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Organic Synthesis

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Chemistry

The definition is in its name: organic synthesis simply means making organic compounds from scratch in laboratories or industries.

Having learned all of the theories behind Organic Chemistry, you may wonder, how do you actually use them in real life? Well, organic synthesis is an area where the principles of organic chemistry are applied. It is a topic that requires you to use what you’ve learned in organic chemistry and work out a solution. By the end of this series you should be able to connect the dots between the different principles you have covered in the previous explanations on organic chemistry, and truly understand how the different functional groups interrelate with each other.

Importance of organic synthesis

As chemistry students, you may no doubt ponder the importance of organic synthesis. You might ask yourselves, why is it that scientists are working so hard in figuring out how organic compounds can be made?

You should already know that most organic compounds come from living things. For example, ethanol comes from the fermentation of biomass. Ethanol is an example of a simple and abundant organic compound, but there are more complex organic compounds that are important but less common in nature.

One good example is the drug aspirin. Aspirin originates from willow bark. However, extracting aspirin from it is too time-consuming and wasteful, as willow bark only contains very small amounts of aspirin.

As such, scientists have developed steps to synthesise aspirin from laboratory compounds such as salicylic acid. That way aspirin can be produced with a high yield and low cost.

Therefore, one can say that the key importance of organic synthesis is to produce organic compounds (for example drugs and pesticides) efficiently.

Organic Synthesis Chemical structure of aspirin and salicylic acid StudySmarter

Aspirin synthesis, Olive [Odagbu] StudySmarter Originals

Organic synthesis flow chart

Before we discuss the organic synthesis flowchart, let’s cover a few key terms relating to organic synthesis.

The molecule to be synthesised in organic synthesis is called the target compound. The target compound is usually derived from a ‘scaffold’, known as the starting material. As you can see from the aspirin example above, aspirin is the target compound whereas salicylic acid is the starting material.

Organic synthesis of the target compound, therefore, involves figuring out steps to convert the starting molecule to the target compound. To achieve this, functional groups of both the target group and starting molecule are identified. Once that is done, you then figure out the steps to convert the functional group of the starting molecule to that of the target molecule. You can use the flowchart detailed below to help you identify the relevant steps.

Organic Synthesis aliphatic and aromatic functional groups interchangeability StudySmarter

Organic synthesis routes, Olive [Odagbu] StudySmarter

The organic synthesis route can be either in one step or it might require multiple steps. A step corresponds to a single reaction.

Of course, you may identify multiple possible steps to convert from the functional group of the starting molecule to that of the target molecule. In such instances, a key rule is to keep the number of steps as small as possible to maximise the product yield.

Furthermore, when deciding on the most appropriate reaction step(s), do not forget to consider the reagents and conditions relating to the step(s) you have chosen. Whether the reagent is oxidising, reducing, or dehydrating, or whether heat and or a catalyst is required - these are the questions you should ask yourselves when deciding on the most appropriate reaction steps. Scientists would also consider which molecules or steps are cheaper, safer, and produce fewer waste products and a higher yield, to keep the costs and the risks as low as possible.

Another option to decide how to produce a certain compound is to start from the final compound and retrace the steps needed to produce it from other (more common, cheaper, safer) molecules, as the starting material. This is called retrosynthesis.

Retrosynthesis is the process of coming up with a synthesis pathway starting from the end molecule (target molecule) instead of the initial one.

Organic synthesis examples

The two organic synthesis examples covered in the AQA syllabus include the synthesis of propanoic acid from 1-bromopropane and propylamine from ethene. Please refer to Synthetic Routes for a detailed breakdown and explanation of each synthetic step.

Mapping the synthesis of propanoic acid from 1-bromopropane

Below is a diagram showing how the synthesis of propanoic acid from 1-bromopropane is mapped.

Organic Synthesis mapping of the synthesis of propanoic acid from 1-bromopropane StudySmarter

The synthesis of propanoic acid from 1-bromopropane, Olive [Odagbu] StudySmarter Originals

How do you map a synthetic route?

These are the steps to follow when mapping a synthetic route:

  1. From the functional group interconversion flowchart above, list out the possible molecules that can be made from the starting molecule and the molecules that can be converted into the target molecule.

  2. Identify any common intermediates between the starting material and the target. In this case, propan-1-ol is the intermediate.

  3. List out the reaction steps. In the case of the synthesis of propanoic acid from 1-bromopropane, it entails a two-step reaction that is as follows:

1-bromopropane propan-1-ol → propanoic acid

Mapping the synthesis of propylamine from ethene

Likewise, below is a diagram showing how the synthesis of propylamine from ethene is mapped.

Organic Synthesis mapping of the synthesis of propylamine from ethene StudySmarter

Synthesis of propylamine from ethene, Olive [Odagbu] StudySmarter

The synthesis of propylamine from ethene is slightly more complex. The steps relating to its mapping are listed as follows:

  1. From the functional group interconversion flowchart above, list out the possible molecules that can be made from the starting molecule and the molecules that can be converted into the target molecule.

  2. Identify any common intermediates between the starting material and the target.

  3. In this case, there is no common intermediate. As such, you need to determine whether any molecules that can be made from the starting molecule can be converted into one of the molecules that is derived from the target molecule. For the above case, a haloalkane can be converted into propanenitrile.

  4. List out the reaction steps. In the case of the synthesis of propylamine from ethene, it entails a three-step reaction that is as follows:

ethene → haloalkane → propanenitrile → propylamine

The development of the olefin metathesis method was an innovation in the field of organic synthesis. This method comprises a diverse set of reactions in forming and rearranging double bonds so that the side groups linked by them can be exchanged between two molecules. This method involves metal catalysts. The researchers who discovered it; Dr. Yves Chauvin, Professor Robert H. Grubbs, and Professor Richard R. Schrock, were granted the Nobel Prize for chemistry in 2005.

