Induction nitrobenzene

A silicon atom might be expected to release electrons inductively, but because of empty 7-orbitals shows the overall character ( + 7 —717). Nitration of trimethylsilylbenzene with nitric acid in acetic anhydride at —10 to o °C gives 25-5,39-8,30-2 and 6-8 %, respectively, of 0-, m-, and /)-nitro-trimethylsilylbenzene and nitrobenzene, with a rate of reaction relative to that of benzene of about 1-5. The figures give no indication of an important conjugative effect. 

In nitrobenzene the nitro group has a large electron affinity, and accordingly draws electrons away from the ring. The resonance effect works in the same direction, and, as a result, all positions have a deficiency of electrons. The meta positions are least affected, and the substitution takes place there with difficulty. In aniline, the inductive effect and the resonance effect oppose each other, but the latter wins out, and very easy o-p substitution takes place. 

Aromatic nitrocompounds (see Fig. 21) such as nitrobenzene and the dinitrobenzenes diminish the rate of polymerization of styrene without suppressing it altogether and without introducing an induction periodi.e., they are typical retarders. Larger quantities are required to produce significant reductions in the rate, and the retardation persists throughout the polymerization, suggests... 

Figure 5.4-61. Induction times 4-nitrotoluene, iso, ad nitrobenzene, O iso, ad (adapted from Grewer, 1994).

When 1,2-dichloroethane, DCE (e = 10.37), or u-nitroanisole, o-NA (e = 5.23), was employed instead of nitrobenzene (e = 34.78), the induction time and period with o-NA were obviously less than those with NB or DCE. It should be noted that, in case of o-NA, the sustained oscillation was observable even with cxpatphe of less than 0.01 M, though the oscillation was not observed with NB or DCE. The result suggests that ocsXPhB is the essential factor for the appearance of the oscillation, taking into account that the ion pair formation is more serious in o-NA than in NB or DCE. 

Subsequent DTA investigation showed that an exothermic reaction set in above 75°C after an induction period depending on the initial temperature and concentration of reactants, which attained nearly 300°C, well above the decomposition point of the cyclic ester component (170°C). The reaction conditions used could have permitted local over-concentration and overheating effects to occur, owing to slow dissolution of the clumped solid ester and aniline in the nitrobenzene solvent [ ] Crude carbyl sulfate contains excess sulfur trioxide [2]. 

Menshutkin reaction between jV,Ar-dimethyl-d6-aniline and methyl tosylate in nitrobenzene at 51.3°C (21) is consistent with an inductive KIE resulting from the increased electron density on the nitrogen (the nucleophilicity), a steric explanation was preferred for three reasons. 

Deprotonation provides the necessary electron push to kick out the electron pair joining C(6) with the nitrobenzene oxygen. If, however, N(l) is alkylated (as with the nucleosides and nucleotides), OH catalysis is much less efficient since it now proceeds by deprotonation from N(3) (with the uracils) or from the amino group at C(4) (with the cytosines). In these cases the area of deprotonation is separated from the reaction site by a (hydroxy)methylene group which means that the increase in electron density that results from deprotonation at N(3) is transferable to the reaction site only through the carbon skeleton (inductive effect), which is of course inefficient as compared to the electron-pair donation from N(l) (mesomeric effect) [26]. Reaction 15 is a 1 1 model for the catalytic effect of OH on the heterolysis of peroxyl radicals from pyrimidine-6-yl radicals (see Sect. 2.4). 

Reduction of Nitrobenzenes. Nitrobenzene was injected in small increments into 200 ml. of prehydrogenated (258 ml. of H2) cyanocobaltate(II) solution (0.15M cobalt, GN/Co = 5.1). After an induction period of approximately 4 minutes, hydrogen absorption commenced ... 

