6.2.8: Reactions of nitriles

Question 1

What are nitriles?

Answer 1

• Organic chemicals that have a -CN functional group.
• The -CN group can undergo other chemical reactions to form a variety of functional groups including amines and carboxylic acids.

Question 2

When do nitriles form amines?

Answer 2

• When they undergo reduction.
• Hydrogen gas can react directly with a nitrile to form a primary aliphatic amine.
• Two hydrogen atoms are added to the nitrogen atom of the nitrile group.

Question 3

What are the conditions needed in the reduction of nitriles?

Answer 3

• A transition metal catalyst, such as nickel, is needed to lower the activation energy to enable this reaction to occur.
• To increase the rate of reaction, the reaction mixture is heated to about 150C with a nickel catalyse, at raised pressure.

Question 4

write the general general equation for the reduction of nitriles.

Answer 4

RCN + 2H2 → RCH2NH2

Where r is a hydrocarbon or hydrogen.

Question 5

In industry, what does the reduction of a nitrile directly with hydrogen use?

Answer 5

• A Raney nickel catalyst.

- This is an alloy made mainly from nickel and a very small amount of aluminium.

Question 6

What is another way of reducing a nitrile?

Answer 6

• Reduction of a nitrile is also possible using a reducing agent such as lithium tetrahydridoaluminate(III), LiAIH4.
• RCN + 4[H] → RCH2NH2

Question 7

What do nitriles form after undergoing hydrolysis?

Answer 7

• Initially, they will form an amide and then an ammonium salt.
• However, this second reaction is so slow that it is not significant.

Question 8

How can the rate of reaction of the hydrolysis of nitriles be increased?

Answer 8

-The rate of reaction can be increased by using a strong acid as a catalyst and heating the reaction mixture under reflux.

Question 9

What do nitriles react to form under acid hydrolysis?

Answer 9

-Carboxylic acids.

Question 10

When ethanenitrile undergoes acid hydrolysis, what is formed and what is the balanced symbol equation?

Answer 10

-Ethanoic acid and an inorganic ammonium salt are formed.

CH3CN + 2H2O + HCl → CH3COOH + NH4Cl

Question 11

In acid hydrolysis of nitriles, why are organic acids (e.g. CH3COOH) formed rather than organic ammonium salt (CH3COONH4)?

Answer 11

• Because he strong acid fully ionises in solution, forming hydrogen ions and chloride ions.
• Once the amide is formed , the bond between the nitrogen and the carbon is broken, making the ethanoate ion.
• This then reacts with the proton from the strong acid to form the carboxylic acid.
• All organic acids are week acids and only partially ionise in solution.
• In these reactions the C (triple bond) N is completely broken through a series of steps via the amide.
• This gives the carboxylic acid and the ammonium salt as the major products