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Aldehydes & KetonesO
2
In General
Fragrant odors Basic building block of housing
materials Hormones Digestion Vision
3
In General
Carbonyl group› C=O› Aldehydes
RCH=O Formyl
› Ketones RC=OR’
4
Nomenclature
Aldehydes› IUPAC end in “al”› Common end in “aldeyde”› Carbonyl C is always #1› Cyclic cpds
Carbaldehyde is ending for most
5
Nomenclature
Aldehydes
CH2 O
O
CH3
O
CH3
O
CH3
methanal(formaldehyde)
ethanal(acetaldehyde)
propanal(propionaldehyde)
butanal(n-butyraldehyde)
6
Nomenclature
Aldehydes
3-methylbutanal
3-butenal
2,3-dihydropropanal(glyceraldehyde)
CH3
CH3 O
CH2
O
O
OH OH
7
Nomenclature
Aldehydes
cyclopentanecarbaldehyde(formylcyclopentane)
benzenecarbaldehyde(benzaldehyde)
2-hydroxybenzenecarbaldehyde(salicylaldehyde)
O
O
O
OH
8
Nomenclature
Ketones› IUPAC end in “one”› Common end in “ketone”› Carbonyl C is never #1, but always gets
low number preference› Cyclic cpds
Carbaldehyde is ending for most
9
Nomenclature
Ketones
propanone(acetone)
2-butanone(ethyl methyl ketone)
3-pentanone(diethyl ketone)
CH3
CH3
O
CH3
O CH3
CH3
O CH3
10
Nomenclature
Ketones
cyclohexanone
2-methylcyclopentanone
3- buten-2-one(methyl vinyl ketone)
O
O
CH3
CH2
CH3
O
11
Nomenclature
Ketones
acetaphenone(methyl phenyl ketone)
benzophenone(diphenyl ketone)
dicyclopropyl ketone
CH3
O
O
O
12
Common Aldehydes & Ketones
Formaldehyde› Simplest aldehyde› Manufactured on large scale (8 billion lbs per
annum) from catalyzed oxidation of methanol CH3OH CH2=O + H2
› Gas at RT (bp = -21˚C) but cannot be stored in free state due to polymerization
› Normally 37% soln called formalin (preservative)
› Most used in making of plastics, insulation, particle board, and plywood
13
Common Aldehydes & Ketones
Acetaldehyde› Boils close to RT (bp = 20˚C)› Made by catalyzed oxidation of ethylene
2 CH2=CH2 + O2 2 CH3CH=O
› ~1/2 is oxidized to acetic acid› Remainder used for production of
1- butanol and others.
14
Common Aldehydes & Ketones
Acetone› Simplest ketone› Large scale production like formaldehyde› Produced from oxidation of propene, isopropyl
alcohol, or isopropylbenzene
› ~30% used directly, great solvent, H2O miscible
› Rest used to make stuff like epoxy resins
CH3CH3
O 2
OOHCH3
CH3d ilu te H 2 S O 4
H 2 O
OH
+ CH3
CH3
O
15
Common Aldehydes & Ketones
Quinones› Cyclic conjugate diketones› Simplest is 1,4-benzoquinone› All are colored and are thus used often as
dyes› Alizarin…used to dye the red coats of the
British Army during American Revolution› Vitamin K is required for normal clotting of
blood
16
Common Aldehydes & Ketones
O O
OH
OHO
O1,4-benzoquinone
alizarinOH
CH3
OH
CH3
CH3CH3CH3CH3
vitamin K
Vitamin K
17
Synthesis of Aldehydes & Ketones
Oxidation› 1˚ ROH gives aldehyde› 2˚ ROH gives ketone› Cr reagents (PCC) are common
CH3 OHo x id iz in g
a g e n tCH2 O
18
Synthesis of Aldehydes & Ketones
Friedel-Crafts Acylation› Recall the rxn?› Makes aromatic ketones
+O
Cl A lC l3
O
+ ClH
benzophenonebenzyl chloride
19
Synthesis of Aldehydes & Ketones
Hydration of terminal alkynes› Gives methyl ketones› Catalyzed by acid and mercuric ion
CH3CH
H + , H 2 O
H g + +CH3
CH3
O
20
Aldehydes & Ketones in Nature
Many have pleasant odors Used in the perfume industry Extremely expensive to gather from
natural producers Chanel No. 5 (my mom’s fave perfume)
was first perfume to use synthetic organic chemicals in 1921
21
Aldehydes & Ketones in Nature
O
O
O
CH3
O
OH
benzaldehyde cinnamaldehyde vanillin
22
The Carbonyl Group
C atom is sp2 hybridized Bond angles? C=O bond length is 1.24Å (compared
to 1.43Å for C-O in ROH and ROR O is more EN than C
› Makes a polar bond
23
The Carbonyl Group
Most carbonyl reactions are nucleophilic attacks on the carbonyl C
C=C usually is attacked by an electrophile
Due to polarization, physical properties differ from HC’s and ROH’s› bp’s are higher than HC’s, lower than
ROH’s
24
The Carbonyl Group
C=O is permanently polarized› Positive part of one molecule is attracted
to negative part of another molecule› Dipole-dipole forces, weaker than H-bonds,
stronger than LDF
25
The Carbonyl Group
C=O’s with low MW are soluble in water› Can form H-bonds with water or ammonia
26
An Overview of Nucleophilic Addition to Carbonyl Groups
Why does the attack occur? If rxn occurs in hyroxylic solvent (water
