Editing Aldehyde (section)

===Oxidative routes===
The largest operations involve [[methanol]] and [[ethanol]] respectively to [[formaldehyde]] and [[acetaldehyde]], which are produced on multimillion ton scale annually. Other large scale aldehydes are produced by [[autoxidation]] of hydrocarbons: [[benzaldehyde]] from [[toluene]], [[acrolein]] from [[propylene]], and [[methacrolein]] from [[isobutene]].<ref name=Ullmann>{{cite book |doi=10.1002/14356007.a18_261.pub2 |chapter=Oxidation |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2015 |last1=Teles |first1=J. Henrique |last2=Hermans |first2=Ive |last3=Franz |first3=Gerhard |last4=Sheldon |first4=Roger A. |pages=1–103 |isbn=978-3-527-30385-4 }}</ref><ref name=CH2O/> In the [[Wacker process]], oxidation of ethylene to acetaldehyde in the presence of copper and palladium catalysts, is also used.  "[[Green chemistry|Green]]" and cheap oxygen (or air) is the oxidant of choice.

Laboratories may instead apply a wide variety of specialized [[oxidizing agent]]s, which are often consumed stoichiometrically. [[Oxidation with chromium(VI) complexes|chromium(VI) reagents are popular]]. Oxidation can be achieved by heating the alcohol with an acidified solution of [[potassium dichromate]]. In this case, excess [[dichromate]] will further oxidize the aldehyde to a [[carboxylic acid]], so either the aldehyde is [[distillation|distilled]] out as it forms (if [[Vapor pressure|volatile]]) or milder reagents such as [[pyridinium chlorochromate|PCC]] are used.<ref>{{OrgSynth | author = Ratcliffe, R. W. | title = Oxidation with the Chromium Trioxide-Pyridine Complex Prepared in situ: 1-Decanal | collvol = 6 | collvolpages = 373 | year = 1988 | prep = cv6p0373}}</ref>

A variety of reagent systems achieve aldehydes under chromium-free conditions.  One such are the [[hypervalent organoiodine compounds]] (i.e., [[2-Iodoxybenzoic acid|IBX acid]], [[Dess–Martin periodinane]]), although these often [[Carbonyl oxidation with hypervalent iodine reagents|also oxidize the α position]].   A [[Lux-Flood acid]] will activate other pre-oxidized substrates: [[Sulfonium-based oxidation of alcohols to aldehydes|various sulfoxides]] (e.g. the [[Swern oxidation]]), or amine oxides (e.g., the [[Ganem oxidation]]).  Sterically-hindered [[nitroxyl]]s (i.e., [[TEMPO]]) can [[Oxoammonium-catalyzed oxidation|catalyze aldehyde formation with a cheaper oxidant]].

Alternatively, [[vicinal diol]]s or their [[Organic redox reaction|oxidized sequelae]] ([[acyloin]]s or [[Alpha hydroxy acid|α-hydroxy acids]]) can be oxidized with [[Bond cleavage|cleavage]] to two aldehydes or an aldehyde and [[carbon dioxide]].<ref>{{cite journal|last1=Ōeda|first1=Haruomi|title=Oxidation of some α-hydroxy-acids with lead tetraacetate|journal=Bulletin of the Chemical Society of Japan|date=1934|volume=9|issue=1|pages=8–14|doi=10.1246/bcsj.9.8|doi-access=free}}</ref><ref>{{cite journal|last1=Nwaukwa|first1=Stephen|last2=Keehn|first2=Philip|title=Oxidative cleavage of α-diols, α-diones, α-hydroxy-ketones and α-hydroxy- and α-keto acids with calcium hypochlorite [Ca(OCl)2]|journal=Tetrahedron Letters|date=1982|volume=23|issue=31|pages=3135–3138|doi=10.1016/S0040-4039(00)88578-0}}</ref>