Beckmann rearrangement 251569 222459491 2008-06-29T13:12:03Z DOI bot 6652755 Citation maintenance. Formatted: title. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. The '''Beckmann rearrangement''', named after the German chemist [[Ernst Otto Beckmann]] ([[1853]]–[[1923]]), is an [[acid catalysis|acid-catalyzed]] [[rearrangement reaction|rearrangement]] of an [[oxime]] to an [[amide]]. <ref>{{cite journal | author= E. Beckmann | title = Zur Kenntniss der Isonitrosoverbindungen | journal = [[Ber.]] | year = 1886 | volume = 19 | pages = 988–993 | doi = 10.1002/cber.188601901222 }}</ref><ref>{{cite journal | author=L. G. Donaruma, W. Z. Heldt | title=The Beckmann rearrangement. (Review) | journal=Org. React. | year=1960 | volume=11| pages=1–156 }}</ref><ref>{{cite journal | author=R. E. Gawley | title=The Beckmann reactions: rearrangement, elimination-additions, fragmentations, and rearrangement-cyclizations. (Review) | journal= Org. React. | year=1988 | volume=35| pages=14–24 }}</ref> Cyclic oximes yield [[lactam]]s. [[Image:BeckmannRearrangement3.svg|center|The Beckmann Rearrangement]] This example reaction<ref> {{cite journal | author=J. C. Eck, C. S. Marvel | title=Ε-Benzoylaminocaproic Acid | journal=Organic Syntheses, Coll. | year=1939 | volume=19| pages=20|url=http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0076}} {{cite journal | author=J. C. Eck, C. S. Marvel | title=Ε-Benzoylaminocaproic Acid | journal=Organic Syntheses, Coll. | year=1943 | volume=2| pages=76|url=http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0076}} </ref> starting with [[cyclohexanone]] and forming [[caprolactam]] is one of the most important applications of the Beckmann rearrangement, as caprolactam is the feedstock in the production of [[Nylon 6]]. The '''Beckmann solution''' consists of [[acetic acid]], [[hydrochloric acid]] and [[acetic anhydride]], and was widely used to catalyze the rearrangement. Other acids, such as [[sulfuric acid]] or [[polyphosphoric acid]], can also be used. [[sulfuric acid]] is the most commonly used acid for commercial lactam production due to its formation of an ammonium sulfate by-product when neutralized with [[ammonia]]. [[Ammonium sulfate]] is a common agricultural [[fertilizer]] providing nitrogen and sulfur. == Reaction mechanism == The [[reaction mechanism]] of the Beckmann rearrangement is generally believed to consist of an [[alkyl]] migration with expulsion of the hydroxyl group to form a [[nitrilium ion]] followed by [[hydrolysis]]: :[[image:Beckmann rearrangement mechanism.PNG|Beckmann rearrangement mechanism]] In one study, <ref>{{cite journal | author=S. Yamabe, N. Tsuchida, S. Yamazaki | title=Is the Beckmann Rearrangement a Concerted or Stepwise Reaction? A Computational Study | journal=[[J. Org. Chem.]] | year=2005 | volume=70| pages=10638–10644 |doi=10.1021/jo0508346 |url=http://pubs.acs.org/cgi-bin/abstract.cgi/joceah/2005/70/i26/abs/jo0508346.html}}</ref> the mechanism is established [[in silico]] taking into account the presence of [[solvent]] molecules and substituents. The rearrangement of acetone oxime in the Beckmann solution involves three acetic acid molecules and one proton (present as an [[oxonium ion]]). In the [[transition state]] leading to the iminium ion (σ - complex), the methyl group migrates to the nitrogen atom in a [[concerted reaction]] and the hydroxyl group is expulsed. The oxygen atom in the hydroxyl group is stabilized by the three acetic acid molecules. In the next step the electrophilic carbon atom in the nitrilium ion is attacked by water and the proton is donated back to acetic acid. In the transition state leading to the N-methyl acetimidic acid, the water oxygen atom is coordinated to 4 other atoms. In the third step, an isomerization step protonates the nitrogen atom leading to the [[amide]]. [[Image:Beckmann mechanism aliphatic.png|center|600px|The Beckmann rearrangement mechanism]] The same computation with a [[hydroxonium]] ion and 6 molecules of water has the same result but when the migrating substituent is phenyl in the reaction of acetophenone oxime with protonated acetic acid the mechanism favors the formation of an intermediate three-membered π - complex. This π - complex is again not found in the H<sub>3</sub>O<sup>+</sup>(H<sub>2</sub>O)<sub>6</sub>. [[Image:Acetophenone oxime mechanism.png|center|600px|beckmann rearrangement mechanism acetophenone oxime]] With the cyclohexanone-oxime, the relief of [[ring strain]] results in a third reaction mechanism leading directly to the protonated caprolactam in a single concerted step without the intermediate formation of a π - complex or σ - complex. == Cyanuric chloride assisted Beckmann reaction== The Beckmann reaction is known to be catalyzed by [[cyanuric chloride]] and [[zinc chloride]] co-catalyst. For example, cyclododecanone can be smoothly convered to the corresponding [[lactam]], a [[monomer]] for the production of [[nylon 12]].<ref>{{cite journal | author=Y. Furuya, K. Ishihara, H. Yamamoto | title=Cyanuric Chloride as a Mild and Active Beckmann Rearrangement Catalyst | journal= [[J. Am. Chem. Soc.]] | year=2005| volume=127| pages=11240–11241| url=[http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2005/127/i32/abs/ja053441x.html | doi=10.1021/ja053441x S0002-7863(05)03441-4 }}</ref> [[Image:Beckmann example.gif|center|Beckmann reaction]] The [[reaction mechanism]] for this reaction is based on a [[catalytic cycle]] with cyanuric chloride activating the [[hydroxyl]] group via a [[nucleophilic aromatic substitution]]. The reaction product is dislodged and replaced by new reactant via an intermediate [[Meisenheimer complex]]. [[Image:Beckmann mechanism.gif|center|Beckmann cyanuric acid catalytic cycle]] ==Beckmann fragmentation== When the oxime has a [[quaternary carbon atom]] in a anti position to the hydroxyl group a fragmentation occurs forming a [[nitrile]]: :[[Image:Beckmannfragmentation.svg|Beckmann fragmentation]] The fluorine donor in this fragmentation reaction is [[DAST]] <ref>''Fluorinative -cleavage of cyclic ketoximes with diethylaminosulfur trifluoride: an efficient synthesis of fluorinated carbonitriles'' Masayuki Kirihara, Kanako Niimi, Takefumi Momose, [[Chem. Commun.]] '''1997''', (6),599-600 {{DOI|10.1039/a607749h}} </ref>: :[[Image:BeckmannFragmentationKirihara1997.svg|Beckmann Fragmentation Kirihara 1997]] ==References== {{Reflist}} ==See also== Related reactions: * [[Curtius rearrangement]] * [[Dakin reaction]] * [[Schmidt reaction]] * [[Stieglitz rearrangement]] [[Category:Rearrangement reactions]] [[de:Beckmann-Umlagerung]] [[es:Transposición de Beckmann]] [[fr:Réarrangement de Beckmann]] [[ja:ベックマン転位]] [[pl:Przegrupowanie Beckmanna]] [[pt:Rearranjo de Beckmann]] [[zh:贝克曼重排]] [[Category:Name reactions]]