Transcript 無投影片標題 - SKHSBS

Chapter 37
Syntheses and
Interconversions of
Organic Compounds
37.1 Planning Organic Syntheses
37.2 Interconversions of Functional Groups
of Organic Compounds
37.3 Chain Lengthening or Shortening of
Carbon Skeleton
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.122)
The organic compounds that are now known:
•
Only small fractions of them can be isolated from
natural resources
•
All the remaining are synthesized by organic chemists
Reasons for carrying out syntheses:
e.g. To make a new medicine, dye, plastics, pesticide;
To make a new compound for studying reaction
mechanisms or metabolic pathways
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.122)
• The way to plan the synthesis is to think backwards
 From the desired product to simpler molecules that can act
as the precursor for our target molecule
• A synthesis usually involves more than one step
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.123)
There are usually more than one way to carry out a synthesis
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.123)
The feasibility of an organic synthesis depends on a
number of factors:
• Numbers of steps involved in the synthesis
• Availability of starting materials and reagents
• Duration of the synthetic process
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.123)
Numbers of Steps involved in the Synthesis
• Most organic reactions are reversible and seldom proceed
to completion
• As the backward reaction takes place, it is impossible to
have a 100% yield of product from each step of the
synthetic route
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.123)
e.g.
• The yield of desired product is 12.96%
∴
an efficient route of synthesis consists of a minimal
number of steps
• Usually the number of steps is limited to not more than four
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.123)
Availability of Starting Materials and Reagents
• There are often a restricted number of simple, relatively
cheap organic compounds available
e.g.
simple haloalkanes, alcohols of not more than four
carbon atoms, simple aromatic compounds such as
benzene and methylbenzene
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New Way Chemistry for Hong Kong A-Level Book 3B
37.1 Planning Organic Syntheses (SB p.124)
Duration of the Synthetic Process
• The time factor must be considered when planning the
synthetic pathway
∵
many organic reactions proceed at a relatively slow rate
e.g. acid-catalyzed esterification requires the reaction
mixture to be refluxed for a whole day
• Involvement of slow reactions in the synthetic route is
impractical as the reaction will be too long
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.124)
Oxidation
• Oxidation of an organic compound usually corresponds to
increasing its oxygen content or decreasing its
hydrogen content
• Common oxidizing agents used: KMnO4, K2Cr2O7 or
H2CrO4
• KMnO4 is the strongest oxidizing agent and can be used
in acidic, neutral or alkaline medium
• Other oxidizing agents: Tollens’ reagent, Fehling’s
reagent, ozone
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.125)
Potassium Manganate(VII)
1. Mild Oxidation by Potassium Manganate(VII)
Under mild oxidation by alkaline KMnO4, alkenes are
oxidized to diols
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.125)
2. Vigorous Oxidation by Potassium Manganate(VII)
• Occur in acidic or alkaline medium
• Heating is to ensure the vigour of the reaction
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.125)
• Alkylbenzenes are converted to benzoic acid by
vigorous oxidation of KMnO4
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.126)
• 1° alcohols are oxidized to carboxylic acids by vigorous
oxidation of KMnO4
• The oxidation is difficult to stop at the aldehyde stage.
• The way to obtain aldehyde from oxidation is to remove
the aldehyde by distillation as soon as they formed
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.126)
Potassium Dichromate(VI) or Sodium Dichromate(VI)
• The most commonly used chromium(VI) reagent is
H2CrO4 which is prepared by adding CrO3, Na2Cr2O7 or
K2Cr2O7 to aqueous H2SO4
• It oxidizes 1° alcohols or aromatic side chains to
aldehydes but not in good yields
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.126)
• It is most often used to oxidize 2° alcohols to ketones in
excellent yields
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.126)
Tollens’ and Fehling’s Reagents
• Tollens’ and Fehling’s reagents are weak oxidizing agents
which are able to oxidize aldehydes to carboxylate ions
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.126)
Ozone
• Ozonolysis is the most important oxidation reaction of
alkenes
• This reaction provides a method for locating the double
bond of an alkene
• Ozone reacts vigorously with alkenes to form ozonides
and then reduced by treatment with Zn and H2O to give
carbonyl compounds
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.127)
Check Point 37-1
Show how each of the following transformations could be
(a)
accomplished.
(a)
(b)
(b)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.127)
Check Point 37-1
Show how each of the following transformations could be
(c)
accomplished.
