# Epoxide Alcoholysis over M‑BEA Zeolites: Effects of Alcohol Chain Length on Rates and Regioselectivities

## TL;DR

This study shows how alcohol chain length affects the speed and outcome of chemical reactions in zeolite catalysts.

## Contribution

The paper provides direct experimental evidence linking alcohol chain length to reaction rates and regioselectivity in zeolite-catalyzed epoxide ring-opening.

## Key findings

- Turnover rates increase with longer alcohol chain length in both Al-BEA and Zr-BEA zeolites.
- Regioselectivity shifts toward terminal alcohol formation with increasing alcohol chain length.
- Hydrogen bonding, influenced by alcohol chain length, determines regioselectivity rather than nucleophile strength or steric effects.

## Abstract

The structures of nucleophilic reactants affect their
coordination
behavior among solvent molecules and kinetics of reactions with surface
intermediates within the confines of fluid-filled pores of zeolites
and other microporous materials. Consequently, rates and regioselectivities
of diverse chemistries may depend sensitively on nucleophile identity
in manners not observed for classic fluid phase reactions. Here, we
examine the impact of varying the primary alcohol (ROH) chain length
on the kinetics of 1,2-epoxybutane (C4H8O) ring-opening
within Brønsted (Al-BEA) and Lewis acid (Zr-BEA) zeolites. Turnover
rates increase by factors of ∼6 (Al-BEA) and 4-fold (Zr-BEA)
between methanol and 1-hexanol, yet the reaction mechanisms remain
comparable. Despite modest rate differences, apparent activation enthalpies
calculated from rates and activities of solvated reactants decrease
linearly by 12 (Al-BEA) to 33 kJ mol–1 (Zr-BEA)
with increased proton affinity, which suggests bond formation energies
for the nucleophile strongly influence rate increases. The molecular
interpretation of these trends demonstrates, however, that the solvation
of ring-opening transition states by zeolite pore structures and solvent
molecules also governs rates. The impact of local solvating interactions
appears most directly as changes in regioselectivities, which tend
to enhance terminal alcohol formation with increasing ROH chain length.
Regioselectivities largely do not vary with differences in fluid composition
for a given ROH. The addition of H2O increases the number
of hydrogen bonds among reactive species, and trends in regioselectivities
imply that the decreased hydrogen bonding ability of longer chain
ROH, and not the nucleophile strength or steric bulk, determines the
regioselectivities of the resulting products. This work provides direct
experimental evidence that nucleophilicity and hydrogen bonding influence
reaction barriers and regioselectivities in zeolite-catalyzed epoxide
ring-opening, offering pathways to better control reaction kinetics.