Dinitrobenzenes regioselective

Control of the regioselectivity of VNS is important. It is governed by three major factors the structure of the nitroarene the nature of the nucleophile, and the reaction conditions, especially solvent and base. The different effect of methoxy and hydroxy groups is interesting the reaction of l-methoxy-2,4-dinitrobenzene with chloromethyl phenyl sulfone proceeds in... 

A copper salt assists the control of the regioselectivity in VNS for m-dinitrobenzene. For instance, the reaction of m-dinitrobenzene with 4-iodophenol in the presence of copper tert-butoxide gives asymmetrical biphenyl in 78% yield (Eq. 9.34).61... 

The regioselective cross-coupling between anions of bromomalonate esters orbromoacetate esters and m-dinitrobenzene proceeds in the presence of copper fert-butoxide to give the 2-substituted product. Without the copper salt, the 4-substituted isomer is the only product (Eq. 9.35).62... 

Cognate preparation. Reduction of 2,4-dinitrophenol. It is an interesting student exercise to carry out the reduction of 2,4-dinitrophenol under the conditions described above for m-dinitrobenzene. The spectroscopic features of the isolated and purified product, together with the melting point, in comparison with the literature values for the possible isomers, should enable a deduction to be made on the regioselectivity of the reaction. 

HMordenite, HFaujasite-780, HFaujasite 720 and Na-Faujasite zeolites. Among the different catalysts, HFaujasite-720 was the most active and selective catalyst towards 2,4-dinitrotoluene, achieving a yield of dinitrotoluenes of 92 % with a ratio of 2,4- to 2,6- isomers of 4.3 1 in 3 min reaction time. Using this zeolite, l-chloro-2-nitrobenzene and pyrazole were also nitrated regioselectively to obtain l-chloro-2,4-dinitrobenzene in a l-chloro-2,4-dinitro l-chloro-2,6-dinitro ratio of 30 1, and 1,4-dinitropyrazole in 80% yield, respectively. The authors proposed a nitration mechanism in which the protons in the zeolite are replaced by nitronium ions derived from N2Os in a fast pre-equilibrium process. This produces active sites for transfer of nitronium ion from faujasite to aromatic in the rate-controlling step. 

At the dinitration of chlorobenzene, the regioselection in the presence of zeolites was again improved in favour of the 2,4-dinitro isomer 2,4-12,6- = 48) [38]. In the presence of Faujasite-712, the nitration of o-chlorobenzene with N Oj gives a mixture of l-chloro-2,4-dinitro- and l-chloro-2,6-dinitrobenzenes in about 30 1 ratio [39]. Thus, the procedure for the regioselective dinitration of toluene and chlorobenzene described above, which involves the Kyodai nitration in polar organic solvent in the presence of zeolites, provides a new efficient route to 2,4-dinitro derivatives under nonacid conditions. The method is easy to carry out, environmentally benign, and economical. 

Huertas, I., Gallardo, I., and Marquet, J., Direct formation of aromatic C-N bonds. Regioselective amination of m-dinitrobenzene via fluoride promoted nucleophilic aromatic photosubstitution for hydrogen. Tetrahedron Lett., 41, 279, 2000. 

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