- Synthesis and biological evaluation of nitromethylene neonicotinoids based on the enhanced conjugation
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The neonicotinoids with a nitroconjugated system had excellent bioactivity, which could rival imidacloprid, and has been previously reported. However, the photodegradation and hydrolysis of this series of neonicotinoids was very quick according to our further investigation, which cannot be developed as a pesticide further. The approach to further enhance the conjugation was tried not only to increase the bioactivities but also to improve the stability in water and in the sun. A substituted phenyl group was introduced into the furan ring of compound 3. A total of 13 novel neonicotinoid analogues with a higher conjugation system were designed and synthesized. The target molecular structures have been confirmed on the basis of satisfactory analytical and spectral data. All compounds presented significant insecticidal activities on cowpea aphid (Aphis craccivora), cotton aphid (Aphis gossypii), and brown planthopper (Nilaparvata lugens). The stability test exhibited that the stability of novel analogues in water and under the mercury lamp has been improved significantly in comparison to compound 3.
- Lu, Siyuan,Zhuang, Yingying,Wu, Ningbo,Feng, Yue,Cheng, Jiagao,Li, Zhong,Chen, Jie,Yuan, Jing,Xu, Xiaoyong
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p. 10858 - 10863
(2014/01/06)
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- Kinetics of the Reactions between Phenylureas and Nitrous Acid. Part 2. Nitrosation of 2,4,6-Trimethyl- and 4-Bromo-phenylurea
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The kinetics of the reactions between nitrous acid and the 2,4,6-trimethyl and 4-bromo derivatives of phenylurea have been studied at 25 deg C in aqueous perchloric acid solution (+> 0.5-2.0 mol dm-3 and μ 2.0 mol dm-3).The mechanism suggested for the trimethyl derivative is completely analogous to that proposed for phenylurea itself: an initial fast equilibrium step in which the electrophile NO+ attacks the urea oxygen atom is followed by two parallel reaction paths, both of which begin with the rate-controlling loss of a proton by the protonated O-nitroso compound to produce both of its two possible conjugate bases.One of these bases undergoes internal rearrangement to the N-nitroso compound, and the other, after a series of fast steps, yields the corresponding banzenediazonium ion.This is the only final product, since the formation of the N-nitroso compound is reversible.In the case of 4-bromophenylurea the loss of proton by the protonated O-nitroso compound no longer determines the reaction rate of the second of the above reaction paths.The observed kinetics and the suggested reaction mechanism for various ureas allow a value of the order of 0.15 mol-1 dm3 to be calculated for the equilibrium constant between NO+ and substrate on the one hand and the corresponding protonated O-nitroso compound on the other.This value implies that for 2,4,6-trimethylphenylurea and phenylurea proton loss is not diffusion-controlled, which is in keeping with the general base catalysis found previously for phenylurea.
- Castro, Albino,Gonzalez, Manuel,Meijide, Francisco,Mosquera, Manuel
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p. 2021 - 2028
(2007/10/02)
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