Nitration Of Toluene Research Articles

Recovery of nitrotoluenes from wastewater by solvent extraction enhanced with salting-out effect

Toluene extraction enhanced by salting-out effect was employed to recover dinitrotoluene isomers and 2,4,6-trinitrotoluene (2,4,6-TNT) from wastewater of toluene nitration processes (e.g. dinitration or trinitration). The batchwise experiments were conducted to elucidate the influence of various operating variables on the extracting performance, including concentrations and species of inorganic salts, such as NaCl, KCl, Na 2SO 4, K 2SO 4 and MgSO 4, acidity of wastewater, volume ratios of solvent versus wastewater and extraction stages in existence of inorganic salts. It was found that recovery of total organic compounds (TOC) was significantly elevated with increasing concentrations of salts, whose promoting effects were in the following order: NaCl > Na 2SO 4 > K 2SO 4 > MgSO 4 > KCl on the weight basis of wastewater. Besides, high volume ratio of toluene/wastewater (ca. 2.0) was more suitable for recovery of TOC from wastewater with or without addition of NaCl, of which extractable priority was as follows: 2,6-DNT > 2,4-DNT > 2,4,6-TNT. It is remarkable that TOC in wastewater would be almost completely recovered by sequential four stages toluene extraction, promoted continuously by salting-out effect.

Decomposition of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process by ozonation and photo-ozonation

Ozone and UV/O 3 were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid from toluene nitration process. The oxidative degradation tests were carried out to elucidate the influence of various operating variables on the performance of mineralization of total organic compounds (TOC) in spent acid, including reaction temperature, intensity of UV (254 nm) irradiation, dosage of ozone and concentration of sulfuric acid. It is remarkable that the nearly complete mineralization of organic compounds can be achieved by ozonation combined with UV irradiation. Nevertheless, the hydroxyl radicals ( OH) would not be generated by either ozone decomposition or photolysis of ozone under the experimental condition of this study. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS) and further confirmed by gas chromatograph/flame ionization detector (GC/FID), the multiple oxidation pathways of DNT isomers are given, which include o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene, respectively. In addition, oxidative degradation of 2,4,6-TNT leads to a 1,3,5-trinitrobenzene intermediate.

Recovery of nitrotoluenes in wastewater by solvent extraction

Toluene extraction was utilized to recover 2,4-dinitrotoluene (DNT), 2,6-DNT, and 2,4,6-trinitrotoluene (TNT) from wastewater of toluene nitration process. The batch-wise experiments were performed to elucidate the influence of various operating variables on the extracting behavior, including extracting temperature, volume ratios of solvent versus wastewater, agitation time, acidity of wastewater, and extraction stages. It was found that recovery of total organic compounds (TOC) was significantly elevated with increasing extraction temperature. Besides, high volume ratio of toluene/wastewater (2.0) and wastewater acidified to lower pH value enhanced the recovery percentage of TOC, in which extractable tendency was as follows: 2,6-DNT > 2,4-DNT > 2,4,6-TNT. It is worth noting that the nitrotoluenes in wastewater would be almost completely recovered using three sequential stages toluene extraction at the agitation time of 12 min and pH 3.0. It is apparent that this established method is promising for the treatment of wastewater from toluene nitration processed industrially.

Vapor phase nitration of toluene over CuFe0.8Al1.2O4

Abstract Vapor phase nitration of toluene by using CuFe0.8Al1.2O4 as a catalyst was studied by varying strength of nitric acid (10–69%) as a nitrating agent. Water vapor generated during the reaction acts as a diluent for the exothermic process. Varying the reaction temperature in the range of 100–200 °C revealed that below 125 °C lower conversion of toluene to mono-nitro toluene was obtained while above 125 °C dinitro and oxidation byproducts were obtained. The maximum conversion of toluene to mono nitro toluene was 58% with 77% selectivity towards para nitro toluene.

The regiochemistry of the NO3‐promoted gas phase nitration of toluene and phenol with NO2

AbstractProduct studies, kinetic isotope effect measurements, linear free energy relationships and calculations have been used to study the NO3‐promoted nitration of toluene and phenol in presence of NO2. The competition between of a rate‐determining hydrogen abstraction of NO3 to give the benzyl radical and HNO3 and of a rate‐determining addition‐elimination pathway has been evaluated. The preference for the nitration in ortho and para position of toluene and for the ortho position of phenol is suggested to derive from the concerted loss of nitric acid from an intermediate cyclohexadiene.A kinetic analysis suggests reasons for the dependence of the ratio ortho:para‐nitration from the initial concentration of reactants. Copyright © 2006 John Wiley & Sons, Ltd.

