Utilizing the solubility properties of the starting material and product, the reaction yield is significantly enhanced in a system with an undesired consecutive parallel reaction. An excess amount of the starting material is charged at the beginning of the reaction, followed by a partial crystallization of the product during the reaction, The excess unreacted starting material is recovered from the isolated cake by slurry washing and recycling the washing liquors to the next cycle. Through this simple and unique two-filtration recycle process, laboratory and pilot-plant data show a yield improvement from 65% of the original process to 72-82%, as well as a significant reduction of raw material usage.