C16 - Organic Synthesis Flashcards
How is an alkane formed from an alkene?
By hydrogenation (using H2) in the presence of a nickel catalyst at 403K.
It’s an example of electrophilic addition.
What type of reaction is hydrogenation (forming an alkane from an alkene)?
Electrophilic addition.
Hydrogen atoms are electrophile.
What is the test for alkenes?
Reacting it with bromine water.
If an alkene is present, the bromine water turns from orange to colourless due to the breaking of the double bond in the alkene.
How is a haloalkane formed from an alkene?
By the use of a hydrogen halide.
This is an example of electrophilic addition as the hydrogen halide undergoes heterolytic fission.
What type of reaction forms a haloalkane from an alkene?
Electrophilic addition due to heterolytic fission of a hydrogen halide.
How can a haloalkane be formed from an alkane?
By radical substitution due to halogens gaining energy from UV radiation and undergoing homolytic fission to form radicals.
They then form a chain reaction.
What type of reaction forms haloalkane from alkanes?
Radical substitution.
This is due to homolytic fission of halogens by UV radiation.
How can an alkene form an alcohol?
By hydration and electrophilic addition.
This is done in the presence of H2O and H3PO3.
What type of reaction forms alcohol from alkenes?
Electrophilic addition / hydration
What is required for the electrophilic addition of an alkene to form an alcohol?
Water (gas/steam) and phosphoric acid for the alkene to be hydrated.
How is an alkene formed from an alcohol?
The alcohol is dehydrated in an elimination reaction requiring sulphuric acid and forming an alkene and water.
What type of reaction forms an alkene from an alcohol?
Elimination / dehydration in the presence of concentrated sulphuric acid.
What is necessary for the dehydration of an alcohol?
Concentrated sulphuric acid.
How can an alcohol be formed from a haloalkane?
By nucleophilic substitution under reflux using NaOH (aq)
What type of reaction forms an alcohol from a haloalkane?
Nucleophilic substitution
How is a haloalkane formed from an alcohol?
The alcohol is heated under reflux with sulphuric acid and a sodium halide, resulting in nucleophilic substitution.
What conditions are required for a haloalkane to be formed by an alcohol?
Nucleophilic substitution would occur under reflux in the presence of a sodium halide and sulphuric acid.
(A hydrogen halide and sodium hydrogen sulphate are formed in situ)
How do you identify which haloalkane is present in a sample?
You hydrolyse the haloalkane then add silver nitrate to find which halide is present.
White precipitate - silver chloride
Cream precipitate - silver bromide
Yellow precipitate - silver iodide
How fast are haloalkanes hydrolysed?
The rate at which haloalkanes are hydrolysed / carbon-halide bonds are broken depends on bond enthalpy not electronegativity.
C-I has a low enthalpy so is hydrolysed quickly whereas C-F has a higher enthalpy so is hydrolysed slower.
What are the two types of alcohol that can be oxidised to form new products?
Primary and secondary alcohols.
What substance is used as an oxidising agent when oxidising alcohols?
Acidified potassium dichromate (K2Cr2O7 / H2SO4)
It turns from orange to green when reduced.
How are aldehydes made (from alcohols)?
A primary alcohol is heated under reflux (in the presence of potassium dichromate) then distilled to prevent further reflux.
How are carboxylic acids made (from alcohols)?
A primary alcohol is heated under continuous reflux (in the presence of potassium dichromate).
How is a ketone formed (from an alcohol)?
A secondary alcohol is heated under reflux (in the presence of potassium dichromate)
What are the quick fit apparatus?
Round bottom/peak shaped flask
Receiver
Screw-tap adaptor
Condenser
Still head
How can organic compounds be heated slowly?
By reflux
What equipment is needed for heating under reflux?
Round bottom/pear shaped glass
Condenser
Rubber tubing
Stand and clamp
Heat source
Why are anti-bumping granules necessary when heating under reflux?
So that the contents boil slowly.
If not used, large bubbles will form at the bottom of the liquid and make the glassware vibrate or jump violently.
What happen if a stopper is placed on top of the condenser during reflux?
Pressure builds up as the heated air expands due to the stopper resulting in a closed system. This can cause the equipment to explode.
In what way does water flow through the condenser?
In through the bottom and out from the top to ensure the outer jacket is full and the tube remains as cool as possible.
What’s distillation used for?
To separate a liquid from its impurities.
What equipment is used for distillation?
Round bottom/pear shaped flask
Condenser
Rubber tubing
Heat source
Clamp and stand
Screw-cap adaptor
Receiver adaptor
Still head
Thermometer
How are organic products purified?
When preparing organic liquids, water may also be produced, producing two layers within the collection flask.
To prevent disposing of the wrong product, water can be added and the layer which increases in size is the aqueous layer which can be removed using a separating funnel:
1) Ensure the separating funnel tap is closed.
2) Pour the mixture into the separating funnel, add a stopper and invert to mix the the contents.
3) Allow the layers to settle
4) Add water to see which gets bigger (aqueous layer)
5) Place conical flask under funnel, remove stopper and empty the lower layer of liquid.
6) Use another flask to collect second layer.
What’s the procedure for drying an organic liquid?
1) Add the liquid to a conical flask
2) Add some drying agent (e.g. anhydrous calcium sulfate) and gently swirl the the contents to mix together.
3) Place a stopper on the flask to prevent evaporation of products and leave for 10 minutes.
4) If the solid has formed a lump, water is still present. Add more drying agent until the solid resembles a fine powder.
5) Decant the solid from the liquid. If dry, the liquid should be clear.
What are the different functional groups? (10)
Alkene C=C Alcohol -OH Halo alkane -Cl -Br -I Aldehyde -COH Ketone =O Carboxylic acid -COOH Ester -COO Amine -NH2 Acyl chloride -COCl Nitrile -CN
What’s a target molecule?
The compound the chemist is attempting to prepare by organic synthesis.
Synthesis can occur in mor than one stage.