Mineralization of dinitrotoluenes and trinitrotoluene of spent acid in toluene nitration process by Fenton oxidation

Fenton’s reagent, UV/H 2O 2 and UV/Fenton’s reagent were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) of spent acid in toluene nitration process. The bench-scale experiments were conducted to elucidate the influence of various operating variables on the performance of removal of total organic compounds (TOC) from spent acid, including reaction temperature, concentration of ferrous ion and H 2O 2 dosage. It is remarkable that organic compounds were completely mineralized by Fenton oxidation, of which removal efficiency is superior to that of UV/H 2O 2. Nevertheless, it makes slight difference between Fenton oxidation and UV/Fenton oxidation. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of DNT isomers leads to o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene respectively. Besides, the oxidation of 2,4,6-TNT gives the 1,3,5-trinitrobenzene intermediate. Apparently, Fenton oxidation is promising for purification of spent acid industrially.

Nitration of Aromatic Compounds on Silica Sulfuric Acid.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Recovery of dinitrotoluenes and trinitrotoluene from spent acid of toluene nitration process by solvent extraction

Extraction using hexane or heptane solvent was employed to recover dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) from spent acid after toluene nitration process. Multiple stages experiments were conducted to elucidate the influence of various operating variables on the performance of removal of organic compounds from spent acid, including extracting temperature, volume ratio of solvent versus acid, spent sulfuric acid concentration and organic compounds content of the feedstock. It was found that organic compounds extracted reached nearly 78%, of which solubility in spent acid depends strongly upon the sulfuric acid concentration. In both cases of hexane and heptane, the extracting priority of organic compounds is in the following order: 2,3-DNT > 2,6-DNT > 3,4-DNT > 2,4-DNT > 2,4,6-TNT. Furthermore, this method established is promising for regeneration of spent acid preliminarily.

Lanthanide(III) Nitrobenzenesulfonates as New Nitration Catalysts: The Role of the Metal and of the Counterion in the Catalytic Efficiency

AbstractLanthanide(III) complexes of p‐nitrobenzenesulfonic acid, Ln(p‐NBSA)3, m‐nitrobenzenesulfonic acid, Ln(m‐NBSA)3, and 2,4‐nitrobenzenesulfonic acid, Ln(2,4‐NBSA)3, were prepared, characterized and examined as catalyst for the nitration of benzene, toluene, xylenes, naphthalene, bromobenzene and chlorobenzene. The initial screening of the catalysts showed that lanthanum(III) complexes were more effective than the corresponding ytterbium(III) complexes, and that catalysts containing the bulky 2,4‐NBSA ligand were less effective than the catalyst containing p‐NBSA (nosylate) or m‐NBSA ligands. Examination of a series of Ln(p‐NBSA)3 and Ln(m‐NBSA)3 catalysts revealed that there is a clear correlation between the ionic radii of the lanthanide(III) ions and the yields of nitration, with the lighter lanthanides being more effective. The X‐ray single crystal structure of Yb(m‐NBSA)3·6H2O shows that two m‐NBSA ligands are directly bound to the metal centre while the third ligand is not located in the first coordination sphere, but it is hydrogen bonded to one of the water molecules which is coordinated to ytterbium(III). NMR studies suggest that this structure is preserved under the conditions used in the nitration reaction. The structure of Yb(m‐NBSA)3 is markedly different from the structure of the well‐known ytterbium(III) triflate catalyst. The coordination of the nitrobenzenesulfonate counterion to the lanthanide(III) ion suggests that steric effects might play an important role in determining the efficiency of these novel nitration catalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Nitration of Aromatic Compounds on Silica Sulfuric Acid

Nitration of organic compounds has long been a very active and rewarding area of research and is the subject of a large body of literature. Also nitro-aromatics compounds are extensively utilised and act as chemical feedstocks for a wide range of useful materials such as dyes, pharmaceuticals, perfumes, and plastics. Therefore, the nitration of aromatic rings has received considerable attention of late, due to unsolved problems pertaining to regioselectivity, overnitration and competitive oxidation of substrates. Nitration of phenol taken as a special case has been studied by various nitrating agents under different conditions. The nitration of benzene and toluene is one of the most important routs to substituted aromatics in the production of chemical intermediates. The industrial nitration of toluene is performed by means of mixed acid, a mixture of nitric acid, sulfuric acid, and water which leading to excessive acid waste streams and added expense. Also, the separation of the products from the acid is often a difficult and energy consuming process that habitually implies a basic aqueous work-up. Moreover, sulfuric acid is corrosive and is dangerous to transport and handle. The above mentioned disadvantages of the commercial manufacturing process currently used has led to a substantial effort to develop viable alternatives, inter idea using solid acid catalyst, other sources of NO2, organic nitrating agents, metal nitrates, other acids replacing sulfuric acid such as inorganic acidic salts (NaHSO4·H2O, Mg(HSO4), Oxone, ...) and silica sulfuric acid, etc. Our goal, in undertaking this line of work, was three-fold: a) to overcome the limitations and drawbacks of the reported methods such as tedious work-up, strongly acidic media, oxidation ability of the reagents and safety problems (storage, handling, using and also presence of toxic transition metal cations such as Cr, Hg, Cu,... within molecular structure of the reagents), (b) to perform solvent-free organic synthesis which seems to be a highly useful technique, especially for industry possessing many advantages like: reduced pollution, low costs, as well as simplicity in process and handling (these factors are especially important in industry), (c) moreover, to develop an high-yielding onepot synthesis of nitro-aromatics using a novel combination of reagents. In addition, any reduction in the amount of liquid acids needed and/or any simplification in handling procedures would be highly convenient in terms of risk control, economic advantage and environment protection. Recently, we have reported the preparation of silica sulfuric acid I as a stable acidic reagent (solid acid) and showed its catalytic activity in synthetic methodology. In continuation of our studies in this regard, we have found that aromatic rings can be nitrated by using a combination of silica sulfuric acid I, NaNO3 and wet SiO2 under solvent free conditions. Therefore, we wish to report here a one-pot solid phase procedure for the nitration of different kind of aromatic compounds.

