AROMATIC COMPOUNDS 263 



Phthalic Acids. 



The three phthalic acids, or benzene dicarboxylic acids, 

 COOH COOH COOH 



COOH 



Ortho, or Meta, or Para, or 



phthalic acid, isophthalic acid, terephthalic acid, 



are obtained by oxidising the xylenes with nitric acid, or the toluic 

 (methyl benzoic) acids with permanganate. Phthalic acid results from the 

 oxidation of naphthalene. 



They are crystalline solids resembling benzoic acid. Phthalic acid on 

 heating is converted into phthalic anhydride, 



a substance used in making fluorescein, eosin and other dyes. 



CH 8 

 Nitrotoluenes, C 6 HA 



X N0 2 . 



The o- and p-compounds are obtained by nitrating toluene ; the m-com- 

 pound is obtained by indirect methods. They are all solids. 



CH 3 

 Aminotoluenes, or Toluidines, C 6 H 4 <T 



NH 2 . 



o- and p-Toluidine are obtained by reducing o- and p-nitrotoluene ; 

 o-toluidine is an oil, p-toluidine is a crystalline solid. The m-compound is 

 obtained in a similar way and is an oil. 



They yield diazonium salts with nitrous acid and behave generally like 

 aniline. 



Nitfanilines, C 6 H / 



X NH 2 . 



m-Nitraniline is obtained by the partial reduction of m-din!trobenzene 

 with alcoholic ammonium sulphide. The o- and p-nitraniline cannot be ob- 

 tained by nitrating aniline, but are obtained by nitrating acetanilide and 

 saponifying the nitro-acetanilides. 



CH 3 

 Toluene-Sulphonic Acids, C 6 H 4 <f 



X SO 3 H. 



The o- and p-compounds result by sulphonating toluene, the o-compound 

 being the chief product. They yield the cresols on fusion with potash. 



Sulphanilic Acid, C 6 H 4 <^ 



X SO 3 H. 



The p-compound is obtained by heating aniline sulphate at 200 for 

 some hours. 



It is a colourless crystalline solid easily soluble in hot water, very little 

 in cold. It does not behave as a base, but the amino group can be diazotised. 

 It is used largely in making dyes. 



