Title: Lesson 8 Reaction Pathways/Synthetic
Routes
Learning Objectives:
– Summarise all reactions covered so far in a reaction pathways diagram
– Set your classmates challenges involving navigation around the diagram
Refresh


Predict the mechanism (SN1 or SN2)
expected for the reaction of the
following halogenoalkanes with aqueous
KOH.
1-chlorobutane to form butan-1-ol
2-chloro-2-methylpropane to form 2
methylpropan-2-ol.
Describe the mechanism for one of the
above reactions using diagrams with
curly arrows to show electron
movements.
Main Menu
Reviewing Your Notes
You should spend 60
seconds reviewing your
notes from last lesson
before attempting this.
Your notes and mind-map
must be ready for me to
inspect.
Importance of organic synthesis
Chemists are able to construct synthetic pathways to prepare
a desired compound. They design a molecule and then work
out how to make it from readily available precursors.
This is of particular use in the
pharmaceutical industry, where a
molecule can be designed to
have specific functional properties.
A series of reactions is worked out in which each stage
modifies the starting compound in a particular way; for
example, adding a functional group. It is vital for each stage in
the synthesis to be carried out under the right conditions.
3 of 34
© Boardworks Ltd 2010
What we are aiming to be able to do this lesson:
Retro-synthesis: Working backwards




Start with the target molecule (desired product)
By study functional groups, it can be broken down into smaller fragments
(precursors)
Seems a bit
Each precursor is the target for further analysis...
complicated…
This will start a synthetic sequence…
How do I go
about doing
this???
Main Menu
To be able to synthesis reaction pathways…


It is useful to first consolidate knowledge of functional groups…
Then to review all of the reactions we have met in Organic Chemistry…
Main Menu
Recapping Functional Groups
NOTE:
According
to the
syllabus,
you aren’t
expected
to know
acid
chloride,
acid
anhydride
and azo…
6 of 34
© Boardworks Ltd 2010
Identify the functional groups
7 of 34
© Boardworks Ltd 2010
Multiple functional groups
Some compounds, for example paracetamol, contain more
than one functional group.
N-substituted
amide
phenyl
hydroxyl
The chemical reactivity of each functional group is usually
the same as it would be on its own.
8 of 34
© Boardworks Ltd 2010
Predicting compound properties
9 of 34
© Boardworks Ltd 2010
Summary of organic synthesis reactions
10 of 34
© Boardworks Ltd 2010
Recapping Organic Reactions
Lesson/ Reactants needed
PPT
number
Organic product formed
Type of reaction
Mechanism
needed?
3
4
4 and 7
4 and 7
4
4
5
5
5
5
TASK:
• Look through each of the PPTs as shown in the
table
• Look for organic reactions and fill out the
information in the table below (should only include
aliphatics, not aromatics)
• If there are different stages and different products
(e.g. oxidising primary alcohol) then split them into
separate reactions)
• There should be 15 reactions in total (if there are
1o, 2o or 3o reactions that give the same product,
just include that as 1 reaction)
6
6
7
7
7
Main Menu
Type of reaction:
• HINT: There are 5
types…
Mechanism needed…?
• Decide this based on whether there are
nucleophilic/electrophilic/free radical
reactions… If so, this means yes…
What reaction mechanisms have we come across so
far?
Main Menu
Now you have a summary of the different organic
reactions…
Synthetic Routes Mapping Task:
1.
Write down all of the organic compounds that you have identified in both the
reactants and products of the different reactions… (HINT: There should be 15)
2.
Check your answers against the organic reactants and products keyword sheet…
3.
Take 5 different colours and use them as a key for the 5 different types of reactions
4.
Now try to map your organic compounds by linking them with colour coded
arrows to show the reactions between the compounds
Main Menu
A bit of structure if you need it…
Main Menu
A bit more of structure if you need it…
Main Menu
Did you get something like this…?
Main Menu
Retro-synthesis: Working backwards




Start with the target molecule (desired product)
By study functional groups, it can be broken down into smaller fragments
(precursors)
Each precursor is the target for further analysis...
This will start a synthetic sequence…
Main Menu
Main Menu
Main Menu
Summary of organic synthesis reactions
20 of 34
© Boardworks Ltd 2010
Devising a synthetic route (1/2)
1. Write down the possible products that can be made
from the starting material in one step.
2. Write down the possible chemicals that can synthesize
the desired product in one step.
3. Identify possible synthetic pathways.
For example, synthesizing ethylamine from ethanol:
CH3CHO
CH3CH2OH
CH3CH2CN
CH3CH2NH2
CH3COOH
CH3CH2Cl
CH3CH2Cl
CH3CH2OOR
21 of 34
© Boardworks Ltd 2010
Devising a synthetic route (2/2)
Synthesis of propanoic acid (CH3CH2COOH) from ethyl
chloride (CH3CH2Cl):
1. Write down the possible products that can be made from
the starting material in one step.
As the carbon chain increases in length the reaction must
be via a nitrile.
CH3CH2COOH
CH2CH2
2. Write down possible
products from the nitrile.
CH3CH2CN
CH3CH2Cl
3. Identify possible
synthetic pathways.
CH3CH2CH2NH2
CH3CH2NH2
CH3CH2OH
22 of 34
© Boardworks Ltd 2010
Complete the synthetic route
23 of 34
© Boardworks Ltd 2010
Main Menu
Some Challenges

Use your reaction pathways diagrams to help you solve the following
problems

Give the reactants and conditions to produce butan-2-one from a halogenoalkane in
two steps.

A compound is reacted first with hydrogen iodide and then with sodium hydroxide to
form a symmetrical 3o alcohol with a relative mass of 102.2. Suggest structures for the
initial organic reactant and the intermediate product.
Main Menu
Some Challenges

Use your reaction pathways diagrams to help you solve the following
problems

Butylamine can be produced from propane in three steps. Give the reaction
conditions and draw the intermediate products for each step

Ethyl ethanoate can be prepared from ethene over several steps. Outline how you
might do this, naming the intermediate products and giving suitable reaction
conditions
Main Menu
Make your own

Devise problems of a similar nature to those on the previous slide and give
them to your friends to solve.
Main Menu
Key Points

Inter-converting between organic compounds is the bread and butter of an
organic chemist

Reaction pathways are the map that help you navigate from your point of
origin to your destination
Main Menu