Organic Synthesis olefin metathesis method StudySmarter

Metathesis method, Olive [Odagbu] StudySmarter

Organic Synthesis - Key takeaways

  • Organic synthesis is the process of making organic compounds from scratch in laboratories or industries. The key importance of organic synthesis is to produce organic compounds efficiently.
  • The key players in organic synthesis include the starting material and the target compound. Steps (reactions) to reach the target compound need to be planned out taking into account the interconvertability of the groups of the molecules involved.
  • To map the synthesis of a starting material into a target compound, the reaction intermediates are identified, then the reaction steps are written out in consideration of the necessary reagents and conditions.
  • The synthesis map can be planned either from the starting material or from the target compound (retrosynthesis).

Organic Synthesis

Organic synthesis simply means making organic compounds from scratch in laboratories or industries.

In organic synthesis we apply the principles of organic chemistry so we can produce organic compounds effectively.


For example, aspirin comes from the bark of the willow tree. However, extracting aspirin from willow bark is time consuming and wasteful so scientists have developed steps to synthesise aspirin from laboratory compounds like salicylic acid. This way we can produce more aspirin at a lower cost.

The key importance of organic synthesis is to produce organic compounds (for example drugs and pesticides) efficiently.

Organic synthesis of the target compound involves figuring out steps to convert the starting molecule to the target compound. To achieve this, functional groups of both the target group and starting molecule are identified. Once that is done, you then figure out the steps to convert the functional group of the starting molecule to that of the target molecule.

Final Organic Synthesis Quiz

Question

Organic synthesis accounts for the more complex organic compounds that are important but less common in nature. True or false? 

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Answer

True

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Question

Aspirin is made from acetylsalicylic acid. True or false?

Show answer

Answer

False - aspirin is made from salicylic acid. Acetylsalicylic acid is the scientific name of aspirin.

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Question

Suggest why organic synthesis allows drugs and pesticides to be produced efficiently.


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Answer

Organic synthesis minimises the wastage of natural resources and allows organic compounds to be produced in high yields.

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Question

In organic synthesis, the molecule to be synthesised is called the ______ _____. In contrast, the ‘scaffold’ from which the molecule is derived is called the _____ ______.


Show answer

Answer

In organic synthesis, the molecule to be synthesised is called the target compound. In contrast, the ‘scaffold’ in which the molecule is derived from is called the starting material.

Show question

Question

Organic synthesis involves mapping out steps to convert the starting material into the target compound. True or false? 


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Answer

True

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Question

Only the functional groups of the target compound need to be identified to allow the starting material to be converted into the target compound. True or false? 


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Answer

False - identifying the functional groups of the starting material is also crucial in properly mapping out the synthesis of the compound.

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Question

Outline the two key rules for deciding on the most appropriate reaction step(s) for organic synthesis.


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Answer

Choose the reaction with the least amount of steps, consider the reagents and conditions involved that is related to the reaction step(s) chosen.

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Question

Name two examples of organic synthesis pathways.


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Answer

The synthesis of propanoic acid from 1-bromopropane, the synthesis of propylamine from ethene.

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Question

Propan-2-ol is the intermediate in the synthesis of propanoic acid from 1-bromopropane. True or false?

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Answer

False - propan-1-ol is the intermediate.

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Question

The intermediates in the synthesis of propylamine from ethene can be interconvertible from each other. True or false? 


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Answer

True - a haloalkane derived from ethene can be converted into propanenitrile.

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Question

Which factors have to be taken into account to optimise an organic synthesis pathway?

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Answer

The cost of the reagents and each step, the toxicity of the products, minimising the number of steps, minimising the number of side (waste) molecules, use of catalysts or certain temperature changes.

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Question

What is retrosynthesis?

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Answer

The planning of an organic synthesis pathway starting from the target compound (i.e. the last molecule of the steps).

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Question

How do you carry out hydration of alkenes?

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Answer

Alkenes are treated with steam at 300oC and 60-70 atm in the presence of phosphoric acid.

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Question

What is the product of hydration of alkenes?

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Answer

Alcohol

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Question

What do you get when you oxidize an alcohol?

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Answer

Carboxylic acid

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Question

To convert 1-bromopropane to propaneamine, which reaction do you require?

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Answer

Reaction with excess ethanolic ammonia and heat.

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Question

What do you get when you hydrolyse haloalkanes?

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Answer

Alcohol

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Question

Which of the following chemicals is not the same as the others?

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Answer

Propanenitril

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Question

How many steps would it take to synthesize propylamine from ethene?

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Answer

3 steps

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Question

How many intermediate compounds will be formed during the synthesis of propylamine from ethene?

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Answer

2 intermediate compounds.

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Question

How many steps would it take to synthesize propanoic acid from propanenitrile?

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Answer

1 step

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Question

How do you convert propanenitrile to propanoic acid?

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Answer

Reaction with dil. HCl and water, and heat under reflux

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Question

How do you convert an alcohol to an alkene?

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Answer

Reaction of alcohol with concentrated phosphoric acid and heat at 170oC.

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Question

How do you convert carboxylic acid to a primary amide?

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Answer

  1. First, convert carboxylic acid to acyl chloride by reaction with SOCl2.
  2. Then, add ammonia at 20oC to get the primary amide.

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Question

What do get after reduction of an alkene?

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Answer

Alkane

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Question

How can you reduce an alkene to get an alkane?

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Answer

Reaction of alkene with hydrogen in the presence of a metal catalyst (Pd, Pt, or Ni) at 1500

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Question

How do you convert an aldehyde group to a hydroxynitrile group?

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Answer

Reaction with hydrogen cyanide (HCN)

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