O-nitro compounds

Nitrations in acetic anhydride, or in solutions containing benzoyl nitrate ( 5.2) or dinitrogen pentoxide ( 4.2.3) have long been associated with the formation from some aromatics of higher proportions of o-nitro-compounds than are formed under other conditions. 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples of p-nitrophenol. Usually, the o-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pKg values. The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers of known pH (see for example Table 19, p. 43) from a solution of the substance in a suitable solvent such as ethyl ether. This method is more satisfactory and less laborious the larger the difference between the pK value of the impurity and the desired compound. Heterocyclic nitro compounds require similar treatment to the nitroanilines. Neutral nitro compounds can be steam distilled. 

The crude o-nitro-compound is reduced in the usual manner and the product recrystallised from 75 per cent, alcohol. The amine melts at 142-5° C. (corr.), and forms minute pale greenish-yellow lustrous scales, W hich do not exhibit fluorescence in alcohol solution. 

The o-nitro compounds show a much smaller decrease in reduction rate when the nitro group has been hydrogenolyzed, and it was necessary to stop the reduction immediately after absorption of the calculated amount of hydrogen. On further reduction hydrocarbostyril was formed in 80% yield (if R = H, the yield is 90%). 

To a mixture of 103 grams of 62 per cent nitric acid (40° B6) and 300 grams of 80 per cent sulfuric acid, 128 grams of naphthalene is added. The mixture is stirred continuously for 6 hours at 50°C., and then the temperature is raised to 60° during the course of 1 hour. On cooling the mixture, the nitronaphthalene floats as a porous cake on the surface of the acid. It contains about 90 to 92 per cent of the o-nitro compound, 4 to 5 per cent of the j3-nitronaphthalene, 2 to 3 per cent of dinitronaphthalene, and about 0.5 per cent of 2,4-dinitro-l-naphthol (Martins yellow). 

Dingu and Sorguyl /V-Nitro-O-Nitro compounds References Appendix... 

The nitroxonium and nitropyridinium (or nitrocollidinium) ions are efficient nitrating agents. They also can form O-nitro compounds. 

Allhougli niiraie esters continue to be widely used and are important explosives their cliemical properties arc described to a much lesser extent than those of C nitro compounds. This is understandable when considering the wide use of C-nitro comjHiuiids. particularly aromatic ones, not only as explosives but in a great variety of uses as intermediates and finished products, l or this reason the excellent monograph of l atai. series edited by M. Feuer (1). does not cuniatn a chapter on 0 nitro compounds and the only review papers dedicated solely to O nitro compounds were by Boschan. Merrow, Van Dolah (2] and Connon 3l. 

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