Benzene, halogeno-, reactivity

Quantitative eomparisons of aromatic reactivities were made by using the competitive method with solutions of nitronium tetrafluoroborate in sulpholan, and a concentration of aromatic compounds 10 times that of the salt. To achieve this condition considerable proportions of the aromatic compoimds were added to the medium, thus depriving the sulpholan of its role as true solvent thus, in the nitration of the alkyl- and halogeno-benzenes, the description of the experimental method shows that about 50-60 cm of mixed aromatic compounds were dissolved in a total of 130 cm of sulpholan. 

The activated halogenothiophene is more reactive than a similarly activated halogeno-benzene. A quantitative study of the rate of piperidino-debromination of six isomeric bromonitrothiophenes reveals that these substrates react considerably faster than the corresponding bromonitrobenzenes. As in electrophilic substitution, the 2,3-, 2,4- and 2,5-relationships have been equated to ortho, meta and para substitution in benzene derivatives. Although there is some validity in this, a few inexplicable results have been encountered in the above study thus 2-bromo-4-nitrothiophene reacts much faster than either 2-bromo-3-nitro- or 2-bromo-5-nitro-thiophene (64AHC(3)285>. 

More recently nitro derivatives of tluorohenzcne have received sornc attention. Olah, Kuhn and Flood (1 described the nitration of halogeno derivatives of benzene with NO2 BF4 (Made of N2O5, HE and BF3) in tetramethylenesulphonc as a solvent at 25 C and eslabiUhcd different reactivities as compared with benzene (Table Al) ... 

Remark Study of difluorobenzenes54 shows that reactivities of these compounds are altogether what we saw with monofluorobenzenes (Chapter IV.2.1.2.1.) and with polychlorobenzenes. Those halogeno derivatives allow the synthesis of diamino benzenes and, more interestingly, of mono-aminofluorobenzenes. 

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