Chapter 28 Organic synthesis Flashcards
What are nucleophiles?
A species that is attracted to an electron deficient carbon atom with the role of donating a lone pair of electrons
Describe how the CN- (Cyanide) Ion can help in Carbon-Carbon synthesis
Cyanide is an ion containing a negatively charged carbon atom so its a nucleophile
It will react with carbon centres that have a slight positive charge to create a new carbon-carbon bond
Why Isn’t Cyanide used in labs and what substitutes are used instead?
Cyanide is too dangerous to use so a cyanide reagent such as potassium cyanide, sodium cyanide or hydrogen cyanide
Describe fully the reaction between cyanide ions and haloalkanes
- Haloalkanes contain a polar carbon-halogen bond and the halogen is more electronegative than carbon, making that carbon electron deficient
- Nucleophiles like cyanide ions will react with the positive carbon centre in haloalkanes to replace the halogen atom in a nucleophilic substitution reaction
- If you reflux a haloalkane with potassium cyanide in ethanol then the cyanide ions will react with the haloalkane by nucleophilic substitution to form a nitrile
Describe the reaction between cyanide ions with carbonyl compounds
Aldehydes and ketones both contain a polar C=O bond. If you mix them with hydrogen cyanide, the cyanide ion will react with the positive carbon centre to form a hydroxynitrile in a nucleophilic addition
Describe how nitriles can be reduced to amines
In industry, nitriles are reduced using hydrogen gases with a metal catalyst such as platinum or nickel at a high temperature and pressure and form a primary amine
Describe how nitriles can be hydrolysed and state the product
If you reflux a nitrile in dilute hydrochloric acid, then the nitrile group will be hydrolysed to form a carboxylic acid
Describe the Friedel-Crafts reaction to form carbon-carbon bonds with benzene rings
If you reflux benzene with a halogen carrier and either a haloalkane or acyl chloride, then a new carbon-carbon bond will form between the benzene ring and the halogenated carbon in the organic reactant
How can organic solids be purified?
Organic solids can be purified by recrystallisation
Describe the method of recrystallisation
- Very hot solvent is added to the impure solid until it just dissolves
- Solution left to cool down slowly, crystals of the product will form as solution cools
- The crystals are removed by filtration under reduced pressure and washed with ice-cold solvent
Explain why it is very important to use an appropriate solvent when you recrystallise a product
If the product isn’t soluble enough in the hot solvent you won’t be able to dissolve it at all
If the product is too soluble in the cold solvent most of it will stay in solution even after cooling and you’ll lose most of your products giving you a very low yield
Describe how to filter an organic solid under reduced pressure
Pouring the reaction mixture into a Bucher funnel with a piece of filter paper in it, the reduced pressure causes suction through the funnel which causes the liquid to pass quickly into the flask, leaving behind dry crystals
Explain how melting and boiling points can describe the purity of a substance
Most pure substances have a specific melting and boiling point, if the substance is impure then the melting and boiling will occur across a wide range of temperatures
What is an addition reaction?
A reaction when two molecules join together to form a single product and involves the breaking of a double bond
What is a elimination reaction?
Involves the removing of a functional group which is released as part of a small molecule, often a double bond is formed
