Preparation Of Quinazoline-2,4（1G,3G）-Dione And Its Derivatives By Catalytic Conversion Of CO₂ By A Novel Alkaline Ionic Liquid

CO₂ is a non-toxic,inexpensive and abundant C1 resource.It is of great significance to convert CO₂into high value-added chemicals.However,CO₂has thermodynamic stability and kinetic inertness,then the design and synthesis of highly efficient catalysts are critical to promote the CO₂conversion reaction.Quinazoline-2,4（1H,3H）-diones are important pharmaceutical intermediates with a wide range of physiological and pharmacological activities.Synthesis of quinazoline-2,4（1H,3H）-diones from CO₂has attracted wide spread attention.The reaction route can replace the traditional toxic process without by-products,and it meets the requirements of atomic economy and green chemistry.Based on the activation mechanism of CO₂,succinimide（Suc）,N-hydroxysuccinimide（NHS）,1,1,3,3-tetramethylguanidine（TMG）and1,8-diazabicyclo[5.4.0]undec-7-ene（DBU）were used as raw materials to synthesize a series of succinimide-based ionic liquids.Their catalytic activities for conversion of CO₂and 2-aminobenzonitriles to quinazoline-2,4（1H,3H）-diones were studied.The influence of catalyst structures on the catalytic activity was investigated,and the[HTMG][Suc]was chosen as the highest catalyst.The effects of reaction temperature,CO₂pressure,reaction time and the amount of catalyst on the carboxyclization of CO₂and 2-aminobenzonitriles were studied by using the[HTMG][Suc]catalyst.The results showed that a 98%product yield was obtained under the conditions of 60 ^oC,2.0 MPa for 6 h.The general applicability and recycling performance of the[HTMG][Suc]were also examined.The catalyst exhibited high catalytic activity for substrates with different substituents,and the activity did not decrease significantly after five cycles.According to the experimental results,apossible reaction mechanism for the carboxyclization of CO₂and2-aminobenzonitriles catalyzed by the[HTMG][Suc]was proposed.On the basis of CCU strategy,a series of triazolium-based ionic liquid catalysts are designed and synthesized to investigate the integrated performance of CO₂capture and activation.It is found that the catalyst[HTMG][Triz]has the highest catalytic activity in the reaction,which could capture equal moles of CO₂and convert the activated CO₂into quinazoline-2,4（1H,3H）-dione by one-pot method.The reaction is rapid and the product yield was excellent.Compared with the traditional method of directly introducing CO₂into the reactor,the direct conversion of absorbed CO₂saves the energy of desorption from the catalyst.[HTMG][Triz]can activate 2-aminobenzonitrile and CO₂at the same time through hydrogen bonding.Using[HTMG][Triz]as catalyst,the yield of 95%product can be obtained by reaction at 50 ^oC and 0.5 MPa CO₂pressure for 6 h.The CO₂is absorbed for 1 h at 40^oC by[HTMG][Triz]and convert into quinazoline-2,4（1H,3H）-dione at 90 ^oC with a yield of 94%.The catalytic activities of the catalysts on substrates with different substituents are investigated,and high yields are obtained.After the catalyst is recycled for 5 times,the catalytic activity is not significantly affected,and the structure of the recovered catalyst do not change through the test,indicating that the structure of the catalyst is stable.Based on the experimental results,the possible reaction mechanism of[HTMG][Triz]catalyzed carboxyclization of CO₂and 2-aminobenzonitrile is proposed.In order to achieve efficient conversion of low concentration CO₂,a series of aminophenols ionic liquids were synthesized and characterized by simple neutralization method.The catalytic behavior of these ionic liquids on the conversion of simulated flue gas CO₂（15%CO₂,85%N₂）to quinazoline-2,4（1H,3H）-dione was studied respectively.By investigating the effects of different catalyst structures,solvent types and reaction parameters,such as reaction temperature,catalyst dosage and reaction time,on the yield of the product,it was found that using ionic liquid[HTMG][m-AP]as catalyst,DMF as solvent,reaction at 60 ^oC for 12 h,quinazoline-2,4（1H,3H）-dione could be effectively converted into low concentration CO₂with a yield of 97%.Under optimized reaction conditions,the catalytic activities of[HTMG][m-AP]/DMF system on the carboxyclic reaction of the substrate with different substituents and CO₂were investigated,and excellent product yields were obtained.At the same time,the recycling performance of[HTMG][m-AP]/DMF catalytic system was investigated,and the high catalytic activity was still maintained after being reused for 5 times.Finally,the mechanism of carboxylation of CO₂and 2-aminobenzonitriles in[HTMG][m-AP]/DMF was proposed.