Synthesis Of 2,3,5-trimethyl Pyrazine

1,2-Diaminopropane was synthesized by amination of isopropanolamine in the presence of ammonia and a hydrogenation catalyst Raney Ni.The effect of the amount of Raney Ni catalyst,the molar ratio of materials,reaction temperature and reaction time on the experiment were studied.The optimum conditions were as follows:the amount of catalyst used was 4%by weight of the amount of isopropanolamine used,the molar ratio of isopropanolamine to ammomia was 1:3.5,the reaction temperature was 160℃,the reaction was 5h,the molar ratio of hydrogen to isopropanolamine was 1:5.Yield of 1,2-diaminopropane as high as 89%was obtainable and the purity is above 99.5%.The green synthesis technology with very little emission was developed.Synthesis of 2,3,5-trimethylpyrazine from 2,3-butanedione and 1,2-diaminopropane through 2,3,5-trimethyl-5,6-dihydropyrazine was studied.The reaction was comprised of synthesis of 2,3,5-trimethyl-5,6-dihydropyrazine and 2,3,5-trimethylpyrazine.(1) The optimum conditions of 2,3,5-trimethyl-5,6-dihydropyrazine synthesis were established: 2,3-butanedione which was mixed with anhydrous ethyl alcohol(the mass ratio of anhydrous ethyl alcohol to 2,3-butanedione was 5:1) was droped to the mixture of anhydrous ethyl alcohol and 1,2-diaminopropane(the mass ratio of anhydrous ethyl alcohol to 1,2-diaminopropane was 6:1) at the even pace for 3h,the molar ratio of 2,3-butanedione to 1,2-diaminopropane was 1:1.1,the condensation reaction temperature was -5℃.(2) The best dehydrogen oxidation conditions were as follows:air was used as oxidant,the molar ratio of potassium hydroxide and 2,3,5-Trimethyl-5,6-dihydro-pyrazine was 3:1,the mass ratio of ethanol to 2,3,5-trimethyl-5,6-dihydro-pyrazine 10:1,reaction temperature 68℃,reaction time 7h,the total yield of this two-step reaction was 83.0%.