CIE A Level Chemistry复习笔记3.7.2 Nitriles & Hydroxynitriles

• Nitriles are compounds with a -CN functional group
• They can be prepared from the nucleophilic substitution of halogenoalkanes

Propanenitrile, an example of a nitrile

Reaction with KCN

• The nucleophile in this reaction is the cyanide, CN^- ion
• Ethanolic solution of potassium cyanide (KCN in ethanol) is heated under reflux with the halogenoalkane
• The product is a nitrile

Bromoethane reacts with ethanolic potassium cyanide when heated under reflux to form propanenitrile

• Hydroxynitriles are compounds with both a hydroxy (-OH) and cyanide (-CN) functional group
• They can be prepared from the nucleophilic addition of aldehydes and ketones

2-hydroxy-2-methylpropanenitrile

Reaction with HCN

• The nucleophilic addition of hydrogen cyanide to carbonyl compounds is a two-step process
• In step 1, the cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate
• In step 2, the negatively charged oxygen atom in the reactive intermediate quickly reacts with aqueous H+ (either from HCN, water or dilute acid) to form a 2-hydroxynitrile

The cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate which quickly reacts with a proton to form a 2-hydroxynitrile compound

• Nitriles are hydrolysed by either dilute acid or dilute alkali followed by acidification to give a carboxylic acid
  • Hydrolysis is the breakdown of a compound using water

Hydrolysis of nitriles

• Nitriles are hydrolysed by either dilute acid or dilute alkali followed by acidification
  • Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt
  • Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid
• The -CN group at the end of the hydrocarbon chain is converted to a -COOH group

Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid