Editing Pyridine (section)

===Chichibabin synthesis===
The [[Chichibabin pyridine synthesis]] was reported in 1924 and the basic approach underpins several industrial routes.<ref name=tschi/> In its general form, the reaction involves the [[condensation reaction]] of [[aldehydes]], [[ketones]], [[α,β-Unsaturated carbonyl compound|α,β-unsaturated carbonyl compounds]], or any combination of the above, in [[ammonia]] or [[amine|ammonia derivatives]]. Application of the Chichibabin pyridine synthesis suffer from low yields, often about 30%,<ref name='Frank1949'>{{cite journal
|last1=Frank|first1= R. L. |last2=Seven|first2= R. P.| title = Pyridines. IV. A Study of the Chichibabin Synthesis
| journal = Journal of the American Chemical Society
| year = 1949
| volume = 71
| issue = 8
| pages = 2629–2635
| doi = 10.1021/ja01176a008}}</ref> however the precursors are inexpensive. In particular, unsubstituted pyridine is produced from [[formaldehyde]] and [[acetaldehyde]]. First, [[acrolein]] is formed in a [[Knoevenagel condensation]] from the acetaldehyde and formaldehyde. The acrolein then [[condensation reaction|condenses]] with acetaldehyde and ammonia to give [[dihydropyridine]], which is oxidized to pyridine. This process is carried out in a gas phase at 400–450&nbsp;°C. Typical catalysts are modified forms of [[alumina]] and [[silica]]. The reaction has been tailored to produce various [[methylpyridine]]s.<ref name=ul/>

[[File:AcroleinDarstellung.svg|class=skin-invert-image|500px|center|thumb|Formation of acrolein from acetaldehyde and formaldehyde]]
[[File:Pyridin aus Acrolein.svg|class=skin-invert-image|500px|center|thumb|Condensation of pyridine from acrolein and acetaldehyde]]