Alkylation methylnaphthalene

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). 

DMN can be produced by alkylating naphthalene or 2-methylnaphthalene at 250—450°C over ZeoHte catalysts (102,103). However, no commercial technology by this synthetic route had been developed as of 1991, primarily because of low catalytic selectivity. 

The fact that most alkylated benzenes show the same tendency to soot is also consistent with a mechanism that requires the presence of phenyl radicals, concentrations of acetylene that arise from the pyrolysis of the ring, and the formation of a fused-ring structure. As mentioned, acetylene is a major pyrolysis product of benzene and all alkylated aromatics. The observation that 1-methylnaphthalene is one of the most prolific sooting compounds is likely explained by the immediate presence of the naphthalene radical during pyrolysis (see Fig. 8.23). 

Photolytic. Fukuda et al. (1988) studied the photodegradation of 2-methylnaphthalene and other alkylated naphthalenes in distilled water and artificial seawater using a high-pressure mercury lamp. Based upon an experimentally rate constant of 0.042/h, the photolytic half-life of 2-methylnaphthalene in water is 16.4 h. 

In contrast, there are relatively few publications on the conversion of polynuclear aromatics in zeolite catalysts. Lee et al. [16] found unusually high selectivities for 4,4 -diisopropylbiphenyl when dealuminated mordenite was used as catalyst for the alkylation of biphenyl with propene. The reactions of 1- and 2-methylnaphthalene on acid forms of zeolite X, Y, Omega, mordenite and ZSM-5 were studied byDimitrov etal. [17], S o 1 i n a s et... 

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]. 

In this paper, we report on the shape selective isomerization of l methylnaphthalene in suitable zeolite catalysts in which the undesired transalkylation reaction is suppressed. Furthermore, new results concerning the alkylation of 2-methylnaphthalene with methanol are presented in an endeavor to contribute to a critical evaluation of Fraenkel s model. At the same time, the potential of shape selective catalysis for the manufacture of... 

In a preliminary screening, the alkylation of 2-methylnaphthalene was studied using a variety of acid zeolites with different pore widths. In principal agreement with the earlier work of Fraenkel et al. [22-25] it was found that the best selectivities for the slim alkylation products, i. e., 2,3-, 2,6- and 2,7-dimethylnaphthalene, are obtained on HZSM-5 and HZSM-11. On these catalysts it was observed that the alkylation is always accompanied by the undesired isomerization into 1-methylnaphthalene. Moreover, a peculiar deactivation behavior was encountered With time on stream, the yield of 1-methylnaphthalene always dropped while the yield of alkylation products remained practically constant or even slightly increased. An example for the conversion and yield curves is given in Fig. 4. The distribution of the dimethylnaphthalene isomers is shown for the same experiment in Fig. 5. Bearing in mind that in equilibrium one would expect roughly 12 mole-% of each of the slim isomers, the... 

Fig. 5. Alkylation of 2-methylnaphthalene with methanol on HZSM-5 at 400 °C. Composition of the dimethylnaphthalene fraction.

Methylnaphthalene can be methylated shape selectively using HZSM-5 or HZSM-11. The preferred products are 2,3-, 2,6- and 2,7-dimethylnaphthalene, i.e., the slim alkylation... 

The volume change AV associated with intermolecular excimer formation has been determined for naphthalene and various alkyl derivatives through the application of pressure 74). For naphthalene and the two methylnaphthalene isomers, the value of AV = — 16cm3/mole was measured at room temperature. Assuming the sandwich structure for the excimer, and taking the projected area of the naphthalene molecule... 

About half of the 1-methylnaphthalene formed from n-pentylbenzene and 2-phenylpentane isomerizes to 2-methylnaphthalene over platinum on silica-alumina (while over platinum on silica less than 3% of the methylnaphthalene isomerizes to 2-methylnaphthalene). Alkylindan (and alkyl-indene) isomerization is also considerable over platinum on silica-alumina (13, 14). 

