Green Synthesis Of Nitrogen-containing Heterocyclic Compounds And Esters Under Solid Acid Catalysis

With the tremendous development of chemistry and chemical technology,the economic level has been greatly facilitated,bringing continuous improvement in people's daily life.Due to the guidance of national environmental protection policies,the attention on the sustainable development of the society and the requirements of the chemical industry's development,green chemistry has arisen wide attraction.It aims to reduce the generation of waste and the use of toxic and hazardous substances from the early stage,which involves each stage of product design,production,utilization and disposal.As a kind of green and environmentally friendly catalyst,solid acid catalyst is treated as one effective way to realize the concept of green chemistry,as it can effectively solve the problems of traditional acid catalysts such as corrosion of equipment,difficulty in recycling,poor reaction selectivity,environmental pollution and so forth.Thus,it has been widely used in many organic synthesis reactions such as alkylation reaction,polymerization reaction,addition reaction esterification reaction,and so on.This paper mainly studies the application of solid acids in the synthesis of nitrogen-containing heterocyclic compounds and ester compounds,which can be divided into the following three parts:1.The modified metal oxide solid acid was constructed and applied in the synthesis of nitrogen-containing pyrazolopyridine compounds.Phosphoric acid-modified niobic acid catalyst(Nb-OH·PO₄(1 mol))is prepared from raw materials of phosphoric acid and niobium pentoxide,which is then used to catalyze the synthesis of pyrazolopyridine derivatives.Taking raw materials as benzopyrone,aldehyde and aminopyrazole(0.5 mmol each)and catalyst as Nb-OH·PO₄(1 mol)of 0.015 g,the reaction is carried out under the environment of 130? microwave irradiation and 1ml of glycerol solvent for 20 minutes,efficiently constructing twelve pyrazolo[3,4-b]pyridine compounds with a yield of 57-79%.The method is proved to be simple and easy to operate due to the short reaction time,the excellent selectivity,the high yield and it is environmental friendliness.2.Based on the actual situation of the enterprise,a solid acid catalyst modified by proton acid is constructed to catalyze the synthesis of tri-n-butyl citrate in order to solve the problems during the production.By using attapulgite(ATP)as a carrier and adding different Br?nsted acid and Lewis acid modification,multiple solid acids are obtained.The screening result reveals that the H₂SO₄(2 mol)-ATP solid acid modified with 2mol/L sulfuric acid provides the best catalytic effect.The reaction conditions are:the molar ratio of citric acid to n-butanol is 1:5,4%citric acid mass H₂SO₄(2 mol)-ATP is selected as catalyst,the temperature is set at 140?,the reflux reaction time is 6 hours,and 96.8%esterification rate is achieved.The catalyst can be recycled,and the target product with an esterification rate of more than 90%is guaranteed after 4 reactions.With the low preparation cost,outstanding repeatability,low equipment corrosivity,and its environmental friendliness,this catalyst can be considered as an ideal catalyst for this type of reaction,providing a green and environment-friendly method for the synthesis of tri-n-butyl citrate.3.A metal modified solid acid catalyst is constructed to catalyze the synthesis of triisobutyl citrate.Attapulgite(ATP)is used as a catalyst carrier,and different metal-modified ATP solid acids are obtained by metal modification,and then it is chosen as a catalyst during the synthesis of triisobutyl citrate.The experiment demonstrates that SO₄^2-/Sn O₂-ATP prepared by Sn modification offers the best catalytic effect.The final optimal reaction conditions are:the molar ratio of citric acid to isobutanol is 1:5,SO₄^2-/Sn O₂-ATP with 6%solid acid mass is selected as the catalyst,and the reflux reaction is executed at 140? for 6.5 hours to create triisobutyl citrate with 84.4%esterification rate.The catalyst is recyclable,maintaining esterification rate of more than 80%after4 reactions.The environmental friendliness and the recyclable ability of the catalyst makes this reaction become an excellent method for the synthesis of triisobutyl citrate.