Oximes, acid catalyzed rearrangement

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

Caprolactam is discussed more completely in Chapter 11, Section 5. It is made from cyclohexane by oxidation to cyclohexanone-cyclohexanol mixture, formation of cyclohexanone oxime, and acid-catalyzed rearrangement. 

Caprolactam. Essentially all caprolactam is used in the manufacture of nylon 6 fibers. In 1998, global demand reached nearly 7.3 billion lb with 1.7 billion lb used in North America. This is a fast-growing nylon with applications in carpets, textiles, and tires. Caprolactam can be produced from cyclohexane, phenol, and toluene via cyclohexanone. It is then reacted with hydroxylamine to give an oxime. The oxime undergoes an acid-catalyzed rearrangement to give caprolactam. 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

The acid-catalyzed rearrangement of an oxime 2 to an amide 3 is named after... 

A variety of different routes to cyclobutane systems involving non-photochemical means has also been devised. Acid catalyzed rearrangement of fused cyclopropyl ether (61) by Wenkert et al. (97, 98) afforded the bicyclic dione (62), which through a thioketal-desulfurization process and treatment with hydroxylamine yielded oxime (58) (Scheme 12). The shortest synthesis of grandisol is that reported by Billups et al. (Scheme 13) (99). Dimerization of isoprene in the presence of a zero-valent bis-cyclooctadienyl-nickel-phosphite complex gave the cis-cyclobutane diolefin (65), which could be separated in 12—15% yield from the complex product mixture by low-temperature distillation. Selective hydroboration and oxidation afforded grandisol. 

The transformation of oximes to lactams (the Beckmann rearrangement) was one of the earliest such acid-catalyzed reactions to be reported with TS-1 (138) and TS-2 (247) catalysts. The rearrangement of cyclohexanone oxime to e-caprolactam proceeds with high selectivity in the presence of TS-1, with high catalyst stability (138,247). 

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... 

One potential approach for the preparation of benzofuran derivatives involves the acid-catalyzed cyclization of O-aryl oximes 1193. 39 (equation 36). The transformation is analogous to well-known Fisher indole synthesis. The reaction proceeds through a [3,3]-sigmatropic rearrangement of enehydroxylamine 120 to compound 121 followed... 

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... 

Thermal hetero Cope [3,3] - rearrangement of O-arylated oximes (Sheradsky) or acid catalyzed anionic hetero [3,3] and [3,5] - rearrangement of hydroxylamines with N-O bond cleavage.(see 1st edition). 

Most experimental studies have supported the nondissociative mechanism (a) for this reaction,but one study reported the following results the polyphos-phoric acid (PPA)-catalyzed Beckmann rearrangement of pinacolone oxime produced N-f-butylacetamide, while the PPA-catalyzed rearrangement of 2-methyl-2-phenylpropiophenone oxime produced N-benzoyl-a, -dimethyl-benzylamine and benzamide. Carrying out the rearrangement on a mixture of pinacolone oxime and 2-methyl-2-phenylpropiophenone oxime produced the products expected from each reactant, plus Af-f-butylbenzamide and N-acetyl-a,a-dimethylbenzylamine. 

The photo-Beckmann reaction provides the regioisomeric amide compared to the amide t5 ically obtained from the traditional acid-catalyzed Beckmann rearrangement in which the carbon bond anti to the hydroxyl group of the oxime migrates. Instead, the photo-Beckmann... 

The acid-catalyzed Beckmann rearrangement of oximes to amides (see Chapter 11) has two possible rate-determining steps, the first one in each path shown below. Explain how you would use a Hammett plot analysis to distinguish these possibilities. It may be helpful to know that the R group trans to the departing water is the only one that migrates. 

Hydrolysis methods for mono[ C]nitriles and the spectrum of chemical transformations of the resulting [l- C]carboxylic acids differ little from those for their unlabeled counterparts, so that the synthesis of [l- C]tetralones 42 and [l- " C]indanones 46 from w-arylalkyl [ C]nitriles will suffice as examples (Figure 7.11). Acid-catalyzed hydrolysis of 4-phenylbutyro[ C]nitrile followed by polyphosphoric acid-mediated cyclization of the resulting phenyl[l- C]butanoic acid converted it into 42 in 89% radiochemical yield. Sequential bromination and oxime formation provided the a-bromooxime 43, which upon treatment with polyphosphoric acid underwent a Beckman rearrangement to provide the ring-expanded tetrahydro-2H-l-[2- C]benzazepine-2-one derivative 44- This was a key intermediate for the preparation of a series of labeled ACE inhibitors" . The acid-catalyzed cyclization of a mixture of 3-(2-hydroxyphenyl[l- " C]propionic acid and its ethyl ester, prepared by treatment of the propio[ " C]nitrile with ethanolic HCI proved to be a two-step sequence. In the first step, 2- [2- " C ]chromanone I4SI was formed and had to be submitted to... 

For nylon 6, caprolactam is made from the oxime by acid-catalyzed Beckman rearrangement. As shown by reaction 8.4.2, heating caprolactam under nitrogen breaks the carbon-nitrogen bond and gives the polymer. 

Base-catalyzed ring-expansion of benzisoxazolones (217) provides a general route to 2,2-dialkyldihydro-l,3-benzoxazin-4-ones (218) (78CPB549) and the 2,4-dione (220) can be prepared by a Beckmann rearrangement of the oxime (219) (02CB3647). 2-Thion-4-ones (222) are formed from salicylic acids (221) by treatment with triphenylphosphine diisothiocyanate in dichloromethane at -40 °C (78CI(L)806). 

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