Pyridazine
{{short description|Heterocyclic organic compound (C4H4N2)}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 464376879
| ImageFile = Pyridazine 2D numbers.svg
| ImageClass = skin-invert-image
| ImageSize = 135
| ImageAlt = Skeletal formula with numbering convention
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageFileL1=Pyridazine-3D-balls.png
| ImageClassL1 = bg-transparent
| ImageNameL1 = C=black, H=white, N=blue
| ImageAltL1 = Pyridazine molecule
| ImageFileR1=Pyridazine-3D-spacefill.png
| ImageClassR1 = bg-transparent
| ImageNameR1 = C=black, H=white, N=blue
| ImageAltR1 = Pyridazine molecule
| PIN = Pyridazine{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = The Royal Society of Chemistry | date = 2014 | location = Cambridge | page = 141 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter }}
| SystematicName = 1,2-Diazabenzene
| OtherNames = 1,2-Diazine
Orthodiazine
Oizine
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo=289-80-5
| Beilstein = 103906
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 8902
| InChI = 1/C4H4N2/c1-2-4-6-5-3-1/h1-4H
| InChIKey = PBMFSQRYOILNGV-UHFFFAOYAA
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 15719
| EINECS = 206-025-5
| Gmelin = 49310
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 449GLA0653
| PubChem = 9259
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 30954
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C4H4N2/c1-2-4-6-5-3-1/h1-4H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = PBMFSQRYOILNGV-UHFFFAOYSA-N
| SMILES = n1ncccc1
}}
|Section2={{Chembox Properties
| C=4|H=4|N=2
| Appearance=Colorless liquid
| Density=1.107 g/cm3
| MeltingPtC=-8
| BoilingPtC=208
| Solubility= miscible
| SolubleOther = miscible in dioxane, ethanol
soluble in benzene, diethyl ether
negligible in cyclohexane, ligroin
| pKa =
| pKb =
| RefractIndex = 1.52311 (23.5 °C)
}}
|Section3={{Chembox Thermochemistry
| DeltaHf = 224.9 kJ/mol
}}
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|315|319|335}}
| PPhrases = {{P-phrases|261|264|264+265|270|271|280|301+317|302+352|304+340|305+351+338|319|321|330|332+317|337+317|362+364|403+233|405|501}}
| MainHazards=
| FlashPtC= 85
| AutoignitionPt =
}}
|Section8={{Chembox Related
| OtherCompounds = {{unbulleted list|pyridine|pyrimidine|pyrazine}}
}}
}}
Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula {{chem2|C4H4N2}}. It contains a six-membered ring with two adjacent nitrogen atoms.{{cite journal | last1 = Gumus | first1 = S. | year = 2011 | title = A computational study on substituted diazabenzenes | url = http://journals.tubitak.gov.tr/chem/issues/kim-11-35-5/kim-35-5-11-1012-875.pdf | journal = Turk J Chem | volume = 35 | pages = 803–808 | access-date = 2014-04-10 | archive-url = https://web.archive.org/web/20160303181258/http://journals.tubitak.gov.tr/chem/issues/kim-11-35-5/kim-35-5-11-1012-875.pdf | archive-date = 2016-03-03 | url-status = dead }} It is a colorless liquid with a boiling point of 208 °C. It is isomeric with two other diazine ({{chem2|C4H4N2}}) rings, pyrimidine 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, cadralazine, minaprine, pipofezine, and hydralazine.
Synthesis
In the course of his classic investigation on the Fischer indole synthesis, Emil Fischer prepared the first pyridazine via the condensation of phenylhydrazine and levulinic acid.{{cite journal | last1 = Fischer | first1 = E. | year = 1886 | title = Indole aus Phenylhydrazin | url = https://zenodo.org/record/1427407| journal = Justus Liebigs Annalen der Chemie | volume = 236 | issue = 1–2| pages = 126–151 | doi = 10.1002/jlac.18862360107 }} The parent heterocycle was first prepared by oxidation of benzocinnoline to the pyridazinetetracarboxylic acid followed by decarboxylation. A better route to this otherwise esoteric compound starts with the maleic hydrazide. These heterocycles are often prepared via condensation of 1,4-diketones or 4-ketoacids with hydrazines.{{cite book | last1 = Tišler | first1 = M. | last2 = Stanovnik | first2 = B. | title = Advances in Heterocyclic Chemistry Volume 9 | chapter = Pyridazines | year = 1968 | volume = 9 | pages = 211–320 | doi = 10.1016/S0065-2725(08)60374-8 | isbn = 9780120206094}}