Nitro-benzene systems

The system was designed to recycle the HgCl2 in nitro benzene without removal from the reactor. However, the process was severely handicapped by the bad reputation of mercury compounds whatever the strictly controlled... 

D-Labelling studies establish that a cyclopropylcarbinyl metal complex is an intermediate in the nickel-promoted rearrangement of penta-1,4-diene to isoprene. Studies of homoconjugation in diary Imethyl systems show that there is an important contribution from (844) in the methanolysis of p-(4-chloro-3-nitrobenzyl)nitro-benzene. ... 

Almost 200 pesticides were analyzed in various systems using dichloromethane and ethyl acetate (129). These pesticides were visualized by the following selective detection methods (a) o-tolidine-potassium iodide, (b) p-nitro-benzene-diazonium-fluoborate, (c) silver nitrate with UV irradiation, (d) p-dimethylaminobenzaldehyde, (e) bioassays with either fungispores of Aspergillus nigeror an enzyme inhibition method. When horse blood serum was the enzyme source, acetylcholine iodide was its substrate in the presence of 2,6-dichloro-phenol-indophenol. Naphthyl acetate was applied as the substrate for the human blood plasma esterases. The Rf values and detection limits were also published (129). 

This reaction is most often carried out with R = aryl, so the net result is the same as in 14-17, though the reagent is different. It is used less often than 14-17, but the scope is similar. When R = alkyl, the scope is more limited. Only certain aromatic compounds, particularly benzene rings with two or more nitro groups, and fused ring systems, can be alkylated by this procedure. 1,4-Quinones can be alkylated with diacyl peroxides or with lead tetraacetate (methylation occurs with this reagent). 

The sterically unbiased dienes, 5,5-diarylcyclopentadienes 90, wherein one of the aryl groups is substituted with NO, Cl and NCCHj), were designed and synthesized by Halterman et al. [163] Diels-Alder cycloaddition with dimethyl acetylenedicarbo-xylate at reflux (81 °C) was studied syn addition (with respect to the substituted benzene) was favored in the case of the nitro group (90a, X = NO ) (syrr.anti = 68 32), whereas anti addition (with respect to the substituted benzene) is favored in the case of dimethylamino group (90b, X = N(CH3)2) (syn anti = 38 62). The facial preference is consistent with those observed in the hydride reduction of the relevant 2,2-diaryl-cyclopentanones 8 with sodium borohydride, and in dihydroxylation of 3,3-diarylcy-clopentenes 43 with osmium trioxide. In the present system, the interaction of the diene n orbital with the o bonds at the (3 positions (at the 5 position) is symmetry-forbidden. Thus, the major product results from approach of the dienophile from the face opposite the better n electron donor at the (3 positions, in a similar manner to spiro conjugation. Unsymmetrization of the diene % orbitals is inherent in 90, and this is consistent with the observed facial selectivities (91 for 90a 92 for 90b). 

A group with a more powerful (electron-withdrawing) inductive effect, e.g. NOa, is found to have rather more influence. Electron-withdrawal is intensified when the nitro group is in the o- or p-position, for the interaction of the unshared pair of the amino nitrogen with the delocalised it orbital system of the benzene nucleus is then enhanced. The neutral molecule is thus stabilised even further with respect to the cation, resulting in further weakening as a base. Thus the nitro-anilines are found to have related p a values ... 

There is no difference in the ability of photogeneration of radicals between systems that show photosubstitution and systems that do not, for example amines with 3,5-dinitroanisole and m-dinitro-benzene, respectively. This indicates that the formation of radicals from excited aromatic nitro-compounds in the presence of nucleophiles has no direct relation with the photosubstitution reaction. 

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