Amides Beckmann rearrangements

The purpose of the present work is to study comparatively the activity of different acidic solids as catalysts in other "classical" type of molecular rearrangement as it is the conversion of oximes to amides (Beckmann rearrangement, egn.l), by adopting "dry media ... 

The acid catalyzed conversion of oximes over different acidic solids in "dry media under soft conditions gives as major products the amide (Beckmann rearrangement) and the ketone (hydrolysis). The... 

PCI-, may act as a dehydrating agent upon certain organic compounds. It also rearranges o.ximes into amides (Beckmann rearrangement.)... 

When treated with certain reagents, the ketoximes in particular undergo the Beckmann rearrangement to isomeric acid amides (p. 227). 

By treatment of this oxime with phosphorus pentachloride or thionyl fhloride in ether solution, smooth conversion into benzanilide, m.p. 163°, results. The change of any oxime into a substituted amide under the conditions mentioned is usually termed the Beckmann rearrangement. The above example may be represented ... 

BECKMANN Rearrangement or fragmentation Acid catalyzed rearrangement of oximes to amides or cleavage of oximes to nitnies... 

Most aminothiophenes are prepared by the reduction of nitrothio-phenes. Aminothiophenes or their derivatives have also been obtained through the Hofmann rearrangement of the acid amides, which, however, fails with 2-thenamide, in contrast to the 3-isomer. The Beckmann rearrangement of the oxime of 2-acetylthiophene has been applied successfully to the preparation of 2-acetamidothiophene. The free aminothiophenes are very unstable compounds and it has not been possible to distil 3-aminothiophene. They are best stored as the stannic-chloride double salts and give stable acetyl derivatives. 

The Beckmann rearrangement of oximes of the thiophene series has been applied (besides the preparation of 2-acetamidothiophene ) to thiophenocycloalkenones (192) which gave the cyclic amide (193) hydrolyzable to the amine (194). The Beckmann rearrangement was... 

The rearrangement of oximes 1 under the influence of acidic reagents to yield A -substituted carboxylic amides 2, is called the Beckmann rearrangement. The reaction is usually applied to ketoximes aldoximes often are less reactive. 

With aldoximes (R = H) a migration of hydrogen is seldom found. The Beckmann rearrangement therefore does not give access to iV-unsubstituted amides. 

Another important reaction involving migration to electron-deficient nitrogen is the Beckmann rearrangement, in which oximes are converted to amides.282... 

A modification of this method, related to the Beckmann rearrangement, entails treatment of a ketoxime with one equivalent of CDI, then four to five equivalents of a reactive halide such as allyl bromide or methyl iodide (R3X) under reflux in acetonitrile for 0.5-1.5 h. Quatemization of the imidazole ring effectively promotes the reaction by increasing the electron-withdrawing effect. The target amides then are obtained by hydrolysis. High yields, neutral conditions, and a very simple procedure make this modification of the synthesis of amides by azolides a very useful alternative. 1243... 

The stereochemical use of the Beckmann rearrangement in assigning configuration to ketoximes has already been referred to, and it also has a large-scale application in the synthesis of the textile polymer Nylon-6 from cyclohexanone oxime (78) via the cyclic amide (lactam, 79) ... 

A 10-carbon oxime at 60°C was stored in an insulated container, and within 24 h the temperature had risen to 125°C, possibly owing to an exothermic Beckmann rearrangement to an amide. Application of cooling prevented a thermal runaway. 

The quest for a solvent-free deprotection procedure has led to the use of relatively benign reagent, ammonium persulfate on silica, for regeneration of carbonyl compounds (Scheme 6.10) [48]. Neat oximes are simply mixed with solid supported reagent and the contents are irradiated in a MW oven to regenerate free aldehydes or ketones in a process that is applicable to both, aldoximes and ketoximes. The critical role of surface needs to be emphasized since the same reagent supported on clay surface delivers predominantly the Beckmann rearrangement products, the amides [49]. 

Rearrangements Emmons found the reagent suitable for Beckmann rearrangements giving water soluble amides. Thus methyl cyclopropyl ketoxime in the medium of 1, 2-dimethoyethane was treated under reflux with stirring with trifluoroacetic anhydride in 1 hr. and refluxed for 1 hr. more. The cyclopropylamine was obtained. 

The Beckmann rearrangement of oximes to produce amides is promoted by perrhenate ions under phase-transfer catalytic conditions, in the presence of trifluoro-methanesulphonic acid in nitromethane [6]. Under these conditions, the rearrangement reaction is frequently accompanied by the solvolysis of the oxime to the ketone. This can be obviated by the addition of hydroxylamine hydrochloride. No reaction occurs in the absence of the ammonium catalyst or with the O-acetyl oximes. 

Beckmann rearrangement org chem An intramolecular change of a ketoxime into its isomeric amide when treated with phosphorus pentachloride. bek-man re-g ranj-mont ... 

Beckmann, E. Chem. Ber. 1886, 89, 988. Ernst Otto Beckmann (1853—1923) was bom in Solingen, Germany. He studied chemistry and pharmacy at Leipzig. In addition to the Beckmann rearrangement of oximes to amides, his name is associated with the Beckmann thermometer, used to measure freezing and hoihng point depressions. Mazur, R. H. J. Org. Chem. 1961,26, 1289. 

The common name caprolactam comes from the original name for the Ce carboxylic acid, caproic acid. Caprolactam is the cyclic amide (lactam) of 6-aminocaproic acid. Its manufacture is from cyclohexanone, made usually from cyclohexane (58%), but also available from phenol (42%). Some of the cyclohexanol in cyclohexanone/cyclohexanol mixtures can be converted to cyclohexanone by a ZnO catalyst at 400°C. Then the cyclohexanone is converted into the oxime with hydroxylamine. The oxime undergoes a very famous acid-catalyzed reaction called the Beckmann rearrangement to give caprolactam. Sulfuric acid at 100-120°C is common but phosphoric acid is also used, since after treatment with ammonia the by-product becomes... 

The rearrangement of ketoximes to amides was discovered more than a century ago, by Beckmann in 1886 , but remains a topic of current interest and stiU retains great synthetic utility. During the last century the Beckmann rearrangement has been frequently reviewedalthough the last major review was almost two decades ago. 

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