video tutorial Preparation of propionyl chloride

Propionyl chloride synthesis from propionic acid and phosphorus trichloride

Materials

• Propionic acid, anhydrous, 140 ml
• Phosphorus trichloride, 56 ml
• 500 ml round-bottom flask, water bath at room temperature
• Ventilated setup and good airflow
• Addition funnel (pressure-equalized recommended) and appropriate venting for HCl
• Stirring bar and means to stir vigorously

Procedure

• Add dry propionic acid to the dry flask with stirring
• Set up an addition funnel containing phosphorus trichloride on top of the flask
• Vent the system to remove HCl gas; minimize atmospheric exposure
• Start adding phosphorus trichloride slowly, over about 20 minutes, while maintaining stirring
• Expect HCl fumes and a milky coloration as the acid chloride forms; continue to vent safely
• After addition, stir vigorously for about an hour; HCl production continues
• Separate two layers; bottom layer is mostly phosphoric acid

Distillation and workup

• Set up simple distillation with cooling water and a thermometer to monitor distillate temperature
• Distill to about 90 °C; discard the first ~5 ml of distillate (about 55–65 °C) as impurities
• Continue distillation until nothing more distills over (approx. 1.5 hours)
• HCl fumes continue to some extent during distillation
• At the end, a syrupy, viscous layer remains; carefully disassemble apparatus
• Remove the distillate, then carefully add a small amount of water to the top of the still head to destroy any remaining acid chloride (exothermic)

Product and yield

• Propionyl chloride obtained: about 90 ml
• Yield: about 55% (likely lower due to impurities in the starting acid)
• Product fumes in air; store in an extremely airtight container
• Handle water cautiously as it can generate HCl gas and cause phase separation; distill again if higher purity is needed

Notes

• Propionyl chloride is highly reactive and fumes; ensure proper ventilation and safe handling
• HCl gas must be vented away safely
• Storage requires airtight containment; further purification by re-distillation may improve purity

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