Beckmann rearrangements forming

Beckmann rearrangement of cvc7ohexanone oxime. M.p. 68-70 C, b.p. I39 C/12 mm. On healing it gives polyamides. Used in the manufacture of Nylon[6]. Cyclohexanone oxime is formed from cyclohexane and niirosyl chloride. U.S. production 1978 410 000 tonnes, capryl alcohol See 2-octanol. caiH Uc acid See oclanoic acid. 

Beckmann rearrangement of benzophenone oxime to benz-anilide. Dissolve 2 g. of benzophenone oxime in 20 ml. of anhydrous ether in a small conical flask and add 3 g. of powdered phosphorus pentachloride (or 3 ml. of pure tbionyl chloride). Distil off the solvent and other volatile products on a water bath CAUTION ether), add 25 ml. of water, boil for several minutes and break up any lumps which may be formed. Decant the supernatant liquid, and recrystallise, in the same vessel, from boiling alcohol. The product is benzanilide, m.p. 163° confirm this by a mixed m.p. determination with an authentic specimen. 

Toray. The photonitrosation of cyclohexane or PNC process results in the direct conversion of cyclohexane to cyclohexanone oxime hydrochloride by reaction with nitrosyl chloride in the presence of uv light (15) (see Photochemical technology). Beckmann rearrangement of the cyclohexanone oxime hydrochloride in oleum results in the evolution of HCl, which is recycled to form NOCl by reaction with nitrosylsulfuric acid. The latter is produced by conventional absorption of NO from ammonia oxidation in oleum. Neutralization of the rearrangement mass with ammonia yields 1.7 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. The novel chemistry is as follows ... 

Benzoxazoles are produced in high yield from a-acylphenol oximes by a Beckmann rearrangement using zeolite catalysts <95SC3315>. The reaction of the o-benzoquinone 40 with aromatic aldehyde oximes produces the benzoxazoles 41 <95ZOR1060>. The fused oxazolium salts 43 (R = Me, Et, Pr , or Ph R2 = Me or Pr ) are formed from tropone and nitrilium hexachloroantimonates 42 <96JPR598>. 

It explodes on heating or in contact with concentrated acids (the latter possibly involving Beckmann rearrangement and/or polymerisation of the oxime form, which is effectively a 1,3-diene). 

Ozonolysis of alkene 446 in the presence of acetaldehyde afforded diketone 448 through the intermediacy of 447. Ring expansion through Beckmann rearrangement took place when bis-oxime 449 was mesylated and warmed in aqueous tetrahydrofuran (THF). The bis-lactam so formed gave piperidinediol 450 on reduction with lithium aluminium hydride, and this compound was transformed into ( )-sparteine by treatment with triphenylphosphine, CCI4, and triethylamine (Scheme 105) <20050BC1557>. 

Solid-state photochemistry of (—)-2-chloro-2-nitrosocamphane 275 was studied145 by irradiation of the blue-crystal with red light to invert the configuration at C(2) (equation 123). This also causes a photochemically initiated Beckmann rearrangement to form chloroxime 276 to give nitroxide radical 278 (equation 124). The intermediate chloro oxime 276 is proposed to arise from the njr excitation and is believed to be the common intermediate for the photo-epimerization and Beckmann rearrangement. Extended... 

Several explosions or violent decompositions dining distillation of aldoximes may be attributable to presence of peroxides arising from autoxidation. The peroxides may form on the -C=NOH system (both aldehydes and hydroxylamines perox-idise [1]) or perhaps arise from unreacted aldehyde. Attention has been drawn to an explosion hazard inherent to ketoximes and many of their derivatives (and not limited to them). The hazard is attributed to inadvertent occurence of acidic conditions leading to highly exothermic Beckmann rearrangement reactions accompanied by potentially catastrophic gas evolution. Presence of acidic salts (iron(III)... 

