Because the honeycomb reactor was found to be a suitable reactor for aerobic oxidation, the concentration of the reaction solution was returned to that of batch conditions to maximize the throughput (Scheme 3 and Table ). When the reaction solution was passed through the honeycomb reactor three times, the reaction was completed in two cycles. The increased temperature derived from the heat of reaction accelerated the reaction. The quantitative yield by HPLC was 98.3% and the byproduct carboxylic acid 3a was 1.3%. 3a was easily purged by extraction with a weak base such as NaHCO3. From the above discussion, the throughput was improved to 1.4 kg/day (= 57 g/h = 1.83×3.75×138.17 = 948 mg/min), which is suitable for kg-scale aerobic oxidation.