Xylopyranose Ring-Opening by Single and Double Proton Transfers Under Pyrolysis Conditions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Carbohydrate Chemistry

Background:

• Pyrolysis of beta-D-xylopyranose is crucial for understanding carbohydrate decomposition.
• Previous studies focused on established reaction pathways for acyclic product formation.
• The potential energy surface exploration is key to uncovering novel reaction mechanisms.

Purpose of the Study:

• To identify and characterize new transition states (TS) in beta-D-xylopyranose pyrolysis.
• To investigate the synchronous double proton transfer mechanism leading to acyclic products.
• To compare the energetic and kinetic contributions of newly discovered pathways with known ones.

Main Methods:

• Automated exploration of the potential energy surface using quantum chemistry methods.
• Application of multi-path canonical variational transition state theory (MC-CVT).
• Kinetic analysis of reaction rates across a temperature range (320-873 K).

Main Results:

• A novel transition state (TS) pathway for synchronous double proton transfer was identified.
• The new TS exhibits a lower standard activation enthalpy (44.9 kcal/mol) compared to the established channel.
• The rate constant of the new pathway becomes significant in the lower temperature range (320-400 K).

Conclusions:

• The newly discovered TS pathway plays a potentially significant role in acyclic product formation from beta-D-xylopyranose, especially at lower pyrolysis temperatures.
• This finding is particularly relevant for beta-D-xylopyranose trimers with varied C1 and C3 substituents.
• The study advances the understanding of complex carbohydrate decomposition mechanisms under thermal stress.