about 6 g rp acetone the response coefficient is determined by injecting a ptop bht standard under the same dilution conditions this measurement is carried out according to standard e28 96 on an nba 440 u00ae or nba 430 device from the normalab company operating method for examples 1 to 8 comparative and examples 9 to 11 according to the invention 500 g para tertiary octylphenol and possible x g of stearic acid table 1 gives the quantity of stearic acid added as a percentage of the ptop introduced and 2 1 g catalyst sulfuric acid solution at 25 in isopropyl alcohol is added to a 1 liter glass reactor equipped with a mechanical agitator and a refrigerant system in order to ensure an efficient reflux the temperature of the medium is raised to 90 u00b0 c while agitating the formaldehyde solution at 50 in water is maintained at 60 u00b0 c and then allowed to flow in over a period of 30 to 45 minutes while regulating the flow of formaldehyde in such a way as to maintain a temperature of 100 110 u00b0 c in the reactor when the formaldehyde is finished flowing in the assembly is modified in order to permit the distillation of the reaction water then the temperature of the reaction medium is raised progressively toward 130 150 u00b0 c t1 in table 1 while distilling the water of the.