Zeolite nitrobenzene

Adsorption experiments The method developed for the analysis of carbonaceous compounds formed and trapped within the zeolite micropores during catalytic reactions1581 can be adapted for determining the occupancy of micropores by reactant, solvent and product molecules. However, this method cannot be used with compounds sensitive to hydrolysis, such as AA, because of the step of dissolution of the zeolite in a hydrofluoric acid solution necessary for the complete recovery of the organic molecules located within the zeolite micropores.[58] This method was used to determine the composition of the organic compounds retained within the micropores of three different zeolites [H-BEA (zeolite Beta), H-FAU (zeolite Y), and H-MFI (zeolite ZSM-5)] after contact in a stirred batch reactor at 393 K for 4 min of a solution containing 20 mmol of 2-methoxynaphthalene (2-MN), 4 mmol of l-acetyl-2-methoxynaphthalene (1-AMN) and 1 ml of solvent (sulfolane or nitrobenzene) with 500 mg of activated zeolite.[59 61] From the comparison of... 

Whatever the solvent and the zeolite, large differences can be observed between the compositions of RM and AM mixtures and this behaviour confirms that organic molecules compete for adsorption within the zeolite micropores. Sulfolane, a very polar solvent, is more strongly adsorbed than 2-MN whereas the less polar nitrobenzene solvent is less strongly adsorbed (Table 2.2). This explains the lower rate of 2-MN acetylation with A A found with sulfolane as solvent.1591 AMN, the products of this acetylation, are more strongly adsorbed than 2-MN which suggests an autoinhibited process. 

Table 2.2 Composition (wt%) of the reaction mixture (RM) and of the organic compounds adsorbed within the zeolite micropores (AM) after contact of a 2-MN and 1-AMN mixture for 4 min at 393 K with the zeolite in nitrobenzene as solvent...

Most likely, this competition between solvent and the other organic molecules is responsible for the decrease in the initial selectivity for 2-AMN and in deacylation with the increase of solvent polarity there is a decrease in the residence time of 1-AMN molecules within the zeolite pores with consequently less secondary reactions. However at long reaction times, the highest yield in 2-AMN is obtained with nitrobenzene, a solvent of intermediate polarity, and not with the less polar solvents. It is probably because competition with solvent plays a role in both the residence times of 1-AMN and 2-AMN.25... 

HMordenite, HFaujasite-780, HFaujasite 720 and Na-Faujasite zeolites. Among the different catalysts, HFaujasite-720 was the most active and selective catalyst towards 2,4-dinitrotoluene, achieving a yield of dinitrotoluenes of 92 % with a ratio of 2,4- to 2,6- isomers of 4.3 1 in 3 min reaction time. Using this zeolite, l-chloro-2-nitrobenzene and pyrazole were also nitrated regioselectively to obtain l-chloro-2,4-dinitrobenzene in a l-chloro-2,4-dinitro l-chloro-2,6-dinitro ratio of 30 1, and 1,4-dinitropyrazole in 80% yield, respectively. The authors proposed a nitration mechanism in which the protons in the zeolite are replaced by nitronium ions derived from N2Os in a fast pre-equilibrium process. This produces active sites for transfer of nitronium ion from faujasite to aromatic in the rate-controlling step. 

The catalytic gas-phase hydrogenation The catalysts are Al203 Si02 (possibly as processes for nitrobenzene can be carried out zeolites) and oxide mixtures of Mg, B, Al, and... 

Acetylation of 2-methoxynaphthalene (2MN) with acetic anhydride (AA) was carried out in a batch reactor over a HBEA zeolite with a framework Si/Al ratio of 15 (HBEA 15). The standard operating conditions were the following temperature of 120°C, 500mg of catalyst previously activated at 500°C overnight under dry air flow, solution containing 35 mmol of 2MN (C2MN = 3,43mol l 1), 7 mmol of AA (Caa = 0,68 mol.I 1) and 4 cm3 of nitrobenzene. 

