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Original proposal and method by Aidan Wong, performed by Aidan Wong, Will Barbour, Tom Ruane and Livy Jong
The Procedure:
The Procedure:
https://labmonk.com/synthesis-of-salicylic-acid-from-alkyl-salicylate
3ml of methyl-salicylate is transferred to approximately 50ml of 6M NaOH solution inside a 200ml reflux apparatus. Insert boiling chips.
The solution is refluxed under roaring blue bunsen flame for 30-45 minutes, starting from when the mixture starts to boil.
If the reaction mixture is oily, cloudy, or smells of oil of wintergreen, reflux for several more minutes. At the end the solution should be clear. Boiling chips are removed.
The solution is transferred to a 250 ml beaker.
Solution of 6M strong acid is added slowly, stirring with a glass rod. A pH probe is used to determine when the pH reaches 2 at which point no more acid should be added. This ensures that the acid is in excess and as much of the sodium salicylate reacts to form salicylic acid as possible. Yield, therefore, is maximised.
The beaker of solution and crystals is cooled in an ice bath for ten minutes.
It is then vacuum filtered and rinsed with ice-cold deionised water.
The product is then heated again and allowed to cool, first to RTP and then using an ice bath to cool further. The product should recrystalize
The product is then left to air dry. The yield was found to be 80.64% by the original researchers- masses could be taken using a mass balance throughout to determine the yield if desired.
Day 1: Salicylic Acid
Day 1: Salicylic Acid
The first step of the process is to synthesise salicyclic acid from the oil of wintergreen, a commonly sold essential oil.
Methyl Salicylate (oil of wintergreen) will be alkaline hydrolysed under reflux to form sodium salicylate, an intermediate, as well as methanol and water. This is then further reacted with a strong acid which will protonate the sodium salicylate leading to the formation of sodium sulfate (aq) and the desired product, salicylic acid, in an acid base reaction.
Safety Precautions:
Safety Precautions:
afety is something we have very much seriously taken into consideration. We are choosing to carry out this procedure ourselves as we do not want to endanger others, who may not have had experience working with chemicals nearly this concentrated.
As we are working with highly corrosive chemicals in excess of 6M, the following precautions will be taken:
Latex gloves to be worn at all times to prevent corrosion of skin in case of accidents
Eye protection to be worn at all times
Lab coat to be worn at all times
When the reaction mixture is exposed we will work in a fume cupboard
In the unlikely event of contact with skin there will also be water taps on hand to wash off alkali/acid.
As we are working with naked flames with highly concentrated chemicals for a prolonged period of time the following precautions will be taken:
Heatproof mat to be used
The apparatus will never be left unaccompanied or unmonitored
The apparatus will be kept far from any flammable material
The salicylic acid crystals themselves pose little danger however will be left far from any other pupils when stored as a precaution. Parafilm will be placed over the container as a further precaution, just in case.
Day 2: Synthesis of Acetylsalicylic Acid (Aspirin)
Day 2: Synthesis of Acetylsalicylic Acid (Aspirin)
In this experiment salicylic acid will be reacted with acetic anhydride in the presence of a highly concentrated sulfuric acid catalyst to form acetylsalicylic acid, also known as apsirin, our desired final product. Ethanoic acid will also be formed. The final product will be crystallised twice and further steps are taken to remove impurities. We hope this does not take a third day but this may become necessary due to unforeseen complications.
The Procedure:
The Procedure:
Weigh out two grams of salicylic acid and transfer into 125ml conical flask
Add 5 ml of 10M acetic anhydride followed by 5 drops of highly concentrated sulfuric acid. Use a dropper. Swirl gently until salicylic acid dissolves.
Gently heat on steam bath for 10+ minutes.
Allow the flask to cool to room temperature.
After no more crystallisation occurs, add 50ml of dH2O.
Transfer into ice bath and allow to cool
Filter out the crystals using a Buchner funnel. Use some of the filtrate to rinse out the conical flask if necessary.
Record the weight of the crude solid which probably contains water.
Stir the solid with 25 ml of a saturated aqueous sodium bicarbonate solution in a 150ml beaker until all signs of reaction have ceased.
Filter solution through a Buchner funnel to remove any insoluble impurities that may have been formed. Wash the beaker with 5-10ml dH2O and filter this too.
Stirring, carefully pour filtrate into an ice-cold HCl solution. 13.5ml HCl in a 150 ml beaker. Cool in an ice bath. Ensure the solution is acidic using blue litmus paper.
After the aspirin has completely precipitated out filter the solid by suction filtration and wash three times with 5ml of cold water each,
Remove all the liquid from crystals by pressing with a clean stopper or cork,
Air dry the crystals, transfer to a watch glass to dry.
Test for unreacted SA using ferric chloride.
Weigh when the product is completely dry, this can be sped up with gentle heating
The following steps are optional
Dissolve final product in 2-3 ml of hot ethyl acetate in a small conical flask. Swirl. Ensure product is completely dissolved while heating in steam bath continuously.
Cool to room temperature then in an ice bath.
Collect product via (vacuum) filtration
Rinse out of the flask with a few ml of cold petroleum ether
Wait for product to completely dry before collecting. Weigh using a mass balance if desired.
Safety Precautions:
Safety Precautions:
Safety is something we have very much seriously taken into consideration. We are choosing to carry out this procedure ourselves as we do not want to endanger others, who may not have had experience working with chemicals nearly this concentrated.
As we are working with highly corrosive chemicals, some of them way in excess of 6M, the following precautions will be taken:
Latex gloves to be worn at all times to prevent corrosion of skin in case of accidents
Eye protection to be worn at all times
Lab coat to be worn at all times
When the reaction mixture is exposed we will work in a fume cupboard
In the unlikely event of contact with skin there will also be water taps on hand to wash off alkali/acid.
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