( 281 ) 



of isomers were the follo\>inf^. Firstlj^ all six isomers were known, 

 altiiough the mode of preparation of some of them left much to be 

 desii*ed. Secondh', this series gave an opportunity to test V. Meyer's 

 "ester rule" with a much more extensive material than hitherto and 

 .to stud)^ what influence is exercised by the presence of two groups 

 present in the different positions in the core, on the esterilication 

 ■velocity^ and to compare this with that velocity in the monosub- 

 stituted benzoic acids. Thirdly, tlie dissociation constants of these acids 

 could be subjected to a comparative research and their values con- 

 nected with tliose of the esterification constants. Finally, the melting 

 points and sp. gr. of the acids and their esters could be investigated 

 in their relation to these same constants in other such series. 

 - The six dinitrobenzoic acids were prepared as follows. The sym- 

 metric acid 1,3,5, (1 always indicates the position of the carboxyl 

 group) was obtained by nitration of benzoic acid or of 7?z-nitroben- 

 zoic acid. All the others were prepared by oxidation of the correspon- 

 ding dinitrotoluenes. This oxidation was carried out partly by per- 

 manganate in sulphuric acid solution, partly by prolonged boiling 

 with nitric acid (sp. gr. 1.4) in a reflux apparatus. 



We had to prepare ourselves three of the dinitrotoluenes, namely, 

 (1,3,4), (1,3,6) and (1,3,2), {CH, on 1); (1.2,4) and (1,2,6) are com- 

 mercial articles whilst (1,3,5) was not wanted because the orre- 

 sponding acid, as already stated, w^as readily accessible- by direct 

 nitration of benzoic acid. As will be seen the three dinitrotoluenes 

 which had to be prepared are all derivatives of m-nitrotoluene and 

 it was, tlierefore, tried which of those might be obtained by a further 

 nitration of the same. 



?/i-Nitrotoluene, which may now be obtained from de Haen in a 

 pure condition and at a reasonable price was, therefore, treated with 

 a mixture of nitric and sulphuric acids at 50^. On cooling the 

 nitration-product a considerable amount of 1,3,4 dinitrotoluene crys- 

 tallised out, which could be still further increased by fractionated 

 distillation in vacuo of the liquid portion ; the highest fractions always 

 became solid and again yielded this dinitrotoluene, so that finally 

 about 65 grms. of dinitrotoluene (1,3,4) were obtained from 100 grms. 

 of ?7i-nitrotoluene, 



As the fractions with a lower boiling point, although almost free 

 from dinitrotoluene (1,3,4), did not solidify on cooling, it was thought 

 probable that they might contain, besides a little of the above dinitro- 

 toluene, more than one of tiie other isomers, whose formation in the 

 nitration of y//-nitrololueno is theoretically possible. If we consider 



19 



Proceedings Royal Acad. Amsterdam. Vol IX. 



