ANHYDRIDES OF ORGANIC ACIDS 229 



Benzoyl thiosulphite crystallises . in well-defined colourless 

 crystals. 



Sulphur. Molecular Weight 



(in Benzene F.P. Method). 



Found 21-32 per cent. 281 



(C 6 H S COO) 2 S 2 requires . 20'92 per cent. 306 



The compound is extremely unstable and soon turns yellow 

 owing to spontaneous decomposition, the products of which 

 are benzoic anhydride, sulphur dioxide and free sulphur, 

 as shown by the equation : 



2(C 6 H 5 COO) 2 S 2 = 2(C 6 H 5 CO) 2 0+S0 2 +3S. 



That the formation and decomposition of this substance 

 take place quantitatively is shown by the following Table, 

 where the weights are given of the crude products from 

 3*4 grams of sulphur chloride and 12'5 grams (instead of 

 11 '5 grams) of silver benzoate. The theoretical quantities 

 are calculated by means of the above equations from the 

 weight of sulphur chloride used : 



Calculated. Found. 



Weight of benzoyl thiosulphite (after 

 filtration from silver chloride and dis- 

 tillation of ether), . . . . 7'6 g. 7'6 g. 



Weight of sulphur (residue after extraction 



of the benzoic anhydride with ether), - 95 g. 0'90 g. 



Weight of anhydride (after distillation 



of ether from the ethereal extract), . 5' 65 g. 5 - 60 g. 



The method is widely general, and has been applied to a 

 large number of unsubstituted fatty and aromatic acids and 

 to acids containing halogen and nitro groups, the reactions in 

 all cases being exactly similar to those just described : with 

 acids of high molecular weight such as stearic and naphthoic 

 acids the last traces of sulphur cannot be completely removed. 

 In general, after the decomposition of the intermediate 

 compound is complete, a change which is accelerated, as would 

 be expected, by the application of heat, the anhydride can be 



