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The mechanism of sorbitol dehydration in hot acidic solutions
Author(s) -
Kondo Tomomi,
Sasaki Takehiko,
Shiga Motoyuki
Publication year - 2021
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.26710
Subject(s) - metadynamics , chemistry , dehydration , ab initio , computational chemistry , density functional theory , protonation , sorbitol , dehydration reaction , transition state , reaction mechanism , potential energy surface , concerted reaction , molecular dynamics , dimethyl ether , reaction intermediate , organic chemistry , catalysis , ion , biochemistry
Sugar alcohol dehydration in hot water is an important reaction that allows for environmentally friendly biomass conversion without the use of organic solvents. Here, we report a free‐energy analysis by metadynamics (MTD) simulations based on ab initio density functional theory and semiempirical density‐functional tight‐binding method to understand the mechanism of dehydration reactions of d ‐sorbitol (SBT) in hot acidic water. Comparing the results of ab initio and semiempirical MTD, it was found that the latter gives a reliable free energy surface of SBT dehydration reaction, although the results vary upon the inclusion of dispersion correction. It was found that the reaction proceeds consistently via an S N 2 mechanism, whereby the free energy of protonation of the hydroxyl group created as an intermediate is affected by the acidic species. This mechanism was further verified by real‐time trajectories started from the transition state using ab initio molecular dynamics simulations. The free energy barriers of the reaction pathways leading to five‐membered ether products are lower than those leading to six‐membered ether products, in agreement with experiment. This outcome can be ascribed, in part, to our finding that the reaction barrier of the pathway is correlated to the stability of the SBT confined conformation at the initial stage of the reaction.