Post on 16-Dec-2015
Organic Chemistry
Aldehydes and Ketones
Chapter 17
Aldehydes and Ketones
Carbonyl Group C=O Present in aldehydes and ketonesC
O
H
C
O
HR C
O
HR C
O
R'R C
O
R'R
Aldehydes Ketones
Aldehydes
Aldehydes Sometimes abbreviated RCHO Contain at least one H connected to the C
C
O
HR C
O
HR
Aldehydesbenzaldehyde
C
O
H
benzaldehyde
C
O
H
acetaldehyde
CHCH3
O
acetaldehyde
CHCH3
Oformaldehyde
H2C O
formaldehyde
H2C O
Ketones
Ketones Carbonyl C is connected to two alkyl groups RCOR’
C
O
R'R C
O
R'R
Ketones
acetoneCH3CCH3
O
acetoneCH3CCH3
O
methyl ethyl ketone
C OCH2CH3
CH3
methyl ethyl ketone
C OCH2CH3
CH3
Nomenclature
IUPAC– Suffix is “-al” for the aldehydes– Suffix is “-one” for the ketones– # indicates position of ketone
propanalCHCH2CH3
O
propanalCHCH2CH3
O
3-hexanone
CH3CH2CCH2CH2CH3
O
3-hexanone
CH3CH2CCH2CH2CH3
O
Nomenclature
NOTE:
Ketone,
Not keytone
From Yahoo Images
1-chloro-4-penten-2-oneCH2CCH2CHH2C
O
Cl1-chloro-4-penten-2-one
CH2CCH2CHH2C
O
Cl
Nomenclature
An Aldehyde or Ketone takes precedence over any previously considered group
5-chloro-4-hydroxypentanal
CHCH2CH2CHCH2
OOH
Cl5-chloro-4-hydroxypentanal
CHCH2CH2CHCH2
OOH
Cl
Nomenclature
Common names - aldehydes
benzaldehyde
C
O
H
benzaldehyde
C
O
H
acetaldehyde
CHCH3
O
acetaldehyde
CHCH3
Oformaldehyde
H2C O
formaldehyde
H2C O
Nomenclature
Common names - ketones– Some are always used
acetoneCH3CCH3
O
acetoneCH3CCH3
O
methyl ethyl ketone
C OCH2CH3
CH3
methyl ethyl ketone
C OCH2CH3
CH3
benzophenone
CO
benzophenone
CO
- Others name each R group and end with “ketone”
methyl t-butyl ketone
C
O
C
CH3
CH3
CH3
CH3
methyl t-butyl ketone
C
O
C
CH3
CH3
CH3
CH3
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Physical PropertiesCarbonyls: 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
C O
C O
C O
H OH
yes!
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!
CH2CH3 OH
ethanol
+ K2Cr2O7H+
acetaldehyde
CHCH3
O
acetaldehyde
CHCH3
O
+ K2Cr2O7H+
acetic acid
CCH3 OH
O
CH2CH3 OH
ethanol
+ K2Cr2O7H+
acetaldehyde
CHCH3
O
acetaldehyde
CHCH3
O
+ K2Cr2O7H+
acetic acid
CCH3 OH
O
Practice a couple …………..
How do you make Ketones?
Ketones from Oxidation of 2o alcohols
CH3CHCH3
OH
2-propanol
+ K2Cr2O7H+
acetone
CH3CCH3
O
acetone
CH3CCH3
O
+ K2Cr2O7H+
N.R.
CH3CHCH3
OH
2-propanol
+ K2Cr2O7H+
acetone
CH3CCH3
O
acetone
CH3CCH3
O
+ K2Cr2O7H+
N.R.
Practice a couple …………..
Oxidation of Aldehydes
Aldehydes are easily oxidized– KMnO4
– K2Cr2O7
– even air oxidation carboxylic acid!
