Exo-enzyme like degradation of a polysaccharide by an inorganic solid acid catalyst

Inulin is a β(1 → 2) linked linear fructose polymer, the reducing end of which is capped by a glucose residue. Upon dissolution in aqueous HCl the polymer is statistically split. During the reaction progress the ratio of glucose to fructose increases and the concentration of sucrose, as an intermediate product, goes through a maximum. However, when the splitting is performed on a dealuminated faujasite zeolite, the ratio of glucose to fructose is constant and equal to the average degree of polymerization; sucrose does not appear as intermediate product. This behavior is explained by a sequential splitting starting from the end of the polymer (exo-mechanism). If the glucose or fructose end is preferred is unknown. Adsorption studies of the polymer fragments show that the polymer enters the pore mouth of the zeolite with a penetration depth limited to the length of maximal 3 saccharide units. The protons in that surface region are 4-5 times more catalytically active than those in HCl.