In order to further study the herbicidal activity of 3-substituted benzyl-6-(trifluoro- methyl)pyrimidine-2,4(1H,3H)-dione derivatives and find new herbicides, sixteen new 3-substituted benzyl-6-(trifluoromethyl)pyrimidine-2,4(1H,3H)-dione derivatives were syn-thesized and confirmed by ¹H NMR, IR spectra and elemental analysis. The bioassay results showed that the title compounds herbicidal activity, selectivity and action mode were influenced by the sub-stituent at 1-position for pyrimidine ring. Quantitative structure-activity relationship studies showed that when the test grass was rape, their herbicidal activity was mainly related with substituent molar refractivity (MR); when the test grass was barnyard grass, their herbicidal activity was mainly related with the electronic parameters of the substituents at the para-position of benzene ring. When the substituent at 1-position for pyrimidine ring was hydrogen, the inhibition against rape was improved, while when the substituent at 1-position for pyrimidine ring was methyl group, the inhibition against barnyard grass was improved.

Key words: 6-(trifluoromethyl)pyrimidine-2,4(1H,3H)-dione, quantitative structure-activity relationship, herbicide