Homologation reaction

A homologation reaction, also known as homologization, is any chemical reaction that effects an overall increase of the carbon skeleton of a saturated reactant molecule.^[1] The reactants undergo a homologation converting them into the next member of the homologous series. For example the reaction of aldehydes and ketones with diazomethane or methoxymethylenetriphenylphosphine effectively inserts a methylene (-CH₂-) unit in the hydrocarbon chain and the reaction product is the next homologue.

Additional recommended knowledge

How to quickly check pipettes?

What is the Correct Way to Check Repeatability in Balances?

Weighing the right way

Examples of homologation reactions include:

• Seyferth-Gilbert homologation
• Displacement of a halide by a cyanide group, which can be reduced to an amine, see: Kolbe nitrile synthesis
• Kiliani-Fischer synthesis, where an aldose molecule is elongated through a three-step process consisting of:
  1. Nucleophillic addition of cyanide to the carbonyl to form a cyanohydrin
  2. Hydrolysis to form a lactone
  3. Reduction to form the homologous aldose
• Wittig reaction of an aldehyde with methoxymethylenetriphenylphosphine, which produces a homologous aldehyde.
• Arndt-Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue (ie. contains one additional carbon atom)
• Kowalski ester homologation, an alternative to the Arndt-Eistert synthesis. Has been used to convert β-amino esters from α-amino esters through an ynolate intermediate.^[2]

Some reactions increase the chain length by more than one unit. For example, the following are considered two-carbon homologation reactions:

• Nucleophilic addition to ethylene oxide, resulting in a ring-opening and producing a primary alcohol with two extra carbons.
• Malonic ester synthesis, which produces a carboxylic acid with two extra carbons.

See also

• Homologous series

References