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CHAPTER 13: ALDEHYDES AND KETONES
Before you can learn about aldehydes and ketones, you must first know something about the nomenclature of carboxylic acids since many of the names of aldehydes and ketones are derived from the names of the corresponding carboxylic acids.
Carboxylic acids:
R-COOH, R-CO2H,
Common names:
HCO2H formic acid formica ant
CH3CO2H acetic acid acetum vinegar
CH3CH2CO2H propionic acid “first salt”
CH3CH2CH2CO2H butyric acid butyrum butter
CH3CH2CH2CH2CO2H valeric acid valerans
ALDEHYDES COMMON NAMESSTEM PLUS ALDEHYDE
R-CHO R-CO2H
HCHO
FORMALDEHYDE
HCO2H
FORMIC ACIDFORMICA - ANTS
CH3CHO
ACETUM - SOUR
CH3COOHACETALDEHYDE
ACETIC ACID
CH3CH2CHO CH3CH2CO2H
PROPIONALDEHYDE PROTOS PION - FIRST FAT PROPIONIC ACID
CH3CH2CH2CHO CH3CH2CH2CO2H
BUTRYM - BUTTERBUTYRALDEHYDEBUTYRIC ACID
CH3CH2CH2CH2CH2CHO
CAPROALDEHYDE CAPER - GOAT
CH3CH2CH2CH2CH2CO2H
CAPROIC ACID
4
Chapter 18
NAMING ALDEHYDES
IUPAC: Replace -e with -al. The aldehyde carbon is number 1. If -CHO is attached to a ring, use the suffix -carbaldehyde.
CH
O
HCH3
Cl
C
O
H
OH
H3CHC=HC C
O
H
2-Chloropropanal 3-Hydroxypropanal 2-Butenal
C
O
H H CH3
O
H CH3 CH2 C
O
H H3CH2CH2C C
O
H
Common Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde
IUPAC Methanal Ethanal Propanal Butanal
NOMENCLATURE
Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde.
Benzaldehyde p-Nitrobenzaldehyde o-Hydroxybenzaldehyde p-Methoxtbenzaldehyde
O
H
O
H
O2N
O
H
OH O
H
H3CO
KETONES: STRUCTURE AND NOMENCLATURE General formula: RCOR’ (R and R’=alkyl or aryl) Common name: listing the alkyl substitutents attached
to the carbonyl group, followed by the word ketone. IUPAC system: relpace the ending –e by the suffix –one.
The chain is numbred in such a way as give the lowest number to the C=O group.
Common Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone
Acetone Acetophenone Benzophenone
IUPAC Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone
CH3 C CH3
O
CH3 C C6H5
O
CH3 C CH=CH2
O
H5C6 C
O
C6H5
CH3CH2CCH3
O
CH3CH2CCH2CH3
O
ethyl methyl ketone diethyl ketone
CH3CCH2CH2CH3
O
methyl n-propyl ketone
(o)phenones:
Derived from common name of carboxylic acid, drop –ic acid, add –(o)phenone.
CR
O
C
O
H3CC
O
benzophenone acetophenone
C2H5 C
O
O
C2H5
CHO
O
OH
C2H5 C
O
O
C2H5
CHO
O
OH
Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal
13
Chapter 18
BOILING POINTS More polar, so higher boiling point than
comparable alkane or ether. Cannot H-bond to each other, so lower boiling
point than comparable alcohol.
=>
14
Chapter 18
SOLUBILITY
Good solvent for alcohols. Lone pair of electrons on oxygen of carbonyl
can accept a hydrogen bond from O-H or N-H. Acetone and acetaldehyde are miscible in
water.
=>
Aldehydes synthesis 1) oxidation of primary alcohols:
RCH2-OH + K2Cr2O7 (potassium dichromate) RCH=O+ H2
RCH2-OH + C5H5NHCrO3Cl RCH=O+ H2
(pyridinium chlorochromate, or PCC)
[With other oxidizing agents, primary alcohols RCOOH]
CH3CH2CH2CH2CH2OH
+ K2Cr2O7 CH3CH2CH2CH2CO2H
1-pentanol
pentanoic acid
K2Cr2O7, special conditions!CH3CH2CH2CH2CH=O
pentanalvaleraldehyde
CH2OHC5H5NHCrO3Cl
pyridinium chlorochromate
CH=O
benzaldehydebenzyl alcohol
CH3CH2CH2CH2CH2OH
1-pentanol
Aldehyde synthesis: Primary alcohols
Aldehyde synthesis: 2) reduction of acid chloride
LiAlH(O-t-Bu)3
lithium aluminum hydride tri-tert-butoxide
O
Cl
isovaleryl chloride
O
Hisovaleraldehyde
RC
O
Cl
LiAlH(O-t-Bu)3
RC
O
H
CO
Cl
LiAlH(O-t-Bu)3C
O
H
LiAlH(O-t-Bu)3
benzoyl chloride benzaldehyde
CH3CHCH2CO
Cl
CH3
CH3CHCH2CO
H
CH3
isovaleryl chloride isovaleraldehyde
Ketone synthesis: 1) oxidation of secondary alcohols
NaOCl
cyclohexanol cyclohexanone
isopropyl alcohol acetone
K2Cr2O7
H OH O
H3CC
CH3
O
CH3CHCH3
OH
Ketone synthesis: 2) Friedel-Crafts acylation
RCOCl, AlCl3 + ArH + HClAlCl3
ArCR
O
Aromatic ketones (phenones) only!
CH3CH2CH2CO
Cl+
AlCl3CH3CH2CH2C
O
butyrophenone
+AlCl3
m-nitrobenzophenone
O2N
C Cl
O
CO
O2N
+AlCl3
C Cl
O
NO2
NR
Friedel Crafts acylation does not work on deactivated rings.
ACETALS ANDHEMICETALS Acetal: two –OR groups bonded to the same
carbon Hemiacetal: one –OR group and one –OH
group bonded to the same carbon
ENOLIZATION Keto-Enol Tautomerism
Tautomerism: interconversion between two structures that differ by the placement of an atom or group
Slow in neutral conditions, sped up in acid or base catalyzed systems
Enol content is very small, <<<1% for most aldehydes and ketones