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%.