ethyl 2-(4-isobutylphenyl)propanoate ethyl 2-(4-isobutylphenyl)propionate Ibuprofen ethyl α-Methyl-4-(2-methylpropyl)benzeneacetic acid ethyl ester Benzenacetic acid, alpha-methyl-4-(2-methylpropyl)-, ethyl ester Einecs 255-291-9 Hydratropic acid, p-isobutyl-, ethyl ester Ibuprofen ethyl ester