The effect of solvent polarity on the activity and selectivity of the HBEA zeolite was examined on the acetylation of 2MN with acetic anhydride as well as on the transacylation of 2MN with isomer I. The reactions were carried out in solvents of various polarities under the following conditions temperature of 120°C, 500mg of HBEA and 35mmol of 2MN (3,43 mol.l 1), 7mmol of AA (O Smol.l 1) and 4 cm3 of solvent (sulfolane, nitrobenzene, 1,2-dichlorobenzene or 1-methylnaphthalene) for acylation and 20 mmol of 2MN (4 mol.l 1), 4 mmol of I (1 mol.l 1) in 3,3 cm3 of solvent for transacylation. The Et parameter defined by Dimroth et alu was used for characterizing the solvent polarity. 

Over HBEA zeolites, acetylation of 2-methoxynaphthalene with acetic anhydride leads mainly to l-acetyl-2-methoxynaphthalene. However, the desired product, i.e. 2-acetyl-6-methoxynaphthalene, precursor of Naproxen is obtained at long reaction time by an intermolecular irreversible isomerization process. A very selective production of II (83%) can be obtained by acetylation of 2-methoxynaphthalene over a commercial HBEA zeolite (Si/Al = 15) at 170°C, with nitrobenzene as a solvent. With dealuminated HBEA samples (framework Si/Al ratio between 20 and 40), better results could be expected. Furthermore, preliminary experiments showed that this selective synthesis of 2-methoxynaphthalene can be carried out in a flow reactor system. 

After our success in nitrating moderately active monosubstituted benzenes with acetic anhydride and nitric acid over zeolite p,11 we decided to try the use of trifluoroacetic anhydride and nitric acid over zeolite p for nitration of deactivated substrates. Although trifluoroacetyl nitrate is known to be more active than acetyl nitrate, it has not been widely used in nitration reactions.15 Nitrobenzene has been successfully nitrated using fuming nitric acid and trifluoroacetic anhydride in equimolar proportions at 45-55 °C.16 However, no dinitration of toluene was reported. 

Figure 1. The dependence of the shift of the absorption bands (AX) on the electrostatic potential of the exchange cations (e/r), A, in the case of adsorption of (1) aniline, (2) p-phenyl-enediamine, (3) pyridine, (4) nitrobenzene on LiX, NaX, KX, RbX, and CsX zeolites...

The oxidation of aniline was carried out in the liquid phase over a series of transition metal - substituted molecular sieves. For low oxidant/aniline ratios, azoxybenzene (AZY) was the major product formed over Ti-containing catalysts, the reaction was limited by diffusion for medium pore zeolites like TS-l and mesoporous silicas were preferred as they permitted the use of both H2O2 and tert-butyl hydroperoxide as oxidants. Higher oxidant/aniline ratios (>2) led to the formation of nitrobenzene (NB), whose selectivity was proportional to the catalyst concentration. In contrast, vanadium containing molecular sieves were only active with TBHP and aniline was converted very selectively into nitrobenzene for all oxidant concentrations. 

In this study protonated large pore zeolites of different structures (HY, HBeta and HMordenite) and framework Si-to-Al ratios were used in liquid phase in a batch reactor. The zeolites were calcined at 500°C and the hydrolysis was conducted at 75°C. The procedure was optimised in terms of solvent, activation, type and amount of catalyst for the hydrolysis of nitroacetanilides, currently carried out with 10 % sulphuric acid [14], and then extended to other substituted amides. The reaction, followed by GC with nitrobenzene as internal standard, was clean and no by-products or degradation were detected. 

