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Ketone & Aldehyde
Jully TanSchool of Engineering
EP101 / EG101 2
Learning Outcome At the end of this chapter, students are able to:
Provide nomenclature of the ketone and aldehyde Physical properties of ketone and aldehyde Synthesis and reaction of ketone and aldehyde
EP101 / EG101 3
Chapter 16Aldehydes and Ketones I
Nucleophilic Addition to the Carbonyl Group
The general structure of the carbonyl group is
C=OH
R
::
OC
The general formula for an aldehyde is
And that for a ketone is C=OR'
R:
:
C=OH
H
::
There is also the unique aldehyde, formaldehyde, in which there are two hydrogen atoms attached to the carbonyl group.
The R groups can be either alkyl or aryl.
EP101 / EG101 4
Nomenclature of Aldehydes
Common names are derived from those of the corresponding carboxylic acids by dropping the "(o)ic acid" and adding "aldehyde."
OH
O
H
O
Acetic acid Acetaldehyde
O
OH
O
HBenzoic acid Benzaldehyde
IUPAC (systematic) names are based on the following rules when the aldehyde function has priority and is named by use of a suffix.
(1) Select the longest continuous chain containing the -CHO and use as the parent the name of the alkane of that chain length.(2) Replace "e" in the alkane name with "al."
(3) Number from the end where the carbonyl group is located and follow all the other rules for locating substituent groups.
4-Phenylpentanal2,2-Dimethylbutanal
H
O
H
OEXAMPLES:
EP101 / EG101 6
IUPAC systematic names for ketones are based on these rules:
(1) The name of the longest alkane chain present that contains the carbonyl group is used as the parent.
(2) Replace the "e" in the alkane name with the suffix "one" and indicate the carbonyl position by a number. Number from the end that gives the lower number to the ketone position.(3) Designate the substituents and their positions in the usual way.
2-Pentanone
2-Methyl-4-phenyl-3-pentanone
O
O
Note use of alphabetical order.
O
(E)-3-Penten-2-one
Note provision for C C bond.
EP101 / EG101 7
Physical Properties of Aldehydes and KetonesBecause of the polar carbonyl group ( ~ 2.3-2.8 D), aldehydes and ketones have higher boiling points than hydrocarbons of comparable size. However, they have lower boiling points than alcohols of comparable size because only the latter have intermolecular hydrogen bonds.
CH3CH2CH2CH3 CH3CH2CH CH3CCH3 CH3CH2CH2OHO= O=
Butane Propanal Acetone 1-PropanolMW 58 58 58 60
BP -0.5 oC 49.0 oC 56.1 oC 97.2 oC
Aldehydes and ketones form hydrogen bonds to water molecules and consequently the lower MW ones are soluble in water up to about C6. The smallest ones (formaldehyde and acetone) are miscible with water.
O
HO H
HO H
EP101 / EG101 8
Synthesis of Ketones & Aldehydes
Oxidation of alcohol Ozonolysis of alkene Friedel-crafts acylation Mercuric catalysed hydration of alkynes Ketone from nitriles
EP101 / EG101 9
Synthetic Methods for AldehydesBecause aldehydes are between 1o alcohols and carboxylic acids in the oxidation-reduction sequence, they can be synthesized by either selective oxidation of 1o alcohols or by selective reduction of carboxylic acid derivatives.
RCH2OH RCHO= RCOOH[O]
[H]
[O]
[H]or
RCOX
Selective Oxidation with Pyridinium Chlorochromate (PCC)PCC
CH2Cl21-Heptanol Heptanal (78%)
PCC is
It is a unique Cr +6 oxidant. Other oxidants carry oxidation on to the carboxylic acid stage because aldehydes are more easily oxidized than alcohols.
OH H
O
N H Cl CrO3
Reduction of Carboxylic Acids
Aldehydes can be prepared by controlled reduction of carboxylic acids. Acids can be reduced with lithium aluminum hydride (LAH), a powerful reducing agent, but the process goes all the way to 1o alcohols.
RCOHO= LiAlH4
ether solvent RCHO= LiAlH4
facileRCH2OH
Lithium aluminum hydride (lithium tetrahydridoaluminate) and other metal hydride reducing agents, transfer hydride ion (H:-) to the electropositive carbon of the carbonyl group.
Al
H
HH
H
-Li+
C=O+ -
EP101 / EG101 10
Ozonolysis of alkenes.
CH
RC
R'
R''
1)
2)
O3
(CH3)2SC
H
RO + CO
R'
R''
Friedel-Crafts acylation Acid chloride/AlCl3 + benzene ketone
Ketone SynthesesOxidation of Secondary Alcohols
H OH
Cyclohexanol
K2Cr2O7 or CrO3
H2SO4
O=Cyclohexanone
These oxidations generally proceed well with few side reactions.
