March 28, 2023

In this video we are making aspirin (acetylsalicylic acid) by acetylating salicylic acid with acetic anhydride.

Welcome back everyone today we are going to make some acetyl salicylic acid also known as aspirin for this 69 grams of salicylic acid 55 milliliters of acetic anhydride 58 milliliters of glacial acetic acid as a solvent distilled water and ethanol are needed besides that we also used five milliliters of acetic anhydride containing a little less than fifteen percent

Of sulfuric acid as a catalyst i don’t know the reason for this but the color of this changed red over time it is probably still good enough to be used as a catalyst like in every single one of my preparations the ethanol was empty the distilled water was nearly empty and the glacial acetic acid was frozen in the bottle glacial acetic acid melts at about 16 degrees

Celsius we put it onto a heater to melt it the distilled water was refilled from a big canister and i tried to first siphon the ethanol but after this didn’t work because the canister is already nearly empty i used the funnel and spilled a bunch of it before proceeding we put on some gloves and safety goggles we then started off by weighing out approximately 69

Grams of salicylic acid we ended up with 69.4 grams salicylic acid is a white fluffy looking powder breathing in dust of it is definitely unpleasant and should be avoided using a ground glass joint the salicylic acid was quickly transferred to one liter round button flask using this device which is specifically produced only for poking at salicylic acid we were

Able to free the salicylic acid from the fungal with the use of a measuring cylinder we measured out 55 milliliters of glacial acetic acid and 5 milliliters of glacial acetic acid containing 15 sulfuric acid the sulfuric acid is required as a catalyst other acids might also be used but i am unsure about that after a still fish has already been added the acetic

Anhydride sulfuric acid mixture was transferred to the flask if you have pure sulfuric acid you could just add a few drops of this here’s an excellent example of why you should melt the reagent you want to use completely before pouring it the block of glacial acetic acid eyes started to move and a bunch of it was built this happened not one but two consecutive

Times i learned from my mistakes and it won’t happen again but this is an example of why gloves and safety goggles must always be worn in any lab after cleaning up everything the glacial acetic acid was added to the rest of the solution it doesn’t participate in reaction but it’s just used as a solvent in my experience it increases the yield significantly after

Everything has been added reflux was set up the condenser was flushed with water and we were done ready to begin both heating and steering were turned on on the top of the flask you can see that some glacials see the gas that actually started to freeze it will soon melt again and go down into the mixture on the top we added one of these hose adapters to keep at

Least some of the moisture out it took about 10 minutes until everything started boiling and by this moment we were left with a clear and just a little red solution reaction taking place can be seen above salicylic acid reacts with acetic anhydride under acidic conditions to form acetic acid and acetyl-salicylic acid if water was present acetyl-salicylic acid

Would hydrolyze back to salicylic acid under acidic conditions for this reason this reaction can’t be performed with glacial acetic acid but acetic anhydride or acetyl chloride must be used after 180 minutes of continuous refluxing the heating mantle was turned off the apparatus was then disassembled a magnetic stirrer was set up and the reflux column was taken

Off the magnetic stirrer was turned on and afterwards 400 milliliters of ice-cold distilled water were added acetylsalicylic acid has a poor solubility in water but a high solubility in acetic acid by adding water we were able to crash out a lot of the aspirin to decrease solubility even further an ice bath was set up magnetic stirrers fortunately go through a lot

Of materials the magnetic stereo helped us speed up the cooling process steering was continued until the temperature of 7 degrees celsius was reached we were left with this pudding-like looking mass although it looks delicious you should not eat it aspirin is toxic in large doses and it would also smell horrible because of a lot of acetic acid present a vacuum

Filtration was carried out to get rid of the majority of the water if you take a look at this filtration and cringe yes i should definitely get a bigger filtration funnel and a bigger flask for this kind of stuff once the filtration was finished we were left with this crude aspirin which does not look pure everything was put back into the one liter around by the

Flask which was still dirty as a solvent 150 milliliters of 96 ethanol were added the solution was heated until everything dissolved and then we added about 150 milliliters of distilled water again the distilled water acts to decrease the solubility of the acetyl salicylic acid i first let the beaker stand like this in hopes for some stuff that crashed out but

It didn’t then i put it into an iceberg and afterwards i decided to put it into the freezer overnight the next day after the recrystallization it looked like this still extremely dirty before continuing we got rid of the majority of the water by gravity filtration and afterwards washed it a single time with distilled water you can have a closer look at the crude

Product it honestly looks like and this is unacceptable just take a look at all of those impure spots in there before i’ll do a second recrystallization we are going to dry it in a vacuum chamber over anhydrous calcium chloride the air was sucked out and because of the reduced pressure the water started to boil soon afterwards the second recrystallization will

Be done in the solvent that doesn’t contain water and therefore complete dryness is necessary after it was mostly dried it looked like this air was let back into the vacuum chamber and we were ready for a recrystallization because my hot plate broke and i don’t have any other chance to do this we have to improvise and i built this extremely dangerous diy hot

Plate definitely can’t recommend anyone to repeat this because it’s fire hazard and it’s not really safe we added a small amount of 96 ethanol turned on the power supply and waited for it to dissolve it was probably way too much ethanol but we should still get some cleaner product dot blade did its job very well and at some points all of the acetyl salicylic

Acid dissolved once it had dissolved completely we were left with this sort of orange but clear solution the fact that we were left with a clean solution stated that we were finished here the hot blade was switched off and the beaker was placed in the freezer the next day a gravity filtration was performed for some strange reason most of the acetyl salicylic acid

Crashed out after the gravity filtration and therefore i decided to do a second one this was the stuff that crashed out after the first filtration we will just filter this again and afterwards going to label it as dirty acetyl sulcellic acid after the filtration we were left with these two things on the right side you can see the cleaner seal size of the gaset on

The left side you can see the dirty stuff it was powderized and left overnight in these paper trays to dry completely once it was dry it was packed into pre-weight bags for storage in the end we were left with 34.8 grams of acetyl salicylic acid this corresponds to yields around forty percent i decided not to recover any product from the solvent because it wasn’t

Worth my time i still have about three hundred grams of pure acetyl salicylic acid left i was able to reach eighty percent yields on a smaller scale with an excess of acetic anhydride a few years ago as a solvent thirty percent ethanol was used i performed the test for salicylic acid on both of these samples using the method listed above here and it proved that

None of these samples contained any salicylic acid or only a really small amount of it if you liked today’s video make sure to drop me one of these and consider subscribing if you don’t want to miss out on other awesome chemistry content in the future also if you like it feel free to support me on patreon i wish all of you a nice day until next time bye you

Transcribed from video
Making aspirin (acetylsalicylic acid) By Thy Labs