Of m-xylene

Colourless crystals, m.p. 345-347" C with sublimation, obtained by oxidation of m-xylene. 

Nitration of m xylene is directed ortho to one methyl group and para to the other... 

The oxidation of m-xylene produces isophthalic acid. The reaction occurs in the liquid-phase in presence of ammonium sulfite ... 

A further procedure will be described only for m-xylene, for which we obtained the following values of the constants fci = 173.7, fc2 = 84.2 mole hr-1 kg-1 atm-1 K — 20.6, Ko = 25.8 atm-1. The conclusions drawn from the study of consecutive hydrodemethylation were similar for all the three xylenes studied (100). The influencing of individual reactions by products and by the intermediate product was determined experimentally, by measuring their effect on the reaction of m-xylene and toluene. The adsorption coefficients, which express this effect, are listed in Table III. 

Values of Adsorption Coefficients Kj (atm 1) of Products Obtained in the Study of Demethylation of m-Xylene and Toluene... 

Fig. 6. Dependence of relative molar concentrations Wj/nA0 of reaction components on reciprocal space velocity W/F (hr kg mole-1) in the consecutive demethylation of m-xylene. Temperature 330°C, catalyst Ni-AljOs (55% wt. AljOs), initial molar ratio of reactants 0 = 5. The curves were calculated (1—xylene, 2—toluene, 3—benzene) the points are experimental values.

Some results which are consistent with this mechanism have been obtained by Ishii and Yamashita385, who found that the kinetics of the reaction of m-xylene with formaldehyde and hydrogen chloride (to give the 4-substituted product) were third-order overall. However, this was followed by a slow di-chloromethylation which was of zeroth-order, but no interpretation or further mechanistic details are available. 

A mixture of m-xylene (2,4 g, 22.6 nunol), alumina-supported copper(II) bromide (50.5 g), and carbon tetrachloride (60 ml) was placed in a 100 ml round-bottom flask and stirred with a Teflon-coated magnetic stirring bar at 80°C for 1 h. 

From this it is possible to calculate the overall theoretical rate ratio for acetylation of m-xylene relative to benzene, since this is one-sixth the sum of the partial rate factors (in this case 1130), and the isomer distribution if the reaction is kinetically controlled. The overall rate ratio actually is 347 and the calculated and observed isomer distributions are listed in Table 11.2. In this case, and in many others, agreement is fairly good, but many cases are known where the effects are not additive. For example. 

TABLE 11.2 Calculated and Experimental Isomer Distributions in the Acetylation of m-Xylene... 

The water-insoluble salts such as Cs2,5Ho., iPWi204o efficiently catalyse dehydration of 2-propanol in the gas phase and alkylation of m-xylene and trimethyl benzene with cyclohexene this catalyst is much more active than Nafion-H, HY-zeolite, H-ZSM-5, and sulphated zirconia (Okuhara et al., 1992). 

ILLUSTRATION 3.1 USE OF A DIFFERENTIAL METHOD TO DETERMINE A PSEUDO REACTION RATE EXPRESSION FOR THE IODINE CATALYZED BROMINATION OF m-XYLENE... 

The products for which the cyclo-C4 isomerization intermediate has been suggested, can also be explained by a sequence of vinyl insertions. Thus, two vinyl insertions would be adequate to explain the formation of m-xylene from 2,3,4-trimethylpentane. Although we have seen in previous sections that extensive reaction sequences are possible on platinum, isomerization by a single vinyl insertion process on chromium oxide is relatively difficult, and the chance of two occurring in sequence would therefore be expected to be very low. In fact, the proportion of m-xylene is comparable to that of o- and p-xylene. 

TABLE 3.1.1.5.1 Reported aqueous solubilities of m-xylene at various temperatures Bohon Claussen 1951 Polak Lu 1973 Sanemasa et al. 1982 Shaw 1989b (IUPAC) ... 

Reported vapor pressures of m-xylene at various temperatures and the coefficients for the vapor pressure equations... 

An aromatic hydrocarbon feedstock consisting mainly of m-xylene is to be isomerised catalytically in a process for the production of / -xylene. The product from the reactor consists of a mixture of p-xylene, m-xylene, o-xylene and ethylbenzene. As part of a preliminary assessment of the process, calculate the composition of this mixture if equilibrium were established over the catalyst at 730 K. 

Case (a). The large excess of m-xylene allows neglect of its variation in concentration and only variation in [ICI] need be taken into account. Try... 

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. 

The structure of SSZ-35 (IZA structure code STF) as viewed in the [001] direction is shown in Fig. 17. The dimensions of the 10-MR structures are 5.5 x 6.1 A and the diameter of the 18-MR structures is 12.5 x 9 A. This pore structure is in contrast to the structure of SSZ-44 (IZA structure code SFF) shown in Fig. 18, where the 10-MR structures are nearly spherical (5.8 A) and the 18-MR structures are slightly larger (12.9 x 9 A). These small differences in pore size apparently translate into startling differences in reactivity. A study of m-xylene conversion shows a high degree of isomerization versus disproportionation, which is consistent with a 10-MR pore system (47). The interesting data is the para to ortho selectivity in the isomerization products, where SSZ-44 exhibited a higher para/ortho... 

This side reaction leads to undesirable losses of xylenes. With REHY zeolite as catalyst, disproportionation occurs at a rate comparable to that of isomerization of m-xylene (8), e.g., 14% disproportionation at 16% isomerization. In fact, the product, trimethylbenzene, is postulated as an important intermediate in isomerization (8). 

The second reason is that Satchell [78] has shown that in the protonation of m-xylene by catalysts composed of stannic chloride and acetic acid or the three chloroacetic acids as co-catalysts, the rate of reaction is inversely related to the aqueous acidity of these acids. Satchell rightly points out that, since the polymerisations are complicated reactions the rates of which are also affected by the terminating efficiency of the anion derived from the co-catalyst, no valid conclusions can be drawn from such studies about catalytic efficiency in any fundamental sense. He interprets the order of effectiveness of the cocatalysts in terms of the stability of the complexes which they form with the metal halide. 

Fio. 9. LB. spectra of m-xylene (broken line) and of its proton addition complex (solid line) in the system nt-xylene-GaCls-HCl at 77°K. (Perkampus and Baumgarten, 1964a.)... 

Within the series of methylbenzenes, the effect of the methyl groups is very well reproduced by this relationship. Using the values for the squares of the coefficients and the experimental -values, — 8a/j8 is found to have a value of 0-4. On taking hyperconjugation into account in the case of m-xylene, Sa/)3 is found to have a value of 0-08, which does not explain the difference logiT—log. o = 6 5 (Mackor et al., 1958b). 

Flo. 5. Sterio hindrance to dissociative chemisorption in doubly flanked ortho position of m-xylene resulting in complete ortho deactivation. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

Figure 6.4 Separation of m-xylene from Cj-aromatics using NaY adsorbent.

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