synthesized from ammonia, aldehydes, and nitriles, a few combinations of which are suited for pyridine itself. Various name reactions are also known, but they are not practiced on scale. In 1989, 26,000 tonnes of pyridine was produced worldwide. Other major derivatives are 2-, 3-, 4-methylpyridines and 5-ethyl-2-methylpyridine. The combined scale of these alkylpyridines matches that of pyridine itself. Among the largest 25 production sites for pyridine, eleven are located in Europe (as of 1999). The major producers of pyridine include Evonik Industries, Rütgers Chemicals, Jubilant Life Sciences, Imperial Chemical Industries, and Koei Chemical. Pyridine production significantly increased in the early 2000s, with an annual production capacity of 30,000 tonnes in mainland China alone. The US–Chinese joint venture Vertellus is currently the world leader in pyridine production. Chichibabin synthesis The Chichibabin pyridine synthesis was reported in 1924 and the basic approach underpins several industrial routes. In its general form, the reaction involves the condensation reaction of aldehydes, ketones, α,β-unsaturated carbonyl compounds, or any combination of the above, in ammonia or ammonia derivatives. Application of the Chichibabin pyridine synthesis suffer from low yields, often about 30%, 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 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 °C. Typical catalysts are modified forms of alumina and silica. The reaction has been tailored to produce various methylpyridines. Dealkylation and decarboxylation of substituted pyridines Pyridine can be prepared by dealkylation of alkylated pyridines, which are obtained as byproducts in the syntheses of other pyridines. The oxidative dealkylation is carried out either using air over vanadium(V) oxide catalyst, by vapor-dealkylation on nickel-based catalyst, or hydrodealkylation with a silver- or platinum-based catalyst. Yields of pyridine up to be 93% can be achieved with the nickel-based catalyst. Pyridine can also be produced by the decarboxylation of nicotinic acid with copper chromite. Bönnemann cyclization The trimerization of a part of a nitrile molecule and two parts of acetylene into pyridine is called Bönnemann cyclization. This modification of the Reppe synthesis can be activated either by heat or by light. While the thermal activation requires high pressures and temperatures, the photoinduced cycloaddition proceeds at ambient conditions with CoCp2(cod) (Cp = cyclopentadienyl, cod = 1,5-cyclooctadiene) as