the chemistry of aldehydes and ketones by dr. nahed nasser
TRANSCRIPT
THE CHEMISTRYTHE CHEMISTRYOF ALDEHYDES AND OF ALDEHYDES AND
KETONESKETONES
ByByDr. Nahed NasserDr. Nahed Nasser
CONTENTSCONTENTS
• Bonding in carbonyl compounds
• Structural differences between aldehydes and ketones
• Drawing aldehydes and ketones
• Nomenclature of aldehydes and ketones
• Physical properties of aldehydes and ketones
•Preparation of aldehydes and ketones
•Reactions of adehydes and ketones
ALDEHYDES & KETONESALDEHYDES & KETONES
CARBONYL COMPOUNDSCARBONYL COMPOUNDSCarbonyl compounds contain CO group, they include aldehydes, ketones, acids and
acid derivativesBonding the carbon is sp2 hybridised and formsthree sigma (s) bonds
the unhybridised 2p orbital of carbon is overlaps with a 2p orbital of oxygen to form a pi () bond
as oxygen is more electronegative than carbon the bond is polarized
PLANAR WITH
BOND ANGLES OF 120°
P –ORBITALS
ORBITAL OVERLAP
NEW ORBITAL
The implications of these effects are :higher melting and boiling points compared to analogous alkanes lower boiling points than analogous alcohols more soluble than alkanes but less soluble than alcohols in aqueous media
Difference ALDEHYDES (RCHO) - at least one H attached to the carbonyl group thus the aldehydic group (CHO) is always terminal
KETONES RCOR’ (R and R’=alkyl or aryl )- two carbons attached to the carbonyl group
C = OH
CH3
C = OH
H
C = OCH3
CH3
C = O
C2H5
CH3
Structural differences between aldehydes Structural differences between aldehydes and ketonesand ketones
Aldehydes and ketones contains the same functional group, the carbonyl group (> C = O).
5
Drawing aldehydes and ketonesDrawing aldehydes and ketones
Molecular Formula C3H6O
Structural Formula C2H5CHO CH3COCH3
Bond line formula
C = OH
C2H5
C = OCH3
CH3
O
O
H
O
NOMENCLATURE Of CARBONYL COMPOUNDSNOMENCLATURE Of CARBONYL COMPOUNDS
IUPAC Nomenclature of Aldehydes:• Find the longest continuous carbon chain contains the CHO group to get the name of the parent hydrocarbon, the ending e is then replaced by the suffix –al.
C
O
H H CH3
O
H CH3 CH2 C
O
H H3CH2CH2C C
O
H
IUPAC: Methanal Ethanal Propanal Butanal
Common: Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde
• The CHO group is assigned the number 1 position and takes precedence over other functional groups that may the present such as –OH, C=C, OR, C=O, for example:
H
O
3-Hydroxypropanal
O
2-Butenal
H
OCl
-Chlorobutyraldehyde
HO
3-ChlorobutanalIUPAC:
Common -Hydroxypropionaldehyde
7
• Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde.
O
H
O
H
O2N
O
H
OH O
H
H3CO
IUPAC: Benzaldehyde 4-Nitrobenzaldehyde 2-Hydroxybenzaldehyde 4-MethoxybenzaldehydeCommnon: Salicylaldehyde Anisaldehyde
Nomenclature of Nomenclature of KetonesKetones
• Common namesCommon names: : derived by listing the alkyl substitutents attached to the carbonyl group in alphabetical order, followed by the word ketone.
• IUPAC names: IUPAC names: derived from the parent hydrocarbon and relpacing 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.
IUPAC: Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone
Common: Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone
Acetone Acetophenone Benzophenone
CH3 C CH3
O
CH3 C C6H5
O
CH3 C CH=CH2
O
H5C6 C
O
C6H5
C2H5 C
O
O
C2H5
CHO
O
OH
IUPAC: Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal
PHYSICAL PROPERTIES OF KETONES AND ALDEHYDE
• Because the polarity of the carbonyl group, aldehydes and ketones are polar compounds.
• Dipole-dipole attractions,Dipole-dipole attractions, although important, are not as strong as interactions due to hydrogen bonding. As a result, the boiling points of aldehydes and ketones are higher than those of non polar alkanes, but lower than those of alcohols.
