Alkylation of naphthalene

Isopropylnaphthalenes produced by alkylation of naphthalene with propjdene have gained commercial importance as chemical intermediates, eg, 2-isopropylnaphthalene [2027-17-OJ, and as multipurpose solvents, eg, mixed isopropylnaphthalenes. Alkylation of naphthalene with alkyl haUdes (except methyl hahdes), acid chlorides, and acid anhydrides proceeds in the presence of anhydrous aluminum chloride by Friedel-Crafts reactions (qv). The products are alkylnaphthalenes or alkyl naphthyl ketones, respectively (see Alkylation). 

Isopropylnaphthalenes can be prepared readily by the catalytic alkylation of naphthalene with propjiene. 2-lsopropylnaphthalene [2027-17-0] is an important intermediate used in the manufacture of 2-naphthol (see Naphthalenederivatives). The alkylation of naphthalene with propjiene, preferably in an inert solvent at 40—100°C with an aluminum chloride, hydrogen fluoride, or boron trifluoride—phosphoric acid catalyst, gives 90—95% wt % 2-isopropylnaphthalene however, a considerable amount of polyalkylate also is produced. Preferably, the propylation of naphthalene is carried out in the vapor phase in a continuous manner, over a phosphoric acid on kieselguhr catalyst under pressure at ca 220—250°C. The alkylate, which is low in di- and polyisopropylnaphthalenes, then is isomerized by recycling over the same catalyst at 240°C or by using aluminum chloride catalyst at 80°C. After distillation, a product containing >90 wt % 2-isopropylnaphthalene is obtained (47). 

Polynuclear Aromatics. The alkylation of polynuclear aromatics with olefins and olefin-producing reagents is effected by acid catalysts. The alkylated products are more compHcated 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 zeoHtes 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-methylnaphthalene [91-57-6] is increased by applying a ZSM-5 catalyst to give a 2-/1- ratio of about 8 (102). 

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. 

Some data on the alkylation of naphthalene by 2-bromopropane using A1C13 under different conditions are given below. What factors are responsible for the differing product ratios for the two solvents, and why does the product ratio change with time ... 

Some data for the alkylation of naphthalene by isopropyl bromide under various conditions are given. 

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]. 

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... 

IPN and DIPN isomers at 80% conversion in the alkylation of naphthalene over HM with Si02/Al203 ratio from 10 to 220 at 250 °C under constant propylene pressure of 0.8 MPa.67,68 The catalytic features of HM with low and high ratios were also quite different. Significant changes in the selectivities for... 

Studies of Lewis acid-catalyzed isomerization of alkylnaphthalenes were carried out by Olah and Olah in connection with alkylation of naphthalene with alkyl halides.88 Methyl-, ethyl-, isopropyl- and ferf-butylnaphthalene readily undergo isomerization with A1C13 in CS2 solution. The rate of isomerization and the equilibrium concentration of the p isomer were found to increase with increasing branching of the alkyl substituent (Table 4.3). 

It was observed that all three straight-chain butenes give similar product distribution in alkylation of naphthalene ... 

Alkylation with isobutylene under similar conditions167 and alkylation with propylene catalyzed by perfluorosulfonic acids,168 in turn, lead to 2-substituted naphthalenes. As was shown by Olah and Olah,169 the kinetic alkylation of naphthalene, even in case of rm-butylation, gives preferentially the 1-isomers, which, however, isomerize very fast to the thermodynamically preferred 2-alkylnaphthalenes. Great care is therefore needed to evaluate kinetic regioselectivities. 

Alkylation. Naphthalene can be easily alkylated, Isopropvlnaphthalenes produced by alkylation of naphthalene with propylene have gained commercial importance as chemical intermediates. e.g., 2-isopropylnaphthalene, and as multipurpose solvents, e.g, mixed isopropylnaphthalenes. 

