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Aldehydes and Ketones
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Nomenclature:
Aldehydes, common names:
Derived from the common names of carboxylic acids;
drop ic acid suffix and add aldehyde.
CH3CH3CH2CH2CH=O CH3CHCH=O
butyraldehyde isobutyraldehyde(-methylpropionaldehyde)
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Aldehydes, IUPAC nomenclature:
Parent chain = longest continuous carbon chain containing
the carbonyl group; alkane, drop e, add al. (note: no
locant, -CH=O is carbon #1.)
CH3
CH3CH2CH2CH=O CH3CHCH=O
butanal 2-methylpropanal
H2C=O CH3CH=O
methanal ethanal
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Ketones, common names:
Special name: acetone
alkyl alkyl ketone or dialkyl ketone
H3CC
CH3
O
CH3CH2CCH3O
CH3CH2CCH2CH3O
ethyl methyl ketone diethyl ketone
CH3CCH2CH2CH3O
methyl n-propyl ketone
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(o)phenones:
Derived from common name of carboxylic acid, drop ic
acid, add (o)phenone.
CR
O
C
O
H3CC
O
benzophenone acetophenone
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Ketones: IUPAC nomenclature:
Parent = longest continuous carbon chain containing the
carbonyl group. Alkane, drop e, add one. Prefix a locant
for the position of the carbonyl using the principle of lower
number.
CH3CH2CCH3
O
CH3CH2CCH2CH3
O
2-butanone 3-pentanone
CH3CCH2CH2CH3
O
2-pentanone
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Aldehydes, syntheses:
1. Oxidation of 1o alcohols
2. Oxidation of methylaromatics
3. Reduction of acid chlorides
Ketones, syntheses:
1. Oxidation of 2o alcohols
2. Friedel-Crafts acylation
3. Coupling of R2CuLi with acid chloride
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Aldehydes synthesis 1) oxidation of primary alcohols:
RCH2-OH + K2Cr2O7, special conditions RCH=O
RCH2-OH + C5H5NHCrO3Cl RCH=O
(pyridinium chlorochromate)
[With other oxidizing agents, primary alcohols RCOOH]
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Aldehyde synthesis: 2) oxidation of methylaromatics:
+ CrO3, (CH3CO)2O
geminaldiacetate
H2O, H+
CH3
Br Br
CH O
OC C
H3C
O
O
H3C
Br
CHO
p-bromobenz ldehyde
Aromatic aldehydes only!
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Aldehyde synthesis: 3) reduction of acid chloride
LiAlH(O-t-Bu)3
lithium aluminum hydride tri-tert-butoxide
O
Cl
isovaleryl chloride
O
H
isovaleraldehyde
RC
O
Cl
LiAlH(O-t-Bu)3
RC
O
H
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Ketone synthesis: 1) oxidation of secondary alcohols
NaOCl
cyclohexanol cyclohexanone
isopropyl alcohol acetone
K2Cr2O7
H OH O
H3C C CH3
O
CH3CHCH3
OH
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Ketone synthesis: 2) Friedel-Crafts acylation
RCOCl, AlCl3 + ArH + HCl
AlCl3
ArCR
O
Aromatic ketones (phenones) only!
CH3CH2CH2CO
Cl+
AlCl3CH3CH2CH2C
O
butyrophenone
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Ketone synthesis: 3) coupling of RCOCl and R2CuLi
RCOCl + R'2CuLi
RC
O
R'
Cl
O
+ ( 3 2)2 uLi
O
Isobutyryl chloride 2-Methyl-3-pentanone
lithium diethylcuprate
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Aldehydes & ketones, reactions:
1) Oxidation
2) Reduction
3) Addition of cyanide
4) Addition of derivatives of ammonia
5) Addition of alcohols
6) Cannizzaro reaction
7) Addition of Grignard reagents
8) (Alpha-halogenation of ketones)
9) (Addition of carbanions)
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nucleophilic addition to carbonyl:
CO
+ Y Z C
Z
OY
H
H
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Mechanism: nucleophilic addition to carbonyl
C
O
+ Z
RDS
C
O
Z
CO
Z
+ Y COY
Z
1)
2)
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Mechanism: nucleophilic addition to carbonyl, acid catalyzed
C
O
+ H C
OH
C
OH+ H
RDS
C
OH
H
C
OH
H
C
OH
+ H
1)
2)
3)
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1) Oxidation
a) Aldehydes (very easily oxidized!)
