On-line attenuated total reflection infrared spectroscopy (ATR-IR): a powerful tool for investigating the methyl cyclopentenone synthesis process.

On-line attenuated total reflection infrared spectroscopy (ATR-IR) was used to gain a good understanding of the kinetics and mechanism for methyl cyclopentenone (MCP) synthesis from 2-methylfuran and formaldehyde in a four-step reaction. Combining in situ IR monitoring and a quantitative univariate model, the mechanisms for the main side reactions were discussed in depth. The presence and forming mechanism of the side product generated in step 1 (Mannich reaction) were reported for the first time. Off-line 1H NMR and GC-MS were used as reference tools to further clarify the structure of the side product. Results also show that an undesirable side reaction will take place if the reaction time for step 2 is longer than 3 h. Possible mechanisms for side reactions and optimized experimental conditions were suggested for the purpose of improving the selectivity of the main reaction to efficiently facilitate the yield of MCP. The present study demonstrates that on-line ATR-IR can be a powerful tool to gain insight into the process understanding of various chemical reactions, providing a solid theoretical foundation for highly efficient, large-scale synthesis of MCP.