Pyridazine is an

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the molecular formula . It contains a six-membered

ring (The) Ring(s) 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 Arts, entertainment, and media Film and TV * ''The Ring'' (franchise), a ...

with two adjacent

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

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 envi ...

of 208 °C. It is

isomeric In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibility ...

with two other

diazine In organic chemistry, diazines are a group of organic compounds having the molecular formula . Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen. There are three structural isomers: * pyrida ...

() 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 oth ...

and

pyrazine Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-lik ...

Occurrence

Pyridazines are rare in nature, possibly reflecting the scarcity of naturally occurring

hydrazines Hydrazines (R2N−NR2) are a class of chemical compounds with two nitrogen atoms linked via a covalent bond and which carry from one up to four alkyl or aryl substituents. Hydrazines can be considered as derivatives of the inorganic hydrazine ( ...

, common building blocks for the synthesis of these heterocycles. The pyridazine structure is a popular

pharmacophore 300px, An example of a pharmacophore model In medicinal chemistry and molecular biology, a pharmacophore is an abstract description of molecular features that are necessary for molecular recognition of a ligand by a biological macromolecule. IUPAC ...

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) is a fourth-generation cephalosporin. Spectrum of bacterial susceptibility and resistance Most of the strains of '' Stenotrophomonas maltophilia '' Stenotrophomonas maltophilia'' is an aerobic, nonfermentative, Gram-negati ...

cadralazine Cadralazine is an antihypertensive of the hydrazinophthalazine chemical class Chemical classification systems attempt to classify elements or compounds according to certain chemical functional or structural properties. Whereas the structur ...

minaprine Minaprine (INN, USAN, BAN; brand names Brantur, Cantor) is a monoamine oxidase inhibitor antidepressant drug that was used in France for the treatment of depression until it was withdrawn from the market in 1996 because it caused convulsion ...

pipofezine Pipofezine, sold under the brand name Azafen or Azaphen, is a tricyclic antidepressant approved in Russia for the treatment of major depressive disorder, depression. It was introduced in the late 1960s and is still used today. Pipofezine has bee ...

, and

hydralazine Hydralazine, sold under the brand name Apresoline among others, is a medication used to treat high blood pressure and heart failure. This includes high blood pressure in pregnancy and very high blood pressure resulting in symptoms. It has bee ...

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 Heterocyclic compound, heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by ...

, Emil Fischer prepared the first pyridazine via the condensation of

phenylhydrazine Phenylhydrazine is the chemical compound with the formula . It is often abbreviated as . It is also found in edible mushrooms. Properties Phenylhydrazine forms monoclinic prisms that melt to an oil around room temperature which may turn yellow ...

and

levulinic acid Levulinic acid, or 4-oxopentanoic acid, is an organic compound with the chemical formula, formula CH3C(O)CH2CH2CO2H. It is classified as a keto acid. This white crystalline solid is soluble in water and polar organic solvents. It is derived from d ...

. The parent heterocycle was first prepared by oxidation of

benzocinnoline Benzo 'c''innoline is a tricyclic organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemic ...

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 ...

. A better route to this otherwise esoteric compound starts with the maleic hydrazide. These heterocycles are often prepared via condensation of 1,4-

diketone In organic chemistry, a dicarbonyl is a molecule containing two carbonyl () groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls ...

s 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 hazardous unless handled in solution as, for example, hydraz ...

References

{{Authority control Simple aromatic rings