The main intermediate of the rearrangement may be a nitrilium ion (225) in some cases or an imidate (226) in others. The resulting intermediate reacts with water to produce the amide (218) after tautomerization. If other nucleophiles (Nu ) are present, they can intercept the reactive intermediates (both inter- or intra-molecularly) and several different imino-substituted derivatives (227) can be formed. These rearrangement-addition reactions will be analysed later in this chapter as they can effectively broaden the scope of the Beckmann rearrangement reaction (Sections VI.D.2 and VI.E.2). 

Rare-earth exchanged [Ce ", La ", Sm"" and RE (RE = La/Ce/Pr/Nd)] Na-Y zeolites, K-10 montmorillonite clay and amorphous silica-alumina have also been employed as solid acid catalysts for the vapour-phase Beckmann rearrangement of salicylaldoxime 245 to benzoxazole 248 (equation 74) and of cinnamaldoxime to isoquinoline . Under appropriate reaction conditions on zeolites, salicyl aldoxime 245 undergoes E-Z isomerization followed by Beckmann rearrangement and leads to the formation of benzoxazole 248 as the major product. Fragmentation product 247 and primary amide 246 are formed as minor compounds. When catalysts with both Br0nsted and Lewis acidity were used, a correlation between the amount of Br0nsted acid sites and benzoxazole 248 yields was observed. 

The Beckmann rearrangement of ketoximes with triphenylphosphine and iV-chloro-succinimide occurs at room temperature almost instantaneously and their corresponding secondary amides are obtained in high yields (equation 83). The triphenylphosphine 271 is activated by the iV-chlorosuccinimide 270 affording the salt 272, which is attacked by the iV-hydroxy group of the oxime 217 forming the intermediate 273. 

The Beckmann rearrangement of cyclohexanone oxime catalysed by solid metaboric acid (286) has also been investigated (equation 94). When ketoximes, mixed with 286 (formed from boric acid at 100°C/0.1 Torr), are heated (140°C/7-42 h) the corresponding amides or lactams are produced in excellent yields (62-92%). Under the... 

When the nucleophile is already present as a part of the starting oxime (for example, a heteroatom or a C=C double bond), intramolecular trapping of the electrophilic intermediate is possible and a new cycle is formed. This transformation is usually referred to as a Beckmann Rearrangement-Cychzation reaction. Two modes of ring closure may be possible, depending on the oxime structure (equations 111 and 112) ... 

Novel a,/ -unsaturated amide derivatives at C(4) of chromones 335 were synthe-sized (equation 124). Oximes 332 and 333 rearranged in the presence of PCI5 into the same amides 335 in high yields. Spiroisoxazolines 334, formed from oxime 332 by acid treatment, also produce 335 under Beckmann rearrangement conditions. 

Pollini and colleagues converted D(—)-quinic acid in five steps into a chiral oxime 395, R = H in an enantiomeric pure form and subjected this oxime to a Beckmann rearrangement (equation 161). Even though the reaction lacked selectivity, 395 was useful in the synthesis of the chiral epoxide 396, a key intermediate in the synthesis of (—)-Balanol 397. The same authors also prepared the isomeric epoxide 398. 

Nine-membered lactam rings can also be produced by the Beckmann rearrangement. The azonane ring 420 was selectively formed from an eight-membered cyclic ketone 419 by a rearrangement/reduction sequence (equation 175). 

Krow and colleagues investigated the migratory preferences of the Schmidt and Beckmann rearrangements in norcamphors. Two isomeric lactams are usually formed in the Schmidt reaction but one lactam is obtained almost exclusively in a Beckmann reaction (equation 178). 

The electrophilic intermediate formed during the Beckmann rearrangement may be trapped by nucleophiles other than water. Strictly speaking, these reactions do not fit into the classical rearrangement reaction type. However, due to the fact that the carbon framework changes during the course of the reaction and to the similarities with the classical Beckmann rearrangement process, this topic will be analysed in the present chapter. 

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