Table XII presents compositional data for the aromatic hydrocarbons present in the anthracene oil. Compounds in the -12(H), -14(H), -18(H), and -22(H) series account for 78% of the aromatic hydrocarbons. The -12(H) compounds identified by GC/MS include naphthalene, 1- and 2-methylnaphthalene and at least 5 naphthalenes possessing 2 alkyl carbons. By GC/MS, acenaphthene and biphenyl account for 94% and 6%, respectively, of the first homolog in the -14(H) series. The parent member of the -18(H) series (C2.4H10 waS PreParat -ve -y isolated using GC and identified by UV and NMR to be >98% phenanthrene. The dominance of phenanthrene over anthracene in both high- and low- temperature coal tars has been previously noted (29,30,40,41,42,43). Thus, phenanthrene and presumably its alkylated homologs comprise the -18(H) Z series and account for 15.4% of the anthracene oil. The initial homolog in the -22(H) series, is comprised of 58%...

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

The first example involves the vapors of naphthalene and its alkyl derivatives. These volatile compounds are ubiquitous to fossil-fuel operations. Only naphthalene itself has an OSHA concentration limit, which is 10 ppm. The most abundant member of the naphthalene family in, for example, the condensate from the Synthane gasification process (II) is 2-methylnaphthalene, melting at 35°C. Although it is recognized as a fairly active tumor promoter (12), little consideration has been given to the effects upon health of chronic exposure to its vapor. There is no OSHA limit on the maximum permissible concentration. 

Sn-silicalites of MFI, MEL and MTW stmctures with Si/Sn > 30 have been synthesized hydrothemally under basic conditions. The unit cell volume eraansion in each case, though linear with respect to Sn content (upto 3 Sn per unit cell in MFI and MEL silicalites), does not correspond to theoretical T-atom substitution by Sn " ions. The well-dispersed SnOx units can be described as structural defects with octahedral coordination and are active in the oxidation of a number of organic substrates (phenol, toluene, m-cresol and m-xylene) with aqueous H2O2. These are similar to vanadium silicalites (VS-1 and VS-2), as both hydroxylation or the aromatic nucleus and the oxidation of the alkyl substituent are catalysed. Due to the presence of Sn + in large pores, Sn-ZSM-12 sample is able to oxidize bulkier naphthalene and 2-methylnaphthalene more effectively than the medium pore Sn-MFI and Sn-MEL silicalites. 

The alkylation of the naphthenic cation causes formation of complex aliphatic carbonium ions. Transformation of such intermediates according to Poustma [30] gives the molecules of light saturated hydrocarbons and aromatics. It is generally accepted that the formation of condensed aromatic rings being a coke precursors is difficult in the pores of ZSM-5 zeolite. The fact that the products of the toluene transformation reaction in all cases contained 1 - and 2-methylnaphthalene seems to prove their formation from the olefinic or naphthenic carbocations. Transformation of the naphthenic carbocations occuring in zeolite pores and on the external zeolite surface is the most probable source of methyinaphthalene isomers [23]. 

The reaction can be smoothly applied to a broad variety of alkyl-substituted benzene and naphthalene derivatives 2,3-dimethyl-, 2,5-dimethyl-, or 2,3,5,8-tetramethylnaphthalene and l-hydroxy-2-methylnaphthalene are converted by CH3Re03/H202 in good to excellent yields (60-100 %) see Table 1 and eqs. (1) and (2) [7, 8]. 

Friedel-Crafts alkylation reactions are, in general, accompanied by isomerization processes. Olah et a/. reported the results of the water-promoted, AlCb-catalyzed isomerization of o-, m- and p-di-f-bu-tylbenzene. No ortho isomer was present in the equilibrium mixture. The isomerization of o-di-r-bu-tylbenzene was very rapid largely due to relief of steric strain. In these and other related sterically hindered arenes, intramolecular isomerization and not dealkylation was observed. Isomerization of di-and mono-methylnaphthalenes, catalyzed by HF-BF3, was also reported. Isomerization of /i-alkyl-toluenes and -xylenes, catalyzed by AICI3 at room temperature, afforded chiefly /n-/i-alkyltoluenes and /n-/i-alkylxylenes, respectively. The process leading to the meta isomer has a lower energy than the other processes. 

While steric effects of alkyl groups may be present in the hydrogenation of alkylnaphthalenes they are by no means the only effect. Competitive hydrogenation of 2-methyl- and 2-t-butylnaphthalene showed that the latter was hydrogenated somewhat more slowly. In experiments with Raney nickel catalyst at 1000 psig and 200°, the ratios of tetralin isomers were the same whether the methylnaphthalene and i-butylnaphthalene were hydrogenated separately or competitively ... 

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