Oxides, Beckmann rearrangement catalyst

Under solvent-free conditions, one-step Beckmann rearrangement of a variety of ketones and aldehydes proceeded in the presence of alumina sulfuric acid 285 (equation 93). Good selectivities were also obtained in the rearrangement of aldoximes to primary amides using zinc oxide as catalyst " (equation 93). 

There is, as is well known, a close similarity between the crystalline and porous structures of silicalite-1 and silicalite-2. The same similarity therefore exists between TS-1 and TS-2, and it appears logical that they should have very similar catalytic properties. TS-2 has been evaluated as a catalyst for many different reactions, such as Beckmann rearrangement of cyclohexanone oxime with vapor-phase reactants H202 oxidation of phenol, anisole, benzene, toluene, n-hexane, and cyclohexane and ammoximation of cyclohexanone. As described in detail in Section V.C.3, differences that had been claimed between the catalytic properties of TS-1 and those of TS-2 have not been substantiated. Later investigations have shown that, when all the relevant parameters are identical, the catalytic activities of TS-1 and TS-2 are also identical. The small differences in the crystalline structure between the two materials have no influence on their catalytic properties (Tuel et al., 1993a). 

In classical processes cyclohexanone is converted to the corresponding oxime by reaction with hydroxylamine (see Fig. 2.27). The oxime subsequently affords caprolactam via the Beckmann rearrangement with sulphuric or phosphoric acid. Alternatively, in a more recent development, not yet commercialized, a mixture of cyclohexanone, ammonia and hydrogen peroxide is directly converted to cyclohexanone oxime over a titanium(IV)-silicalite (TS-1) catalyst. This route is more direct than the classical route and reduces the amount of salt formation but it involves the use of a more expensive oxidant (H2O2 rather than O2). 

The TS-1 catalyzed hydroxylation of phenol to a 1 1 mixture of catechol and hydroquinone has already been commercialized by Enichem. Another reaction of considerable commercial importance is the ammoximation of cyclohexanone to cyclohexanone oxime, an intermediate in the manufacture of caprolactam. It could form an attractive alternative to the established process that involves a circuitous route via oxidation of ammonia to nitric acid followed by reduction of the latter to hydroxylamine (see Fig. 10). The ammoximation route employs a more expensive oxidant (H202) but is shorter and produces considerably less salt. However, we note that is does not provide a complete solution to the salt problem as substantial amounts are also produced in the subsequent Beckmann rearrangement of the oxime. The answer to this problem is probably also in the deployment of an efficient solid catalyst. 

E-Caprolactam is an important starting material for the production of nylon-6. It is synthesized by the Beckmann rearrangement reaction of cyclohexanone oxime catalyzed by a solid acid catalyst. Many solid acid catalysts, such as mixed boron oxide [1-3], Si02-Al203 [4,5], metal phosphates [6-8] and moclified zeolites [3,9-12], are reported to catalyze the cycdohexanone oxime rearrangement. The acid function of the catalyst is essential to effect the rearrangement reaction. 

Shouro, D., Moriya, Y, Nakajima, T., and Mishima, S. 2000. Mesoporous silica ESM-16 catalysts modified with various oxides for the vapor-phase Beckmann rearrangement of cyclohexanone oxime. App/. Catal. A.- Gen. 198 275-282. 

Mesoporous silica FSM-16 catalysts modified with various oxides were used in the vapor-phase Beckmann rearrangement of The selective formation of the lactam 6 was improved by using FSM-16 supported by AI2O3, ZnO and CdO. 

The first step consists of the air oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone as described in Section 9.2.2.1. The mixture is fractionated by distillation and the cyclohexanol is dehydrogenated to cyclohexanone over a catalyst such as copper. The combined cyclohexanone fractions are then treated with aqueous hydroxylamine sulphate at 20—95°C to form the oxime. The reaction mixture is neutralized with aqueous ammonia or sodium hydroxide and the crude oxime separated as an oily layer. This is stirred with concentrated sulphuric acid at 120 C and the oxime undergoes the Beckmann rearrangement to give caprolactam. In one process, the solution containing the lactam is continuously withdrawn from the reactor and rapidly cooled to below 75°C to minimize hydrolysis. The solution is then further cooled and neutralized with aqueous ammonia. Crude caprolactam separates as an oil and is purified by distillation under reduced pressure. 

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