The invention relates to the use of ionic liquids tertiary phosphine oxides derivatives with terminal amino group, represented by the formula [R1R2P(O)[(CH2)nNR3R4R5]+A-, wherein R1 and R2 are the same or different and represent independently an alkyl or aryl group, especially phenyl, R3R4R5 are the same or different and represent independently hydrogen atom, an alkyl group with C1 to C6 carbon atoms, an aryl group, especially an imidazole ring, wherein at least one substituent is not hydrogen, A- is Cl, (CF3SO2)2N, n ≥ 4, as a means of herbicidal properties.In the use according to the invention as ionic liquids tertiary phosphine oxides derivatives with a terminal amino group, are used 4-[t-butyl(phenyl)phosphinyl]-n-butyl-N-methylimidazolium chloride, 4-[benzyl-t-butylphosphinyl]-n-butyl-N-methylimidazolium chloride, bis(trifluoromethylsulfonyl) 4-[t-butyl(phenyl)phosphinyl]-n-butyl-N-methylimidazolium imide and bis(trifluoromethylsulfonyl) 4-[benzyl-t-butylphosphinyl]-n-butyl-N-methylimidazolium imide.
