Degradation acids obtained in the synthesis of carboxylic acids, in particular dicarboxylic acids, having from 8 to 16 carbon atoms may be isolated by separating the degradation acids in the form of a solid from the crude reaction mixture, then washing the degradation acids in the form of an oil with water at an elevated temperature. The resulting degradation acids having low oxidant and metal contents, and the metal catalyst may be recirculated back to the process.