Nucleophilic Molar Ratio-Driven Kinetic Behavior in the Ring-Opening of Epoxidized Castor Oil Using Methanol and Hydrogen Peroxide

Abstract

Epoxidized castor oil (ECO) is a renewable platform chemical that can be converted into polyols through nucleophilic ring-opening, providing a sustainable route to bio-based polymers. To date, limited studies have explored concentration-dependent reaction rate coefficient behavior and numerical modeling in nucleophilic systems, especially concerning the ring-opening of epoxidized castor oil, underscoring the novelty and contribution of this work. This study examined the kinetics of ECO ring-opening with nucleophile (methanol and hydrogen peroxide) under varying molar ratios, with emphasis on the highest ratio (ECO: nucleophile = 1:1.5). For methanol-mediated ring-opening reactions, the ring-opening achieved a reaction rate coefficientof 0.0274 min⁻¹ (R² = 0.9214), indicating efficient conversion at elevated methanol loadings. Hydrogen peroxide-assisted reactions recorded a slightly lower rate constant of 0.0202 min⁻¹ (R² = 0.8596), reflecting its dual role as nucleophile and oxidant, which can introduce side pathways at higher concentrations. As there are no previous studies using consecutive first oder mechanism, this study have demonstrated that the numerical modeling yielded excellent agreement with experimental data, with R² = 0.998 for hydrogen peroxide and R² = 0.991 for methanol, supported by residuals tightly distributed within ± 0.03 without systematic deviation. These results confirm that the nucleophilic attack (\(\:{k}_{1}\))is the rate-limiting step, while the subsequent propagation to polyols (\(\:{k}_{4}\)) occurs rapidly once initiated is known as the rate-determining step. By combining reaction rate analysis with validated modeling, this work provides quantitative insight for optimizing green polyol synthesis and contributes to advancing sustainable polymer technologies.