The invention relates to 2-substituted pyrimidines of the formula I in which the index n and these substituents R1, R2 and R3 are as defined in the description and R4 is as defined below: R4 corresponds to one of the formulae where Ra is hydrogen, C1-C6-alkyl, C2-C8-alkenyl, C2-C8-alkynyl, C3-C6-cycloalkyl or C1-C4-alkoxy and R5 is hydrogen, C1-C6-alkyl, C2-C6-alkenyl, C2-C6-alkynyl, C1-C4-alkyloxy-C1-C2-alkyl, phenyl-C1-C2-alkyl or phenyloxy-C1-C2-alkyl, to processes for preparing these compounds, to compositions comprising these compounds and to their use as pesticides.