Beet Ann Beet Rather Synthetic

In order to improve environment, many countries have banned or limited high toxic pesticides. Being extensive, high effectual, safe, low toxic and low residual and going with environment has been the orientation in pesticide development. Desmedipham and phenmedipham fall into the class of Dicarbamate type herbicides. They do no harm to crops and can prevent or kill ma,ny types of weeds with broad leaves in a field of beet. Not much of this type of pesticides is left over in soil and root tubers.This dissertation studies mainly the synthesis of desmedipham and phenmedipham and their intermediates, ethyl-(3-hydroxyphenyl)carbamate, phenyl isocyanate, methyl-(3-hydroxyphenyl)carbamate and /n-tolyl isocyanate, thus obtaining better technology in our experiments. The structure of desmedipham and phenmedipham are characterized by IR, 1H-NMR and MS.Based on concerned literature, we have synthesized N-hydroxyphenyl carbamic acid esters from /n-aminophenol and chloroformate. Compared with other ways, this method has advantages of high yield and high purity. As to ethyl-(3-hydroxyphenyl)-carbamate, the better reaction conditions are as follows: reaction temperature is 15℃; the ratio of/n-aminophenol to ethyl chloroformate (molar ratio) is 1:1.15; reaction time is 1 hour. The yield is 94%, based on /n-aminophenol. As to methyl-(3-hydroxy phenyl)carbamate: reaction temperature is 10℃; the ratio of /n-aminophenol to methyl chloroformate (molar ratio) is 1:1.15; reaction time is 1 hour. The yield is 84%, based on w-aminophenol.In order to improve safety, we replace phosgene by trichloromethyl chloroformate in synthesis of isocyanate. As to phenyl isocyanate, the better reaction conditions are as follows: the ratio of aniline to trichloromethyl chloroformate (molar ratio) is 1:1, the reaction time is 3 hours at the refluxing temperature. The yield of phenyl isocyanate is 84%, based on aniline. As to m-tolyl isocyanate, the ratio of m-toluidine to trichloromethyl chloroformate (molar ratio) is 1:1, the reaction time is 3 hours at the refluxing temperature. Based on m-toluidine, the yield of m-tolylisocyanate is 95%.The better reaction conditions in which desmedipham is synthesized are as follows: reaction temperature is 50℃; the ratio of ethyl-(3-hydroxyphenyl) carbamate to phenyl isocyanate is 1:1.1. Based on ethyl-(3-hydroxyphenyl) carbamate, the yield is 93% or higher than 93%. The purity of desmedipham is 99%. As to phenmedipham, the better conditions are: reaction temperature is 50℃; the ratio of methyl- (3-hydro-xyphenyl)carbamate to m-tolyl isocyanate is 1:1.1. Based on methyl-(3-hydroxy-phenyl)carbamate, the yield is 95% or higher than 95%. The purity of phenmedipham is 95%.Based on m-aminophenol, the total yield of desmedipham is 88% or higher than 88%, the total yield of phenmedipham is 80% or higher than 80%.The experimental products have been sent to be registered in USA and our mass-production of the products will begin soon.