More on halogenoalkanes Friday, 21 September 2018

More on halogenoalkanes Objective: To know about some more reactions of halogenoalkanes Outcomes: To know the reaction with potassium cyanide to produce nitriles To know the reaction with ammonia to produce primary amines, including knowing the mechanism To know the reaction with ethanolic potassium hydroxide to produce alkenes

Reflux Reflux video

Making Nitriles Nitriles contain – C ≡ N Halogenoalkanes react under reflux with potassium cyanide, KCN, dissolved in ethanol to produce nitriles E.g. CH3CH2Br + CN-  CH3CH2CN + Br- What happens to the length of the carbon chain? It increases by one, this is a useful way to increase the length of the carbon chain

Making Nitriles These reactions proceed by a nucleophilic substitution mechanism. The CN- ion acts as a nucleophile. It is similar to that with :OH-, but :CN- is the nucleophile They are named according to the number of carbon atoms in the longest chain containing the nitrile group. CH3CH2CN is propanenitrile not ethanenitrile

More on halogenoalkanes Objective: To know about some more reactions of halogenoalkanes Outcomes: To know the reaction with potassium cyanide to produce nitriles To know the reaction with ammonia to produce primary amines, including knowing the mechanism To know the reaction with ethanolic potassium hydroxide to produce alkenes

Making Amines Amines contain the amino group –NH2 They are based on NH3 but one or more of the hydrogen atoms are replaced by alkyl groups Primary halogenoalkanes react with ammonia to make primary amines. The halogenoalkane is warmed with excess ethanolic ammonia (ammonia dissolved in ethanol) The ammonia swaps places with the halogen to form a primary amine. E.g. CH3CH2Br + 2NH3  CH3CH2NH2 + NH4Br Can you suggest a mechanism?

Making Amines Mechanism (nucleophilic substitution) Pg 93 CGP, 59 Edexcel

Examples Of Amines CH3NH2 Methylamine or Aminomethane or Methanamine CH3CH2NH2 Ethylamine or aminoethane or ethanamine

More on halogenoalkanes Objective: To know about some more reactions of halogenoalkanes Outcomes: To know the reaction with potassium cyanide to produce nitriles To know the reaction with ammonia to produce primary amines, including knowing the mechanism To know the reaction with ethanolic potassium hydroxide to produce alkenes

Halogenoalkanes reacting with ethanolic potassium hydroxide When halogenoalkanes are reacted with a warm alkali dissolved in ethanol you get an alkene. The reaction is heated under reflux. E.g. What sort of reaction is this? Elimination reaction, the hydroxide ions are acting as a base to remove an H+ ion from the halogenoalkane Pg 93 CGP

More on halogenoalkanes Objective: To know about some more reactions of halogenoalkanes Outcomes: To know the reaction with potassium cyanide to produce nitriles To know the reaction with ammonia to produce primary amines, including knowing the mechanism To know the reaction with ethanolic potassium hydroxide to produce alkenes

Questions page 59 workbook Revision guide CGP pg 93 Edexcel pg 59

More on halogenoalkanes Objective: To know about some more reactions of halogenoalkanes Outcomes: To know the reaction with potassium cyanide to produce nitriles To know the reaction with ammonia to produce primary amines, including knowing the mechanism To know the reaction with ethanolic potassium hydroxide to produce alkenes