Triazine herbicide

Triazine herbicide is a broad-spectrum herbicide with triazine as the basic chemical structure. According to the uniform distribution of N atoms on the benzene ring, it can be divided into two types: s-trinitrobenzene and non-tris-benzene. Nowadays, it is mainly tris-benzenes, and its chemical structure is as follows: Figure 1 shows the chemical structure of triazine herbicides X=Cl, SCH3, OCH3, etc.; R1, R2, R3=H, lower alkyl or alkene Base; R4 = lower alkyl or alkenyl. Brief History In 1952, A. Gast et al first discovered the herbicidal activity of chlorazine. In 1956, the high activity of simazine was discovered and developed by the Swiss company Geigy. Since then, triazine herbicides have developed rapidly, with the largest production of atrazine, which is still one of the most important varieties of herbicides in the world. In recent years, the development trend of such compounds is: improving the processing dosage form, improving the application technology, further improving the efficacy and saving the drug; mixing with alachlor, acetochlor, butachlor, chlorpyrifos, cyanazine, etc. Improve the control effect on weeds in corn fields and reduce pollution to groundwater sources. The heterogeneous triazine herbicide, oxazinone, was discovered in 1971. The triazine ring or heterocycle is combined with the benzene ring of the sulfonylurea bridge and its ortho substituent to form a new type of highly efficient herbicide such as chlorsulfuron. Its outstanding advantages are a wide range of herbicides and a very small amount. Basic traits The water solubility of such agents is the largest in the "pass" category, the second in the "net" class, and the smallest in the "Tian" class. Most of the triazine herbicides are relatively stable in nature and therefore have a long shelf life, low toxicity to humans and animals, and little toxicity to fish. It has a systemic absorption effect, which can be quickly absorbed by the roots after soil treatment, and is transported upwards to the leaves along the transpiration flow in the xylem, while the agents absorbed from the leaves are not substantially transported, and the "Tian" type weeding such as Ximazin The agent is absorbed by the roots, and only atrazine has a stronger ability to absorb from the leaves. The "net" class such as chlorpyrifos is easier to absorb from the roots, stems and leaves, has a rapid effect, and has strong herbicidal activity, and has a great lethal effect on newly emerged weeds. It is easy to decompose in the soil, so the residual effect period is short, usually 1 to 2 months. The "pass" type has the highest water solubility and a large herbicidal activity, but the selectivity is poor. The main mechanism of action is to inhibit photosynthesis and affect the synthesis of assimilation products. The order of inhibition of several major metabolic processes such as chlorpyrifos, chlorhexidine and chlorpyrifos on photosynthesis is photosynthesis, lipid synthesis, RNA synthesis and protein synthesis. Chlorophyll may be the main pigment in the toxic effect of triazine herbicide. The toxicity is proportional to the illuminance, and the herbicide does not work in the dark. The toxic effect is the strongest at wavelengths of 428 and 658 nm. The striated herbicide blocks the flow of electrons from water to chlorophyll, causing oxidation of chlorophyll and gradual destruction of the layered structure of the chloroplast. In addition, by inhibiting the electron transfer system in photosynthesis, the accumulation of nitrite in the leaves leads to damage to sensitive plants. Chlorosis is the main symptom of the herbicide efficacy of this class. First, the tip of the leaf is chlorotic and dry, then the edge of the leaf turns yellow, and finally the whole plant is dead. The selectivity of triazine herbicides comes from three conditions. 1 Differences in plant heredity: The resistance of cultivated crops to atrazine and simazine is: corn, alfalfa, potato, sorghum, soybean, millet and sugar beet; 2 difference selection; 3 biochemical detoxification : Drug-resistant crops are capable of degrading triazine herbicides, so they are safer. The most prominent example is that the benzoxazinone contained in corn can inactivate the hydroxylation of atrazine and the like; the triazine herbicide can also detoxify with the glutathione conjugate in the resistant crop. The triazine herbicide can be photolyzed and degraded in the soil by dehalogenation, N-dealkylation, deamination and ester hydrolysis, ring cleavage and the like. The classification according to the different substituents of X on the base ring and the characteristics of the English name suffix can be divided into: -Cl substituted English noun tail - zine Chinese general noun tail is "Tian", -SCH3 replaced by -tryne commonly known as " The net "class", replaced by -OCH3 - is known as the "pass" class. Most of the triazine herbicides currently developed are mesotriazoles (N atoms are uniformly distributed on the benzene ring), and important non-homogenous triazines such as oxazinone. The application of triazine herbicides can be applied to a variety of dry crops, and some varieties of the "net" category can also be used in paddy fields. Figure 2 shows a triazine herbicide and its suitable crop. Triazine herbicides mainly kill weed shoots, have no lethality to seeds, and have no effect on their germination. Atrazine, cyanazine, etc. can also be used for stem and leaf treatment before the three-leaf stage of post-emergence weeds, and the effect is better. The most resistant to triazine herbicides are corn, alfalfa, sugar cane, apples, grapes, etc., sorghum, carrots, celery, potatoes, cotton, sunflower, peas, soybeans, etc. have strong resistance to some of them. Medicinal, some sensitive plants can use the difference or the head with a protective cover to enhance their safety. The duration of the “Tianjin” category is generally longer. Pay attention to the crops after the arrangement, or reduce the dosage or mix with other medicines. The effect of wemazin on the control of weeds and genus is superior to atrazine. Atrazine is safe for weeding in sorghum, and can be mixed before sowing, pre-emergence or post-emergence treatment. "Net" herbicides have strong activity on stems and leaves, so stems and leaves can be treated in the early post-planting period. Sugarcane has strong resistance and does not require strict varieties. The application of atrazine, chlorpyrifos, etc. in the orchard should be applied before the rainy season, and it is effective in the rainy season. Due to the high water solubility of atrazine, the mobility in the soil is also large. The long-term high-dose application is easy to be washed by the rain to the deep layer, affecting the groundwater quality, and because the atrazine has damage to the stomach, kidney and liver tissues of the mammal. It has adverse effects on genetic material DNA, etc. Some countries such as Germany have begun to stop or control application. China has begun to adopt a combination of alachlor and butachlor to slow down its shortcomings.