Mordenite etc. Dodecatungstophosphoric acid (DTPA) and the ion exchange resin catalysts showed maximum activities. Clay based catalysts and sulphated zirconia showed a moderate activity. Zeolites did not demonstrate any activity to the reaction due to pore size restriction. A 100% selectivity towards the ortho product (l-acetyl-2-methoxy naphthalene) was observed for almost all the reactions for all the catalysts. The para product (2-methoxy-6-acetyl naphthalene) was formed when the aluminium chloride was used as a homogeneous catalyst with nitrobenzene as the solvent. The reaction product was isolated and conformed by the melting point, FT-IR, H-NMR, etc. The reaction is intraparticle diffusion limited. A different catalyst would be required to get p-product selectively. 

Substituted mesoporous silicas are very promising catalysts for the oxidation of arylamines in the liquid phase. Indeed Gontier and Tuel have reported that the performance of TS-1 was considerably poorer than large pore zeolite Ti- and V-substituted molecular sieves for the oxidation of aniline.36 At low oxidant/ aniline ratios it was found that azoxybenzene was the major product using Ti-substituted molecular sieves. In contrast, V-substituted molecular sieves were very selective towards the conversion of aniline to nitrobenzene. The difference between the Ti and V molecular sieves was attributed to the greater number of active oxidising sites in the V-HMS, leading to further oxidation of azoxybenzene into nitrobenzene. 

The catalytic vapour-phase nitration of benzene with aqueous nitric acid has been carried out on modified Y zeolites. The influence of various ultrastabilization and activation procedures on the catalytic activity and stability of the materials was investigated. The modified Y zeolites were characterized by physico-chemical methods, and correlations between catalyst properties and catalytic performance are discussed. It was found that modified Y zeolites are active catalysts for the vapour-phase nitration of benzene, and that both nitrobenzene space time yield and catalytic stability are strongly dependent on the preparation procedure. Thus, stable catalysts for the vapour-phase nitration of benzene were obtained by acid treatment of low sodium ultrastabilized Y zeolites. 

In order to obtain viable vapour-phase nitration catalysts, it is important to study both the factors leading to a deactivation of the modified Y zeolites, and the conditions influencing the selectivity to the desired product. In the present study, we show that zeolites can afford nitrobenzene, free of nitrophenolic by-products, and containing only traces of dinitrobenzenes at high benzene and nitric acid selectivity. 

Fig. 36. Wavelength shift AA. of the electronic band of aniline (1), p-phenylenediamine (2), pyridine (3) and nitrobenzene (4) adsorbed on zeolites UX, NaX, KX, RbX and CsX as a function of the electrostatic potential U=e/r (A) of the respective nonframework cation. Reprinted with permission from [106], Copyright 1971 American Chemical Society...

The desired product 2-acetyl-6-methoxynaphthalene (21) is obtained in 80% yield in the presence of a polar solvent such as nitrobenzene and zeolite HBEA as catalyst, because it has a more restricted pore structure that allows the preferential formation of isomo- 21 less hindered with respect to isomCTs 19 and 20 [56]. 

Metallic palladium on zeolite gives PhNCO fi om nitrobenzene with 35 % selectivity in dichlorobenzene at 240 °C and 200 atm [29], It has also been reported that zeolite Y exchanged with palladium (II), alone or in the presence of pyridine, gives PhNCO from nitrobenzene at 220-240 °C and 250 atm [30]. At... 

The nitrations of benzene and nitrobenzene by dinitrogen pentaoxide in carbon tetrachloride have been studied. It was concluded that dinitrobenzenes could be formed directly from benzene without the intermediacy of nitrobenzene. It was suggested that the initially attacking species is NOs and that dinitrobenzenes could be formed by the reaction of the intermediate formed by such attack reacting with NO2, formed by N2O5 decomposition above 25 °C. The reactions of 2-nitrotoluene, l-chloro-2-nitrobenzene, and l-chloro-4-nitrobenzene with dinitrogen pentaoxide in dichloromethane at 0°C are catalysed by certain zeolites giving near quantitative yields. In this process the activated site on the zeolite may provide an incipient nitronium ion for reaction. 

Also obtained by acylation of 2-methoxynaphthalene with propionic anhydride in nitrobenzene in the presence of zeolite-beta catalysts [7840]. 

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