Synthesis of Caprolactam

Not only strong acid sites but also relatively weak acid sites could be utilized in the development of improved industrial processes. One of the most significative examples is the new Sumitomo process for caprolactam manufacture, which combines a first step of ammoximation (originally developed by the Eni group [241-243]) with a second step of Beckmann rearrangement based on the use of silicalite-1 (Eigure 2.32). 

The first step operates in the liquid phase with ammonia and H2O2 as the reactants and titanium-silicalite (TS-1) as the catalyst. TS-1 is a zeolite, developed by Eni, having a structure that belongs to the same MEI family as ZSM-5, but in which A1 is absent (acid sites are detrimental for selectivity) and substituted by tetravalent Ti ions, which can activate H2O2 and give selective reactions of oxidation (Eigure 2.33 see also Chapter 6 on propene oxide for further aspects). 

Silicalite-1 is a high Si zeolite with an MEI structure and in which the weak Bronsted acid sites derive from the presence of defects [244, 245]. The active sites of the catalyst are silanol nests (very weak acidity) located close to the pore mouth of 

working initially with DuPont and then later with Shell, have developed a process using butadiene and carbon monoxide feedstocks to make caprolactam without ammonium sulfate production in the mid-1990s. Called Altam, the process employs four steps - carbonylation, hydroformylation, reductive amination and cyclization. DSM claims cost reductions of 25-30%, simplified plant operations and lower energy consumption, but the process never reached commercial scale. 

To complete the analysis of caprolactam process, it should be also considered how the cyclohexanone is produced, starting from the raw material, which is benzene. 

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The discovery of the new titanium silicates and of their catalytic properties in H2O2 oxidation reactions has had a major impact in catalytic science and its industrial applications. One 10,000 ton/year plant for the production of catechol and hydroquinone has been operating since 1986 with excellent results. Moreover, successful tests conducted on a 12,000-ton/year pilot plant for cyclohexanone ammoximation (Notari, 1993b) could be followed soon by an industrial-size plant that would greatly simplify the synthesis of caprolactam. Both these examples are clear indications of the potentials of the new oxidation chemistry made possible by the new materials. 

Fig. 14.42. Industrial synthesis of caprolactam via the Beckmann rearrangement of cyclohexanone oxime.

Benzoic Acid. Benzoic acid can be produced by the LPO of toluene using a catalyst such as cobalt or manganese. Domestic production of benzoic acid was about 130 million lb in 2000. Of this amount, about one half went to make phenol or phenolic derivatives. Other uses are in the synthesis of caprolactam and terephthalic acid, and as food additive, and as a plasticizer and resin intermediate. 

What are the names and/or type of rearrangements shown in Fig. 8.1, and synthesis of caprolactam ... 

Although NH2OH can act as an oxidizing agent, it is usually used as a reductant. Its main use is in synthesis of caprolactam and oxime derivatives, but it is also used as an 02 scavenger. 

Chromium substituted aluminophosphate-5 is an active and recyclable catalyst for the selective decomposition of cyclohexenyl hydroperoxide to 2-cyclohexen-l-one. The product is of potential industrial interest for the synthesis of caprolactam. 

Aliphatic and alicyclic molecules such as cyclohexane undergo photosub-stitution with nitrosyl chloride (Pape, 1%7). The reaction is of considerable industrial importance in the synthesis of -caprolactam, an intermediate in the manufacture of polyamides (nylon 6). (Cf. Fischer, 1978.) At long wavelengths a cage four-center transition state between alkane and an excited nitrosyl chloride molecule is involved, as indicated in Scheme 63. In contrast to light-induced halogenation, photonitrosation has a quantum yield smaller than unity, and is not a chain reaction. 

Since its discovery some 55 years ago, the synthesis of caprolactam has been the subject of intense research and development. Interest in alternative routes continues today and current activities receiving a lot of attention are carbon monoxide-based routes under development by DSM, EniChem and DuPont [32]. Numerous routes using a variety of feedstocks have been patented and many have been piloted, however, only seven have actually been commercialized. The first was the process developed by I. G. Farben based on Schlack s chemistry known today as the Rashig or conventional route. Other commercial routes are the CAPROPOL process, the BASF process, the DSM-HPO process, the Allied process, the Toray PNC process, and the SNIA Viscosa process. 

We are particularly interested in the Wacker oxidation of cyclohexene as the product, cyclohexanone, is a starting material in the synthesis of caprolactam, which is an intermediate in nylon production. Furthermore, we have strong interest in oxidation of acrolein in particular and acryhc compounds in general. Acrolein oxidation leads to a convenient route to 1,3-propanediol, while methyl acrylate oxidation leads to a starting material for adhesives. 

Figure 2.11 shows schematically the individual processes for the synthesis of caprolactam. The solid lines indicate processes that have been practiced commercially. As can be seen, all processes start from materials that belong to the group consisting of phenol, benzene, toluene, and cyclohexane. The chemistry of different processes has been reviewed [27,90,91]. Commercially, processes 1, 2, and 3 as shown in Figure 2.11 are important. The principal intermediates are cyclohexanone and cyclohexanone oxime for process 1, cyclohexanone oxime for process 2 [92-95], and cyclohexane carboxylic add for process 3. 

Among some more recent developments is a one-step synthesis of caprolactam from cyclohex-... 

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