Study On The Synthesis Of The N-Alkyl-Paracyclophane

Parylene thin film is made of paracyclophane and its derivatives by chemical vapor deposition.It has become a world-leading coating material since 1960s.Better properties can be obtained by modifying paracyclophane,and the film is applied to biomedicine,aerospace,integrated circuits and other high-tech fields.The long chain alkyl substituted p-xylene can form a film of higher flexibility,higher thermal stability and better solubility,which was expected to expand into new application market.In this paper,the preparation technique of 4-n-propyl[2.2]paracyclophane and4,12-dipropyl[2.2]paracyclophane were studied,aiming to reduce the research cost of long-chain alkyl substituted p-xylene cyclodimer and make it have the prospect of industrial production.First of all,the synthesis route of 4-n-propyl[2.2]paracyclophane was studied.4-n-propyl[2.2]paracyclophane was obtained from p-xylene by Friedel-Crafts acylation and deoxyhydrogenation reduction.In the synthesis process of Friedel-Crafts acylation,the influence of variety of catalyst,solvent type,reactant ratio and reaction time on the yield of aromatic ketone 4-propionyl[2.2]paracyclophane was studied,and the optimal reaction conditions was as follows:under nitrogen protection,anhydrous aluminium chloride as catalyst,dichloromethane as solvent and n（propionyl chloride）:n（chloride）:n（p-xylene）=1.4:1.6:1,mixing reaction under-15℃for 30 min,the average yield reached 70.1%.Secondly,catalytic hydrogenation,NaBH₄/AlCl₃reduction and Wolf-Kishner-Huang reduction were investigated in the reduction process of aromatic ketone 4-propionyl[2.2]paracyclophane.The results show that the catalytic hydrogenation method has poor selectivity and is not suitable for this reaction.The latter two methods can successfully synthesize 4-n-propyl[2.2]paracyclophane.The optimum reaction conditions of NaBH₄/AlCl₃ reduction method are as follows:using tetrahydrofuran as the reaction solvent,the molar ratio of sodium borohydride to aromatic ketone is 3:1,the molar ratio of aluminum chloride to aromatic ketone is 2:1,the reaction temperature is 70℃,the yield of product is about 40%.The optimum reaction conditions of Wolf-Kishner-Huang reduction method are as follows:diethylene glycol as the reaction solvent,the molar ratio of hydrazine hydrate to aromatic ketone is 4:1,the molar ratio of potassium hydroxide to aromatic ketone is 4:1,The reaction was carried out at the reflux temperature for 2h,then the temperature was increased to 215℃and the reduction was continued for 3h,the yield of product can reach 93.6%.The total yield of acylation and reduction was up to 65.6%.Finally,the synthesis route of 4,12-dipropyl[2.2]paracyclophane was studied.Using 4-n-propyl[2.2]paracyclophane as raw material,aromatic ketone was obtained by Friedel-Crafts acylation,then the aromatic ketones are reduced by Wolf-Kishner-Huang reduction to obtain the final product 4,12-dipropyl[2.2]paracyclophane.The optimum reaction conditions of acylation step are as follows:under nitrogen protection,anhydrous aluminium chloride as catalyst,dichloromethane as solvent,the molar ratio of propionyl chloride and 4-n-propyl[2.2]paracyclophane is 1.2:1,the molar ratio of anhydrous aluminium chloride and 4-n-propyl[2.2]paracyclophane is 1.4:1,mixing reaction under-15℃for 20 min,and the average yield was up to 92.14%;Reduction step optimum reaction condition is:with DEG as solvent,the molar ratio of hydrazine hydrate and aromatic ketone is 4:1,the molar ratio of potassium hydroxide and aromatic ketones is 5:1.The reaction was carried out at the reflux temperature for 2h,then the temperature was increased to 210℃and the reduction was continued for 3h.The average yield of the optimized reaction was 82.34%,and the total yield of the two-step reaction was up to 79.9%.