Synthesis Of 2-methyl-1-naphthaldehyde

Aromatic aldehyde and derivative thereof are widely used in various industries such as medicine,dye,pesticide,perfume and so on,among them,2-methyl-1-naphthaldehyde is a starting material for the synthesis of vitamin K and a,(3-unsaturated lactones in fine chemical industry.At present,the existing methods for synthesizing 2-methyl-1-naphthaldehyde had some disadvantages,such as high catalyst cost,difficult to obtain raw materials,harsh reaction conditions,low yield,high energy consumption and high risk factor,which were difficult to industrialize.Therefore,this paper newly developed a "three-step"synthesis route,and selected 2-methylnaphthalene as starting material to prepare 2-methyl-1-naphthaldehyde through reaction processes of chloromethylation,hydrolysis and TEMPO catalyzed.The main research contents of this topic were:We firstly used acetonitrile and anhydrous ethanol as recrystallization reagents to prepare the required standards based on the physico-chemical properties and structures differences of intermediates and target product.Then,we developed qualitative and quantitative analysis methods of 2-methylnaphthalene,1-chloromethyl-2-methylnaphthalene,2-methyl-1-naphthalenemethanol and 2-methyl-1-naphthaldehyde by using high performance liquid chromatography,mass spectrometry and nuclear magnetic resonance spectroscopy.It was confirmed the feasibility of this process.In the study,single factor method and orthogonal experiment method were used to respectively optimize conditions of chloromethylation,hydrolysis,and oxidation to increase the yield and selectivity of target product and intermediates.In the process of chloromethylation,we chose paraformaldehyde and HCl as chloromethyl source,hydrochloric acid and ZnCl2 as cocatalyst,and optimized four factors of reaction time,temperature,ratio of raw materials and catalyst.The optimum process conditions were:reaction time of 10 h,reaction temperature of 65 ?,ratio of raw materials of 3:1.Under this condition,the yield of 1-chloromethyl-2-methylnaphthalene could reach 97.15%and the selectivity was more than 99%.In the hydrolysis reaction,the reaction system changed from solid-liquid two-phase to liquid-liquid two-phase as the temperature increases,and the reaction was extremely inefficient in heterogeneous system.In order to solve this problem,the traditional hydrolysis process of halohydrocarbon was improved by introducing the phase transfer catalyst PEG-2000 in order to increase the yield of hydrolysate.The results showed that addition of trace amounts of PEG-2000 could greatly increase reaction rate,which showed that the presence of phase transfer catalyst could play a very good catalytic effect.Subsequently,we optimized reaction time,temperature,solvent and nucleophilic reagent to obtain optimum process conditions:reaction time of 8 h,reaction temperature of 95 0C,water as solvent,Na2CO3 as nucleophilic reagent,molar ratio of 1-chloromethyl-2-methylnaphthalene to Na2CO3 of 1:1.5.Under this condition,the yield of 2-methyl-1-naphthalenemethanol could reach 98.20%and the selectivity was greater than 99%.In the oxidation reaction,we adopted a catalytic oxidation system which were composed of air and TEMPO composite catalysts with both economic and environmental benefits for the problem of environmental pollution and excessive oxidation of stoichiometric oxidants(such as KMnO4,K2Cr2O7,and HNO3).The study found that copper salts had a great influence on reaction.CuCl,a univalence copper-salt,showed a good catalytic effect and could conduct an directly direct oxidation from alcohols to aldehydes in an alkali-free state after comparison and screening.Then,we optimized reaction time,solvent and catalyst amount.The obtained optimum conditions were:reaction time of 42 h,acetonitrile,room temperature,ordinary pressure,ratio of catalyst to 2-methyl-1-naphthalenemethanol of 3:1.Under this condition,the yield of 2-methyl-1-naphthaldehyde was 95.85%and the selectivity was greater than 99%.