(c)
(d)
(d)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.128)
Reduction
Reduction of an organic compound usually corresponds to
increasing its hydrogen content or decreasing its oxygen
content
Examples:
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.128)
Hydrogen with Transition Metal Catalyst
• Hydrogen is added to the C = C and C  C bonds in alkenes
and alkynes in the presence of transition metal catalysts
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.129)
• Nitriles or nitro compounds are reduced to amines by
hydrogen in the presence of transition metal catalysts
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.129)
Lithium Tetrahydridoaluminate
• LiAlH4 is a powerful reducing agent
• It reduces carboxylic acids, esters, aldehydes, ketones,
amides, nitriles and nitro compounds
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.129)
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.129)
• LiAlH4 cannot normally reduce unsaturated centres
like C = C and C  C bonds and benzene ring
• Reduction with LiAlH4 must be carried out in anhydrous
solutions
∵ LiAlH4 reacts violently with water
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.130)
Sodium Tetrahydridoborate
• NaBH4 is a less powerful reducing agent than LiAlH4
• It reduces aldehydes and ketones only
• It can be used in water or alcohols
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.130)
Check Point 37-2
Which reducing agent, LiAlH4 or NaBH4, would you use to
carry out the following transformations?
(a)
(b)
(c)
(a) LiAlH4
(b) LiAlH4
(c) NaBH4
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.130)
Zinc, Tin, Tin(II) Chloride or Iron with
Hydrochloric acid
Aromatic nitro group can be reduced to amines by treatment
with HCl and Fe, Zn or Sn, or a metal salt such as SnCl2
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.131)
Substitution
• Free radical substitution of alkanes with halogens forms
haloalkanes
• A mixture of mono-, di- and poly-substituted
haloalkanes is formed
RH + X2  RX + HX
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.131)
• Various aromatic compounds can be prepared from benzene by
electrophilic substitution of a hydrogen atom by substituents
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.131)
• Haloalkanes can be converted into alcohols, nitriles or
amines by substitution reactions
R – X + OH–  R – OH +
X–
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.131)
Addition
• Addition of alkenes and alkynes with various reagents can produce
haloalkanes, haloalcohols, alcohols, alkanes and polymers
(X = Cl or Br)
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.132)
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.132)
• Carbonyl compounds undergo addition reaction with
hydrogen cyanide for form hydroxyalkanenitriles
• Addition of hydrogen to nitriles yields amines
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.132)
Elimination
• Haloalkanes can be converted to alkenes by elimination with
alcoholic KOH or NaOH
•
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Dihaloalkanes (with one halogen atom on each of two adjacent
carbon atoms) can be converted to alkynes by elimination
New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Interconversions of Functional Groups of
Organic Compounds (SB p.132)
• Alcohols undergo dehydration to give alkenes by
treatment with conc. H2SO4
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Methods of Chain Lengthening
• The carbon chain is lengthened by one when
haloalkanes react with NaCN to form nitriles
• Hydrolysis of nitriles gives carboxylic acids, while
hydrogenation of nitriles gives 1° amines
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
• The carbon chain is also lengthened by one when carbonyl
compounds react with HCN to form 2-hydroxyalkanenitriles
• Hydrolysis of the 2-hydroxyalkanenitriles yields
2-hydroxycarboxylic acids
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Methods of Chain Shortening
• In Hofmann degradation of amides, the carbon chain
is reduced by one carbon atom
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.134)
In the triiodomethane formation reaction (iodoform
reaction) of alcohols containing the
aldehydes or ketones containing the
group and
group, the
carbon chain is also degraded by one carbon atom
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.134)
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New Way Chemistry for Hong Kong A-Level Book 3B
37.2 Chain Lengthening or Shortening of Carbon Skeleton (SB p.134)
• In ozonolysis, alkenes react with ozone to from ozonide
which is reduced by using Zn and H2O to produce a
mixture of carbonyl compounds resulting from the
cleavage of the C = C bond
• The cleavage of the C = C bond results in the
degradation of carbon chain
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New Way Chemistry for Hong Kong A-Level Book 3B
37.3 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Check Point 37-3
By means of simple chemical equations, indicate how you
would carry out the following conversion, which may
involve more than one step. Give the reagents for each
step and
(a) indicate the major product formed.
(a)
Answer
44
New Way Chemistry for Hong Kong A-Level Book 3B
37.3 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Check Point 37-3
By means of simple chemical equations, indicate how you
would carry out the following conversion, which may
involve more than one step. Give the reagents for each
step(b)
and indicate the major product formed.
(b)
Answer
45
New Way Chemistry for Hong Kong A-Level Book 3B
37.3 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Check Point 37-3
By means of simple chemical equations, indicate how you
would(c)
carry out the following conversion, which may
involve more than one step. Give the reagents for each
step and indicate the major product formed.
(c)
Answer
46
New Way Chemistry for Hong Kong A-Level Book 3B
37.3 Chain Lengthening or Shortening of Carbon Skeleton (SB p.133)
Check Point 37-3
By means of simple chemical equations, indicate how you
would (d)
carry out the following conversion, which may
involve more than one step. Give the reagents for each
step and indicate the major product formed.
(d)
Answer
47
New Way Chemistry for Hong Kong A-Level Book 3B
The END
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New Way Chemistry for Hong Kong A-Level Book 3B