SANGER-RIEGEL. — PYROSULPH. CHLORIDE-CHLORSULPH. ACID. 705 



boiling point, and, indeed, not only to the apparent exclusion of (1) 

 and (3), but to the completion of (2). 



In addition to the phenomena of dissociation as expressed by the 

 above reactions, we have found that the sulphur trioxide formed by 

 the dissociation dehydrates the chlorsulphonic acid to a slight extent, 

 giving pyrosulphuryl chloride.®® 



(6) 2SO2OHCI + SO3 ^ S2O5CI2 + S02(OH)2. 



As to the character of the dissociation at temperatures above the 

 boiling point, we can ourselves offer no direct evidence. Behrend ** 

 obtained a good yield of sulphuryl chloride by heating in a closed tube 

 at 170° to 180°, and considered that reaction (2) took place. Beckurts 

 and Otto *^ explain the reaction by the equations 



(7) 2SO2OHCI = CI2 + H2S2O6, 



(8) H2S2O6 = SO2 + S02(OH)2, 

 (9)_Cl2 + SO2 = SO2CI2. 



Since they found chlorine and sulphur dioxide in the closed tube at 

 180°, reaction (9) would not be complete. But Ruff found the equilib- 

 rium at 170° in a closed tube to be 



(2) 2SO2OHCI ^ SO2CI2 + S02(OH)2 

 2.5 mol. 1 mol. 1 mol. 



and lowered the temperature of complete decomposition to the boiling 

 point by the catalyser. As in the presence of the catalyser Ruff found 

 that no more sulphuryl chloride was formed by passing chlorine and 

 sulphur dioxide into the boiling chlorsulphonic acid than without 

 them, they were not essential to the formation of sulphuryl chloride, 

 and reaction (9) evidently did not take place. It is also unnecessary 

 to assume reactions (7) and (8) to explain the formation of sulphur 

 dioxide and chlorine. 



Ruff considered that at temperatures higher than 180° reactions 

 (1) and (3) took place; Heumann and Kochlin^s that chlorsulphonic 

 acid was completely dissociated at 442°, according to reaction (5), but 

 at 184° they found the dissociation incomplete. 



That sulphuryl chloride, chlorine and sulphur dioxide are coexistent 

 products of the dissociation at temperatures short of that necessary for 



*" For the hydration of pyrosulphuryl chloride by sulphuric acid, v. p. 717. 

 VOL. XLVII. — 45. 



