A2-Level Advanced Organic Chemistry
Hydrogen cyanide reacts with carbonyl groups in nucleophilic addition reactions forming hydroxynitriles:
Hydrogen cycande is highly reactive (and toxic), it can be prepared ‘in situ’ using a metal cyanide (KCN or NaCN) and sulfuric acid (H SO ).
The length of the carbon chain in a carbonyl molecule can be extended using this reaction
Carbonyl - Nucleophilic Addition of HCN
When hydrogen cyanide is added to a carbonyl group, nucleophilic addition occurs.
Hydrogen cyanide is a dangerous substance that is highly toxic. Due to this, hydrogen cyanide is often produced in solution with the carbonyl compound that it is to react with. A metal cyanide ion (usually NaCN or KCN) is added with dilute sulfuric acid. The metal cyanide dissociates in solution releasing CN⁻ ions and the dilute sulfuric acid releases H⁺ ions.
Cyanide ions (CN⁻) are strong nucleophiles that are attracted to the carbon with a slight positive charge in a carbonyl.
The lone pair of electrons on the carbon in the nitrile get donated to the slightly positive carbon in the carbonyl. The C=O bond breaks, with the oxygen atom gaining a pair of electrons and a negative charge.
The H⁺ ions in solution (from the sulfuric acid) then form a bond with the negatively charged oxygen and an –OH group is formed.
If a carbonyl undergoes this nucleophilic addition, a new type of compound called a ‘hydroxynitrile’ is produced.
This reaction is very important in chemistry as it allows a carbon to carbon bond to be formed, enabling the length of the carbon chain in a molecule to be increased. Carbon to carbon bonds are difficult to form in organic chemistry and this mechanism provides a possible route.