Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula . It contains a six-membered

ring Ring may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell :(hence) to initiate a telephone connection Arts, entertainment and media Film and ...

with two adjacent nitrogen atoms. It is a colorless liquid with a

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

of 208 °C. It is isomeric with two other diazine () rings,

pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other ...

and pyrazine.

Occurrence

Pyridazines are rare in nature, possibly reflecting the scarcity of naturally occurring hydrazines, common building blocks for the synthesis of these heterocycles. The pyridazine structure is a popular pharmacophore which is found within a number of herbicides such as credazine, pyridafol and pyridate. It is also found within the structure of several drugs such as

cefozopran Cefozopran (INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they als ...

, cadralazine, minaprine, pipofezine, and hydralazine.

Synthesis

In the course of his classic investigation on the

Fischer indole synthesis The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by Emil Fischer. Today ...

, Emil Fischer prepared the first pyridazine via the condensation of phenylhydrazine and levulinic acid. The parent heterocycle was first prepared by oxidation of

benzocinnoline Benzo 'c''innoline is a tricyclic organic compound with the formula C12H8N2. Formally this species is derived by oxidative dehydrogenation of 2,2'-diaminobiphenyl. This heterocycle reacts with iron carbonyls to form C12H8N2Fe2(CO)6.R. P. Benn ...

to the pyridazinetetracarboxylic acid followed by

decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...

. A better route to this otherwise esoteric compound starts with the

maleic hydrazide Maleic hydrazide, often known by the brand name Fazor is a plant growth regulator that reduces growth through preventing cell division but not cell enlargement. It is applied to the foliage of potato, onion, garlic and carrot crops to prevent sprou ...

. These heterocycles are often prepared via condensation of 1,4- diketones or 4-ketoacids with

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

References

{{Authority control Simple aromatic rings