Zeolite oxime

Benzoxazoles are produced in high yield from a-acylphenol oximes by a Beckmann rearrangement using zeolite catalysts <95SC3315>. The reaction of the o-benzoquinone 40 with aromatic aldehyde oximes produces the benzoxazoles 41 <95ZOR1060>. The fused oxazolium salts 43 (R = Me, Et, Pr , or Ph R2 = Me or Pr ) are formed from tropone and nitrilium hexachloroantimonates 42 <96JPR598>. 

Sticking with nylon production, high-silica pentasil zeolites are used by Sumitomo to overcome environmental issues associated with the conversion of cyclohexanone oxime to caprolactam (Chapter 1, Scheme 1.4). 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Beckmann rearrangement of oxime is an acid catalysed reaction. The environmental problems associated with the use of sulphuric acid instigated interest to use number of solid acid catalysts [1], There are only scanty references about Lewis acid ion-exchanged MeAlPOs. Beyer et al. [2], Mihalyi et al. [3] and Mavrodinova et al. [4] already suggested the presence of Lewis acid metal ions as MO+ species in zeolites. The present study focussed the synthesis and characterisation of Fe3+, La3+ and Ce3+ ion-exchanged MAPO-36. The catalytic results of Beckmann rearrangement of cyclohexanone oxime over ion-exchanged catalysts are delineated in this article. 

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 initial adsorption of the oxime in zeolites was studied through a combination of solid-state NMR spectroscopy and theoretical calculations ". The calculated adsorption complexes formed over silanol groups and complexes over Brpnsted acid sites in zeolites are depicted. This study suggests that the A-protonated oxime is formed over Brpnsted acid centers, but not over weakly acidic silanol groups. It has been also suggested that weakly acidic or neutral silanol groups or silanol nests are active catalysts of the rearrangement reaction ... 

According to Limtrakul and colleagues the mechanism of the Beckmann rearrangement of the oxime molecule on the Br0nsted acid site of a zeolite proceeds according to the following steps outlined in equation 73. 

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 ". 

It has been described the reaction of cyclohexanone oxime with solids of different nature, as zeolites (refs. 4 and 5) and aluminum phosphates (ref. 6), giving rise to the Beckmann rearrangement product, E-caprolactame when the reactions are carried out in the gas phase at relatively high temperatures (>300°C). 

Ramamurthy et al. have examined enantioselective and diastereoselective ODPM rearrangements of cyclohexadienone and naphthalenone derivatives within MY zeolites, where M is an alkali ion [38, 39]. For example, in Scheme 4.27, in NaY in the presence of several chiral inductors such as ephedrine, pseudoephedrine, and camphorquinone-3-oxime, an enantioselective ODPM rearrangement of 65 and 66 took place to afford 68 in 30% ee yield. In the frame of the chiral auxiliary approach, the compound 67 linked to (S)-ephedrine was irradiated within NaY to give 68 in moderate diastereoselective excess (de) (59%). Interestingly, the reaction media of KY, RbY, and CsY reverse the diastereoselectivities. The cation-dependent diastereo-meric switch has been discussed with respect to the N- or O-functional group in 67 [39]. Recently, Arumugan reported that the irradiation of naphthalenones 65 linked chiral auxiliaries (R3 = COO(—)-Ment or (S)-NHCH(Me)Ph) in Li+ or Na + Nafion resulted in chiral products ( 14% de) [40],... 

The rearrangement of cyclohexanone oxime to caprolactam is still an important step in nylon production, and the heterogeneously catalyzed Beckmann rearrangement has been extremely well investigated (4, 16-19). In order to obtain catalysts that couple a high lactam selectivity to long lifespan, careful tuning of the zeolite properties is required. Some important factors are ... 

Strong acid zeolites with 12-MR pores do not seem suitable candidates for the Beckmann rearrangement therefore. However, provided a diluting alcohol such as 1-hexanol is fed together with cyclohexanone oxime, long catalyst lifetimes and high selectivities can be observed, even for H-Beta and H-USY. Clearly, the 1-... 

As already discussed in Chapter 1, the commercialization, by Sumitomo [GO-64], of a vapor phase Beckmann rearrangement of cyclohexanone oxime to caprolactam over a high-silica MFI (ZSM-5 type) zeolite (Fig. 2.21) is another benchmark in zeolite catalysis. The process, which currently operates on a 90000 tpa scale, replaces a conventional one employing stoichiometric quantities of sulfuric acid and producing ca. 2 kg of ammonium sulfate per kg of caprolactam. 

Similarly, for the vapor phase Beckman rearrangement of, e.g., cyclohexanone oxime into caprolactam (Scheme 12) the zeolite structure was initially thought to be the most decisive factor for selectivity. Small pore zeolite HA (pore size 4A) produced caprolactam with only... 

Most of the catalytic activity of zeolites has been concerned with their ability to act as shape selective solid acids. The vapor phase Beckmann rearrangement of cyclohexanone oxime over HY zeolite at 300°C gave caprolactam in 80% selectivity at 82% conversion (Eqn. 10.22). 5... 

A second approach to isolating redox metal ions in stable inorganic matrices, thereby creating oxidation catalysts with interesting activities and selectivities, is to incorporate them in a zeolite lattice framework. The first example of such a redox zeolite was the synthetic titanium(IV) zeolite, titanium siliealite (TS-1), developed by Enichem [30-32]. TS-1 was shown to catalyze a variety of synthetically useful oxidations with 30% H202, such as olefin epoxidation, oxidation of primary alcohols to aldehydes, aromatic hydroxylation, and ammoxi-mation of cyclohexanone to cyclohexanone oxime (see Fig. 9). 

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