Transcription
Welcome everyone. Today, I will show you how to make propionyl chlorides. This stuff can be used in chemistry to make esters very easily.
For the preparation, we are going to use a little over two moles of benzoyl chloride and exactly two moles of propionic acid. I had to rebottle the benzoyl chloride for a few reasons, but I actually got both these chemicals from Laboratorium Discounter. If you know them yet, they’re a Dutch chemical seller; they are selling a lot of stuff. And if you want to order from them while also getting a 7% discount, use the code on screen or in the video description.
I assume that most of you have never heard of this method of making acid chlorides beforehand. That’s reasonable; I haven’t heard of it before, too. So let me explain what we are going to do. The usual routes used are thionyl chloride and HCl gas, but in the lab you also often use oxalyl chlorides because it’s very convenient, phosphorus chlorides, or other routes like oxalyl chloride. These routes can be used for most carboxylic acids. Benzoyl chloride cannot be used for most carboxylic acids. When using benzoyl chloride, it is important that the resulting carboxylic acid chloride is a somewhat slow-boiling liquid. This method is suited for propionyl chloride and acetyl chloride. I don’t know about butyryl chloride and anything above that, but for propionyl chloride, it works decently well.
We measured out 235 milliliters of benzoyl chloride and 150 milliliters of propionic acid. These two chemicals were simply mixed, and when you heat them up, you get propionyl chloride, which distills off in solution. You have an equilibrium between acid and acid chlorides, and as propionyl chloride can easily be distilled off, we can remove it from the equation. The heat plate was set to a temperature of 200 degrees C, and what came over at a temperature of between 60 and 85 degrees C was propionyl chloride. Propionyl chloride has a boiling temperature of about 80 degrees Celsius, and as the boiling point of propionic acid itself is much higher than that, the liquid coming over in our temperature range can be accepted as decently pure propionyl chloride. The entire distillation took about 2 hours, and it got slower towards the end. I could have continued it to get an even higher yield, but I figured out that it wasn’t worth it, and I just stopped it.
And there you have it. This is our finished propionyl chloride. It’s a clear liquid which produces nasty fumes. For storing it, you need to use a tight-sealing storage bottle before filling it up. I weighed it on a scale in order to determine the yield. We ended up with 83 grams, which represents a yield of 45 percent. You could improve the yield by distilling for longer, but you don’t want to crank the temperature up too much because you could contaminate your product with benzoic acid. On screen, you can now see what happens when you add water. Propionyl chloride instantly hydrolyzes and forms propionic acid and hydrochloric acid.
You also don’t need to throw away the leftovers. You can still get some useful benzoic acid by adding distilled water, heating it up to dissolve it, decanting it off, and letting the benzoic acid crystallize out. I ended up using a lot of distilled water, heating it up, crystallizing it out, and reusing the distilled water because there was so much benzoic acid. But while heating, we got this very interesting lava lamp-like looking effect. Watching benzoic acid crystallize out is also mesmerizing and looks like a snow globe. We ended up recovering 196 grams of benzoic acid, so this does not have to go to waste and can still be used for other projects.
Let’s talk about reasons why you even want to make propionyl chlorides. Occasionally, I like to make esters, and you are going to get another video on that soon. And if you want to make esters, you can simply mix an acid chloride with your alcohol, and you get the ester and hydrogen chloride. This method is very quick. In this case, our alcohol was thymol, and I added the propionyl chloride to it and heated it up with a lighter for about 30 seconds. But after that, the reaction was finished. As I used a small excess of propionyl chloride to make the ester, this clear liquid consists of propionyl chloride, our ester, and hydrogen chloride. To get rid of the hydrogen chloride and isolate our ester, I added distilled water and later on a small amount of sodium bicarbonate. It was shaken; the ester separated out and it was transferred to a vial. All of this was done in under 6 minutes.
And there you go. Now you know how to make propionyl chlorides. I hope you liked today’s video, and I would especially like to thank all of my patrons because you guys make it possible to film even cooler stuff. If you would like to become a Patreon, while getting your name at the end of these videos, access to a few Patreon-exclusive videos, while also supporting me, I would appreciate if you check out the link in the video description. Thanks for watching and have a nice day.