CH3CH2CH2CH=O + K nO4, etc. CH3CH2CH2COOH
carboxylic acid
CH3CH2CH2CH=O + Ag+ CH3CH2CH2COO
- + Ag
Tollens test for easily oxidized compounds like aldehydes.
(AgNO3, NH4OH(aq))
Silver mirror
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b)Methyl ketones:
RC
CH3
O
+ OI-
RC
O-
O
+ CHI3
iodoform
test for methyl ketonesYellow ppt
CH3CH2CH2CCH3 + (xs) NaOI CH3CH2CH2CO2- + CHI3
O
2-pentanone
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2) Reduction:
a) To alcohols
H2, i
aBH4 or Li lH4
then H+
C
O
C
OH
H
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H2, Pt
1. NaBH4
2. H+
O
cyclopentanone
OH
cyclopentanol
C CH3
O
CHCH3
OH
acetophenone 1-phenylethanol
H
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Reduction
b) To hydrocarbons
NH2NH2, OH-
Zn(Hg), HCl
Clemmensen
Wolff-KishnerC
O
CO
CH2
CH2
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3) Addition of cyanide
C
O 1. CN-
2. H+
C
CN
OH
cyanohydrin
O + NaCN; then H+
OH
CN
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4) Addition of derivatives of ammonia
O+
N+ H2OH2N G
(H+)
G
HN
phenylhydrazine
H2N NH2
hydrazine
H2N OH
hydroxylamine
HN NO2
O2N
2,4-dinitrophenylhydrazine
H2N NH
O
NH2
semicarbazide
H2NH2N
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CH2 CHO
phenylacetaldehyde
+ H2NOH CH2 CH NOH
an oxime
O + H2NHNCNH2
O H+
NHNCNH2
O
a semicarbazonecyclohexanone
CH3CH2CH2CH2CHO + NHNH2
phenylhydrazine
hydroxylamine
semicarbazide
pentanalCH3CH2CH2CH2CH N NH
a phenylhydrazone
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5) Addition of alcohols
C
O+ ROH, H+
C
OR
OR acetal
C
OH
OR hemiacetal
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CH2CHO(xs) EtOH, H+
CH2 CHOEt
OEt
O (xs) CH3OH, dry HClOCH3
OCH3
acetal
ketal
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6) Cannizzaro reaction. (self oxidation/reduction)
a reaction ofaldehydes without -hydrogens
CHO
Br
conc. NaOH
CH2OH COO-
Br Br
+
CH3OH + HCOO-H2C=O
conc. NaOH
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CH3 HBr CH3 g CH3CH3CHCH2OH CH3CHCH2Br CH3CHCH2 gBr
H+
K2Cr2O7 CH3CH3CH2OH CH3CH=O CH3CHCH2CHCH3
special cond. OH
4-methyl-2-pentanol
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Formaldehyde is the most easily oxidized aldehyde. When
mixed with another aldehyde that doesnt have any alpha-
hydrogens and conc. NaOH, all of the formaldehyde is
oxidized and all of the other aldehyde is reduced.
Crossed Cannizzaro:
CH=O
OCH3
OH
vanillin
+ H2C=Oconc. NaOH
CH2OH
OCH3
OH
+ HCOO-
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7) Addition of Grignard reagents.
C
O
+ RMgX C
O
R
MgBr
C
O
R
MgBr
+ H2O C
OH
R
+ Mg(OH)Br
largeralcohol
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Planning a Grignard synthesis of an alcohol:
a) The alcohol carbon comes from the carbonylcompound.
b) The new carbon-carbon bond is to the alcohol carbon.
C
O
+ RMgXH+
C
OH
R
New carbon-carbon bond