SANGER-EIEGEL. — PYROSULPH. CHLORIDE-CHLORSULPH. ACID, 703 



hydrochloric acid passed for seven hours. The product, distilled with 

 hydrochloric acid, gave 107 g. distillate under 162° (theory, 97 g.). 



17. 550 g. oleum (89.3 per cent), treated asiu Preparation 16, gave 

 on distillation with hydrochloric acid, 375 g., boiling mainly from 149° 

 to 151° (theory, 333 g.). 



The amount of chlorsulphonic acid formed in the Williamson reaction 

 depends upon the percentage of sulphur trioxide in the oleum not com- 

 bined as sulphuric acid. The sulphuric acid is unchanged. No pyro- 

 sulphuryl chloride is formed. Attempts to increase the yield from a 

 low oleum by addition of phosphorus pentoxide during the chlorina- 

 tion, according to Muller,^^ were unsatisfactory. While the total 

 weight of product was somewhat increased, yet it was probable that 

 some pyrosulphuryl chloride was formed by the dehydration of the 

 chlorsulphonic acid by phosphorus pentoxide. 



The reaction mixture is best distilled in a current of hydrochloric 

 acid. As will later be shown, the chlorsulphonic acid thus obtained is 

 fairly pure and is made no purer by distillation, owing to the partial 

 dissociation at the boiling point. A pure product is obtained only by 

 crystallization, as will be shown. 



Purification of Chlorsulphonic Acid and Determination of Constants. 



The instability of chlorsulphonic acid under heating was to be in- 

 ferred from the work of other observers, but we hoped to be able to 

 purify it by distillation at reduced pressure, and proceeded for some 

 time under that assumption. It became evident, however, that all our 

 efforts to get a pure product by distillation, whether at normal or re- 

 duced pressure, were nullified by the invariable presence of decomposi- 

 tion products, and that the decomposition was relatively complex. 

 While the subject requires further investigation, we may state here, 

 however, the facts concerning the dissociation which appear most prob- 

 able from our work and that of others. 



The Dissociation of Chlorsulphonic Acid. — Under ordinary condi- 

 tions of temperature and pressure, and in absence of moisture, chlor- 

 sulphonic acid is stable. If, however, it is subjected to diminished 

 pressure or to increased temperature, or to a combination of the two, 

 a partial breaking down occurs, which is proportional to the change of 

 conditions. We regard this breaking down, from our own observations 

 and those of others, as taking place primarily in two directions, which 

 we may represent as follows: 



(1) 2SO2OHCI T^ 2SO3 + 2HCI 



and (2) 2SO2OHCI = SOaClj + S02(OH)2. 



