It could be possible that you are sulfating the alcohol or even the acid group or both? Thus under anhydrous conditions, I think sulfated products will be more thermodynamically favored than acetylated products. Sulfated products will be far more soluble in water or sulfuric acid than would be acetylated products.
I would think that using more water in the reaction would help. The reason is that the heat of mixing of sulfuric acid is a very strong function of water concentration, but the heat of hydrolysis of acetic anhydride is not. So raising the concentration of water a little bit will disfavor sulfation significantly by lowering the heat of mixing of sulfuric acid, but will leave the heat of hydrolysis of acetic anhydride the same.
It's worth noting that this argument is purely thermodynamic, not kinetic. But I don't think sulfation reactions are kinetically hindered under ambient conditions, so although it isn't always true, I think thermodynamic arguments are valid in this case. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Failed synthesis of aspirin due to excess sulfuric acid Ask Question.
Asked 6 years, 6 months ago. Active 2 years, 8 months ago. Viewed 6k times. Improve this question. Adding a large excess of aqueous acid would also hydrolyze the anhydride LS Thanks for answer. Vacuum filtration will separate the crystalline aspirin away from everything else in the reaction mixture except for any salicylic acid that did not react.
The aspirin should be analyzed for the presence of any contaminating salicylic acid. FeCl 3 reacts with phenols alcohol groups attached to aromatic rings to produce colored complexes.
Notice that salicylic acid contains the phenol functional group but aspirin does not. Therefore, the more salicylic acid that contaminates your aspirin, the darker the color will be with FeCl 3.
Section 2: Safety Precautions and Waste Disposal. Safety Precautions:. Use of eye protection is recommended for all experimental procedures. Sulfuric acid H 2 SO 4 is highly corrosive. Avoid contact with your eyes, skin, and clothing. In case of contact, rinse with plenty of water. Ask instructor to assist with the cleaning of any spills. Acetic anhydride is a lachrymator its vapor irritates the eyes causing tears to flow. Keep it in the fume hood. Waste Disposal:.
The reaction mixtures used in this experiment may be safely disposed of in the sink, followed by copious amount of running water. Solids, aspirin and salicylic acid, should be disposed of in the regular trash container. Section 3: Procedure. Part 1: Synthesis of Aspirin. Prepare a boiling-water bath by filling a mL beaker with about mL of tap water.
Put the beaker on the hot plate. Weigh out about 2. To do this, first tare a piece of weighing paper This means to put a piece of paper on the balance and press the zero or tare button.
It is OK to weigh a little extra mass do not return excess salicylic acid to its container as this might contaminate the entire amount if your spatula is not perfectly clean.
Record the mass of the solid. Place this solid into a mL Erlenmeyer flask other sizes may be acceptable. In the fume hood , measure out 4 mL of acetic anhydride in a small graduated cylinder and add it to the flask. From this point on, keep your flask under the hood, because it now contains acetic anhydride the vapors of acetic anhydride are very irritating.
Add about 5 drops of concentrated sulfuric acid. This will be the catalyst for the reaction. Place the flask in the boiling water bath and clamp it in place.
Heat the reaction for at least 15 minutes. Put at least 60 mL of laboratory water into a mL beaker or similar size. Then put this beaker in an ice-water bath. Use this cold water in steps 9, 12, 13, and 14 below. After the reaction has heated for at least 15 minutes, remove it from the boiling water bath.
In 1 or 2 mL portions, add about 10mL cold water to the reaction, swirl the reaction between each mL portions. This water will react and destroy any remaining acetic anhydride. Put the flask with the reaction into an ice water bath Fig. Crystals of aspirin should form. Chill for at least 10 minutes in order to obtain the maximum amount of crystalline product. Collect the aspirin crystals by vacuum filtration.
To prepare a vacuum filtration set up:. To ensure the reaction goes as quickly as possible we have to heat it. But how do you heat a reaction to boiling point without losing most of the product by evaporation? A reflux condenser is a long sealed glass tube surrounded by a water jacket through which cold water is pumped.
The hot gas produced rises up the tube and is cooled by the running water causing the gas to condense and return to the mixture as liquid thus saving your precious aspirin. After the reaction has been heated for some time we add ice to stop it. Slowing or stopping a reaction is known as quenching.
The ice has another role to play. Aspirin is only slightly soluble in water so if you add it to the reaction mixture the product would rather clump together than be in the water phase. We then need to separate the solid from the rest of the unwanted mixture. This can be done by pouring the entire contents of your flask through a fluted filter. Fluting increases the surface area available for the liquid to seep through, speeding up the filtration.
Before aspirin can be used it needs to be as pure as possible. No one wants to put a tablet in their mouth if there are some unknown impurities in it! There are various ways of finding out how clean your final product is and these are discussed in the video above.
Acylation of salicylic acid. One of the biggest considerations that any scientist has is safety. Is what you are doing safe for you and everyone around you? If not what measures can we put in place to reduce the risk? Lets start with the obvious things.
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