Nitrobenzene. Observations made on the formation of cyanocobaltate(II) in the presence of excess nitrobenzene, and on the addition of an excess of this substrate to the prehydrogenated complex, were identical to those made with benzoquinone as the substrate. However, a difference was noted when less than stoichiometric quantities of nitrobenzene were added. After a short induction period of approximately 4 minutes, hydrogen absorption commenced, 3.3 atoms of hydrogen being absorbed per mole of substrate (no absorption occurred with benzoquinone in the absence of added alkali). Further additions of small incre-... 

The electrical conductivity isotherms of these systems are represented in Fig. 2, and the data are given in Tables 6-9. Tbe product x rf, which was used in our earlier papers [ 1] as a suitable measure of the extent of basic ionization in sulphuric acid solutions, can here be substituted simply by conductivity [6], because the differences in viscosities of these mixtures in the region of sulphuric acid are not considerable. It can be seen that the values of the electrical conductivities increase in the order nitrobenzene < m-nitrotoluene < o-nitrotoluene < p-nitrotoluene. This means that the basicities of these compounds increase in the same order, our results in that respect being in complete agreement with the conclusions of Gillespie and Solomons [6]. This increase of basicity is the result of the positive inductive influence of the methyl group in the benzene ring, but steric effects also play some part [6]. 

Asymmetric epoxidation.1 Simple, unfunctionalized olefins are epoxidized at 20 in nitrobenzene to (R)-cpoxidcs with 15-35% ce. Chemical yields are 70%. Alkyl substitution increases the rate of epoxidation, but steric hindrance decreases the asymmetric induction. 

Sodium chloroaurate (NaAuCl4 2HaO) initiates polymerization of VCZ both thermally and photochemically. When the polymerization is conducted in nitrobenzene, photopolymerization under illumination of near ultraviolet to visible light proceeds with remarkable rapidity, whereas thermal polymerization starts after an induction period as shown in Fig. 8. This is a unique example of photoacceleration of cationic polymerization. Since the initiation mechanism is different from known cationic polymerization, the thermal system will be mentioned briefly before the discussion of the photochemical system. 

It can be seen from this figure that the steady state production of nitrosobenzene is preceded by an induction period, in which aniline is the main product. Further, small amounts of azobenzene and azoxybenzene are formed throughout the reaction. The existence of an autoredox reaction implies that a selectivity of 100% from nitrobenzene to nitrosobenzene is impossible. After the induction period the selectivity of nitrobenzene to nitrosobenzene becomes above 90% of the reduction products. The extent of conversion of nitrobenzene is also time dependent. In the steady state situation about 20% of the nitrobenzene is converted, after an initial conversion of 65%. 

J.A. Bond, et al., Induction of hepatic and testicular lesions in Fischer 344 rats by single oral doses of nitrobenzene. Fundam. Appl. Toxicol. 1 389-394, 1981. 

The nitro group has a considerable influence on the properties of the whole molecule of an aromatic compound. For example, owing to the presence of the nitro group, nitrobenzene does not take part in the Friedel-Crafts reaction. The reactivity of a chlorine atom, brought about by the presence of a nitro group in the ortho or para position, may be represented by a diagram based on the induction effect (la). 

Recently Rumanian authors (77) reported that N-vinylcarbazole polymerizes rapidly without induction period to solid products under the influence of nitromethane or nitroethane at 70° C. In nitrobenzene diluent the polymerization is even faster and somewhat higher molecular weight products are formed. The polymerization mechanism is visualized as follows ... 

Therefore the electron substituent effects in radical dianions of 2-substituted 5(6)-nitrobenzimidazoles are transmitted with approximately equal contributions of inductive and resonance components. A similar picture is observed for para-substituted nitrobenzene radical anions also [689, 883], Actually, the aN(N02) correlation of 2-substituted 5(6)-nitrobenzimidazoles RDA (RDA BI) with the aN(N02) of para-substituted nitrobenzene RA (RA Bz) indicates the same mechanism of substituent effects transmission but with different intensity, as shown in equation (3.4) ... 

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