Transcript Aldehydes and ketones

Organic Chemistry
Aldehydes and Ketones
Chapter 17
Aldehydes and Ketones
 Carbonyl
 Present
Group C=O
O
C H
in aldehydes and ketones
O
R
C
O
H
Aldehydes
R
C
R'
Ketones
Aldehydes
 Aldehydes
 Sometimes
abbreviated RCHO
 Contain at least one H connected to the C
H2 C
O
formaldehyde
O
O
O
C H
R
CH 3 CH
C
H
acetaldehyde
benzaldehyde
Aldehydes
Ketones
 Ketones
 Carbonyl
C is connected to two alkyl groups
 RCOR’
O
O
CH 3 C CH 3
acetone
CH 3
R
C
R'
CH 3 CH 2 C O
methyl ethyl ketone
Ketones
Nomenclature
 IUPAC
– Suffix is “-al” for the aldehydes
– Suffix is “-one” for the ketones
– # indicates position of ketone
O
CH 3 CH 2 CH
propanal
O
CH 3 CH 2 CH 2 C CH 2 CH 3
3-hexanone
Nomenclature
NOTE:
Ketone,
Not
keytone
From Yahoo Images
Nomenclature
 An
Aldehyde or Ketone takes precedence
over any previously considered group
OH
O
Cl CH 2 CH CH 2 CH 2 CH
5-chloro-4-hydroxypentanal
O
H2C CH CH 2 C CH 2 Cl
1-chloro-4-penten-2-one
Nomenclature
 Common
H2 C
names - aldehydes
O
formaldehyde
O
O
C
H
CH 3 CH
acetaldehyde
benzaldehyde
Nomenclature
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 Common
names - ketones
– Some are always used
O
O
C
CH 3 C CH 3
acetone
benzophenone
- Others name each R group and end with “ketone”
CH 3
CH 3 CH 2 C O
methyl ethyl ketone
CH 3 O
CH 3 C
C
CH 3
CH 3
methyl t-butyl ketone
Physical Properties
Carbonyls:
 Cannot form H bonding with each other:
 There is NOT an H connected to a F, N, O
 Aldehydes and Ketones are POLAR molecules
and form dipole interactions
 Gives higher boiling and melting points
C

O
Physical Properties
 Aldehydes
and Ketones
– can form H bonds with water!
– solubility in water is about the same as alcohols
yes!
C
O
C
C
O
O
H O
H
Physical Properties
 Strong
odors
– Ketones generally have pleasant odors
» perfumes, flavoring agents
– Aldehydes odors vary
» some pleasant
 cinnaminaldehyde, vanillin
» some not pleasant
 formaldehyde
Many are found in natural products
http://www.youtube.com/watch?v=KDohVakqkic
How do you make Aldehydes?
 Aldehydes
from Oxidation of 1o alcohols
– Problem is over oxidation to ACID!
CH 3 CH 2 OH + K2Cr 2O7
H+
O
CH 3 CH
acetaldehyde
ethanol
O
CH 3 CH
acetaldehyde
+ K2Cr 2O7
H+
O
CH 3 C OH
acetic acid
Practice a couple …………..
How do you make Ketones?
 Ketones
from Oxidation of 2o alcohols
OH
CH 3 CH CH 3
2-propanol
+ K2 Cr 2 O7
O
CH 3 C CH 3
acetone
+ K2 Cr 2 O7
H+
O
CH 3 C CH 3
acetone
H+
Practice a couple …………..
N.R.
Oxidation of Aldehydes
 Aldehydes
are easily oxidized
– KMnO4
– K2Cr2O7
– even air oxidation
O
O
CH 3 CH
acetaldehyde
carboxylic acid!
+ KMnO 4
CH 3 C OH
acetic acid
Oxidation of Ketones
 Ketones
resist oxidation:
– under mild or normal conditions, no reaction
– more severe conditions yield mixtures
– CO2 and H2O under extreme conditions
O
CH 3 C CH 3
acetone
normal
conditions
[O]
N.R.
This difference in reactivity can be used to
Tell the difference between an aldehyde and ketone
Reaction
1. Oxidation – Tollens Test
- Benedicts Test
2. Reduction – Hydrogen addition
– NaBH4 reagent
3. Addition of Alcohols – hemiacetal/acetal
and tautomerism
Tollen’s Test
 The

Silver Mirror Test
Oxidation of Aldehydes
 Ag+ ion in aq. ammonia
 NO reaction with KETONES
Ag(NH3)2+ + aldehyde
Ag+ + 2 NH3
Ag(NH3)2+ + RCHO
Silver Mirror
Ag(NH3)2+
Ago + RCOO- + 4NH3
Benedict’s Test

Oxidation of Aldehydes
 Cu++ ion, aqueous
 Orange to red ppt.
 NO reaction with KETONES
Cu2+
Cu++ + aldehyde
Cu+
Cu+(oxide) + acid
Benedict’s Test

