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

Abstract

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 S_N2 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.