DFT study of the mechanism of nitration of toluene with nitronium

AbstractReaction profiles of the isomeric nitration of toluene with nitronium ion were studied. Stationary points including three isomeric transition states were successfully located and characterized for the first time by employing hybrid DFT procedures at the B3LYP/6–311G** level without any restriction on the internal coordinates. Further correlation energy corrections by MP2/6–311G**//B3LYP/6–311G** were performed to evaluate the activation barrier heights. Mechanistic studies on the geometry, charge, energy and IR spectrum of the stationary points were carried out to illustrate the microscopic nitration process. A comparison of the nitrations of toluene and benzene shows that the methyl group plays dual roles in the nitration of toluene for its inductive and superconjugative effects. That is, the introduction of a methyl group creates favorable sites for the attacker and stabilizes the isomeric toluene–NO complexes. Both roles are critical to the positional selectivity. The order of the activation barrier height is para < ortho < benzene < meta. This relative reactivity order is not changed with either B3LYP/6–311G** or MP2/6–311G**//B3LYP/6–311G** calculations, although the absolute magnitude of the latter is larger. The order of the stability of complexes is p‐toluene–NO > o‐toluene–NO > m‐toluene–NO > benzene–NO. The relationship between the energy and the electron migration of NO2 group was established to elucidate the stabilization caused by the interaction between the two moieties of the complex. The vibrational shifts of tetrahedral C—N and C—H bonds suggest that the nitration of toluene may undergo the classical electrophilic substitution pathway, namely an SE2 mechanism. Copyright © 2004 John Wiley & Sons, Ltd.

Recovery of high purity 2,4-dinitrotoluene from spent mixed acid in toluene nitration process

Two easy practical methods for recovery of high purity 2,4-dinitrotoluene (DNT) from spent mixed acid in toluene nitration process are established. One is the dilution manner which produces high purity crystal of 2,4-DNT (>99 wt.%) by addition of proper amounts of deionized water into the spent mixed acid. The other is a refrigeration method which also evaluates high purity crystal of 2,4-DNT (>98 wt.%) by means of simply cooling down spent mixed acid below 283 K. According to the analysis of gas chromatograph–mass spectrometer (GC–MS), the ingredients of crystals were identified. Further, the influence of dilution procedure, refrigeration treatment, and adjustment of pH value on the performance of abatement of total organic compounds (TOC) were elucidated in this research. It was found that the organic compounds dissolving in aqueous spent mixed acid are in equilibrium with the organic phase of dinitrotoluene isomers. Besides, the solubility of each organic component in spent acid depends upon the concentration of spent sulfuric acid.

Influence of the properties of zeolite BEA on its performance in the nitration of toluene and nitrotoluene

The nitration of toluene and 2-nitrotoluene was investigated using different batches of zeolite BEA. In the nitration of toluene, notable differences in the product composition were obtained depending on the batch of BEA used. In the nitration of 2-nitrotoluene, all the catalysts displayed a good selectivity, but different conversions. Steaming improved the performance of the catalysts, but strong dealumination with oxalic acid had a negative effect. The positive effect of steaming was attributed to the enhanced transport of the reaction products out of the pores. Lewis acidity did not seem to play a role in the nitration reaction. A high concentration of Brønsted sites was detrimental, because it slowed down the diffusion of the products, but a small concentration of Brønsted sites was required to catalyze the heterogeneous reaction.

