Model for random hydrolysis and end degradation of linear polysaccharides: application to the thermal treatment of mannan in solution

The kinetics for homogeneous hydrolysis of mannan was studied in a batch reactor at temps. from 160 to 220 Deg. A formate buffer ensured a pH of 3.8-4.0, measured at 25 Deg. Samples were analyzed for oligosaccharides at a d.p. of ?6 and also for the total amt. of mannose after acid hydrolysis. A math. model with 2 reactions, i.e., (1) random hydrolysis of the glucosidic bonds; and (2) degrdn. of the reducing end of the mol., describes accurately the time course of oligosaccharides. Optimized rate consts. follow closely an Arrhenius relationship, with the degrdn. having a higher activation energy (140 kJ/mol) than the hydrolysis (113 kJ/mol). The math. model has the advantage that prodn. of small mols. is independent of the initial chain-length distribution, as long as the av. initial chain length is some 5 times longer than the largest species measured. It can be applied to 1st-order depolymn. of other linear polymers with 1 link type in order to det. reaction rate consts. or make predictions about mol. wt. distribution on the base of known reaction rate consts. [on SciFinder (R)]