Editing Acetaldehyde (section)

==Production==
In 2013, global production was about 438 thousand tons.<ref>{{cite news |last1=WMStrategy |title=The Global Acetaldehyde Market Projected to Drop to 406 Thousand Tons by 2023 |url=https://www.wm-strategy.com/news/the-global-production-of-acetaldehyde-is-expected-to-stabilize-in-the-upcoming-years |access-date=20 October 2024 |publisher=Williams & Marshall Strategy |date=May 20, 2019 |language=English |quote=The global acetaldehyde market was equal to 438 thousand tons in 2013.}}</ref> Before 1962, [[ethanol]] and [[acetylene]] were the major sources of acetaldehyde. Since then, ethylene is the dominant [[raw material|feedstock]].<ref name=Ull/>

The main method of production is the oxidation of [[ethene]] by the [[Wacker process]], which involves oxidation of ethene using a [[homogeneous catalysis|homogeneous]] palladium/copper catalyst system:

:{{chem2|2 CH2\dCH2 + O2 -> 2 CH3CH\dO}}

In the 1970s, the world capacity of the Wacker-Hoechst direct oxidation process exceeded 2 million tonnes annually.

Smaller quantities can be prepared by the partial [[oxidation]] of ethanol in an exothermic reaction.  This process typically is conducted over a silver catalyst at about {{convert|500–650|C|F}}.<ref name=Ull/>
: {{chem2|2 CH3CH2OH + O2 -> 2 CH3CH\dO + 2 H2O}}
This method is one of the oldest routes for the industrial preparation of acetaldehyde.

===Other methods===
====Hydration of acetylene====
Prior to the [[Wacker process]] and the availability of cheap ethylene, acetaldehyde was produced by the [[hydration reaction|hydration]] of [[acetylene]].<ref name="Dmitry2007">{{Cite journal| title = Hydration of Acetylene: A 125th Anniversary |author1=Dmitry A. Ponomarev |author2=Sergey M. Shevchenko | journal = [[J. Chem. Educ.]] | volume = 84 | issue = 10 | year = 2007 | pages = 1725 | url = http://jchemed.chem.wisc.edu/HS/Journal/Issues/2007/OctACS/ACSSub/p1725.pdf | doi = 10.1021/ed084p1725| bibcode = 2007JChEd..84.1725P }}</ref> This reaction is catalyzed by [[mercury (element)|mercury(II)]] salts:
:{{chem2|C2H2 + Hg^{2+} + H2O -> CH3CH\dO + Hg}}
The mechanism involves the intermediacy of [[vinyl alcohol]], which [[tautomer]]izes to acetaldehyde. The reaction is conducted at {{convert|90–95|C|F}}, and the acetaldehyde formed is separated from water and mercury and cooled to {{convert|25–30|C|F}}. In the [[wet oxidation]] process, [[iron(III) sulfate]] is used to reoxidize the mercury back to the mercury(II) salt. The resulting [[iron(II) sulfate]] is oxidized in a separate reactor with [[nitric acid]].<ref name=Ull/>

The enzyme [[Acetylene hydratase]] discovered in the strictly  anaerobic bacterium ''[[Pelobacter acetylenicus]]'' can catalyze an analogous reaction without involving any compounds of mercury.<ref>{{cite journal | url=https://link.springer.com/article/10.1007/s00775-015-1330-y | doi=10.1007/s00775-015-1330-y | title=Acetylene hydratase: A non-redox enzyme with tungsten and iron–sulfur centers at the active site | date=2016 | last1=Kroneck | first1=Peter M. H. | journal=Journal of Biological Inorganic Chemistry | volume=21 | issue=1 | pages=29–38 | pmid=26790879 | s2cid=17179063 }}</ref> However, it has thus far not been brought to any large-scale or commercial use.

====Dehydrogenation of ethanol====
Traditionally, acetaldehyde was produced by the partial [[dehydrogenation]] of ethanol:
: {{chem2|CH3CH2OH -> CH3CH\dO  +  H2}}
In this endothermic process, ethanol vapor is passed at 260–290&nbsp;°C over a copper-based catalyst. The process was once attractive because of the value of the hydrogen coproduct,<ref name=Ull>Eckert, Marc ''et al.'' (2007) "Acetaldehyde" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim {{doi|10.1002/14356007.a01_031.pub2}}</ref> but in modern times is not economically viable.

====Hydroformylation of methanol====
The [[hydroformylation]] of [[methanol]] with catalysts like cobalt, nickel, or iron salts also produces acetaldehyde, although this process is of no industrial importance.  Similarly noncompetitive, acetaldehyde arises from [[synthesis gas]] with modest selectivity.<ref name=Ull/>