Process for preparing 4,6-bis(aryloxy)pyrimidine derivatives. A process is provided for preparing 4,6-bis(aryloxy)pyrimidine derivatives. The process is conducted in water as reaction medium and catalyzed by one or more tertiary-amine catalyst(s). It has been found that a water based reaction substantially free of organic solvents can be carried out providing excellent yields by the addition of one or more tertiary-amine catalysts to the reaction medium. This provides a clean reaction and produces the desired product in high yields.