Zeolite Lewis acid catalyst

Good yields and high diastereoselectivities were obtained by using zeolites in combination with Lewis-acid catalyst [21]. Table 4.7 illustrates some examples of Diels-Alder reactions of cyclopentadiene, cyclohexadiene and furan with methyl acrylate. Na-Y and Ce-Y zeolites gave excellent results for the cycloadditions of carbocyclic dienes, and combining these zeolites with anhydrous ZnBr2 further enhanced the endo diastereoselectivity of the reaction. An exception is the cycloaddition of furan that occurred considerably faster and with better yield, in comparison with the classic procedure [22], when performed in the presence of sole zeolites. 

Traditionally, the production of LABs has been practiced commercially using either Lewis acid catalysts, or liquid hydrofluoric acid (HF).2 The HF catalysis typically gives 2-phenylalkane selectivities of only 17-18%. More recently, UOP/CEPSA have announced the DetalR process for LAB production that is reported to employ a solid acid catalyst.3 Within the same time frame, a number of papers and patents have been published describing LAB synthesis using a range of solid acid (sterically constrained) catalysts, including acidic clays,4 sulfated oxides,5 plus a variety of acidic zeolite structures.6"9 Many of these solid acids provide improved 2-phenylalkane selectivities. 

Alumina, silica, clays, and zeolites are increasingly used as acidic or basic supports [26], Cycloaddition reactions often require Lewis-acid catalysts if good yields are to be obtained. Clay and doped silica gel catalysts have emerged as useful alternatives to the use of Lewis acids. Cycloaddition offuran (5) under solvent-free conditions, catalyzed by K10 montmorillonite, results in a decrease in the reaction time the endo-exo relationship is no different that obtained by use of classical heating (Scheme 9.2) [27]. 

Several other miscellaneous heterogeneously catalyzed reactions have been performed in the liquid phase. Hexane was successfully oxyfunctionalized with aqueous hydrogen peroxide by use of the zeolite TS-1 catalyst [50] and microwave-promoted acetalization of a number of aldehydes and ketones with ethylene glycol proceeded readily (2 min) in the presence both of heterogeneous (acidic alumina) and homogeneous (PTSA, Lewis acids) catalysts [51], Scheme 10.7. 

Catalytic conversions in the monoterpene field have been reviewed recently [13-15]. There is an ongoing transition from conventional homogeneous catalysts (mineral acids, zinc halides) to solid Bronsted and Lewis acid catalysts. Thus, limonene can be alkoxylated with lower alcohols using zeolite H-Beta as the catalyst [16] at room temperature already, with high selectivity and conversion (Scheme 5.3). The alkoxy compounds are applied as fragrances with, dependent on the length of R, characteristic odors. 

In the Takasago process ZnBr2 is used as the Lewis acid catalyst for the ring closure. Recently, zeolite Sn-Beta has been reported [20] as a heterogeneous and... 

Almost all ethylbenzene is produced commercially by alkylating benzene with ethylene, either in the liquid phase with aluminium chloride catalyst or in the vapour phase with a synthetic zeolite or Lewis acid catalyst (Coty et al., 1987 Cannella, 1998). 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

These results strongly pointed toward the involvement of the acidic hydroxyl groups in the catalytic reaction as suggested by Benesi (157), since the maximum activity was obtained when the zeolite was completely deammoniated. In addition, catalysts which had been dehydroxylated by high-temperature calcination demonstrated low activity. Thus, Benesi proposed that the Brtfnsted acid sites rather than the Lewis acids were the seat of activity for toluene disproportionation. This conclusion was supported by the enhancement in toluene disproportionation activity observed when the dehydroxylated (Lewis acid) Y zeolite was exposed to small quantities of water. As discussed previously, Ward s IR studies (156) indicated a substantial increase in Brdnsted acidity upon rehydration of dehydroxylated Y sieve. 

Lewis acid catalysts were discussed in the acrylic monomer section. They are used at about 10% concentration vs monomer. Although no significant research has been done with them, other than looking for new ones, they most likely work by activating the monomers. Type Y zeolites catalyze GTP at about 25% concentration vs initiator. Conversions are quantitative and... 

Recently, imidazole has been successfully applied as a catalyst for the acetylation of carbohydrates in acetonitrile [199]. A variety of other catalysts in combination with excess of acetic anhydride and solvent includes sodium acetate [200], sulfuric acid [201], perchloric acid [202], and a number of Lewis acid catalysts such as, iodine [203], Sc(OTf)3 [204], Cu(OTf)2 [205], C0CI2 [206], BiOCl-SOCl2 [207], LiC104 [208], FeCls [209], BiCls [210], and a series of heterogeneous catalysts such as, montmorillonite K-10 [211], zeolites [212], nafion-H [213], HC104-Si02 [214], or molecular sieves [215]. Recently, a ZnCl2-sodium acetate combina-... 

