Studies On The Synthesis Of Quinolines From The Reaction Of C₁-C₄ Alcohols And Aniline Over Heterogeneous Catalysts

Quinoline and alkylquinolines are important classes of heterocyclic compounds of high industrial importance.These compounds are the starting materials for the design of many pharmaceuticals,herbicides,fungicides,corrosion inhibitors and acid-binding agents.Quinolines have also been used as high boiling basic solvents in the laboratory.Quinolines are usually synthesized from traditional liquid phase reaction with homogeneous catalyst,which have many drawbacks:for example,the most widely employed method,Skraup's synthesis,as well as other similar methods utilize high amounts of sulfuric acid and high temperatures.Recent unprecedented environmental pressure and the resulting drive towards clean technologies force the scientific community to develop ecologically friendly alternative routes.In fact,there are several advantages like continuous production,simplified product recovery,catalyst regenerability,absence of acid waste stream,etc.for carrying out this reaction in the vapour phase when compared to the conventional liquidphase routes.Compared to unsaturated carbonyl compounds,C₁-C₄ alcohol are stable and inexpensive,and its synthesis of quinoline compounds is rarely seen in the literature.Therefore,the synthesis of quinoline compounds from C₁-C₄ alcohols with heterogeneous catalyst has particular theoretical and pragmatic meaning,which o wns a capacious development foreground.In this paper,vapor phase quinolines synthesis has been performed using a fixed-bed,down-flow reactor.Quinolines synthesis conducted over a series of metal salt catalysts supported on the different Si/Al ratio of the HZSM-5 zeolites,Y zeolites and USY zeolites produces mainly quinoline and ramifications from C₁-C₄ alcohols and aniline.The preparation and texture properties of the catalysts were studied,and the catalytic reaction mechanism was also discussed.The dissertation focuses on the following parts:?1?In this work,a series of modified HZSM-5 zeolites,Y zeolites and USY zeolites were prepared by transition metal ions exchange,impregnation and acid and alkali treatment methods.The skeleton structure of catalysts,surface area,pore size distribution,surface defects,acidic property and the concentration of ion exchange had been characterized by means of modern tec hniques such as physico chemical adsorption?BET?,X-ray powder diffraction?XRD?,N₂-adsorption at low temperature,atomic absorption?AAS?,Fourier transform infrared?FT-IR?,scanning electron microscopy?SEM?,NH₃ temperature programmed desorption?NH₃-TPD?,quantitative determination of Br?nsted acid sites method based on pyridine adsorption IR.The research showed that partial skeleton T atomic of molecular sieve were removed after acid and alkali treatment,which leads to the formation of mesoporous.The surface of catalysts were introduced the active metal group by the transition metal ions exchange method,the modification also leads to the removal of the skeleton Al of the molecular sieve,and part of the transition metal components were embedded into the skeleton and the pore of molecular sieve;Especially,the modification was significantly reduced the concentration of Br?nsted acid sites and increased the concentration of Lewis acid sites.?2?In this work,various factors affecting the reaction over kinds of catalysts were studied,including:the different catalyst carrier,the Si/Al ratio of the catalyst,the loading metal ions,the nature of catalyst activity and the catalyst preparation method,as well as the inert carrier gas flow rate,reaction temperature,reaction time,etc.The optimum reaction condition of synthesizing quinolines from aniline and alcohols had been explored in this research.For the reaction of aniline and alcohols,the Zn Cl₂/Ni-USY-Acid catalyst exhibited the best performance.The C₁-C₄ alcohols except methanol and ethanol could react with aniline to produce the corresponding quinoline compounds,and the reactions of glycerol,1,3-PDO,and propanol could reach the total yield of nearl y 80%of quinoline compounds.The reaction of propanol and aniline provided a 97.6%conversion of aniline and 81.7%total selectivity of quinolines with 60.6%yield to 2-ethyl,3-methylquinoline at 683 K with Zn Cl₂/Ni-USY-Acid catalyst(propanol/aniline=3/1,H₂,0.4 h^-1).?3?Study on reaction mechanism of aniline and C₁-C₄ alcohols.The study of catalyst characterization and reaction performance evaluation showed that larger pore size and higher specific surface are beneficial to the formation of quin oline compounds.The concentration ratio of B/L acid sites was the most critical factor affecting the performance of the catalyst.The reaction mechanism of aniline and C₁-C₄ alcohols has been proposed:For the reaction of polyhydric alcohols and aniline,alcohols were converted to aldehydes after dehydration reaction firstly,and the second step,unsaturated aldehydes were formed by the condensation reaction of aldol,then unsaturated aldehydes reacted with aniline,finally the quinolines were synthesized by the aromatization reaction;For the reaction of monohydric alcohols and aniline,N-alkyl aniline was formed firstly and then N-alkyl aniline was converted to Schiff base with dehydrogenation reaction,after the dimerization reaction of Ph=N-R^-,the quinolines were synthesized by the aromatization reaction finally.Quinolines could not synthesized by methanol and ethanol because the corresponding schiff base of methanol and ethanol were diffic ult to dimerization.The Lewis acid sites of catalysts promoted the adsorption and activation of alcohols and aniline,and the high ratio of L/B acid sites concentration was propitious to the synthesized of quinolines from aniline and C₁-C₄ alcohols.?4?Study on in situ FT-IR transmission.The in situ infrared spectroscopy of pyridine adsorption was carried out on the USY?Ni-USY and Zn Cl₂/Ni-USY catalysts.The results showed that the ratio of L/B acid sites concentration was increased after the modification.The adsorption and desorption of aniline and n-propanol on modified USY catalyst were researched via in situ FT-IR transmission method.It was identified that the reaction of aniline and propanol generated predominantly quinolines,including 2-ethyl,3-methylquinoline and other alkyl quinoline,N-alkyl aniline and other byproducts.There were predominantly two possible routes for the formation of quinolines,which required predominantly Lewis acid site and Bronsted acid site,respectively.In route one,aniline was adsorbed on the Br?nsted acid sites firstly,then reacted with the propanol?detached or weak adsorbed state?to form the N-propylaniline ion,which could be turned to N-propylaniline after desorption or reacted with another aniline molecule to form the imine.Then the2-ethyl,3-methylquinoline was synthesized from bimolecular reaction of imine.In route two,aniline was absorbed on the Lewis acid sites of catalysts with?-electron,and propanol was turned into propylaldehyde after dehydrogenation on Lewis acid sites.Then the aniline and propylaldehyde?both adsorbed state?reacted to form imine,finally 2-ethyl,3-methylquinoline was synthesized.The results of catalytic reaction experiment showed that high ratio of L/B acid sites concentration was propitious to the synthesis of 2-ethyl,3-methylquinoline,and also lead to the formation of N-propylaniline.Therefore,route two was more significant to the route one in the generation of quinolines from the reaction of aniline and propanol.