Lanthanide(III) complexes of aromatic sulfonic acids as catalysts for the nitration of toluene

Ytterbium(III) complexes of benzenesulfonic acid, Yb(BSA) 3, p-toluenesulfonic acid, Yb(Tos) 3, and 2-naphthalenesulfonic acid, Yb(NSA) 3, were prepared and tested as possible catalyst for the nitration of toluene. With a loading of 5–10 mol% of Yb(BSA) 3 and Yb(NSA) 3, a quantitative conversion of toluene to nitrotoluene was achieved within 5 h, while Yb(Tos) 3 was slightly less active and 77% of nitrated products were obtained. The catalysts can be easily recovered after the reaction, and 1 H NMR spectroscopy of analogous diamagnetic lanthanide(III) catalysts showed that the recovered catalysts were identical to the freshly prepared ones. The ratio of ortho: meta: para products was in all reactions 52:6:42, which is consistent with a direct electrophilic attack by the nitronium ion, NO 2 +.

Factors determining the suitability of zeolite BEA as para-selective nitration catalyst

The nitration of toluene and 2-nitrotoluene with acetyl nitrate was investigated using several solid acid catalysts. In the nitration of toluene, enhanced para-selectivity was observed only with zeolite BEA. For the nitration of 2-nitrotoluene, all the catalysts displayed good para-selectivity, but only BEA led to high yields. The superior performance of BEA was due to the fact that only with this zeolite did the heterogeneously catalyzed reaction compete successfully with the homogeneous nitration in the liquid phase. Geometrical considerations showed that the high para-selectivity of BEA was not caused by classical transition-state selectivity but was induced by the reaction of the arene with a surface-bound acetyl nitrate complex. The existence of this complex was supported by NMR measurements, which showed that its formation is a specific property of zeolite BEA.

A Practical Approach of Continuous Processing to High Energetic Nitration Reactions in Microreactors

Continuous processing in microreactors represents a novel way for the safe and expedient conduct of high energetic reactions and potentially hazardous chemistry. Apart from handling benefits (such as minimised problems inthe scale-up process), reactions in microreactors proceed under precisely controlled conditions providing improved yields and product quality compared to the batch procedure. In this paper, the potential of this technology is exemplarily determined in the crucial nitration of the pharmaceutically relevant intermediate 1-methyl-3-propyl-1H-pyrazole-5-carboxylic acid (1). Further fundamental nitration examples demonstrate the unproblematic handling of hazardous H 2 SO 4 / HNO 3 mixtures for the nitration of 2-methylindole (4) and pyridine-N-oxide (6) or even the explosive acetyl nitrate Ac 2 O/HNO 3 (nitration of toluene, 8) in the continuous reaction mode.

A Microreactor for the Nitration of Benzene and Toluene

Narrow channel microreactors have been evaluated for the reaction of immiscible liquid-liquid systems. In order to stimulate rapid interphase mixing and mass transfer, alternating slugs of organic and aqueous phases were generated at a "T" piece and flowed down an etched channel in a glass substrate. The detailed flow behavior was recorded photographically. Finally, some benzene and toluene nitration experiments were performed in stainless steel and PTFE capillary tubing in order to explore the industrial potential of microreactors for chemical production.

Modelling and constraint optimisation of an aromatic nitration in liquid–liquid medium

A methodology, which determines the operating conditions simultaneously optimising the chemical yield and considering the safety aspect, has been developed for a chemical reaction which is carried out batch-wise. To illustrate the methodology, the aromatic nitration of toluene by mixed acid has been chosen as a typical exothermic and non-selective reaction. This reaction takes place in a two-phase medium and, therefore, involves simultaneously chemical reaction and mass transfer phenomena. A kinetic model recently proposed for the slow and fast liquid–liquid reaction regimes was integrated to the mass balance. Nitration experiments were carried out in order to compare experimental composition profiles with simulated ones. Afterwards, an optimisation procedure has been used to maximise conversion, by manipulating the operating conditions subject to safety constraints. The p-nitrotoluene yield was chosen as the criterion to be maximised. Experimental validation for the optimisation procedure has been carried out. A monofluid heating–cooling system controlled by a predictive controller was used for the temperature control of the reactor. Simulation and experimental results are presented, discussed and compared.

An infrared study on the MoO 3/SiO 2 catalytic system employed in toluene nitration

The 15% MoO 3/SiO 2 catalyst obtained by calcination of the (NH 4) 6Mo 7O 24·4H 2O/SiO 2 system at various temperatures, as well as upon its use in the reaction of toluene nitration using 65 or 100% HNO 3, was studied by IR spectroscopy. The calcination process conducted at 240, 300, or 550 °C proceeds first through the formation of the Keggin structures, silicomolybdic acid, then, of molybdenum trioxide. All the molybdenum phases on the silica support obtained were found to be active in the toluene nitration process.

ChemInform Abstract: Regioselective Double Kyodai Nitration of Toluene and Chlorobenzene over Zeolites. High Preference for the 2,4‐Dinitro Isomer at the Second Nitration Stage.

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