By What Means Can Propionyl Chloride be Prepared?

Propionyl chloride can be prepared by reaction of propionic acid with phosphorus trichloride, phosphorus pentachloride, sulfoxide chloride or phosgene.

The following steps and precautions are introduced in detail for the preparation of propionyl chloride by reaction of propionic acid with phosphorus trichloride:

Steps of the preparation of propionyl chloride by reaction of propionic acid with phosphorus trichloride

(1) Installation of the instrument: In the oil bath pot of the heat-collecting magnetic stirrer, a 250ml eggplant-shaped flask is installed with the agitator, and the eggplant-shaped flask mouth is successively installed with the distillation head, thermometer, straight condenser tube and tail pipe.The two branches of the tail pipe are connected with a 50ml eggplant-shaped flask (which is used to collect the front cut fraction), a 100ml conical flask (which is used to collect the product and should be weighed).The tail pipe shall be connected with CaCl₂ drying pipe and gas absorption device successively with rubber pipe.

(2) Preparation of propionyl chloride: 18.5ml propionic acid and 8.7ml phosphorus trichloride are added into the eggplant-shaped flask. The oil bath pot is heated to 50℃ and maintained at this temperature for 3 hours.

(3) Distillation of propionyl chloride: heat the oil bath pot, collect the front cut fraction in 50ml eggplant-shaped flask, and collect the main distillate fraction in a drying and weighed 100ml conical flask, add a cork, weigh and calculate the yield coefficient.

Precautions for the preparation of propionyl chloride by reaction of propionic acid with phosphorus trichloride

(1) This experiment should be conducted without water, as both phosphorus trichloride and propionyl chloride would decompose with water.

(2) Latex pipe is connected with tail pipe and drying pipe, and rubber pipe is connected with drying pipe and funnel.

(3) Use 10ml measuring cup to measure phosphorus trichloride and 25ml measuring cup to measure propionic acid. When taking the reagent, do not pour the excess part back into the reagent flask to prevent contamination.

(4) Phosphorus trichloride is corrosive and should not be touched by the skin.

(5) Calibrate the temperature of the sensor by placing a thermometer in the oil bath pot near the wall of the eggplant-shaped flask. At the beginning of heating, the temperature should not be set at 50℃. It can be slightly lower to avoid excessive temperature in case of steaming out the raw materials.

(6) When distilling propionyl chloride, the external bath temperature should not be too high (below 130℃), in order to avoid the coking of phosphite.

(7) The front cut fraction shall be recycled and shall not be dumped into the sewer.

(8) The amout of the first cut fraction in this experiment will not be very large. Since the thermometer has not been calibrated, the temperature cannot be the same, so it can be collected when the temperature is stable.

(9) Phosphite may stick to the bottom of the flask and has a strong irritation. At this moment, after the eggplant-shaped flask is a little cold, add appropriate amount of sodium hydroxide solution to wash, pour the scrub solution into the sewer, and that will be ok.

(10) The corks of the conical flasks used to preserve the products should neither be too tightly packed nor be shaken, to prevent the decomposition gases escaping from the corks and spattering on the eyes or skin.