Carbon-Carbon bond formation

In a nutshell

Carbon-carbon bond synthesis is used to lengthen the carbon chain. Reagents which have a nucleophilic or electrophilic carbon atom are used to form a new carbon-carbon bond.

Equations

These are general chemical equations. You will need to be able to use these when you write equations for specific substances.

$haloalkane \ + \ cyanide \xrightarrow[ethanol]{reflux} nitrile \ + \ salt \\ \ \\carbonyl \ + \ cyanide \rightarrow hydroxynitrile$

Cyanides

Cyanides are nucleophiles which can attack an electron deficient carbon atom.

Nucleophilic substitution

A nitrile can be produced by reacting cyanide in ethanol with a haloalkane via a nucleophilic substitution reaction. This is because the halogen is more electronegative than the carbon, giving rise to a polar bond and a partially positive carbon atom.

$haloalkane \ + \ cyanide \xrightarrow[ethanol]{reflux} nitrile \ + \ salt$

Example

$chloromethane \ + \ potassium \ cyanide \xrightarrow[ethanol]{reflux} acetonitrile \ + \ potassium \ chloride \\ \ \\CH_3Cl \ + \ KCN \xrightarrow[ethanol]{reflux} CH_3CN \ + K^+Cl^-$

Nucleophilic addition

Hydroxynitriles (cyanohydrins) can be produced by reacting acidified cyanide with a carbonyl compound. The cyanide acts as a nucleophile and attacks the partially positive carbon and adds itself to the molecule.

$carbonyl \ + \ cyanide \rightarrow hydroxynitrile$

Example

$propanone \ + \ sodium \ cyanide \xrightarrow{H^+} 2-hydroxy-2-methylpropanenitrile \\ \ \\C_3H_6O \ + \ NaCN \xrightarrow{H^+}C_3H_6OHCN \\ \ \\Structural \ formula \ of \ the \ product: \ CH_3CHCH_3(OH)CN$

General Mechanism

Chemistry; Synthesis; KS5 Year 12; Carbon-Carbon bond formation

Risk assessment

Potassium cyanide is an irritant. It can react with moisture to produce hydrogen cyanide (toxic gas). To reduce risks when working with potassium cyanide, perform the experiment in a fume cupboard.

Important: Always wear safety goggles, a lab coat and gloves when carrying out a chemistry experiment.

Friedel-Crafts reactions

Friedel-Crafts reactions can be used to make new carbon-carbon bonds with benzene. Friedel-Crafts alkylation adds an alkyl group to the benzene ring. Friedel-Crafts acylation adds an acyl group to the benzene ring.