Preparation of the vicinal nitro-isophthaUc acid {1, 3, 2). Grevingk has 

 observed that in the nitration of m-xylene with nitric and sulphuric acid 



CH, 

 N0,/\ 



there is formed, besides the symmetric dinitro-m-xjlene | | 



\/CIl3 



NO2 



as main product, also the vicinal isomer | | . On reduction 



NO2 

 w^ith hydrogen sulphide both dinitroxylenes pass into nitro-xylidenes 



CHg 



which are comparatively easy to separate. The nitro-xylidene | | 



\/CH3 



yields by elimination of the NH^-group vicinal nitro-m-xylene. Whilst 

 however, Grevingk states that he obtained a yield of 257o of vicinal 

 nitroxylidene we have never obtained more than a few per cent of 

 the same so that the preparation of vicinal nitro-m-xylene in this 

 manner is a very tedious one, at least when large quantities are 

 required. When it appeared tlmt the "fabrique de produits chimiques 

 de Thann et Mulhouse" exported this nitroxylene, the oxidation, 

 although to some extent with material of our own manufacture, has' 

 been mainly carried out with the commercial product. This oxidation 

 was also done with permanganate in alkaline solution. The vicinal 

 nitro-isophthalic acid is a compound soluble with great difficulty in 

 cold, but fairly soluble in hot water, crystallising in small beautiful, 

 shining needles, which melt at 300^. It crystallises without any water 

 of crystallisation and is readily soluble in alcohol and ether, from 

 which it is again deposited in small needles. 



The three possible mononitroisophthalic acids having now been 

 obtained, we could take in hand the problem to ascertain the nature 

 of the byproduct formed in the nitration of isopthalic acid. After the 

 bulk of the nitroisophtalic acid formed had been removed by crystal- 

 lisation, a residue was left which was far more soluble in water 

 than this acid, which pointed to the presence of the asymmetric 

 nitro-acid and which, indeed, could be separated by fractional crystal- 

 lisation. We will see presently how it was ascertained that the 

 nitration product was really only a mixture of the symmetric and 

 the asymmetric acid. 



As in the determination of the relative quantities in which the 

 nitration products are formed, use was made of solubility determina 



