Study On Synthesis Of 1,2-Pentanediol And Optimization Of Process Conditions

1,2-pentanediol is the key intermediate in the preparation of propiconazole, the domestic market demand mainly relies on imports to meet. Syntheic methods of 1,2-pentanediol were summarized in detail, and a comparison was made between advantages and shortcomings of these synthesis methods. On this basis, a new feasibility synthetic route was designed. This route mainly contained two steps, in the first step, the intermediate 1-hydroxy-2-pentanone was synthesized by cross-acyloin condensation between n-butyraldehyde and paraformaldehyde. In the second step, 1-hydroxy-2-pentanone reacted with hydrogen in the presence of hydrogenation catalyst to prepare 1,2-pentanediol. The technological conditions of each reaction were investigated separately, and the structures of the products were analyzed and charaeterized.The main research work and results are showed as follows:(1) Experimental conditions for depolymerization of paraformaldehyde were discussed. The effects of some factors such as reaction time, reaction temprature, solvents, and bases on the depolymerization were investigated. The results were showed as follows: paraformaldehyde is 2.25g, ethanol or methanol is 15mL, triethylamine is 1g, reaction temperature is 70 ~ 80℃. Under the above conditions, paraformaldehyde was completely dissolved after 30 ~ 40min.(2) 1-Hydroxy-2-pentanone was synthesized by the reaction between n-butyraldehyde and paraformaldehyde. The effects of some factors such as raw ratio, catalyst, bases and solvent on the reaction were investigated. The optimal conditions were as follows: under nitrogen protection, n(n-butylaldehyde):n(paraformaldehyde)=1:1.5, 3- ethylbenzothiazolium bromide as umpolung catalyst, triethylamine as base, n (n-butylaldehyde):n(catalyst):n(triethylamine) = 1:0.1:0.15, reaction temperature is 70℃, anhydrous alcohol as reaction solvent, the volume is 15mL, the reaction time is 6h. Under the above conditions, six times repeated trials were carried out, an average yield of 1-hydroxy-2-pentanone was 56.67%. The structure of the product was confirmed by IR, MS and 1HNMR.(3) Hydrogenation reaction conditions of 1-hydroxy-2-pentanone were studied. The effects of some factors such as catalyst, solvent, reaction pressure and reaction temperature on the reaction were investigated by single factor experiment and orthogonal test, the optimal conditions were as follows: The amount of 1-hydroxy-2-pentanone is 33g (0.324mol), the amount of hydrogenation catalyst Pd/C is 3.5%(compared to 1-hydroxy-2-pentanone quality), anhydrous ethanol as solvent, the volume is 150mL, hydrogen pressure is 1.2MPa, reaction temperature is about 55℃, stirring speed is 350r/min, the reaction time is 9h. Under these conditions, 1-hydroxy-2-pentanone conversion rate was more than 94%, the yield of 1,2-pentanediol was about 90%. The structure of the product was confirmed by IR, MS and 1HNMR.