organic synthesis. how can we form this? substitution? no; the pi bond will break before br...
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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
CH3For more lessons, visit www.chalkbored.com
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