+ KMnO4
acetaldehyde
CHCH3
O
acetic acid
CCH3 OH
O
+ KMnO4
acetaldehyde
CHCH3
O
acetic acid
CCH3 OH
O
Oxidation of Ketones Ketones resist oxidation:
– under mild or normal conditions, no reaction– more severe conditions yield mixtures
– CO2 and H2O under extreme conditions
CH3CCH3
O
acetone
normalconditions
N.R.CH3CCH3
O
acetone
normalconditions
N.R.[O]
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 Silver Mirror
Ag+ + 2 NH3 Ag(NH3)2+
Ag(NH3)2+ + RCHO Ago + RCOO- + 4NH3
Benedict’s Test
Oxidation of Aldehydes Cu++ ion, aqueous Orange to red ppt. NO reaction with KETONES
Cu++ + aldehyde Cu+(oxide) + acid
Cu+Cu2+
Benedict’s Test
Oxidation of Aldehydes overall reaction
C
O
HRaldehyde
+ 2 Cu2+ + 5 OH -
C
O
O-Rcarboxylic acid (ion)
+ 2 Cu2O + 3 H2O
C
O
HRaldehyde
+ 2 Cu2+ + 5 OH -
C
O
O-Rcarboxylic acid (ion)
+ 2 Cu2O + 3 H2O
Cu2O
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
acetaldehyde
CHCH3
OH2
catalystethanol
CH2CH3
OH
acetaldehyde
CHCH3
OH2
catalystethanol
CH2CH3
OH
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
acetoneCH3CCH3
OH2
PtCHCH3
OH
CH3
2-propanolacetone
CH3CCH3
OH2
PtCHCH3
OH
CH3
2-propanol
2-butenalCHCHCHCH3
OH2
Ni butanaldehyde
CHCH2CH2CH3
O
2-butenalCHCHCHCH3
OH2
Ni butanaldehyde
CHCH2CH2CH3
O
Addition of H2 using NaBH4
Reduction to Alcohols– NaBH4 does not allow the reaction of the carbon
carbon double bond
OH
O
OH
NaBH4
H2O
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
acetaldehydeCHCH3
O
+ethanol
CH2CH3 OH CCH3 H
OH
OCH2CH3
hemiacetal(not isolated)
acetaldehydeCHCH3
O
+ethanol
CH2CH3 OH CCH3 H
OH
OCH2CH3
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)
CCH3 H
OCH2CH3
OCH2CH3
acetal
H+
CH2CH3 OHCCH3 H
OH
OCH2CH3
hemiacetal(not isolated)
CCH3 H
OCH2CH3
OCH2CH3
acetal
H+
CH2CH3 OHCCH3 H
OH
OCH2CH3
hemiacetal(not isolated)
+ H2O
Addition of Alcohol - Acetals
acetaldehydeCHCH3
O
+ethanol
CH2CH3 OH CCH3 H
OH
OCH2CH3
hemiacetal(not isolated)
CCH3 H
OCH2CH3
OCH2CH3
acetal
H+
CH2CH3 OHCCH3 H
OH
OCH2CH3
hemiacetal(not isolated)
Step 1
Step 2
+ H2O
Formation of Acetals
Addition of R-OH– acid catalyzed, 2 moles of alcohol react
butyraldehyde + isopropyl alcohol
CH3CHCH3
OH
CHCH2CH2CH3
OH+
?
Formation of Acetals
Addition of R-OH– acid catalyzed, 2 moles of alcohol react
butyraldehyde + isopropyl alcohol
CH3CHCH3
OH
CHCH2CH2CH3
OH+
CHCH2CH2CH3
O
CH
OCH
H3C CH3
H3C CH3
acetal
Draw the Hemi
Formation of Acetals
Acetal reaction in equilibrium
CHCH2CH2CH3
O
CH
OCH
H3C CH3
H3C CH3
+ 2 H2OH+
CHCH2CH2CH3
O
CH3CHCH3
OH
+ 2CHCH2CH2CH3
O
CH
OCH
H3C CH3
H3C CH3
+ 2 H2OH+
CHCH2CH2CH3
O
CH3CHCH3
OH
+ 2
Formation of Acetals
Acetal reactions
CH2CH2 C H
O +
ethanol
CH2CH3 OHH+
?
Formation of Acetals
Acetal reactions
?CH2 OH
+CHCH3
OH+
Formation of Acetals
Hemiacetal reactions (formation of hemiacetals)
– likely when within the same molecule
CHCH2CH2CH2CH2
OOHor
HO O O OH
a cyclic hemiacetal
11
2
2
3
3
45 5
4
Formation of Acetals
Cyclic hemiacetals– Reacts with a 2nd. molecule of alcohol– Results in a cyclic acetal
O OH
a cyclic hemiacetal
+ R'-OHH+ O OR'
a cyclic acetal
Formation of Acetals
Which are hemiacetals / acetals?
OCH3CH2 CH2CH2 OH
CHCH3 OH
CH3O
CH3CCH2CH2CH3
CH2 CH3O
CH3O
OHOCH3
OH
OCH3
O
OH
O
OCH3OCH3CH2 CH2 OH
CH3CCH3
OH
CH3OCH3CHCHCH2CH2CH3
OH CH2 CH3O
1 2 3
4 5 6
7 8 9 10
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Keto-Enol Tautomerism
Equilibrium that exists Keto (carbonyl) to Enol (alkene/alcohol)
acetaldehyde
CC
O
HH
H
H
CC HH
H
O H
"enol" form
Keto-Enol Tautomerism
Equilibrium called Tautomerism
acetaldehyde
CC
O
HH
H
H
CC HH
H
O H
"enol" formKeto form
(more stable) (less stable)
Keto-Enol Tautomerism
Equilibrium called Tautomerism
2,4-pentanedione
CH3CCH2CCH3
OO
"enol" form
CH3CCH2CCH3
OOH
(more stable)
Most enols areless stable
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Important Compounds
Formaldehyde– Gas at RT
– Soluble in H2O
– Formalin» 37% formaldehyde
» found in labs
» preserves by denaturing proteins
– Used to produce polymers
formaldehyde
C OH
H
Important Compounds
Acetaldehyde– bp 21o C– Converted to trimer
» 3 units of acetaldehyde
» called paraldehyde
» once used as a hypnotic/sleep-producer
acetaldehyde
CC O
H
H
H
H
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” acetone
CCC
O
H
H
H
H
H
H
Important Compounds
-chloroacetophenone– lachrymators
» tearing of eyes, etc.
– Used as a tear gas– Active ingredient in “Mace”
-chloroacetophenone
CH2C O
Cl