Naphthalenes alkylation over zeolites

In agreement with this, the analysis of the products forming during the alkylation over MCM-22 samples at different reaction time showed that about 80-90 wt. % of the recovered material is adsorbed on the external surface (phenol, o-TBP and p-TBP), whereas only about 10-20 wt.% is formed inside the zeolite ( coke constituted by p-TBP, naphthalenes, 9,10-dihydro-phenanthrene and acenaphthylene). Coke molecules could be formed in both supercages and sinusoidal channels. However, in the large supercages they would be converted into bulkier compounds, which is not the case. Therefore they are most likely located in the sinusoidal channels. 

The alkylation of naphthalene and 2-methylnaphthalene with methanol and their ammoxidation were investigated by F r a e n k e 1 et al. [22-25] on zeolites ZSM-5, mordenite and Y. In the alkylation over HZSM-5 - unlike on H-mordenite or HY - the slim isomers, namely 2-methylnaphthalene as well as 2,6- and 2,7-dimethylnaphthalene, again clearly predominated. These authors suggest that such shape selective reactions of naphthalene derivatives occur at the external surface of zeolite ZSM-5, in so-called "half-cavities" [22, 24, 25]. D e r o u a n e et al. [26,27] went even further and generalized the concept of shape selectivity at the external surface. Based, in part, on Fraenkel s experimental results, Derouane [26] coined the term "nest effect". This whole concept, however, is by no means fully accepted and has recently been severely questioned in the light of results obtained in catalytic studies with a much broader assortment of ten-membered ring zeolites [28]. 

Finally, highly regioselective dialkylation of naphthalene has been achieved over zeolite HM using ter/-butanol as alkylating agent. By optimisation of the reaction parameters, 2,6-di-ter/-butylnaphthalene has been obtained in a yield of 60 % with a 2,6/2,7 ratio of over 50. This is the highest yield of a 2,6-dialkylnaphthalene and easily the highest 2,6/2,7 ratio yet reported from a direct dialkylation of naphthalene. 

The formation of di- and tri-alkyl aromatics and b henyls from their aromatic precursor is a consecutive reaction, in A hich first the mono-substituted aromatic conopound is formed which subsequently reacts to form the di-alkyl compund. This was observed in the shape selective ethylation of bphenyl [91] isopropjdation of naphthalene [92] over H-Mordenite and the isopropylation of napthalene over HY [63], Therefore, if a dialkyl-isomer is the desired product, the reaction conditions (reaction time/readence time, partial pressures and tenperature) have to be optimized to obtain the the maximum yield of this de ed product. With shape selective catalysts the formation of poly-substituted aromatic compounds can be suppressed because they are not able to diffuse out of the channels of the zeolites [63]. 

The physical properties of the two samples of H-ZSM-11 (1) and (2) and the catalytic activity for naphthalene alkylation with methanol are listed in Table 2. The surface area of the zeolites were measured by the BET method using nitrogen as the adsorbate. Calcined zeolites were used in order to obtain the total surface and uncalcined zeolite template n-Bu4N" for the external surface area, according to Sato [18]. From the data presented in the Table 2 it follows that the reaction takes place on the external surface because the naphthalene conversion was higher over H-ZSM-11(2) than over H-ZSM-ll(l). 

Selective dkylation of benzene and alkylbenzenes over various zeolites has been studied extensively since the 1960 s, as summarized in many reports [Venuto and Landis, 1968 Yashima et al., 1970 Kaeding et al., 1981 Haag, 1984 Chen and Garwood, 1986 Yashima, 1988 Dwyer, 1991 Bhat et al., 1992 Chen et al., 1996 Xu et al., 1996]. However, until recently, little attention has been paid to selective alkylation of two-ring aromatics such as naphthalene and biphenyl. Naphthalene and its derivatives are rich in liquids derived from coals via carbonization, pyrolysis and liquefaction. Due to the need for monomers for making the advanced polymer materials shown in Scheme I, (3-selective naphthalene alkylation has become an important subject. In particular, 2,6-dialkyl substituted naphthalene (2,6-DAN) is needed now for making the monomers for PEN, PBN and LCPs shown in Scheme 1. 

Shape-Selective Alkylation of Naphthalene with Isopropanol over Zeolites in Mesitylene Solvent at 250°C for 2 h [Song and Kirby, 1994]... 

Catalysis over Typical Zeolites - In the alkylation of naphthalene, a-alkylation occurs in the initial stage because -positions are more reactive than P-positions. However, the (3/a ratio in the product mixture increases with the increase of reaction temperature and time on stream. Figure 8 shows the three reaction paths for producing diisopropylnaphthalene (DIPN) isomers. The reactions are (1) alkylation, (2) isomerization, and (3) transalkylation. Isomerization and transalkylation accompany the rearrangement of isopropyl groups. The zeolite type and reaction conditions, e.g., temperature and time on stream, usually determine the type of reaction path.4... 

Isopropylation over HY, HL and Other Zeolites - The catalysis over HY and HL was quite different from that over HM.61 63 The further isopropylation of IPN and DIPN isomers was quite rapid in spite of the higher number of bulky isopropyl groups. The yield of IPN had a maximum value during the initial stage of the reaction, and then decreased with reaction time. At longer periods, the product amounts decreased as follows DIPN > IPN > TrIPN. Because the catalytic activities correlate well with the pore surface areas of the zeolite, the isopropylation occurs predominantly inside the pores. These results indicate that HY and HL have enough space for the isopropylation of naphthalene inside their pores. Naphthalene and its alkylates can easily enter into and diffuse out of the pores. 

