Abstract: The 2,6-Naphthalenedicarboxylic acid (2,6-NDA) is the precursor of polyester polyethylene naphthalate (PEN),and the highly symmetric structure of 2,6-NDA endows the straight-chain polymer with superior performance in heat resistance,gas blocking and chemical stability.The 2,6-NDA can be obtained by the oxidation of 2-methyl-6-acyl naphthalene which can be synthesized by 2-methylnaphthalene acylation.In order to understand the mechanism and the process of the acylation of 2-methylnaphthalene,the authors employed the 2-methyl naphthalene (2-MN) as reactant,the AlCl3 as catalyst and the propionyl chloride as acylating agent to implement the acylation reaction.Results showed that the 2-MN conversion rate could reach 92.53% and the product selectivity was 89.98% under the reaction conditions of acylation reaction at 25 ℃ for 5 h with the molar ration of n(2-MN):n(propionyl chloride):n(AlCl3)=1∶1.4∶1.7.15% methanol recrystallization processing could obtain 99.99% 2-methyl-6-propionyl naphthalene.The obtained pure product was systematically characterized to identify the molecular structure by using gas chromatography,mass spectrometry,infrared spectroscopy,1H spectrum,13C spectrum,two-dimensional nuclear magnetic resonance techniques and the ChemDraw software structure prediction.Based on the above structural characterization and combined with the structure prediction by using the ChemDraw software,the acylated product was identified to be the 2-methyl-6-propionyl naphthalene.The speculated mechanism of the 2-methylnaphthalene acylation indicated that the reason why the 2-methyl-6-propionyl naphthalene being the main acylated product is due to the steric-hindrance effect imposed by the large size complex molecule during the Friedel-Crafts acylated reaction.