The Hammick reaction, named after Dalziel Hammick

Dalziel Hammick

Dalziel Llewellyn Hammick FRS , was an English research chemist. His major work was in synthetic organic chemistry. He promulgated Hammick's rule, which predicts the order of substitution in benzene derivatives, while the Hammick reaction is used in the synthesis of larger molecules.-Early life:The...

, is a chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 described as a thermal decarboxylation

Decarboxylation

Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...

 of α-picolinic

Picolinic acid

Picolinic acid is a pyridine compound with a carboxyl side chain at the 2-position. It is an isomer of nicotinic acid, which has the carboxyl side chain at the 3-position. It is a catabolite of the amino acid tryptophan.- Chelating properties :...

 (or related) acids

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 in the presence of carbonyl

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 compounds to form 2-pyridyl

Pyridine

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

-carbinols.
Using p-cymene

Cymene

Cymene, or p-cymene, is a naturally occurring aromatic organic compound. It is classified as a hydrocarbon related to a monoterpene. Its structure consists of a benzene ring para-substituted with a methyl group and an isopropyl group...

 as solvent has been shown to increase yields.

Reaction mechanism

Upon heating α-picolinic acid will spontaneously decarboxylate forming a zwitterion

Zwitterion

In chemistry, a zwitterion is a neutral molecule with a positive and a negative electrical charge at different locations within that molecule. Zwitterions are sometimes also called inner salts.-Examples:...

 (2). In the presence of a strong electrophile

Electrophile

In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...

, such as an aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

, the zwitterion will react with the carbonyl faster than protonating. Upon proton transfer the desired carbinol (4) is formed.