Aryl Ketones by Friedel-Crafts Acylation
+Butanoyl chloride
AlCl3
Phenyl propyl ketoneCl
OO
Ozonolysis of Alkenes
1,2-Dimethylcyclopentene
O3
CH2Cl2, -78 oCZn
H2O
2,6-Heptanedione
OO
EP101 / EG101 11
Ketones by Hydration of AlkynesAlkynes, like alkenes, add water in the presence of electrophilic catalysts such as H+ or Hg2+. Hydration of alkynes is conducted in aqueous solutions of sulfuric acid with mercuric sulfate as catalyst. It follows Markovnikov's rule, with the hydrogen attaching to the carbon with the greater number of hydrogens.
-C C-Alkyne
+ H2OHgSO4
H2SO4
-C=C-H
OH"Enol"
(or vinylic alcohol)
fast -C-C-H
H
O=
The "enol" rapidly rearranges to the ketone. The enol and ketone constitutional isomers actually are connected by an equilibrium which usually lies heavily on the side of the ketone. This process called tautomerization is catalyzed by acid.
-C=C-H
:OH:O
HH+ H2O + -C C-
H
H :OH
=
+Conjugate acid of ketone
Enol form(less stable)
+H
-C C-H
H :O:
= H3O++
Keto form(more stable)
EP101 / EG101 12
Ketones from NitrilesReaction of a nitrile with either a Grignard or organolithium reagent, followed by hydrolysis, yields a ketone.
R-C N:
Nitrile(R = alkyl or aryl)
+ R'-M ether R-C-R'N-M=
Imine saltR-C-R'
O=H3O+
H2O
The nitrile is a polar function similar to a carbonyl. The carbanionic center of an organometallic reagent adds to the electropositive carbon of the nitrile producing the salt of an imine.
-+
During aqueous workup, the imine is hydrolyzed to a ketone.
R-C=N-M
:
+ H-O-H R-C=N-R'
H
:
Imine
hydrolysis R-C=O:R'
:
R' - +
- +
EP101 / EG101 13
Examples
Butanenitrile(1) ether
(2) H3O++
O
Butyrophenone (Phenyl propyl ketone)
MgBrN
Benzonitrile
+N:Li
(1) ether(2) H3O+
EP101 / EG101 14
Characteristic Reactions of Aldehydes and Ketones
Reduction reactions Alcohol formation Alkane formation
Oxidation reactions Nucleophilic addition reactions
Grignard additions to form alcohols Addition of water (hydration) to form gem-diols Addition of alcohols to form acetals/ketals
EP101 / EG101 15
Reduction Reactions of Reduction Reactions of Aldehydes and KetonesAldehydes and Ketones
Alcohol formation Hydrogenation Hydride reduction
Alkane formation Clemmensen reduction Wolff-Kishner reduction
R C
OH
H2 / PtR CH2OH
R CO
H R CH2OHLiAlH4ether
H2OH+
R CO
H R CH3conc. HClZn(Hg)
R CO
H R CH3NH2NH2
OH- / H2O
EP101 / EG101 16
Oxidation of Aldehydes Oxidation of Aldehydes and Ketonesand Ketones
Conversion of Aldehydes to Carboxylic acids Oxidation of Aromatic Aldehydes/Ketones to Benzoic acid derivatives Haloform reaction of methyl carbonyls
EP101 / EG101 17
Aldehyde / Ketone Oxidations HIO4
C
O
C
O
HR RCOOH + HCOOH +HIO3
R C
O
H RCOOHAg(NH3)2+
(Tollens reagent)
C
O
H
or
C
O
R
COOHKMnO4 or K2Cr2O7
²
CH3 C
O
RX2
OH- / H2OHCX3 + RCOO-
Ar C
O
Hor (ArCOOH)
EP101 / EG101 18
Aldehyde / Ketone Nucleophilic Aldehyde / Ketone Nucleophilic Addition ReactionsAddition Reactions
R C R'O
R"MgXH+
H2OR C
OHR'
R"
R C R'O
R C R'O
R C R'O
H2OC
R
R'
OH
OH
dry HClR''OH C
R
R'
OH
OR"C
R
R'
OR"
OR"hemiketal ketal
H+ or OH-gem diol
HCN CR
R'
OH
CNcyanohydrin
R C R'O
H2N G ( H2O)- C N GRR'
EP101 / EG101 19
Ketals: Acetals of KetonesAcetal (ketal) formation with ketones is generally not a favorable process:
CR'
R
OR''
OR''+ H2O
H+
C=OR'
R+ 2 R''OH
KetalKetone H+
As in the hydration reaction, the equilibrium heavily favors the ketone.
Cyclic ketals, formed from 1,2- or 1,3-diols, are an exception:
C=OR'
R+ HOCH2CH2OH
1,2-Ethanediol(ethylene glycol)
H+
H+C
R'
R
O-CH2
O-CH2+ H2O
Cyclic ketal (stable)
Cyclic acetals or ketals hydrolyze easily in aqueous acid solution:
C=OR'
R+ HOCH2CH2OHH+
CR'
R
O-CH2
O-CH2+ H2O
excess