or ROH), a proton is usually added to the O
27
An Overview of Nucleophilic Addition to Carbonyl Groups
Carbonyl cpds are weak Lewis bases due to lone pairs on O
Acids can catalyze the addition of weak nucleophiles to carbonyl cpds through protonation
28
An Overview of Nucleophilic Addition to Carbonyl Groups
Nucleophiles add reversibly› Good leaving groups, CB of SA
Nucleophiles add irreversibly› Poor LG, CB of WA
In general, ketones are less reactive than aldehydes› Steric…sp2 v. sp3, R v. H› Electronic…alkyl groups are electron-
donating…ketones have two
29
Addition of Alcohols: Formation of Hemiacetals and Acetals
Alcohols are oxygen nucleophiles› OR goes to C, and H goes to O
Because ROH’s are weak nucleophiles, acid catalyst must be used
Product is a hemiacetal› Contains both alcohol and ether on same C
Addition is reversible
30
Addition of Alcohols: Formation of Hemiacetals and Acetals
Mechanism of hemiacetal formation has 3 steps› Carbonyl O is protonated by acid catalyst› ROH’s O then attacks carbonyl C› Proton is then lost from resulting +O
Each step is reversible
31
Do You Get It?
Write an equation for the formation of a hemiacetal from acetaldehyde, ethanol, and an acid catalyst. Show each step in the rxn mechanism.
32
Addition of Alchols: Formation of Hemiacetals and Acetals
Excess ROH means hemiacetals react further to produce acetals
Hydroxyl group of hemiacetal is replaced by an alkoxyl group.
Acetals have two ether groups on same C
33
Addition of Alchols: Formation of Hemiacetals and Acetals
Mechanism of acetal formation
34
Addition of Alchols: Formation of Hemiacetals and Acetals
Mechanism of acetal formation
35
Addition of Alchols: Formation of Hemiacetals and Acetals
Aldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal…5-hydroxypetanal
36
Addition of Alchols: Formation of Hemiacetals and Acetals
Aldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal…5-hydroxypetanal
37
Addition of Alchols: Formation of Hemiacetals and Acetals
Cpds with hydroxyl group 4 or 5 C’s from the aldehyde group tend to form cyclic hemiacetals and acetals due to lack of strain
Carbohydrates
38
Addition of Alchols: Formation of Hemiacetals and Acetals
Ketones also form acetals If a glycol is used, product is cyclic
39
Addition of Alchols: Formation of Hemiacetals and Acetals
Summary› Aldehyde or ketone reacts with ROH› Hemiacetal is formed› Further ROH makes acetal
40
Addition of Water: Hydration of Aldehydes and Ketones
Water is an oxygen nucleophile, like ROH’s Can add reversibly
41
Addition of Water: Hydration of Aldehydes and Ketones
Aside from formaldehyde hydrate most other hydrates cannot by isolated because they lost water…Keq<1
One exception is trichloroacetaldehyde (chloral)› Forms a stable crystalline hydrate, chloral hydrate,
CCl3CH(OH)2
› Used as a sedative
42
Addition of Grignard Reagents and Acetylides
Grignard reagents act as carbon nucleophiles toward carbonyl cpds› Grignard reagent adds irreversibly to the
carbonyl carbon, forming a new C-C bond› Favorable because product (an alkoxide) is a
much weaker base than the starting carbanion› The alkoxide can be protonated to give an
ROH
43
Addition of Grignard Reagents and Acetylides
Useful route to alcohols› Type of carbonyl determines class of ROH› Formaldehyde gives 1˚ ROH’s
44
Addition of Grignard Reagents and Acetylides
Other aldehydes give 2˚ ROH’s
45
Addition of Grignard Reagents and Acetylides
Ketones give 3˚ ROH’s
46
Addition of Grignard Reagents and Acetylides
Other organometallic cpds like organolithium cpds and aceylides react with carbonyl cpds similarly to Grignard reagents
47
Addition of Hydrogen Cyanide: Cyanohydrins
HCN adds reversibly to carbonyl group of aldehydes and ketones to make cyanohydrins› Hydroxyl and cyano group attached to same C› Basic catalyst is needed
48
Addition of Hydrogen Cyanide: Cyanohydrins
Acetone reacts as follows:
49
Addition of Hydrogen Cyanide: Cyanohydrins
Cyanohydrins play important role in the defense system of the millipede› Two-chambered gland like the bombadier
beetle› Benzaldehyde cyanohydrin is stored and then
converted to a mixture of benzadehyde and hydrogen cyanide and secreted
50
Addition of Hydrogen Cyanide: Cyanohydrins
Write an equation for the addition of HCN to benzaldehyde.
