Para-substituted nitrobenzenes

Nitrobenzene reacts with the O-trimethylsilyl ketene acetal 663 in the presence of tris(dimethylamino)sulfur(trimefhylsilyl)difluoride (Me2N)3S(Me3SiF2) (TASF) to give the O-silylated adduct 1007 a, which can be oxidized in situ, e. g. by bromine, to give the 4-substituted nitrobenzene 1008 in an overall yield of 79% [87] (Scheme 7.28). With less hindered ketene-acetals, however, mixtures of ortho- and para-substituted nitrobenzenes are obtained. Yet, on reaction of 4-fluoronitroben-zene with the cyclic O-trimethylsilyl ketene acetal 1009 the ortho-substitution product 1010 is obtained in 79% yield [87]. 

In the presence of KOH, /m(benzotriazol-l-yl)methane 729 reacts with nitrobenzenes to produce />-(/fc (bcnzo-triazol-lyl)methyl]nitrobenzenes 730 (Scheme 114) <1996TL347>. This vicarious nucleophilic substitution of hydrogen <1991S103> can be considered as a convenient way to />-nitrobenzaldehydes 731. Meta and para substituted nitrobenzenes do not react with compound 729 under these conditions, probably due to steric reasons, but 1-nitronaphthalene reacts producing a naphthalene analog of derivative 730. 

However, it should be emphasized that the OH loss also occurs from meta- and para-substituted nitrobenzenes provided a side-chain of more than one carbon atom and at least one a-hydrogen atom is present. This loss of OH shows up to a minor, but nevertheless significant, extent. 

Lipkowitz54 studied the 170 shifts of some meta- and para-substituted nitrobenzenes. However, the high concentrations and small range of substituents investigated make these data of limited use. 

Substituent effects on the 170 chemical shifts in meta- and para-substituted nitrobenzenes are presented in Table 13, showing that these shifts are quite sensitive to the nature of the substituent, and range over nearly 40 ppm. Examination of Table 13 shows that the direction of substituent effects is different for 15N and 170 shifts, with electron-withdrawing substituents (such as NO2, CN or CF3) causing upheld 15N and... 

The 6-yl radicals produced by (the selective) [23, 24] addition of OH to C(5) of the C(5)/(6) double bond of naturally occurring pyrimidine bases, nucleosides and nucleotides or those formed by H-abstraction from C(6) of 5,6-dihydro-pyrimidines [25] react with para-substituted nitrobenzenes by addition (k 6xl0 to 2 X s ) to yield nitroxyl-type radicals which were... 

Gough, K.M. and Kaiser, K.L.E., QSAR of the acute toxicity of para-substituted nitrobenzene and aniline derivatives to Photobacterium phosphoreum, in QSAR 88. Proceedings of the Third International Workshop on Quantitative Structure-Activity Relationships in Environmental Toxicology, Turner, J.E., England, M.W., Schultz, T.W., and Kwaak, N.J., Eds., National Technical Information Service, U.S. Department of Commerce, Springfield, VA, 1988, pp. 111-121. 

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) ... 

Nitroarenes are reduced to azoxybenzenes by Bi KOH or Bi NaBH in alcoholic solvents (Scheme 14.113) [239]. Under microwave irradiation the reduction proceeds much more rapidly to give azobenzenes (Scheme 14.114) [239 b]. para-Substituted nitrobenzenes are reduced to para-substituted anilines by Bi-(NH4)2SO4 (Scheme 14.115) [240]. The combined use of BiClj and a reducing agent converts nitroarenes into azoxybenzenes, N-hydroxyanilines, or anilines, depending on the reagents and reaction conditions employed [241-244]. 

Hashimoto S, Kano K. 1970. Photochemical reduction of para-substituted nitrobenzenes in isopropanol. Tetrahedron Lett 40 3509-3512. 

Arylsulfonylindazoles, novel S-HTe receptor antagonists, have been synthesized via the VNS reactions of para-substituted nitrobenzenes with carbanion of chloromethyl aryl sulfones followed by hydrogenation of the nitro group (Scheme 102). Further reaction of ortAo-aminobenzyl sulfones with sodium nitrite-acetic acid gave the desired 5-substituted indazoles of potential biological activity [237, 238]. 

FIGURE 1 Plot of thetoxicities of para-substituted nitrobenzenes (pTm,jQ2) of the general formula N02-CgH4-X versus their octanoi/water partition coefficients (log P) data from TABLE 1. 

---