334 BENZOIC ACID. 



A mixture of concentrated nitric and sulphuric 

 acids converts it into nitrosulphobenzoic add. C 6 H 3 (^"0 2 ) 

 ( CO.OH n -, i ., 



I SO 2 OH w developed crystals, easily soluble in 



water which, when treated with ammonium hydro- 

 sulphide, is transformed into amidosulphobenzoic acid, 



iOO OTT 

 SO 2 ' OH rad^ting, colorless needles. 



When distilled with phosphorus chloride, sulphoben- 

 zoic acid yields metachlorbenzoyl chloride. 



Parasulphobenzoicacid, C 7 H 6 S0 5 = C 6 H< 1 ^ OH 



Is formed in varying quantities, together with the 

 preceding compound, in the preparation of the latter ; 

 and by oxidizing parasulphotoluene with potassium 

 bichromate and sulphuric acid. The free acid is very 

 similar to the meta-acid ; is not, however, deliquescent. 

 The acid barium salt, (C 7 H 5 S0 5 ) 2 Ba + 3ITO, crystallizes 

 in long, flat needles, which are very difficultly soluble 

 in water. 



( OO OTT 



Disulphobenzoic acid, C 6 H 3 , 2 - 2 Is formed 



by the action of concentrated sulphuric acid and phos- 

 phoric anhydride on benzoic acid in sealed tubes. 

 Crystalline, deliquescent mass. The neutral barium 

 salt, (C 7 H 3 S 2 8 ) 2 Ba 3 + TITO, crystallizes in small, well- 

 formed prisms. 



Thiobenzoic acid, C 6 H 5 .CO.SH. Is obtained by 

 the action of benzoyl chloride on an alkaline solution 

 of potassium sulphite and precipitation with hydro- 

 chloric acid. "White, radiating, crystalline mass. Fus- 

 ing point, 24. But slightly soluble in warm water. 

 Not distillable alone, but very easily with water va- 

 por. In ethereal solution, in contact with the air, it 

 easily becomes oxidized, forming benzoyl disulphide 

 (C 6 H 5 .CO) 2 S 2 . 



A thiobenzoic acid, C 6 H 5 .CS.OH, isomeric with the 

 foregoing, is formed, together with benzoic acid, by the 