51
Addition of Nitrogen Nucleophiles
Ammonia, amines, and other related cpds have a lone pair on the N and thus act as a nucleophile toward a carbonyl C
52
Reduction of Carbonyl Cpds
Aldehydes and Ketones are easily reduced to 1˚ and 2˚ alcohols, respectively
Metal hydrides used to reduce› Irreversible nucleophilic attack› LiAlH4 or NaBH4
53
Reduction of Carbonyl Cpds
The original product is an aluminum alkoxide Then hydrolyzed by water and acid to give
ROH Net result is addition of H across the C=O
O1 . L iA lH 4
2 . H + , H 2 OOH
H
54
Oxidation of Carbonyl Cpds
Aldehydes are more easily oxidized than are ketones
Oxidation of an aldehyde gives an acid with the same number of C’s
Oxidizing agents include KMnO4, CrO3, Ag2O
CH3O
C rO 3 , H +
Jo n e s re a g e n tCH3
O
OH
OA g 2 O
O
OH
55
Oxidation of Carbonyl Cpds
Tollens Silver Test› Silver-ammonia complex ion is reduced by
aldehydes but not by ketones› If test tube is clean, a mirror forms by the
metallic Ag› Used to “silver” glass using formaldehyde (cheap)
56
Keto-Enol Tautomerism
Aldehydes and Ketones may exist as an equilibrium mixture of two forms› Keto and enol forms› Differ in the location of a proton and a double
bond Tautomerism (Greek…same part)
› Structural isomers› Not resonance contributors
57
Keto-Enol Tautomerism
In order for an enol form to exist carbonyl C must have an H attached to the carbon adjacent to the carbonyl group› Known as the -hydrogen and is attached to
the -carbon
58
Keto-Enol Tautomerism
Most simple aldehydes and ketones exist primarily in the keto form› Keto more stable› Acetone, 99.9997% keto form
Phenols have mainly enol form
OH
HH
O
59
Keto-Enol Tautomerism
Carbonyl cpds that do not have an -hydrogen cannot form enols and exist only in keto form
H
O
H
H
O O
60
Acidity of -Hydrogens: the Enolate Anion
-Hydrogen is more acidic than normal H attached to a C› Carbonyl C carries a partial + charge, attracting
bonding electrons away from the -H…make it easy for a base to remove the -H
› Resulting anion is stabilized by resonance…enolate anion
61
The Aldol Condensation
Enolate anions may act as carbon nucleophiles
Enolate can add reversibly to the carbonyl group of another aldehyde or ketone…known as aldol condensation
Simplest is the combination of two acetaldhyde molecules due to treatment with an aqueous base
62
The Aldol Condensation
63
The Aldol Condensation
Step 1…base removes -H to form enolate anion
Step 2…enolate anion adds to the carbonyl carbon of another acetaldehyde molecule, making a new C-C bond
Step 3…alkoxide ion form in step 2 accepts a proton from the solvent, thus regenerating the OH- needed for the first step
64
The Aldol Condensation
3-hydroxyaldehydes are always formed Since -C acts as a nucleophile, the product
always has just one C between the aldehyde and alcohol C’s
Does not matter how long the C chain is in the starting aldehyde
65
The Mixed Aldol Condensation
Enolate anion of one carbonyl cpd can be made to add to the carbonyl carbon of another cpd
Consider acetaldehyde and benzaldehyde (has no -H) when treated with base