Nitrotoluene indicators

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

The addition of a secondary solute or wavelength shifter can serve to offset much if not all of the action of tagged nitrocompds in reducing counting efficiency. For expl nitrocompds, a shift of the emission spectrum considerably into the visible region where absorption effects are not so pronounced is clearly indicated. The secondary solute POPOP has been found to be most efficient for this purpose (Ref 2). This enhanced effect on the scintillation process is illustrated in Fig 2 for p-Nitrotoluene... 

In this work, Brand and Horning158 showed that the rate of sulphonation of phenyltrimethylammonium ion was linearly related to the calculated concentration of protonated sulphur trioxide HSO3, indicating it to be the electrophile. Added sulphate anions reduced the rate for 4-nitrotoluene in direct proportion to their concentration, and this followed from the equilibrium... 

We used DFT to optimize the geometries of various Hammett bases on cluster models of zeolite Brpnsted sites. For p-fluoronitrobenzene and p-nitrotoluene, two indicators with strengths of ca. -12 for their conjugate acids, we saw no protonation in the energy minimized structures. Similar calculations using the much more strongly basic aniline andogs of these molecules demonstrated proton transfer from the zeolite cluster to the base. We carried out F and experimental NMR studies of these same Hammett indicators adsorbed into zeolites HY and HZSM-5. 

Fig. 18 Invariant composition of nitrotoluene isomers obtained from various nitrating agents, with their (varying) reactivities indicated by the substrate selectivity (k/ko for toluene relative to benzene). The nitrating agents are identified by numbers in footnote 49 of ref. 235a. Reproduced with permission from Ref. 235a.

In the [Ru(CO)3(dppe)] catalysed carbonylation of para-nitrotoluene (Eq. (6)) HP IR spectroscopy indicated conversion of the Ru(0) complex into an oxidised species with v(CO) bands at higher frequency [41]. A mechanism involving single-electron-transfer from the nitroaromatic to the Ru complex was proposed. 

A very reactive nitrogen atom is required to convert benzenes or naphthalenes into pyridines, and there are a number of such reactions which involve nitrenes or nitrenoid species. A number of substituted benzenes have been treated with sulfonyl diazide or carbonyl diazide and moderate yields of pyridines recorded (27CB1717). Thus p-xylene gives 2,5-dimethylpyridine there is no indication of the fate of the carbon atom which is lost. More controlled reaction is possible in intramolecular insertions. The examples in which o-nitrotoluene is converted into a derivative (759) of 2-acetylpyridine, and where 2,3-diazidonaphthalenes give 3-cyanoisoquinolines (760) are quoted in a review (81 AHC(28)231>. 

Problem 11.17 Indicate by an arrow the position(s) most likely to undergo electrophilic substitution in each of the following compounds. List the number of the above rule(s) used in making your prediction, (a) m-xylene, (6) p-nitrotoluene, (c) m-chloronitrobenzene, (d) p-methoxytoluene, (e) p-chlorotoluene, (/) m-nilrotoluene, (g) o-methylphenol (o-cresol). 

Similarly with the raising of the b.p. in violet or reddish-violet soln. of iodine in benzophenone, carbon disulphide, ethyl chloride, chloroform, carbon tetrachloride, ethylene chloride or benzene or in brown soln. of ethyl alcohol, methyl alcohol, thymol, ethyl ether, methylal, or acetone. The values for the last three solvents were rather low, presumably because of the chemical action of solute on solvent. High values with benzene are attributed to the formation of a solid soln. of solvent and solid. Confirmatory results were found by J. Hertz with naphthalene, and by E. Beckmann and P. Wantig with pyridine. The results by I. von Ostromisslensky (o-nitrotoluene), by G. Kriiss and E. Thiele (glacial acetic acid), and by H. Gautier and G. Charpy indicate polymerization, but they are not considered to be reliable. 

