Degradation of A Nonreducing Cellulose Model, L,5-Anhydro-4-O-β-D-Glucopyranosyl-D-Glucitol, Under Kraft Pulping Conditions

The title compound (1, 1,5-anhydrocelloblitol) was degraded at 170°C in kraft pulping liquor (l. 01 NaOH, 0.21 Na2S) to determine whether the sulfur anions affect the rate-determining and/or product-determining steps of glycosldic bond cleavage. Since the extent of hydrolysis of S−2 to form HS− and HO− was unknown, 1 was also degraded In NaOH solutions simulating total hydrolysis 1.was NaOH, 1.4 ionic strength [μ]) and no hydrolysis (1.01 NaOH, 1.6 μ). The proportion of glycosyl-oxygen bond cleavage (88%) and oxygenaglycon bond cleavage (12%) was the same in all three cases. The rate constant for degradation of 1 under the kraft conditions was equal to that for the NaOH control degradation simulating total hydrolysis of S−2, but greater than that for the control simulating no hydrolysis. This indicates that S−2 is hydrolyzed under these kraft conditions to HS− and HO−, and that HS− does not participate in the rate-determining steps of glycosldic bond cleavage. Since HS− is a stronger nucleophile than HO−, these results also Imply that HO− does not cleave the glycosldic linkage by SN2 mechanisms. The yields of 1,6-anhydro-β-D-glucopyranose (1) from glycosyl-oxygen bond cleavage and 1,5-anhydro-D-glucitol (1) from oxygen-aglycon bond cleavage were lower for degradations of 1 in the kraft liquor than in the NaOH controls. This is due to HS− Involvement in the product-determining steps of the degradation of 1.