Process optimization and mechanism study on microwave-assisted synthesis of n-Butyl cyanoacrylate

Abstract

N-Butyl cyanoacrylate (NBCA) is an important monomer widely used in biomedical adhesives and industrial instant bonding materials. However, its conventional synthesis process suffers from high energy consumption, undesired side reactions, and low efficiency, which restrict its large-scale application. To overcome these limitations, this study introduces a new and efficient microwave-assisted Knoevenagel condensation approach for the synthesis of NBCA. This work systematically optimized the key process parameters, elucidated the mechanism of microwave field effects, and conducted a comprehensive assessment of the process greenness by establishing a Sustainability Index.
Initially, the conventional synthesis of NBCA via oil-bath heating was investigated and optimized. The optimal conditions were determined as follows: n-butyl cyanoacetate to formaldehyde molar ratio of 1.05:1, pyridine catalyst dosage of 0.25 mL (based on 0.5 mol formaldehyde), reaction temperature of 160–190°C, and reaction duration of 4 h. Under these conditions, a product yield of 68% was achieved, confirming the effectiveness of process optimization.
Subsequently, a microwave-assisted synthesis process was developed to further improve reaction efficiency and sustainability. Under the optimized conditions (microwave power of 800 W and reaction time of 70 minutes), the product yield reached 72%, while the reaction time was shortened by approximately 71% compared to the conventional method. Mechanistic studies revealed that microwave fields effectively promoted molecular polarization and accelerated collision frequency, thereby reducing the activation energy (Ea) from 51.8 kJ/mol (conventional heating) to 11.9 kJ/mol—an impressive 77% reduction. This study confirms that microwave-induced resonant vibration of polar molecules enhances molecular motion and establishes localized energy gradients, thereby accelerating reaction kinetics.
A quantitative comparison of the green performance was conducted by constructing a Sustainability Index model. The results demonstrated that the microwave-assisted process achieved an energy consumption per unit mass of 6.48 kWh/kg, representing a reduction of approximately 78% compared to the conventional process (29.41 kWh/kg). The environmental factor was 1.40, about 38% lower than that of the conventional process (2.27). The comprehensive Sustainability Index, integrating multiple metrics, revealed that the SI value for the microwave-assisted process (0.394) is about 50.5% lower than that of the conventional process (0.796), confirming the significant advantages of the microwave route in terms of efficiency, cleanliness, and sustainability.
In summary, this work not only provides an efficient alternative for the green synthesis of NBCA but also offers a theoretical foundation and practical reference for the industrial-scale application of microwave intensification technology in fine chemical production.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Tao Wu (Supervisor), Xiang Luo (Supervisor) & Mina Liu (Supervisor)