Caprolactam via ammoximation

Another pertinent example is provided by the manufacture of caprolactam [135]. Current processes are based on toluene or benzene as feedstock, which can be converted to cyclohexanone via cyclohexane or phenol. More recently, Asahi Chemical [136] developed a new process via ruthenium-catalysed selective hydrogenation to cyclohexene, followed by zeolite-catalysed hydration to cyclo-hexanol and dehydrogenation (Fig. 1.49). The cyclohexanone is then converted to caprolactam via ammoximation with NH3/H202 and zeolite-catalysed Beckmann rearrangement as developed by Sumitomo (see earlier). 

The TS-l 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 above mentioned ammoximation of cyclohexanone to cyclohexanone oxime66, 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 (figure 4). 

The ammoximation of cyclohexanone to cyclohexanone oxime (Scheme 9.1) is an important industrial process, because the oxime is an intermediate for the formation of s-caprolactam, the monomer for nylon-6, that is currently manufactured on a scale of 4 Mton p.a. TS-1 catalyses the ammoximation of ketones, including cyclohexanone, in liquid phase in the presence of ammonia and hydrogen peroxide. The reaction proceeds through hydroxylamine as an intermediate, which is generated at the active site via complexes of framework titanium with ammonia and hydroperoxide. The hydroxylamine then reacts with cyclohexanone molecules that are weakly adsorbed within the pores or can diffuse out into solution. The reaction is a general one, and can be apphed to the ammoximation of a wide range of ketones. 

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