Table 3 AIMD-calculated reaction free energies for fructose dehydration

Solvent system	Catalyst/anion	Oxocarbenium ion formation^a (kJ mol⁻¹)	Proton abstraction^‡b (kJ mol⁻¹)	Total free energy of activation^‡c (kJ mol⁻¹)
H₂O	H⁺	57	35	92
H₂O	H⁺/Cl⁻	58	35	93
75% GVL/25% H₂O	H⁺	49	35	84
75% GVL/25% H₂O	H⁺/Cl⁻	44	30	74
90% GVL/10% H₂O	H⁺	43	33	76
90% GVL/10% H₂O	H⁺/Cl⁻	38^d	29	67
90% GVL/10% H₂O	H⁺/TfO⁻	43^e	33^e	76
90% GVL/10% H₂O	H⁺/HSO₄⁻	45	33	78

^aThe values for oxocarbenium ion formation are the reaction free energies for the simultaneous protonation of the C2 hydroxyl of fructose and the elimination of water that forms. ^bThe proton abstraction values refer to the activation free energies for water to deprotonate the oxocarbenium ion that forms. ^cThe apparent activation barrier listed as the total activation free energy is the sum of the free energy of the reaction to form the oxocarbenium ion and the activation free energy to deprotonate it. ^dThe free energy of oxocarbenium ion formation in 90% GVL/10% H₂O (w/w) with HCl required a correction calculated from the 75% GVL/25% H₂O (w/w) system to ensure the complete dissociation of the H⁺ and Cl⁻ in the initial reactant state as discussed in the Supplementary Discussion. ^eThe triflate anion migrated away from fructose and local water molecules during the free energy sampling and partitioned between the water and GVL domains away from the active site. The numbers reported in this column were therefore taken from the 90% GVL/10% H₂O (w/w) system without an anion. The double dagger (‡) symbol is a descriptor that refers to the transition state

Quick links

Search