The Friedel-Crafts alkylation of naphthalene often yields a variety of products. For this reason it is not frequently used. A better method of placing an alkyl group involves reduction of the ketone formed from procedure XVI-4 using either the Wolff-Kiscliner or Clcmmcnscn reductions. 

GaCl3 catalyzes the aromatic alkylation of naphthalene 118 or phenanthrene with cycloalkanes such as decalin 117. The C-C bond formation predominantly takes place at the least hindered positions of the substrates, and equatorial isomers 119 and 120 regarding the cycloalkane moiety are generally obtained together with 121 (Table 45).449,450... 

The Fajula group also recently studied the alkylation of naphthalene with tert-butanol.57 Over H-beta 2-te/t-butylnaphthalene was obtained as the main product together with relatively small amounts of the di-terr-butylnaphthalenes. Over HY 2,6-and 2,7-di-terf-butylnaphthalene the major products, demonstrating again the more spacious Y-pore system. 

Two areas of current interest where we have been investigating the use of zeolites to gain much needed selectivity enhancements are the nitration of aromatic substrates and the alkylation of naphthalene. Some of our progress is reported in this paper. 

Amoco chemicals have commercialised a procedure that uses o-xylene as starting material. However, this synthesis of naphthalene-2,6-dicarboxylic acid involves five steps, including isomerisation of 1,5-dimethylnaphthalene to 2,6-dimethylnaphthalene. The direct regioselective alkylation of naphthalene (9, Scheme 5) is therefore more attractive, and has been investigated by, amongst others, NKK, Chiyoda and Catalytica.22 Synthesis of 10 by this approach is complicated, however, by the possible formation of nine other dialkyl isomers, which can be difficult to separate from the 2,6-isomer. 

Alkylation of naphthalene gives both a- and /3-monoalkyl products, the /3-compound usually predominating. "... 

Methylnapthalene (2-MN) and 2,6-dimethylnapthalene (2,6-DMN) can be selectively produced by isomerisation and disproportionation of 1 -methylnapthalene (1 -MN) or by direct alkylation of naphthalene. The observed reactivity for the isomerisation of 1 -MN and 2-MN over HZSM-5, HZSM-11, H-BEA, H-MOR and H-Y led Weitkamp et al. [264] to propose that product shape selectivity dominates, while Fraenkel et al [265] suggest that cavities at the external surface containing strong Bronsted acid sites are responsible for the selectivity. That idea has been followed up by Derouane proposing nest like structures to be important [266 ]. Intuitively this is intriguing, as the situation resembles the coordination... 

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... 

For the selective liquid phase alkylation of naphthalene with propene to form 2,6-diisopropylnaphthalene, mordenite again seems to be the most promising catalyst [42]. However, while this zeolite shows a high selectivity for 13-substitution of naphthalene, its activity is low compared to faujasites [43, 44]. Chemical vapor deposition, variation of the aluminum content and of the solvent are methods used to improve the catalytic behavior of mordenite catalysts in this reaction. Chemical vapor deposition of silicon or zirconium alkoxides were claimed to improve the I3,l3 -selectivity of zeolite Beta in this reaction [45]. A recurrent matter of dispute are the parameters influencing the yield ratio of 2,6- and 2,7-diisopropylnaphthalene. Both molecules are presumed to have the same molecular dimensions. With regard to the formation of 2,6-diisopropylnaphthalene, alkylation with isopropylbromide... 

Figure 5. Effect of the space velocity of naphthalene in the alkylation of naphthalene with methanol using H-ZSM-11 at 360 C.

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. 

Friedcl-Crafts alkylation of naphthalene is of little use, probably for a combination of reasons the high reactivity of naphthalene which causes side reactions and polyalkylations, and the availability of alkylnaphthalenes via acylation or ring closure (Sec. 30.14). 

Gutierrez Blanco C, Casal Banciella D, Gonzalez Azpiroz MD (2006) Alkylation of naphthalene using three different ionic liquids. J Mol Catal A Chem 253 203-206... 

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

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. 

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