There are few but very interesting examples in the literature concerning the synthesis of large molecules with functional groups. Shape-selective halogenation of naphthalene is claimed to proceed over non-acidic zeolites, e.g. the selective monochlorination in the liquid phase with zeolite KL [48], usually carried out with typical Lewis acid catalysts, and the oxyiodination on zeolite KX to 2-iodo and 2,6-diiodonaphthalene [49]. 

Zeolites function as Bronsted or Lewis acid catalysts or (less frequently) as basic catalysts. Examples of the former are alkylation and isomerization of aromatics, such as the isomerization of xylenes an example of the latter is the use of cesium zeolite in the synthesis of the key intermediate, 4-methylthiazole, used in the preparation of the anthelmintic, thiabendazole. 

Following the successful application of zeolites in the major oil refining processes, zeolites entered the field of bulk chemicals synthesis, e.g. ethylbenzene, cumene and recently caprolactam. Their applications in the areas of fine chemicals arc also growing. An important factor is that zeolites, compared to conventional Brocnsted and Lewis acid catalysts, are low-waste catalysts and are regarded as green . After the early review on zeolite-catalyzed organic reactions by Venuto and Landis [ 1J the field has been reviewed several times [2-11],... 

Most of the industrial chlorinations of organic compounds are, at present, performed by free CI2 either in the absence of catalysts or in the presence of Lewis acid catalysts such as the halides of aluminium and iron. The major handicap of the Lewis acid catalysts like FeCb or AICI3, is the difficulty of their disposal, after use in the chlorination reaction, in an environmentally friendly manner. The use of zeolite catalysts in the chlorination processes will avoid corrosion and disposal problems. Work-up procedures to isolate and recover the desired product will also be easier leading to simpler and cleeiner process routes. In addition, if zeolites are used as solid catalysts, one may anticipate that desired changes in selectivity (enhanced para-selectivity in nuclear chlorination of aromatics, for example) may be achieved. Zeolite catalysts are well known to catalyze various synthetic transformations, however, relatively a few reports are available on the selective chlorination of aromatics using zeolite catalysts [1-4],... 

Chlorination of toluene, chlorobenzene, 1,2-dichlorobenzene and naphthalene with chlorine gas is eatalyzed by zeolite catalysts. There is a great potential and possibility for the use of zeolite catalysts in the nuclear chlorination of aromatics in the liquid phase instead of the Lewis acid catalysts like FeCla and AICI3 used at present. The use of zeolites in such cases leads to enhanced yield of the para-isomer thereby lowering the formation of byproducts and the cost of separation. 

Benzylnaphthalenes are used as synthetic intermediate for the production of dyes [1]. Traditionally, these reactions are carried out using Lewis acid catalysts (AICI3, ZnCh) which are less selective compared to the solid zeolite catalysts. In addition, homogeneous catalysts have several disadvantages difficulty in catalyst recovery and use of stoichiometric amount of the catalyst with respect to the benzylating agent. 

As is evident from the Table 2, zeolite H-beta is found to be the most active and selective catalyst in the conversion of benzylchloride and formation of 2-BN. The conversion of benzylchloride over H-beta, H-Y and AICI3 are found to be 32 2, 22.08 and 28.3 wt.% respectively. The corresponding product ratio of 2-BN/l-BN are 0.36, 0.28 and 0.28 respectively. These results show that the Lewis acid catalyst, AICI3 and H-Y do not possess shape-selectivity and naphthalene is attacked preferentially to yield higher amount of 1-BN because 1-position of naphthalene is more reactive than 2-position. Presumably, the higher activity of H-beta may be attributed to its stronger acid sites and stacking faults in the... 

A variety of solid Lewis and Br0nsted acids has been shown to catalyze Diels-Alder reactions. In several instances the results obtained with heterogeneous catalysts were better than those with homogeneous Lewis acid catalysts. Most of the reported reactions of interest in the synthesis of fine chemicals were catalyzed by (modified) zeolites, clays, alumina, or silica. Catalysts with interesting properties were obtained when support materials such as zeolites, alumina, or silica were treated with Lewis acids. These catalysts were moderately selective in diastereo-selective Diels-Alder reactions with chiral dienophiles and induced enantioselec-tivity (up to 31 % e. e.) in the reaction of cyclopentadiene with methacrolein after treatment with chiral derivatives. Excellent enantioselectivity in this reaction (up to 95 % e. e.) was observed with a polymer-supported chiral oxazaborolidinone. Because of their facile recovery and recycling, we expect that solid-acid catalysts will find increasing use in Diels-Alder reactions in the future. 

The CeY zeolite is utilized for the preparation of 4-methylcoumarin by the reaction of phenol with AAN. The formation of PA represents the first step the subsequent acylation at the ortho position, followed by an intramolecular aldol-like condensation, affords the final 4-methylcoumarin in 75% yield (Scheme 5.8). In the entire process, the cerium-catalyst shows a bifunctional character the active centers in the supercage of CeY zeolite, the Ce + ions, act as Lewis acid catalysts, whereas the acid centers H+, formed by the dissociation of water according to the equation Ce + + H2O [Ce(OH)]2+ + H+, act as Bronsted catalysts. 

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