THE PREPARATION OF ANHYDRIDES OF 

 ORGANIC ACIDS 



THE reagents most frequently used for the preparation of 

 anhydrides and chlorides of organic acids are the chlorine 

 derivatives of phosphorous and phosphoric acids, and this 

 notwithstanding the fact that these compounds are difficult to 

 handle, and give rise in some cases to products contaminated 

 with phosphorus compounds which are not easily removed. 

 It thus appears remarkable that chlorides of other inorganic 

 acids have not come into general use for similar purposes. 



The inorganic chlorides generally, however, are no less 

 troublesome to work with than those of phosphorus, but, 

 apart from this, the number of such compounds available 

 for practical purposes is limited. In the third group of the 

 periodic system we have boron trichloride, but the cost of 

 this compound at once puts it out of court as a reagent. In 

 the fourth group occurs carbonyl chloride, the use of which 

 as a means of preparing organic anhydrides has been suggested 

 by Hentschel (Ber., 1884, 17, 1285). Carbon tetrachloride does 

 not appear to have been used, but the application of silicon 

 tetrachloride to this purpose has been patented (U.S. Pat. 

 944372), as has that of silicon tetrafluoride (D. R. P. 171146). 

 In the fifth group none of the chlorides except those of phos- 

 phorus have been employed : the action of nitrosyl chloride 

 on silver salts is referred to below. In the sixth group we 

 have sulphur with the numerous acids derived from its oxides. 

 The most commonly occurring of the chloroanhydrides of these 

 acids is sulphuryl chloride, and this compound has been 

 used for anhydride formation, as has a mixture of sulphur 

 dioxide and chlorine (Abstr., 1906, i. 3, 621 ; D. R. P. 167304). 



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