Beckmann rearrangement process

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. 

Recently, the Sumitomo Chemical Co., Ltd. developed the vapour-phase Beckmann rearrangement process for the production of 8-caprolactam. In the process, cyclohexanone oxime is rearranged to e-caprolactam by using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. The Sumitomo Chemical Co., Ltd. commercialized the combined process of vapour-phase Beckmann rearrangement and ammoximation in 2003 ". 

Note also that the Toray company in Japan produces cyclohexanone oxime directly from cyclohexane by the PNC (photonitrozation of cyclohexanone oxime) process, where cyclohexane is reacted with nitrosyl chloride (NOCl) under UV irradiation. The HCl eliminated in the Beckmann rearrangement process is recovered and recycled into the NOCl production. Also, this process does not produce ammonium sulfate, but it is still too costly. 

Oxadiazoles and 1,2,4-oxadiazoles are heterocyclic aromatic compounds that appear in many bioactive molecules. Previous methods for the synthesis of 1,2,4-oxadiazoles include the coupling of amidoximes with carboxylic acid derivatives, aerobic C—H oxygenation of amidoximes, or a cyclization of nitrile oxides to nitriles. Telvekar and Takale developed the preparation of 1,2,4-oxadiazoles from substituted diketone derivatives through a Beckmann rearrangement process tScheme S.3S1. When treated with diphosphorus tetraiodide in dichloromethane at room temperature, dioximes 150 formed the Beckmann products, 1,2,4-oxadiazoles 151, in excellent yields. 

Ingredients. Nylon-6 is produced commercially from caprolactam [105-60-2] which is the most important lactam industrially. AH industrial production processes for caprolactam are multistep and produce ammonium sulfate [7783-20-2] or other by-products. Approximately 95% of the world s caprolactam is produced from cyclohexanone oxime [100-64-1] via the Beckmann rearrangement (144). The starting material for cyclohexanone can be... 

The oxime is converted to caprolactam by Beckmann rearrangement neutralization with ammonia gives ca 1.8 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. A no-sulfate, extraction process has been described, but incineration of the ammonium bisulfate recovers only sulfur values and it is not practiced commercially (14). 

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 ... 

The conversion of cyclohexanone to cyclohexanone oxime is brought about by the use of hydroxylamine sulphate. The sulphuric acid is neutralised with ammonia to ammonium sulphate and this is separated from the oxime. In the presence of oleum the oxime undergoes the process known as the Beckmann rearrangement to yield the crude caprolactam. After further neutralisation with ammonia the caprolactam and further ammonium sulphate are separated by solvent extraction (Figure 18.7). 

Of the other routes the photonitrosation process involving nitrosyl chloride is in use in Japan. This avoids, at the expense of complicated purification processes, the high yields of ammonium sulphate unavoidably produced in the route involving the Beckmann rearrangement. 

Schopf has also obtained direct evidence for the location of th carbon end of the ethanamine chain by submitting dihydrocodeinoneoximr to a Beckmann rearrangement. This process, the steps in which an illustrated by partial formal for ring III, should provide an aldehydt (XLVc) if the oxime is correctly represented by the Gulland and Robinsoi formula (XLVb) and a ketone (XLVIc) if it has the structure (XLVIb required by the Wieland and Kotake formula. 

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

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]. 

The focus of the next four chapters (Chapters 14-17) is mainly on the theoretical/computational aspects. Chapter 14 by T. S. Sorensen and E. C. F. Yang examines the involvement of p-hydrido cation intermediates in the context of the industrially important heptane to toluene dehydrocyclization process. Chapter 15 by P. M. Esteves et al. is devoted to theoretical studies of carbonium ions. Chapter 16 by G. L. Borosky and K. K. Laali presents a computational study on aza-PAH carbocations as models for the oxidized metabolites of Aza-PAHs. Chapter 17 by S. C. Ammal and H. Yamataka examines the borderline Beckmann rearrangement-fragmentation mechanism and explores the influence of carbocation stability on the reaction mechanism. 

In the field of fine chemical synthesis there is an urgent need to substitute the cleaner technologies for the old polluting ones. It is hoped that the large economic and environmental benefits brought by the recently developed catalysis processes—acetylation of anisole and of veratrole, Beckmann rearrangement, and so forth—will initiate great strides in this field. 

Several pathways may be possible for the Beckmann fragmentation reaction (equations 68 and 69). Stepwise processes may occur (equation 68), but stereospecific concerted fragmentations are also common (equation 69). Stepwise processes may follow different routes, but in most cases the fragmentation may have the same intermediate as the Beckmann rearrangement the nitrilium ion. 

The previous referred inconveniences have prompted an increasing interest in the development of alternative, essentially neutral and more environmental-friendly catalysts to promote the rearrangement of O-unsubstituted oximes. The development of highly efficient and selective transformations and also of processes for catalyst recovery and its reuse are the aim of some of the more recent studies. Much of this work is being done in industry to improve current production processes and is the subject of new patent applications. During the last two decades environment concerns have led to the development of green, simple and cost-effective catalytic systems for the Beckmann rearrangement. 

Fragmentation of the intermediate or concerted formation of nitriles from the activated oxime (Scheme 9, pathway 3) this is the Beckmann fragmentation. In some circumstances this pathway becomes dominant, particularly when there are quaternary carbons adjacent to the oxime. This transformation has found particular utility in ring-cleavage processes (sometimes called abnormal or second-order Beckmann rearrangements). 

Imidates, or even nitrogen compounds produced from imidates by the addition of nucleophiles, may be obtained from oximes by a Beckmann rearrangement-addition process. 

The same strategy had application in several other heterocyclic compounds, to obtain either amine or carboxylic acid derivatives. A process for the production of 4-amino-5-methylpyrazole derivative 325 using the Beckmann rearrangement as a key step was the subject of a new patent ° (equation 119). 

The Beckmann rearrangement was used as a key step (41% yield, under standard conditions) for the synthesis of the natural alkaloid Pumiliotoxin C 359, which was originally isolated from the skin extracts of Dendrobates pumilio (a strikingly coloured Panamanian poison arrow frog) (equation 139). ( )-Pumiliotoxin C was also synthesized by a similar ring formation process by Mehta and Praveen. ... 

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