Thermodynamics of the Hydrolysis Reactions of 1,4-beta-D-xylobiose, 1,4-beta-D-xylotriose, D-cellobiose, and D-Maltose
Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of the following reactions: (1) 1,4-{beta}-Dxylobiose(aq)+H{sub 2}O(I)=2D-xylose(aq); (2) 1,4-{beta}-D-xylotriose+2H{sub 2}O(I)=3D-xylose(aq); (3) D-maltose(aq)+H{sub 2}O(I)=2{alpha}-D-glucose(aq); and (4) D-cellobiose(aq)+H{sub 2}O(I)=2{alpha}-D-glucose(aq). The results of the equilibrium measurements were K = (1.46 {+-} 0.15) {center_dot} 10{sup 3} for reaction (1) and K = (551 {+-} 34) for reaction (3). Although it was not possible to measure directly a value for the equilibrium constant for reaction (4), it was possible to obtain the value K = 657 for this reaction via a thermochemical pathway calculation. The results of the calorimetric measurements were standard enthalpies of reaction {Delta}{sub r}H{sup o} = (0.12 {+-} 0.26) kJ {center_dot} mol{sup -1} for reaction (1) and {Delta}{sub r}H{sup o} = -(0.06 {+-} 0.18) kJ {center_dot} mol{sup -1} for reaction (2). It is noted that values of {Delta}{sub r}H{sup o} for reactions (1) and (2) are equal to each other within their respective experimental errors. This fact is consistent with earlier observations that, for reactions involving the making/breaking of N saccharide linkages, the assignment of characteristic values of {Delta}{sub r}H{sup o}/N or {Delta}{sub r}G{sup o}/N or {Delta}{sub r}S{sup o}/N for a specified linkage, is accurate in predicting the values of {Delta}{sub r}H{sup o}, {Delta}{sub r}G{sup o}, and {Delta}{sub r}S{sup o} for reactions involving saccharides that contain multiples or combinations of such linkages. Also, the values of the standard entropy changes {Delta}{sub r}S{sup o} for the hydrolysis reactions (3) and (4) fall into the range of values {l_brace}(32 to 48) J {center_dot} K{sup -1} {center_dot} mol{sup -1}{r_brace} previously noted for the hydrolysis of six-carbon disaccharides. In order to tie the results of this study into the thermochemical literature, a reaction catalog of related property values was created. Selected property values from this reaction catalog were then used to calculate 'best' values of the standard Gibbs free energy of formation {Delta}{sub r}G{sup o}, the standard enthalpy of formation {Delta}{sub r}H{sup o}, the standard molar entropy S{sub m}{sup o}, and the standard molar heat capacity C{sub p,m}{sup o}, for the substances of interest to this investigation.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 951021
- Report Number(s):
- NREL/JA-270-43083; JCTDAF; MainId:47505; UUID:ec87c796-f0d4-e411-b769-d89d67132a6d; MainAdminId:29597; TRN: US200911%%238
- Journal Information:
- Journal of Chemical Thermodynamics, Vol. 40, Issue 10; ISSN 0021-9614
- Country of Publication:
- United States
- Language:
- English
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