and interact in the pure state by dipole-dipol interaction • they have higher boiling points and are more soluble in water than nonpolar compounds of comparable molecular weight

  30. they are not capable to form intermolecular hydrogen bonding, since, they contain hydrogen bonded only to carbon (no NH or OH group) they have lower b.p. than the corresponding alcohols and carboxylic acids.

  31. low molecular weight aldehydes and ketones (C1-C4) are soluble in water due to H.b formation with water e.g. acetone and acetaldehyde are miscible with water in all proportions.

  32. Chemical Reactions of Aldehydes and Ketones • Structure of carbonyl group: The carbonyl carbon atom is sp2 hybridized, thus it and the three groups attached to it lie in the same plane. The bond angles between the three attached atoms are approximately 120o

  33. The carbon-oxygen double bond consists of a σ bond and a π bond. The more electronegative oxygen atom strongly attracts the electrons of both σ bond and π bond causing the carbonyl group to be highly polarized. The carbon atom bears a partial positive charge and the oxygen atom bears a partial negative charge.

  34. Aldehydes and ketones undergo nucleophilic reactions due to polarization of carbonyl group (# C=C). • Nucleophiles

  35. Relative reactivity of aldehydes and ketones in nucleophilic addition reactions: • Aldehydes are generally more reactive than ketones in nucleophilic addition reactions for two reasons: • Electronic factor (I and R) positive charge of the carbonyl carbon is diminished by electron donating groups. So aldehydes are more reactive than ketones in nucleophilic addition reactions because ketones have two alkyl groups at carbonyl carbon (+ I effect of 2 R groups).

  36. II- Steric factor The intermediate in case of aldehydes is less sterically hindered than in ketones i.e. more stable

  37. I) Addition reactions a) Addition of alcohols • This reaction is acid catalyzed as alcohols is weak Nu & reversible. • Used to protect CO group in alkaline medium, then hydrolyzed with acid to alc & ald or ketone

  38. Mechanism

  39. b) Addition of HCN (formation of cyanohydrins) • Aldehydes & ketones react with aqueous CN and drops of acid • The products are useful to prepare α-hydroxy acids by hydrolysis with acidified H2O

  40. c) Addition of Grignard reagent • RMgX is a strong nucleophile and do not need catalyst, it adds to aldehyde & ketones and the products are hydrolyzed to produce the proper alcohols.

  41. c) Reaction with ammonia derivatives “NH2-y”: • This reaction is addition followed by elimination • The reaction needs weak acid medium

  42. These derivatives are used for purification and identification of carbonyl compounds. • N.B. Reaction with secondary amines: • Aldehydes and ketones containing at least one α-hydrogen react with 20amines to give enamines. The reaction is catalyzed by acid.

  43. Mechanism

  44. II) Cannizzaro reaction(Reaction of Aldehydes containing no α-hydrogen) • For aldehydesonly lacking α- hydrogen • For aromatic aldehydes and aliphatic aldehydes containing no α- hydrogen. • The products of Cannizzaro reaction are an alcohol and the salt of a carboxylic acid "self oxidation reduction ". The concentration of NaOH not less than 30%.

  45. Mechanism: • Carboxylate anion is more stable than alkoxide anion

  46. Crossed Cannizaro reaction: • If two different aldehydes having no α-H, it is called crossed Cannizzaro. • Mechanism

  47. N. B: • The molecule which is attacked by hydroxide anion is the one which is oxidized, and the one which is attacked by hydride ion is the one which is reduced. • Hydroxide anion attacks the more reactive aldehyde (i.e.contains the more elecrophilic carbonyl carbon).

  48. IntramolecularCannizaro reaction:( i.e. occur inside the same molecule) • Mechanism

  49. III) Aldol reaction“Aldol condensation” • Reaction of Aldehydes or ketones having α-hydrogen • (e.g.acetaldehyde and acetone)when heated with dil NaOH the product is aldol

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