Moreau et al.56 obtained unexpected results in the alkylation of naphtalene with 2-propanol over H-Beta in the liquid phase at 200°C. Here a cyclic compound 1 was formed with a selectivity around 40% at 28.5% conversion. When applying HY as the catalyst alkylation to di- and trialkylnaphthalenes was faster but the cyclic compound was not observed. These results illustrate the more confined space within the zeolites Beta channels. The cyclic compound is assumed to be formed through iso-propylation of naphthalene followed by a hydride abstraction giving a carbenium ion, reaction with a propylene and finally ring-closure. 

Alkylation of naphthalene with propylene over H-Y and H-L zeolites gave primarily the di-isopropyl naphthalenes with the 2,6- (9) and 2,7- (10) isomers formed in nearly equal amounts (Eqn. 22.5). Similar results were observed on... 

Gas-phase synthesis of 2MN can be carried out efficiently over H-ZSM-5 and H-ZSM-11 type zeolites. The results are consistent with the Rideal type mechanism for alkylation of naphthalene with methanol. The first step in the alkylation reaction of naphthalene is the chemisorption of methanol on the Bronsted acid sites. Methoxy groups are formed on the surface and according to TPD analysis, naphthalene reacts with them impacting, directly from the gas phase. The reaction seems to occur on the external surface of the crystallites of the medium pore zeolites. Using large pores zeolites, the reaction also takes place also in the channel space, and the selectivity of B derivatives is suppressed. 

Fraenkel, D., M. Cherniavsky, B. Ittah, and M. Levy. Shape-Selective Alkylation of Naphthalene and Methylnaphthalene with Methanol over H-ZSM-5 Zeolite Catalysts. J. Catal., 1986, 101, 273-283. 

Moreau, P., A. Finiels, P. Geneste, J. Joffre, F. Moreau and J. Solofo. Selective Ditilkylation of Naphthalene with Hindered Alkylating Agents over HM and HY Zeolites under Liquid Phase Conditions. Catalysis Today, 1996,31, 11-17. 

Zeolite catalysts due to their shape selectivity, thermostability, the easy separation from the products and the possibility of regeneration of the deactivated catalysts, have been widely used in the field of petrochemistry [2,3]. However, their use in fine organic synthesis has been limited. Recently, zeolite catalysts were found to be active in the alkylation of aromatics, however, there is no report to date on the benzylation of naphthalene. In this paper, we disclose a new catalytic method for the benzylation of naphthalene using zeolite H-beta as the catalyst and benzyl chloride as the benzylating agent. The optimum reaction conditions for the production of more 2-benzylnaphthalene are also examined in this study. The results obtained over H-beta catalyst are compared with zeolite H-Y and the conventional catalyst, AICI3. 

Liquid-phase isopropylation and cyclohexylation of naphthalene over a series of H mordenites and HY zeolites have been studied. These reactions can be carried out efficiently over HY zeolites. High conversions and efficient p, p selectivities are obtained after very short reaction times. The use of cyclohexyl derivatives, cyclohexyl bromide or cyclohexene, as alkylating agents leads to an improvement of the p, p selectivity. Moreover, the 2,6-dicyclohexylnaphthalene is easily separated from the reaction mixture by crystallization. 

Polynuclear Aromatics. The alkylation of polynuclear aromatics with olefins and olefin-producing reagents is effected by acid catalysts. The alkylated products are more complicated than are those produced by the alkylation of benzene because polynuclear aromatics have more than one position for substitution. For instance, the alkylation of naphthalene [91-20-3] with methanol over mordenite and Y-type zeolites at 400—450 C produces 1-methylnaphthalene [90-12-0] and 2-methylnaphthalene at a 2-/1- ratio of about 1.8. The selectivity to 2-meth5lnaphthalene [91-57-6] is increased by applying a ZSM-5 catalyst to give a 2-/1- ratio of about 8 (102). 

The selective alkylation of biphenyl and naphthalene is also possible, and is of commercial interest because 4,4 -diisopropylbiphenyl and 2,6-diisopropyl-naphthalene are used in the synthesis of speciality chemicals, for example for application as liquid crystal polymer materials for displays. For these larger molecules, large-pore zeolites such as mordenite give the best performance for isopropylation of naphthalene, introducing shape selectivity to linear (or more linear) dialkylated products over dialkylated products. 

Fraenkel et al. postulated that H-ZSM-5 crystals contain two types of Brdnsted acid sites [43]. The internal sites are accessible for molecules which can cross the 10-MR barriers and have kinetic diameters lower than 0.58 run. A second type of sites is accessible for molecules with kinetic diameters up to 0.62 nm, and was assigned to half chatmel intersections located on (001) crystal planes. These special pore mouths were thought to be responsible e.g. for the discrimination between ortho- and meta-ethyltoluene isomers and cymene. The key observation at the basis of this hypothesis was that in the alkylation of naphthalene with methanol the "slim" isomers 2-methyl- and 2,6- and 2,7-dimethylnaphthalene were dominating [44,45] over HZSM-5 and HZSM-11 as catalysts, in contrast to what was observed on zeolites with larger pores as H-Mordenite. lire authors suggest that this shape selectivity occurs at the special sites at the external surface of the ZSM-5 or 2 M-11 crystals and advanced the concept of shape selectivity at the external surface. Derouane et al. [46,47] generalized this concept and coined to it the term "nest effect" [46]. 

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