Cyclohexanone ammoxidation

Table 20.6 A summary of catalyst performance reported in [126] for cyclohexanone ammoxidation.

New materials are also finding application in the area of catalysis reiated to the Chemicals industry. For example, microporous [10] materials which have titanium incorporated into the framework structure (e.g. so-calied TS-1) show selective oxidation behaviour with aqueous hydrogen peroxide as oxidizing agent (Figure 5). Two processes based on these new catalytic materials have now been developed and commercialized by ENl. These include the selective oxidation of phenol to catechol and hydroquinone and the ammoxidation of cyclohexanone to e-caproiactam. 

Another recent patent (22) and related patent application (31) cover incorporation and use of many active metals into Si-TUD-1. Some active materials were incorporated simultaneously (e.g., NiW, NiMo, and Ga/Zn/Sn). The various catalysts have been used for many organic reactions [TUD-1 variants are shown in brackets] Alkylation of naphthalene with 1-hexadecene [Al-Si] Friedel-Crafts benzylation of benzene [Fe-Si, Ga-Si, Sn-Si and Ti-Si, see apphcation 2 above] oligomerization of 1-decene [Al-Si] selective oxidation of ethylbenzene to acetophenone [Cr-Si, Mo-Si] and selective oxidation of cyclohexanol to cyclohexanone [Mo-Si], A dehydrogenation process (32) has been described using an immobilized pincer catalyst on a TUD-1 substrate. Previously these catalysts were homogeneous, which often caused problems in separation and recycle. Several other reactions were described, including acylation, hydrogenation, and ammoxidation. 

In one of the most controversial papers published in this field [124], a catalyst made of an alumina-supported V/P/Sb/0 is reported to give very good performance in the ammoxidation of cyclohexanol and cyclohexanone to adiponitrile. 

The ammoxidation of cyclohexanol or cyclohexanone is also reported in one patent [126], using a cyclohexanone/air/ammonia/H20 ratio of 1/10/2.5/10 (the presence of added steam is noteworthy), 450 °C, and a contact time of 1 s. Several catalysts were used, as reported in Table 20.6. The products obtained were aniline, phenol and adiponitrile. 

The ammoxidation of cyclohexanone to cyclohexanone oxime is catalyzed by TS-1 with 98.2% selectivity to cyclohexanone oxime at 99.9 % conversion [177]. Selective oxidation of the nitrogen of ammonia by hydrogen peroxide is a key step of this reaction. The mechanism is still vividly debated and three possible routes are shown in Scheme 20. Recent evidence [163] seems to support a route via intermediate formation of hydroxylamine [mechanism B]. The high selectivity on the other hand supports the postulate that the reaction proceeds via a concerted reaction step that involves the titanium peroxo species, ammonia and cyclohexanone (mechanism C) [177],... 

Scheme 20. Possible oxidation mechanisms for the ammoxidation of cyclohexanone to cyclohexanone oxime.

NHPI has been introduced as an effective system for C—H activation by hydrogen abstraction on several different substrates [30i,j,s,31a-e]. In 2001, Daicel commercialized the process used to synthesize dihydroxyadamantane, and has carried out pilot trials not only for the oxidation of cyclohexane but also for the oxidation of p-xylene to terephthalic acid. In the latter case, the advantage lies in being able to avoid using special anticorrosive metals currently required in the production of terephthalic acid because of the use of bromine. NHPI can also be used as a catalyst for the in situ production of hydroperoxides, reactants for epoxidation and for the oxidation and ammoxidation of cyclohexanone to caprolactone and caprolactam, respectively. 

The porous titanium silicate TS-1 represents one of the great commercial successes of recent years. Despite only being reported for the first time in the last decade, it is already established as an oxidation catalyst in the manufacture of hydroquinone, and processes based on its use as a catalyst in the epoxidation of propene and the ammoxidation of cyclohexanone are near the production stage.14 The use of the increasingly diverse range of molecular sieve solid catalysts is also described in Chapter 2. 

Ammoxidation of cyclic ketones over titanium silicates TS-1 has been performed.38 The reactivity of the cyclohexanones and methylcylcohexanones over TS-1 followed the order cyclohexanone > 2-methylcyclohexanone = 3-methyl-cyclohexanone > 2,6-dimethylcyclohexanone, reflecting the difference in the... 

The ammoxidation process developed by Tao Gosei Chern. Ind. Co. [116], entailing the direct reaction of cyclohexanone, ammonia, and hydrogen peroxide in a liquid phase in the presence of a tungstic add catalyst ... 

An alternative route to cyclohexanone oxime developed in Italy by Enichem is shown in the following reaction. Cyclohexanone oxime is produced by the ammoxidation of cyclohexanone with ammonia and aqueous hydrogen peroxide in the presence of a solid, recyclable catalyst, titanium silicalite (TS-1). This reaction step eliminates approximately one-third of total salt formation. However, the oxime is still converted to caprolactam through the conventional route (Beckmann rearrangement), catalyzed by stoichiometric amounts of sulfuric acid, and produces ammonium sulfate salt. Therefore, this alternative process still leaves something to be desired. 

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