Oxidation of Aldehydes
 overall reaction
O
R C H + 2 Cu2+ + 5 OHaldehyde
O
Cu2O
+ 2 Cu2O + 3 H2O
R C Ocarboxylic acid (ion)
Chemical Properties
 Addition
–
–
–
–
to C=O
Other reactions are ADDITION Reactions
Bond is polar + and Negatives are attracted to C
Positives are attracted to O
+
C 
O 
Addition of H2
 Reduction
to Alcohols
– Hydrogen gas and a catalyst (Ni, Pd, Pt)
– Similar to alkene to alkane reduction
O
CH 3 CH
acetaldehyde
H2
catalyst
OH
CH 3 CH 2
ethanol
Addition of H2
 Reduction
to Alcohols
– Will reduce ketones to 2o alcohols
– Slower reaction than reduction of C=C
» C=C is reduced faster (first) if both C=O and C=C
O
CH 3 C CH 3
acetone
O
CH 3 CH CH CH
2-butenal
H2
Pt
H2
Ni
OH
CH 3 CH CH 3
2-propanol
O
CH 3 CH 2 CH 2 CH
butanaldehyde
Addition of H2 using NaBH4
 Reduction
to Alcohols
– NaBH4 does not allow the reaction of the carbon
carbon double bond
NaBH4
O
OH
H2O
OH
Addition of Alcohol
 In
the addition of R-OH to form an “acetal”
the First step is the formation of a
“hemiacetal”
 This is when an -OH and -OR are both on
same C
O
CH 3 CH
+ CH 3 CH 2 OH
acetaldehyde
ethanol
OCH 2CH 3
CH 3 C H
OH
hemiacetal
(not isolated)
Formation of Acetals
IF strong acid (HCl) is present, a second alcohol
reacts to form the acetal (two -OR groups on C)
OCH 2CH 3
CH 3 C H
OH
hemiacetal
(not isolated)
H+
CH 3 CH 2 OH
OCH 2CH 3
CH 3 C H
OCH 2CH 3
acetal
+ H2O
Addition of Alcohol - Acetals
O
Step 1
OCH 2CH 3
CH 3 CH
+
acetaldehyde
CH 3 CH 2 OH
ethanol
OCH 2CH 3
Step 2
CH 3 C H
OH
hemiacetal
(not isolated)
H+
CH 3 CH 2 OH
CH 3 C H
OH
hemiacetal
(not isolated)
OCH 2CH 3
CH 3 C H
OCH 2CH 3
acetal
+ H2O
Formation of Acetals
 Addition
of R-OH
– acid catalyzed, 2 moles of alcohol react
O
CH 3 CH 2 CH 2 CH
butyraldehyde
OH
CH 3 CH CH 3
+ isopropyl alcohol
H+
?
Formation of Acetals
 Addition
of R-OH
– acid catalyzed, 2 moles of alcohol react
O
CH 3 CH 2 CH 2 CH
butyraldehyde
OH
CH 3 CH CH 3
+ isopropyl alcohol
Draw the Hemi
H+
H3 C CH CH 3
O
CH 3 CH 2 CH 2 CH
O
H3 C CH CH 3
acetal
Formation of Acetals
 Acetal
reaction in equilibrium
H3 C CH CH 3
O
CH 3 CH 2 CH 2 CH
O
H3 C CH CH 3
+ 2 H2O
H+
O
CH 3 CH 2 CH 2 CH
OH
+
2 CH 3 CH CH 3
Formation of Acetals
 Acetal
reactions
CH 2CH 2 C H
+
O
H+
CH 3 CH 2 OH
ethanol
?
Formation of Acetals
 Acetal
reactions
CH 2 OH
+
O
CH3 CH
H+
?
Formation of Acetals
 Hemiacetal
reactions (formation of hemiacetals)
– likely when within the same molecule
5
4
3
2
1
CH 2 CH 2 CH 2 CH2 CH
OH
O
or
5
H
O
O
O
OH
1
2
4
3
a cyclic hemiacetal
Formation of Acetals
 Cyclic
hemiacetals
– Reacts with a 2nd. molecule of alcohol
– Results in a cyclic acetal
O
OH
H+
O
OR'
+ R'-OH
a cyclic hemiacetal
a cyclic acetal
Formation of Acetals
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
 Which
are hemiacetals / acetals?
OCH 3
OH
O CH 2 CH 3
CH 3 CH 2 CH 2 C CH 3
1
O CH 3
CH 3CH 2 O CH 2CH 2 OH
2
3
O
O CH 3
4
CH 3 CH OH
5
OH
OH O CH 2 CH 3
CH 3 CH 2 CH 2 CH CH CH 3
7
CH 3CH 2 O CH 2 OH
OH
OCH 3
O
H
CH 3 C CH 3
O
8
6
OCH 3
9
O CH 3
10
Keto-Enol Tautomerism
 Equilibrium
that exists
 Keto (carbonyl) to Enol (alkene/alcohol)
H
H
C
H
C H
H O
acetaldehyde
H C
C
H
O H
"enol" form
Keto-Enol Tautomerism
 Equilibrium
called Tautomerism
H
H
C
H
C H
H O
Keto form
acetaldehyde
(more stable)
H C
C
H
O H
"enol" form
(less stable)
Keto-Enol Tautomerism
 Equilibrium
O
called Tautomerism
O
CH 3 C CH 2 C CH 3
2,4-pentanedione
OH
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
O
CH 3 C CH 2 C CH 3
"enol" form
(more stable)
Most enols are
less stable
Important Compounds
 Formaldehyde
– Gas at RT
– Soluble in H2O
– Formalin
» 37% formaldehyde
» found in labs
» preserves by denaturing proteins
– Used to produce polymers
H
H C O
formaldehyde
Important Compounds
H H
 Acetaldehyde
– bp 21o C
– Converted to trimer
H
C
C O
H
acetaldehyde
» 3 units of acetaldehyde
» called paraldehyde
» once used as a hypnotic/sleep-producer
Important Compounds
 Acetone
– bp 56o C
– Infinitely soluble in H2O
– Excellent industrial solvent:
» paints, varnishes, resins
» coatings, nail polish
– Produced in the body
» diabetic ketoacidosis
» “acetone breath”
H O H
H
C
C
C H
H
H
acetone
Important Compounds

-chloroacetophenone
– lachrymators
» tearing of eyes, etc.
– Used as a tear gas
– Active ingredient in “Mace”
Cl
H2C
C
O
-chloroacetophenone