IR3535 (Insect Repellent 3535) or Ethyl butylacetylaminopropionate, is an insect repellent. Merck KGaA is the registered trademark owner of IR3535 in the United States. IR3535 is a synthetic insect repellent that is additionally classified as biopesticide by the EPA. It was used in Europe 20 years prior to its registration with the EPA as an active ingredient in February 1999.