Synthesis Of Barbed Hindered Phenols And Their Effects On Liquid Crystalline Stability

Most industrial organic materials, no matter from natural products or synthetic compounds, the oxidation reaction occurs spontaneously. In order to prevent or delay this oxidation process, the antioxidants have been invented, which is simple, effective and does not cause any adverse change.In the liquid crystal field, it is very important to add the antioxidants because the plenty of olefin liquid crystalline compounds have been extensively used in the mixture. The common antioxidants cannot match the requirement of liquid crystal because liquid crystal materials are special opto-electrical materials. In order to find a similar structure with a liquid crystal material, good compatibility, the higher antioxidant properties of hindered phenolic antioxidant, to explore the feasibility of its use as a liquid crystal mixture formula, eighteen antioxidants of4-alkyl-4’-bicyclohexyl-2,6-dialkyl-phenol were synthesized. Therein twelve compounds have not been reported hitherto. Another six compounds were reported in the patent without any specific performance data. This paper explore the conversion method of cyclohexane stereoisomers, optimal conditions for bromination, and evaluated the impact of performance on the different substituents of2,6-position of hindered phenolic and the introduction of the ethylene bridge between the cyclohaxane.The main contents are as follows:1. Twelve antioxidants of4-alkyl-4’-bicyclohexyl-2,6-dialkylphenol were synthes-ized starting from4-(4’-alkyl-cyclohexyl)cyclohexanone,2,6-dimethylphenol and2,6-di-tert-butylphenol via hydroxyl protection, Grignard, dehydration, hydrogenation and cis-/trans-formation. The purity of the target molecules was higher than99%with the yield between25%and55%. Their structures were characterized by Nuclear Magnetic Resonance (NMR), Infrared (IR) and Gas Chromatography-Mass Spectro-metry (GC-MS). The transformation of cyclohexane stereoisomers and the mechanisim of the cis-to the trans-configuration of the cyclohexyl were investigated. Compared with potassium bisulfate, p-toluenesulfonic acid as a catalyst, the dehydration reaction can effectively carry out in a short time, and higher yield, up to92.6%. By using trimethylchlorosilane to protect the phenolic hydroxyl of2,6-di-tert-butylphenol, the reaction can be carried out smoothly, and the yields were above90%.2. Six antioxidants of4-alkyl-4’-bicyclohexyl-2,6-diisopropylphenol were synthesi- zed starting from4-(4’-alkylcyclohexyl)cyclohexanone,2,6-diisopropylphenol via hydroxyl protection, Grignard, dehydration, hydrogenation and cis-/trans-formation. Their structures were characterized by Nuclear Magnetic Resonance (NMR), Infrared (IR) and Gas Chromatography-Mass Spectrometry (GC-MS). The reaction conditions of bromination were examined and found that using bromine as raw of bromide, the reaction can proceed smoothly with high yield.3. By Differential Scanning Calorimetry (DSC), Polarized optical Microscopy (POM), LC Parameters and Gas Chromatography (GC), the effects of antioxidants on the stability of liquid crystal were preliminarily evaluated. The results demonstrated that the substituent of bis-tert-butyl in the ortho-position of phenolic hydroxy gave rise to a superior performance with methyl and isopropyl on the liquid crystal stability. An insection of an ethylene bridge into the bis-cyclohexyl derivatives shown a better light stability than that of bis-cyclohexyl derivatives themselves.In short, the thesis is useful for the synthesis of4-alkyl-4’-bicyclohexyl-2,6-dialkyl phenol and is of great significance to study the relationship between functional groups and performance, which provided information and reference value for the use of antioxidants in liquid crystal material. Comparison with the antioxidant content of50ppm, the content of100ppm proved to be beneficial to the stability of the liquid crystal.