Origin of Difructose Anhydrides from Inulin

A possible mechanism for the origin of the difructose anhydrides from inulin has been suggested by McDonald and Jackson in the following paragraph  

Schlubaeh, Knoop and Liu found indications that a more readily hydrolyzed di-D-fructose anhydride was an intermediate product in the hydrolysis of irisin. 

Jackson and Goergen found that when D-fructose was treated with sulfuric acid under conditions similar to those used in preparing the difructose anhydrides from inulin, no condensation of the D-fructose took place. 

It is interesting to note that the formation of the dioxane ring stabilizes the anhydrides as to their pyranose or furanose structures, difructose anhydride I as 2,1 l,2 -di-D-fructofuranose and diheterolevulosan as 2,1 l,2 -di-D-fructopyranose. 

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