416 
as the propionylsulphurie acid, when hydrolyzed, neutralizes three 
equivalents of a basis, and the sulphonic acid only two equivalents. 
The sulphopropionic acid was separated and weighed in the form 
of its baryumsalt. From 1 molecule propionic acid with sulphur- 
trioxide we got an average yield of 0.85 mol. sulphopropionie acid, 
and from 1 mol. propionic acid anhydride with sulphuric acid 
(monohydrate) 0.55 mol. 
Compared with Francuimont’s method, the reaction with sulphur- 
trioxide is experimentally less simple. The reaction is violent, the 
product is more coloured, the baryumsalt likewise, and the yield is 
various. Only for the preparation of large quantities may the reaction 
be recommended. 
FRANCHIMONT’S reaction, however, is very easy to carry out; but 
it is a drawback, that only half the propionic acid anhydride can 
be transformed into the sulphonic acid, the other half returning to 
propionic acid. 
We have therefore tried to combine the advantages of both 
methods, the better yield of the first and the greater purity of the 
product obtained by the second. 
For this purpose, it is possible to mix propionie acid anhydride 
with sulphuric acid, and to treat the product, containing one 
molecule free propionic acid, with the equimolecular quantity of 
sulphurtrioxide. 
However, it is simpler to let the propionic acid anhydride react 
directly with pyrosulphurte acid. 
(CH)2€Q);,0 HSO, = HCH. CH(SO>H). COE, 
By this method we got an average yield of 0.75 mol. sulphonic 
acid from 1 mol. propionic acid anhydride. 
As the pyrosulphurie acid may be added in the crystallized state 
to the propionic acid, the method is easier than the reaction with 
sulphurtrioxyde. The reaction proceeds more quietly and the product 
is purer. 
We have applied this method to acetic acid anhydride also, but 
for such an easily accessible substance, the original method of 
FRANCHIMONT is simpler. 
For the sulphuration of precious carbonic acid anhydrides, the 
method just described may, however, be recommended for its 
higher yield. 
Groningen, Sept. 8, 1919. Org. Chem Lab. of the Univ. 