The reaction was carried out using Nafion-H and polystyrene sul-phonic acid resin catalyst at 180°C and 140°C, respectively, which are their maximum temperatures of use 2-nitrotoluene solvent and 10% w/w catalyst. Conversions of 20% and 1.5% were obtained at the end of six hours indicating that higher temperatures will be necessary to achieve appreciable rates on these catalysts. Since these catalysts are not structurally stable above the respective temperatures, they appear to be unsuitable for this application. The reaction was also carried out using triflic acid as catalyst at various temperatures. The results are shown in Fig.3. Surprisingly, the reaction did not proceed beyond 40% conversion in spite of the high acidity of the catalyst. 

Take et al. (69) extended the acid strength range of the n-butylamine titration method. They employed indicators such as 4-nitrotoluene (pKa = - 10.5) and 2,4-dinitrotoluene (pKa = - 12.8), which are considerably less basic than the other Hammett indicators used to measure surface acidity. Endpoints were determined spectrophotometrically. These authors found that the acid sites on silica-alumina catalyst had an acid strength corresponding to an H0 between - 10.5 and - 12.8 a few sites had even higher acid strengths (H0 < 12.8). Strong acid sites were eliminated when silica-alumina was poisoned with sodium ions. 

Up to a // value of — 10, all indicators are primary amines and are therefore suitable for the measurement of the Hammett H() function. For stronger acids, new indicators such as nitro compounds have to be used. Although the acidity function scale based upon nitro compounds as indicators may not be a satisfactory extension of the aniline indicator scale, Gillespie and Peel18 have shown that the most basic nitro compound indicator, para-nitrotoluene overlaps in a satisfactory manner with the weakest indicator in the aniline series, 2,4,6-trinitroaniline. Thus, the acidity measurements using the nitro compounds may be considered to give the best semiquantitative picture of the acidity of the various superacid systems. 

The reduction of the mononitrotoluenes to toluidins by the use of iron and hydrochloric acid forms the basis for a method of estimation of the para isomer in crude nitrotoluene. (3) A weighed amount of the mixed toluidins is dissolved in ether, and then ethereal oxalic acid is added. The toluidins all form compounds with oxalic acid, and all but the para compound are soluble in ether. The solution is then filtered, the residue washed with ether, then dissolved in water and titrated with N/10 sodium hydroxide, using phenolphthalein as the indicator. 

Cerfontain and Telder [48] acquired an indication of the possible reversibility of aromatic nitration of anthracene-9-d, and finally Olah and associates [49] obtained evidence of the reversibility of the nitration of 9-nitroanthracene and pentamethylnitrobenzene when they found that these substances catalysed by superacids can yield nitrobenzene, nitrotoluene and nitromesytylene when reacted with benzene, toluene and mesitylene respectively. They suggested the mechanism as follows ... 

As shown in Fig. 1, an induction period of 30-75 min was observed over all zeolite and MCM catalysts in the vapor phase runs. During this induction period, no toluene or products were observed in the effluent toluene and nitrotoluene appeared only when the catalyst seemed to become saturated. Examination of the reactor effluent indicated that this adsorption only occurred when the two reactants were fed to the system simultaneously. AVhen either toluene or NOj was fed separately, no adsorption was observed. For example, in one experiment, toluene was passed over the catalyst for 90 min. without noticeable adsorption. Then, as soon as the NOj flow was started, the toluene signal disappeared for about 50 min., after which both unreacted toluene and nitrotoluene products started to appear. It seems that the presence of NOj enhances the adsorption of the aromatic molecule which in turn is necessary for the catalytic process. However, this extensive adsorption may, simultaneously, cause pore plugging and catalyst deactivation. 

A similar shape selective effect was observed in the liquid phase. Those catalysts with the smaller pore and channel openings were more selective for para-nitrotoluene. However, in the liquid phase, no induction period was observed. Rather, all catalysts exhibited significant deactivation throughout time on stream and after 5 hrs. little of the original activity remained. As shown in Fig. 3, the para selectivity was found to decrease with time on stream. This would indicate that deactivation occurs within the pore channels effectively reducing the preferential capacity of the catalyst to generate the para isomer. The decrease in para selectivity was not evident on Beta zeolite, which has larger pores and may allow for a more uniform production of... 

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