Organic Synthesis

How can we form this?

Substitution?No; the pi bond will break

before Br contributes to a substitution reaction

We could use hydrogenation of 1-bromo-1-butyne (provided only one of the pi bonds break)

Performing an elimination on 1-bromo-2-butanol or 1-bromo-1-butanol would work best.

CH CH2 CH2 CH3

Br

OH

CH CH CH2 CH3

Br

CH2 CH CH2 CH3

C C CH2 CH3

Br

CH2 CH CH2 CH3

Br

OH

Best choice: only one product possible.

How do we choose between reactions?Notice that their may be more than one way to

form a particular compoundThe handout is an oversimplification … There are thousands of reaction mechanisms,

many of which are very specificConsiderations when choosing include …

Yield (how much product forms)Potential for multiple productsEase of separating contaminating structuresType of isomer desiredEconomics: e.g. cost of starting materials

Answers: 1, 21) An addition reaction involves breaking a double

bond and adding two parts of a molecule across the bond

• Examples: 1) halogenation, 2) hydrogenation, 3) hydrolysis, 4) addition polymerization

• The ‘opposite’ of breaking the bond is forming a double bond - i.e. elimination

2) Condensation is a reaction that involves the production of water.

• Examples: 1) elimination, 2) esterification, 3) condensation polymerization

• oxidation is not an example – the H2O comes from H2SO4, not from an organic molecule

Answers: 3a) 1,2-dichlorocyclopentane is best formed via

halogenation of cyclopentene. Substitution using Cl2 would work, but would not be efficient because many other products would form (e.g. 1,2,4-trichlorocyclopentane, etc.)

b) The only way to prepare octane from 4-octyne is via hydrogenation of both pi bonds.(see top of next page for diagram)

+ Cl2 Room temp.

Cl

Cl

c) 2,2,3,3-tetrabromopentane can be formed via substitution using Br2. It is more efficiently formed via the halogenation of 2-pentyne

b)

+ H2

Room temp. C C C C C

H

H

H

H

H

H

H

C

H H

HH

C C

H

H

H

H

H

H

H

C C C C C

H

H

H

C

H H

HH

C C

H

H

H

H

H

H

H

+ Br2

Room temp. C C C C C

H

H

H

H

H

H

H

H

Br Br

BrBr

C C C C C

H

H

H

H

H

H

H

H

d) 1-butene can be formed from the elimination reaction involving 1-butanol. Using 2-butanol could result in either 1-butene or 2-butene and therefore is a less desirable choice.

C C C C

OH

H

H

H

H

H

H

H

H

H

C C C CH

H H

H

H

H

H

H + H2O

catalystheat

e) Propanoic acid is best formed from the oxidation of propanal

C C C

H

H

H

O

H

H

H C C C

H

H

H

O

OH

H

H

+ K2Cr2O7

+ H2SO4

+ Cr2(SO4)3

+ K2SO4

+ H2SO4

f) Ethanol is most easily formed from the hydrolysis of ethene.

g) Ethyl propanoate is an ester, formed via esterification (ethanol plus propanoic acid)

C C

H

OH

H

H

H HC C

H H

H H acid

catalyst + H2O

+OH

O

CH3OH CH3

H+

heatCH3

O CH3

O

+ H2O

O O

OHOH

NH2

O

NH2

OH OH

Formation of a polyamide

O O

OHOH

NH

O

NH2

OH+ H2OO

NH2

NH2OH

Formation of a polyamide

O

NH2

NH2 NH

O O

OHOH

NH

O

OH+ H2O

+ H2OO

NH2

OH

Formation of a polyamide

O

NH2

NH

O

NH2 NH

O O

OHOH

NH

O

OH+ H2O

+ H2O

+ H2O

Formation of a polyamide

O

NH2

NH

O

NH2 NH

O O

OHOH

NH

O

OH

A polyamide “backbone” forms with R groups coming off. This protein is built with amino acids.

Formation of a polyamide

1) salicylic acid + methanol methyl salicylate

O

O

CH3

OH

O

O

H

OH

+ HOCH3

+ H2OH+, heat

Esterification reactions

Note that many of these names have been left as common names

O

O

OH

CH3

CH3

2) salicylic acid + isoamyl alcohol

isoamyl salicylate

O

O

H

OH

+

+ H2OH+, heat

OH CH3

CH3

3) acetic acid + isoamyl alcohol

isoamyl acetate

+ H2OH+, heat

+ OH CH3

CH3

CH3 O CH3

CH3O

CH3 OH

O

4) propanoic acid + isobutyl alcohol

isobutyl propionate

+ H2OH+, heat

+OH

O

CH3OH

CH3

CH3

O

O

CH3 CH3

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