1,2-Pentanediol is an organic compound, a colorless, transparent liquid with a relative density of 0.971, soluble in organic solvents such as alcohols, ethers, and ethyl acetate. 1,2-Pentanediol is a key raw material in the synthesis of the fungicide propiconazole.
It is synthesized using 1-pentene, hydrogen peroxide, and formic acid in a molar ratio of 1:1.5:4. The equilibrium mixture for this reaction is formed through the following procedure: 1-Pentene and hydrogen peroxide (70%) are slowly added simultaneously to formic acid at 40–55°C. After the addition is complete, the mixture is stirred at 55°C for 1 hour and then transferred to a circulating reactor equipped with a circulating pump and an overflow siphon. The reactor is heated to 55°C and circulated. Then, 1-Pentene and formic acid are added through one inlet pipe, while hydrogen peroxide is added through another. An exothermic reaction occurs, and the temperature is allowed to rise to 62–63°C. These components are added at a specific ratio and rate. The equilibrium operation is controlled by a circulating thermostat and carried out for approximately 8 hours. The reaction is then stopped, yielding a large amount of 1,2-pentanediol formate ester. Formic acid and water are removed by vacuum distillation. The residue is hydrolyzed in 25% NaOH solution, followed by solvent extraction, desolventizing, and distillation to obtain 1,2-pentanediol with a yield of up to 91% at 96–98°C/1.3 kPa.
