Synthetic and mechanistic investigation of piperonyl butoxide from dihydrosafrole

摘要

Piperonyl butoxide (PBO) 1 was prepared via the successive chloromethylation and etherification of dihydrosafrole 3. In this work, during the chloromethylation of 3, several by-products such as 5 (the isomer of chloromethyldihydrosafrole 4), 6-propylpiperonyl alcohol 6, bis(chloromethyl)- dihydrosafrole 7 and 8, bis(2-propyl-4,5-methylenedioxyphenyl)methane 9 and di(2-propyl-4,5-methy lene-dioxybenzyl)ether 10 were found. However, it was found that 5, 6, 7, and 8 could undergo a further reaction to the final product (PBO), rather than its derivatives, though the by-products 9 and 10 still existed. Based on these results, the plausible mechanism of the chloromethylation and etherification of 3 was proposed. Furthermore, the reliability of the plausible mechanism was verified by quantum chemical calculations using DFT. In addition, the final product (PBO) was produced with a high selectivity and yield by reducing the by-products 9 and 10.