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LECTURE 6
Dr Ali El-Agamey
CHEM-103:
BASIC ORGANIC CHEMISTRY
DAMIETTA UNIVERSITY
٢Chapter 10 ٢
Reduction of Carbonyl
• Reduction of aldehyde yields 1º alcohol.
• Reduction of ketone yields 2º alcohol.
• Reagents:– Sodium borohydride, NaBH4
– Lithium aluminum hydride, LiAlH4
– Raney nickel
٣Chapter 10 ٣
Sodium Borohydride
• NaBH4 is a source of hydrides (H-)
• Only reacts with carbonyl of aldehyde or ketone, not with carbonyls of esters or carboxylic acids.
٤Chapter 10 ٤
Lithium Aluminum Hydride
• LiAlH4 is source of hydrides (H-)
• Stronger reducing agent than sodium borohydride, but dangerous to work with.
• Reduces ketones and aldehydes into the corresponding alcohol.
• Converts esters and carboxylic acids to 1ºalcohols.
٥Chapter 10 ٥
Reduction with LiAlH4
٦Chapter 10 ٦
Reducing Agents
• NaBH4 can reduce aldehydes and ketones but not esters and carboxylic acids.
• LiAlH4 is a stronger reducing agent and will reduce all carbonyls.
٧Chapter 10 ٧
Catalytic Hydrogenation
• Raney nickel is a hydrogen rich nickel powder that is more reactive than Pd or Pt catalysts.
• This reaction is not commonly used because it will also reduce double and triple bonds that may be present in the molecule.
• Hydride reagents (NaBH4 and LiAlH4) are more selective so they are used more frequently for carbonyl reductions.
٨Chapter 10 ٨
Catalytic Hydrogenation
H
O
٩
Reagent used:
Haloform reaction
Sodium hypohalite
Potassium hypohalite
١٠
Mechanism:
Oxidation
Halogenation
Cleavage
Iodoform(Yellow ppt)
Haloform reaction can convert an alcohol to a carboxylic acid with one less carbon atom.
Haloform reaction
١١
Homework: Which of the following compounds will give a positive iodoform test?
• Ammonia or a primary amine reacts with a ketoneor an aldehyde to form an imine.
• Imines are nitrogen analogues of ketones and aldehydes with a C═N bond in place of the carbonyl group.
• Optimum pH is around 4.5
٣٠Chapter 18 ٣٠
Other Condensations with Amines
٣١Chapter 18 ٣١
C
O
CH2CH3 Zn(Hg)
HCl, H2O
CH2CH2CH3
CH2 C
O
H HCl, H2O
Zn(Hg)CH2 CH3
Homework: Complete the following equations
٣٢Chapter 18 ٣٢
Formation of Acetals
• Acetals can easily be converted into carbonyl compounds and alcohol in the presence of dilute acid (H3O+) (remember reaction is reversible) however, they are stable in the presence
of base.
٣٣Chapter 18 ٣٣
Cyclic Acetals
• Addition of a diol produces a cyclic acetal.• The reaction is reversible.• This reaction is used in synthesis to protect
carbonyls from reaction.
٣٤Chapter 18 ٣٤
Acetals as Protecting Groups
O
H
O
HOOH
H+H
O
OO
• Aldehydes are more reactive than ketones.
٣٥Chapter 18 ٣٥
Reaction and Deprotection
H
O
OO1) NaBH4
2) H3O+
O
H
OH
• The acetal will not react with NaBH4, so only the ketone will get reduced.
• Hydrolysis conditions will protonate the alcohol and remove the acetal to restore the aldehyde.
٣٦Chapter 18
٣٦
The Wittig Reaction
PPh3: triphenylphosphine
The Wittig reaction converts the carbonyl group into a new C═C double bond.
٣٧Chapter 18 ٣٧
Solved Problem
Show how you would use a Wittig reaction to synthesize 1-phenyl-1,3-butadiene.
٣٨Chapter 18 ٣٨
HomeworkShow how you would synthesize the following compound using Wittig reaction.1
Show how you would synthesize the following compound from starting materials containing no more than six carbon atoms.
(a) (b)
٣٩Chapter 18 ٣٩
Homework: choose the correct answer
(1) What is the IUPAC name for the following compound?
2,2,4-trimethylpentane(d)
2,4,4-trimethylpentane(c)
1,1,3,3-tetramethylbutane(b)
1,3-pentamethylpropane(a)
٤٠Chapter 18 ٤٠
Homework: choose the correct answer(2) When a double bond is formed between two atoms, one of the bonds is a sigma bond and the other is a pi bond. The pi bond is created by the overlap of...
s orbitals(d)
p orbitals(c)
sp3 hybrid orbitals(b)
sp2 hybrid orbitals(a)
٤١٤١
Homework: choose the correct answer
(3) For the following two pairs of molecules, identify which partner will have the higher boiling point.
(a) Pair 1: A; Pair 2: C
(b) Pair 1: B; Pair 2: D
(c) Pair 1: A; Pair 2: D
(d) Pair 1: B; Pair 2: C
٤٢Chapter 18 ٤٢
Homework: choose the correct answer
(4) What are the major alkenes formed in the following reaction?
(a)
(b)
(c)
(d)
٤٣Chapter 18 ٤٣
Homework: choose the correct answer
(5) Which product is obtained upon the reaction of (Z)-2-hexene with HBr?
(a) 2,3-Dibromohexane
(b) 2-Bromohexane
(c) 3-Bromohexane
(d) 2-Bromohexane and 3-bromohexane
٤٤Chapter 18 ٤٤
Homework: choose the correct answer(6) Which of the following compounds gives 3-methyl-2-butanol upon reduction with LiAlH4?
(a) a
(b) b
(c) c
(d) d
٤٥Chapter 18 ٤٥
Homework: choose the correct answer
(7) Which of the following sets of reaction conditions will give the product indicated?
(a) (CH3O)2Ag, heat
(b) CH3OH, HO- , separate water
(c) 1) CH3ONa, 2) MeI
(d) CH3OH, H+, separate water
٤٦Chapter 18 ٤٦
Homework: choose the correct answer
(8) What is the product of the following reaction?
(a)
(b)
(c)
(d)
٤٧Chapter 18 ٤٧
Homework: choose the correct answer
(9) When benzaldehyde reacts with HCN and catalytic amounts of NaCN in ethanol, the product is