Study On The Synthesis Of Dimethenamid-P

Dimethenamid-P is one of the acetamide herbicide,non-carcinogenic and low toxicity herbicide,mainly used for soil treatment before sowing and pre-emergence weeding,because there is no company to produce and sell dimethenamid-P now in China,so it has a good developing prospect.In this paper,we study on two important intermediates used in the synthesis of dimethenamid-P:(1)Synthesis of(S)-1-methoxy-2-propylamine: In this work,DL-2-aminopropanol is firstly separated with L-tartaric acid to obtain(S)-2-aminopropanol,and(R)-2-aminopropanol can be recycled by catalytic racemization.Using(S)-2-aminopropanol as raw material,(S)-1-methoxy-2-propylamine was synthesized through a three-step procedure:reaction of amino protection,methylation reaction and deprotection.The mechanism and influencing factors of the reaction is discussed;The optimized the route process is following: methanol was chosen as the solvent during resolution;the mass concentration of the acid salt was 20%-25% when crystallized,and the temperature of crystallization was 0-5°C;the yield was 95.8% when the mole ratio of benzaldehyde to(S)-2-aminopropanol was 1.05:1 and the reaction time was 4h;the mole ratio of methyl sulphate to intermediate(S)-2-benzylideneamino-1-propanol in the methylation process was 1.3-1.4:1,the mole ratio of sodium hydroxide to the intermediate(S)-2-benzylideneamino-1-propanol was 2:1.When the reaction temperature is 15-20?,the yield can reach 98.1%.In the deprotection process,the mole ratio of hydrochloric acid to the methylation product(S)-1-methoxy-N-benzylidene was 1.2:1,the reaction temperature was 50°C,and the yield was 97.0%.The product was identified by nuclear magnetic resonance spectroscopy and infrared spectroscopy.The purity was 99.5% by gas chromatography analysis and the total three-step yield is reached 90.7%.(2)Synthesis of 2,4-dimethyltetrahydrothiophene-3-one:Reference the two synthetic routes reported in the literature,2,4-dimethyltetrahydrothiophen-3-one was synthesized by two methods.In the route one,with the thiolactic acid and methacrylic acid as raw materials,through the two-step reaction of addition reaction,cyclizationdecarboxylation,2,4-dimethyl tetrahydrothiophene-3-one was synthesized;the route two: with thiolactic acid and methacrylic acid as raw materials,after one-step reaction,2,4-dimethyl tetrahydrothiophene-3-one was also syntheiszed.Then the mechanism and influencing factors of the reaction was also discussed.The optimized the route process is following:The best mole ratio of thiolactic acid to methacrylic acid was 1.2:1 in the route one(two-step process),and the yield was 86.5% as the reaction time was 24 h.When the mole ratio of the catalyst to the intermediate2,5-dimethyl-3-thioadipic acid was 0.25,the yield can reach 85.6% and the total of two-step yield was 74.0%.The route two(one-step method)has the following technological conditions: Using ferrous acetate as the catalyst,when the mole ratio of the catalyst to the raw material thiolactic acid was 0.01-0.012,the yield can reach83.1%.The products and intermediates were identified by nuclear magnetic resonance spectroscopy.The purity was 95.1% for the first route,and 97.0% for the second route by gas chromatography analysis.The yield of two steps of route one was 70.4%,and the yield of one step of route two was 80.6%.From the comparison of reaction conditions and yield,it was found that the one-step procedure was better than the two-step ones.