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Pyridine is a heterocyclic organic compound with the chemical formula C5 H5 N. It is Pyridine-sulfur trioxide, C5H5NSO3 (mp 175 °C) is a sulfonation agent. — “Pyridine - Wikipedia, the free encyclopedia”, en.wikipedia.org
Image:Pyridine formula.png, Image:Pyridine.png.  Licensing. Public domainPublic domainfalsefalse. This file is ineligible for copyright and therefore in the public domain, because it consists entirely of information that is common property and contains no original authorship. — “File:Pyridine.svg - Wikipedia, the free encyclopedia”, en.wikipedia.org
The Hantzsch pyridine synthesis or Hantzsch dihydropyridine synthesis is a multi-component organic reaction between an aldehyde such as formaldehyde, 2 equivalents of a β-keto ester such as ethyl acetoacetate and a nitrogen donor such as ammonium. — “Hantzsch pyridine synthesis - Wikipedia, the free encyclopedia”, en.wikipedia.org