Synthesis And Characterization Of Hydrogen-Bonded Liqued Crystalling Compound With Isonicotinic Acid Ester Derivatives

In recent years, liquid crystal displays of flat-panel displays have become mainstream products. Liquid crystal materials are essential for the development of modern society, and then, there is very important practical significance to research and develop liquid crystal materials with excellent function. Hydrogen-bonded liquid crystal, because of its superiority and flexibility in construction and performance, has received considerable interest as a kind of functional material.In this thesis, a series of hydrogen-bonded liquid crystal were synthesized with ca rboxylic acid derivatives (4-alkoxybenzoic acid)as H-bond donor, and isonicotinic acid ester derivatives(schiff isonicotinic acid ester derivatives and azo isonicotinic acid este r derivatives) that involve as H-bond acceptor.Based on the simple and available raw materials such as isonicotinic acid, this issue which followed the design principle of h ydrogen-bonded self-assemble liquid crystal molecule researched Schiff base-type and a zo-type super-molecule liquid crystal compounds. They were synthesized by 4-(((4-(hex oxy) phenyl) imino) methyl)phenyl isonicotinic acid ester and 4-((4-(hexoxy) phenyl) azo) phenyl isonicotinic acid ester as proton acceptor, and alkoxybenzoic acid as proto n donor, through hydrogen bond as connecting group, in succession of etherification, r eduction, condensation, diazotization, coupling reaction and esterification. The obtained compounds were characterized by Fourier transform infrared spectrometer and pulse Fo urier transform NMR spectroscope, and analyzed by polarizing microscope for liquid c rystalline propery.(1) Etherification:In this issue there were two types of alkoxidation, which included the reaction of alkyl bromide with 4-hydroxy benzoic acid and 4-nitrophenol. In the reactions, the different reaction conditions were used,the former compound were added in the absolute alcohol and react at 80℃for about 24 hours. After that, the mixture was added to an appropriate amount of water and dealt with acidification, filtration and recrystallization. The yield of reactant was up to 60%; The latter compound were added in the acetone, mixed with K2CO3 as acid-biding agent and KI as catalyst, reacted at 70℃for 28 hours at least. After that, the mixture was extracted in ether.(2) Reduction reaction:In the process of the synthesis of 4-alkoxy aniline, the nitro reduction was made by hydrated tin chloride. The classical iron reduction can be avoided because of hard-purification of product, pollution of the environment and other issues. In further treatment the amount of saturated solution of sodium hydroxide was the key. If the amount of saturated solution of sodium hydroxide was not sufficient, the formed precipitate floats could not be completely dissolved, which would directly influence the yield. Owing to 4-alkoxy aniline was susceptible to oxidation, it would be better to conserve far away from light.(3) Condensation reaction:It was easy to synthesize the schiff s compound by adding two pellets of molecular sieve in the polar solvent, refluxing at 80℃for about 5 hours. The yield of products was considerable.(4) Diazotization, coupling reaction:The intermediate 4-((4-(hexoxy) phenyl) azo) phenol, which was the basis of this paper, was synthesized by diazotization and coupli ng reaction. The experimental results showed that temperature and solution pH of this reaction were important factors.The system temperature should be controlled at 0-5℃, which could be practiced through controlling the temperature of cold brine bath. For coupling reaction, the system should be kept the pH 9-10 by dropping sodium hydrox ide solution. During the process of purifying the product, the target compound could b e obtained after recrystallization with glacial acetic acid as a kind of solvent.(5) Esterification reaction:Two kind of ester compounds were obtained through DCC/DMAP method. This reaction had low reaction temperature and moderate reaction condition, and it was easy to remove DCU, which was hard to dissolve in most solvent.In the factors of influencing the liquid crystal properties, the carbon chain length has significant influence. For small molecule of schiff s compound, with the growth of carbon chain, the liquid crystal phase temperature and cool spot decrease gradually and the scope of liquid crystal phase temperature widen gradually. The different structures of different compounds not only lead to the difference of intermolecular hydrogen-bond, force and strength, but also influence the formation of different liquid crystal properties. The hydrogen-bonded liquid crystal compounds, which were formed with Schiff's compound and 4-hydroxy benzoic acid by intermolecular hydrogen-bond, have wider range of liquid crystal phase. The reason may be the enhancement of intermolecular force and the increasement of molecular conformation caused by the inducement of hydrogen-bond. As for the H-bonded liquid crystal compounds synthesized by azo compound and 4-hydroxy benzoic acid, they present smectic phase and nematic phase respectively.