Tetramethyladipic acid (TMAA), a starting monomer for several technically important polymers (polyester resins and polyamide fibres) is synthesised by direct carbon–carbon bond formation between the saturated primary carbon atoms of pivalic acid (PA) using a sonoelectrochemical Fenton process. Through controlled electrochemical dissolution assisted by ultrasound radiation, Fe2+ ions are produced in situ from metallic iron in the reaction mixture. The effects of ultrasound with electrolysis, temperature, amount of substrate present, reagent concentration, solution acidity and quantity of electric charge have been examined. Under suitable conditions, the synthesis yield based on initial PA present, hydrogen peroxide used and amount of iron dissolved reached 34, 40 and 75%, respectively and less by-product was observed. These results show significant improvement in terms of direct cost savings by omission of separate preparation of a ferrous salt, fewer side reactions during the dimerisation process, less waste, easier purification; increased efficiency due to recycling of iron ions and improved reactivity of fresh Fe2+ ions. All of these advantages make this sonoelectrochemical approach a much more efficient and environmentally cleaner option.