• The lower aldehydes and ketones are more soluble than alkanes but less soluble than alcohols in aqueous media
C O
C+
O-
O
C O
C
C O
H
O
H CO
Preparation of aldehydes and ketones
1- Oxidation of alcohols
2- Ozonolysis of alkenes
RCH2 OHCrO3/ pyridine
Cu / heatR
O
H
R2CH OH
CrO3/ pyridine
Cu / heat
R C R
O
i) O3
ii) Zn / H2O
CH3CH2CHO + CH3CHO
i) O3
ii) Zn / H2OO
O
Diketone
two aldehydes
3- Hydration of alkynes
4- Friedel Crafts acylation
N.B: -COR group is m-director
C C C C
OH
H
C C
H
OH
+ OH HH2SO4, HgSO4
an enol unstable carbonyl more stable
+ R
O
Cl
AlCl3R
O
• Typical aldehydes and ketones ReactionsTypical aldehydes and ketones Reactions
Reduction (formation of alcohols)Reduction (formation of alcohols)
Nucleophilic addition reactions:
1-Addition of HCN
2- Addition of acetylide anion
3-Addtion of alcohols
4-Addition of ammonia and ammonia derivatives
5- Oxidation reactions
a) By K2Cr2O7 or KMnO4
b) By Iodoform reaction
12
REACTIONS OF ALDEHYDES AND REACTIONS OF ALDEHYDES AND KETONESKETONES
1- Reduction : formation of alcohols1- Reduction : formation of alcohols
Catalytic hydrogenation
/ H
2- By nucleophilic addition of Grignard reagent to 2- By nucleophilic addition of Grignard reagent to aldehydes and ketones (formation of alcohols)aldehydes and ketones (formation of alcohols)
• Addition of RMgX to formaldehyde gives 1◦ alc.• Addition of RMgX to any other aldehyde gives 2◦ alc. • Addition of RMgX to ketones gives 3◦ alc.
R C
O
H
R CH OH
R'
R C OH
R'
R''
R C R'
O
+ R'MgX1) Dry ether
2) H2O
+ R''MgX1) Dry ether
2) H2O
CH3 C
O
H
CH3 CH
OH
C2H5+ C2H5MgX1) Dry ether
2) H2O
+ CH3MgX1) Dry ether
2) H2O
OCH3
OH
H H
O
+ RMgX1) Dry ether
2) H2O H H
OH
R
1 alcohol°
3- Addition of Hydrogen Cyanide: Formation of cynohydrins3- Addition of Hydrogen Cyanide: Formation of cynohydrins
4- Addition of alkynide ions:
R C OH
R'
CN
R C R'
O
+ HCN
O
H
+ HCN
OH
CNCyanohydrin
Benzaldehyde cyanohydrin
O
+ HCN
OH
CN
H2 / Pt
or LiAlH4 and H3O+
OH
NH2
H3O+
Heat
OH
COOH
R C C
R'
OH
C R2
R C R'
O
+
O
+
OH
C C CH3
CR2
C-Na
+
CCH3 C-Na
+
H3O+
H3O+
5- Addition of alcohols:
R C
O
R2
R C OH
R'O
R2
+ R'OH
CH3 C
O
HCH3 CH
OH
OC2H5+ C2H5OH
H+ R''OH
H+ R C OR''
R'O
R2
R2=H:
R2=Alkyl
Aldehyde
Ketone
Hemiacetal
Hemiketal
Acetal
Ketal
H+
C2H5OH
H+ CH3 CH
H5C2O
OC2H5
Hemiacetal Acetal
CH3 C
O
CH3
CH3 C
OH
OC2H5
CH3
+ C2H5OHH
+
C2H5OH
H+ CH3 C
H5C2O
OC2H5
CH3
Hemiketal Ketal
6- Addition of Ammonia and Ammonia Derivatives6- Addition of Ammonia and Ammonia Derivatives
C O
NH3C NH
Imine
NH2OH
HydroxylamineC N
OH
C N
NH2
C N
NH
C N
NH
O2N NO2
C N
NH C NH2
O
Oxime
NH2 NH2
HydrazineHydrazone
NH2 NH
PhenylhydrazonePhenylhydrazine
NH2 NH
O2N NO2
2,4-Dinitrophenylhydrazone
NH2 NH C NH2
O
SemicarbazideSemicarbazone
3- Oxidation reactions3- Oxidation reactionsa)By KMnO4 or K2Cr2O7:
Only aldehydes can be oxidized ketones resist oxidation
b) Iodoform reaction: Iodoform reaction: • This reaction gives positive result with any aldehyde or ketone has a
methyl ketone group (CH3CO) , therefore acetaldehyde is the only aldehyde gives positive iodoform test.
R-CHO or Ar-CHOKMnO4
or K2Cr2O7
RCOOH or ArCOOH
C O
CH3
R+ 3 I2 + 4 NaOH R
O
O-Na
+ + CHI3 + 3 NaI
CH3CH3
O
I2 / NaOHCH3
COONa+ CHI3
18