Module 6: Chapter 28 - Organic Synthesis Flashcards
What is the importance of carbon-carbon bond formation in organic synthesis?
It allows you to:
* Lengthen a carbon chain
* Add a side chain to a benzene ring
* Introduce a new functional group which can then be reacted further
How can you form a Nitrile from haloalkanes?
React haloalkanes with sodium cyanide, NaCN, or with potassium cyanide, KCN, in ethanol
What are the conditions to form a Nitrile from haloalkanes?
Ethanolic
What type of mechanism is the reaction to form a Nitrile from haloalkanes?
nucleophilic substitution
Draw the complete mechanism for the reaction between a haloalkane and sodium cyanide
How can you produce an amine from a nitrile?
React it with hydrogen in the presence of a nickel catalyst
What is the reduction of a nitrile?
The reaction of a nitrile with hydrogen in the presence of a nickel catalyst to produce an amine
What are the conditions for forming an amine from a nitrile?
React with hydrogen in the presence of a nickel catalyst
What is the hydrolysis of a nitrile?
The production of a carboxylic acid from heating a nitrile with a dilute aqueous acid
What is the reaction for the hydrolysis of a nitrile?
Nitrile + aqueous acid -> carboxylic acid + ammonium salt
How can you produce a carboxylic acid from a nitrile?
React it with a dilute aqueous acid
What are 2 reactions that increase the length of the carbon chain?
- Forming a nitrile from a haloalkane
- Forming a nitrile from aldehydes and ketones
What are 2 reactions that add a side chain to a benzene ring?
- Alkylation
- Acylation
What is filtration under reduced pressure?
Filtration under reduced pressure is a technique used for separating a solid product from a solvent or liquid reaction mixture
What apparatus is needed for filtration under reduced pressure?
- Buchner flask
- Buchner funnel
- Pressure tubing
- Filter paper
- Access to filter or vacuum pump (filter pump used at A level)
What is this?
A buchner flask
used for filtrating under reduced pressure
What is this?
A Buchner funnel
used for filtrating under reduced pressure
What is this?
Filter pump
used for filtrating under reduced pressure
Describe the process for filtration under reduced pressure:
- Connect one end of the pressure tubing to the filter pump whilst attaching the other end of the rubber tubing to the Buchner flask
- Attach the filter pump to a tap
- Fit the Buchner funnel to the Buchner flask ensuring that there is a good tight fit by using a rubber bung
- Switch on the tap to which the filter pump is attached
- Check for good suction by placing your hand across the top of the funnel
- Place a piece of filter paper inside the Buchner funnel and wet this with the same solvent used in preparing your solid, you should see the paper being sucked down against the holes in the funnel
- Slowly pour the reaction mixture from a beaker into the centre of the filter paper
- Rinse out the beaker with the solvent so that all of the solid crystals collect in the Buchner funnel
- Rinse the crystals in the Buchner funnel with more solvent and lkeave them under suction for a few minutes so that the crystals start to dry
What is purification by recrystallisation?
A solid product obtained after filtration will contain impurities which can be removed by carrying out recrystallisation. Purification by recrystallisation relies on the desired product and the impurities having different solubilities in the chosebn solvent
Describe how to carry out purification by recrystallisation:
- Pour a quantity of the chosen solvent into a conical flask. If the solvent is flammable, warm the solvent over a water bath. If it is not flammable (i.e water), place the conical flask on a tripod and gauze over a Bunsen and warm the solvent
- Tip the impure sample into a second conical flask or beaker
- Slowly add the solvent to the impure sample until it dissolves in the solvent. you should add the minimum volume of solvent needed to dissolve the solid
- Once the solid has dissolved, allow the solution to cool. Crystals of the desired product should form in the conical flask or beaker. When no more crystals form, filter the crystals under reduced pressure to obtain the dry crystalline solid
How can you determine whether a solid is pure?
Determining the melting point:
* A pure organic substance usually has a very sharp melting range of 1 or 2 degrees
* If the compound contains impurities, the solid melts over a wide range of temperatures and an impure sample also has a lower melting point than a pure sample
What is the melting range of a substance?
The difference between the temperature at which the sample starts to melt and the temperature at which melting is complete
What are the 2 methods to determine the melting point of a solid?
- Using electrically heated melting point apparatus
- Using an oil bath or Thiele tube method
How do you prepare your sample before determining the melting point of a solid?
Bedore taking the melting point of a solid, you should ensure that the sample is completely dry and free flowing:
1. Take a glass capillary tube or melting point tube. Hold one end of the capillary tube in the hot flame of a bunsen burner and rotate the tube in the flame until the end of the tube is completely sealed
2. The capillary tube is allowed to cool, and is then filled with crystals to about 3mm depth. This is usually carried out by pushing the open end of the capillary tube into the solid sample to force some of the solid into the tube
How can you use electrically heated melting point apparatus to determine the melting point of a solid substance?
- Place the capillary tube containing the sample into the sample hole and a 0-300 degrees celcius thermometer in the thermometer hole of the melting point apparatus
- Using the rapid heating setting, start to heat up the sample whilst observing the sample through the magnifying window
- Once the solid is seen to melt, record the melting point. Allow the melting point apparatus to cool
- Prepare a second sample ina. new capillary tube and place in the melting point apparatus and heat up the sample again
- As the melting point is apporached, set to low and raise the temperature slowly whilst obersving the sample. An accurate determination of the melting point can then be obtained
How can you use a Thiele tube or oil bath to determine the melting point of a solid substance?
- Set up the Thiele tube or oil bath
- Attach the capillary tube containing the sample to a thermometer using a rubber band
- Insert the thermometer through a hole in the cork (if using a thiele tube) or clamp the thermometer (if using an oil bath). The end of the thermometer and the end of the capillary tube should dip into the oil
- Using a micro-burner, slowly heat the side arm of the Thiele tube or the oil bath whilst observing the solid. When the solid starts to melt, remove the heat and record the temperature at which all of the solid has melted. It is important to heat the oil slowly when approaching the melting point, and it is advisable to repeat the melting point determination a second time to ensure that you obtain an accurate value
What is this?
A Thiele tube
Identify all the functional groups present in aspartame:
Identify all the functional groups present within capsaicin:
How do you produce a haloalkane from an alkene?
React the alkene with a hydrogen halide
What happens if you react an alkene with a hydrogen halide?
A haloalkane is produced
How do you produce an alcohol from an alkene?
Hydration of an alkene:
React the alkene with steam in the presence of a phosphoric acid catalyst
What happens if you react an alkene with steam in the presence of a phosphoric acid catalyst (hydration of an alkene)?
An alcohol is produced
How do you produce an alkene from an alcohol?
React the alcohol with concentrated sulfuric acid
What happens if you react an alcohol with concentrated sulfuric acid?
You produce an alkene
How do you produce a haloalkane from an alcohol?
React the alcohol with a sodium halide in the presence of a sulfuric acid catalyst
What happens if you react an alcohol with a sodium halide in the presence of a sulfuric acid catalyst?
You produce a haloalkane
How do you produce an alcohol from a haloalkane?
Reflux the haloalkane with sodium hydroxide
What happens if you reflux a haloalkane with sodium hydroxide?
You produce an alcohol