First, measure out 140 ml of liquid propionic acid as anhydrous as possible.

Set up a 500 ml round-bottomed flask on a water bath at room temperature.

This needs to have very good ventilation.

Add the propionic acid to the dry flask and add a magnetic stir bar to the flask.

Stirring is quite important for this reaction to go to completion as you will

Next, measure out 56 ml of liquid phosphorus trichloride.

This is very toxic so do take great care with it and use only with ventilation present.

As you can see it fumes and air so try to work quickly.

Set up an addition funnel on top of the flask and add the phosphorus trichloride to it.

You'll also need a way to vent the flask as a lot of

HCl gas will be produced.

I've used a pressure equalized funnel but you could use a multiple neck flask or other

setup.

Try to minimize the opening to the atmosphere.

With the water bath at room temperature and with stirring, start to add the phosphorus

trichloride.

You shouldn't see much of a temperature increase but add carefully just to be on the safe side.

Our addition here took 20 minutes to complete.

Bye.

start adding you'll see a fog of HCl gas being produced in the flask and the

contents will turn a milky color this is our reaction taking place with the

formation of the acid chloride a lot of HCl gas will start to be produced and

will escape the apparatus make sure you take care to vent this away properly

once action was complete we left the solution stirring vigorously for an hour

continued to be produced during this period

at the end of this time the mixture separates into two layers the bottom

layer is mostly phosphoric acid so now set up the flask for simple distillation

using cool water and a thermometer to monitor the temperature of the

distillate papers we really recommend using a hose

attached to a suitable receiving adapter which can safely vent away HCl

gas

heat the water bath strongly as our aim now is to distill over everything up

until around 90 degrees C

we noticed that around five milliliters of liquid distilled over around 55 to 65

degrees C we discarded this as we think this may be a result of impurities in

our propionic acid

keep heating and the bulk of the distillate should come over above 70

degrees

keep going until nothing more comes over this took about an hour and a half in

this particular case

HCl fumes continue to be produced to a lesser extent throughout the

distillation at the end of the distillation there is only a syrupy

viscous layer remaining in the flask and it perfectly clear distillate take extra

care when disassembling the apparatus

recommend removing the distillate and then cautiously adding a small amount of

water into the top of the still head this will generate some heat but will

destroy any acid chloride remaining in the apparatus here's our product around

90 mils of propionyl chloride this is around a 55% yield which should be

higher but we think our current batch of propionic acid does contain some

impurities which lower this as you can see the product fumes strongly in air

and you will need to keep it safely stored in an extremely airtight

container and take care when opening the reaction with water is pretty rapid

drops of it form a separate layer which jumps around giving off HCl fumes then

disappears you can distill the product again to get it extra pure as it does

still contain a small

change in the amount of propionyl chloride that is present in the product

trace of phosphorus compounds

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