Rearrangements using zeolites

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>. 

Over the past twenty five years, considerable efforts have been made to catalyze the Beckmann rearrangement using zeolites [22]. The experiments... 

Fries rearrangement, 18 336, 337 isomerization and transalkylation of alky-laromatics, 18 329 epoxide transformations, 18 351-352 hydration and ammonolysis of ethylene oxide, 18 351, 352 isomerization, 18 351 framework composition, 33 226-228 hydrogenation, dehydrogenation, and related reactions, 18 360-365 dehydrocyclization of s-ethylphenyl using zeolites and carbonyl sulfide, 18 364, 365... 

Scheme 16 Enantioselective oxa-di-Tr-methane rearrangement using the ionic chiral auxiliary and chirally modified zeolite method.

The industrially significant 2,4-dihydroxybenzophenone can be prepared in 88% yield by the Fries rearrangement of the resorcinol benzoate formed in situ by the reaction of benzoic acid and resorcinol using zeolite-H-beta catalyst (equation 71). A variety of solvents such as butylbenzene and n-decane are used successfully for these reactions. ... 

Part of the rearranged Cu species is then completely blocked as nitrite-nitrate species. These species exhibit no catalytic activity. TG curves may be fitted using equations of type (II) The values of km associated to this step account to the deactivation of the catalysts Small rates in NO accumulation correspond actually to a low deactivation of these catalysts. The deactivation of the catalysts was found to be influenced on the metal loading, the copper precursor salt and the Si/AI ratio in the used zeolite. The presence of a second species like Ce or Sm in a small loading prevents the deactivation. 

Chung et al reported the liquid phase Beckmann rearrangement of 4-hydroxyacetophenone oxime using zeolite H p catalyst. The reaction was found to be an example of active solvent participation. A solvent having higher dielectric constant or more polar nature is preferred in the rearrangement step. 

The Beckmann rearrangement of acetophenone oxime using zeolites as catalysts has been investigated by means of N and C solid-state NMR spectroscopy in combination with theoretical calculations. ... 

Zeolites and clays have been used as effective acid microporous catalysts in certain organic rearrangements useful for the S5mthesis of fine chemicals. For instance, the Claisen rearrangement of allyl aryl ethers 10 followed by intramolecular hydroxyalkylation of the resulting olefin afforded 2-methyldihydrobenzofuran (11) (Scheme 6) [55]. 

Regeneration of high silica zeolite used for Beckmann rearrangement... 

Acid-catalysed rearrangement of epoxides is another widely used reaction in the fine chemicals industry. Here again the use of solid acid catalysts such as zeolites is proving advantageous. Two examples are shown in Fig. 2.25 the isomerization of rsophorone oxide (Elings et al., 1997) and the conversion of a-pinene oxide to campholenic aldehyde (Holderich et al., 1997 Kunkeler etal., 1998). Both products are fragrance intermediates. 

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... 

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

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