Synthesis of Aspirin
Abstract
This report is about the synthesis of Aspirin from Salicylic acid and Acetic anhydride. It talks about the methodology involved, the results obtained and the calculations used to determine how pure the product formed in the experiment was. It also talks about how improvements can be made to increase purity and how to test for purity.
Introduction
Aspirin is commonly used as a painkiller and in low doses can be used as a blood thinner for patients who suffer from blood clots according to WebMD. The chemical IUPAC name is 2-Acetoxybenzoic Acid or Acetylsalicylic acid. Aspirin is an ester which can be synthesised from Salicylic Acid (C7H6O3) and Acetic Anhydride (C4H6O3) from the process esterification.
The equation is C7H6O3 + C4H6O3 ⇌ C9H8O4 + C2H4O2.
According to Encyclopedia.com, in the mid 1700’s Reverend Edmund Stone found Salicylic acid in the “bark of a willow tree”. In 1853 Charles F. Gerhardt produced a “derivative of Salicylic acid”. Later in 1897, Felix Hoffmann “discovered a better method for synthesizing the drug”. Hoffmann paved the way for the modern synthesis process of Aspirin. Since Hoffmann, the process has been refined which has improved purity and efficiency of the product and process respectively.
Equipment Used
50g Salicylic Acid Heating Mantle
80ml Acetic Anhydride 1cm3 Pipette
0.5ml Concentrated Sulphuric Acid Pipette Holder
Round Bottom Flask Ice
750ml Cold Distilled Water Pan (For Ice)
Thermometer Suction Filtration Equipment (Büchner)
Methods
50g of Salicylic acid was mixed with 80ml of Acetic anhydride in the round bottomed flask. 0.5ml of concentrated sulphuric acid was then added using the 1cm3 pipette and pipette holder.
This mixture was then heated gradually using a heating mantle to the steady temperature of 70˚C for 30 minutes. Whilst it was heating it was ensured the sulphuric acid was dispersed by occasionally giving the flask a gentle shake to mix it. The solution in the flask was a pale yellow in colour. The temperature did not exceed 70˚C.
The flask was then cooled to 50˚C and the contents was poured into a beaker containing 750ml of cold water. The beaker was then placed in a pan of crushed ice.
Just before the filtration step, Aspirin of an unknown amount and purity was added to the mixture. This mixture was then placed in the Büchner funnel for vacuum filtration. The vacuum was then turned on and the mixture was left to be filtered until the moisture was gone. The mass of the beaker was weighed and recorded and then the product poured into a final beaker and left for a week.
After a week of completing the experiment the mass of the beaker that contained product was weighed again and recorded.
Using melting point apparatus, the melting point of the product was determined and documented.
Hazard and Risk Analysis
Salicylic acid (3) is a white solid at room temperature. It is a hazardous irritant if it comes in contact with skin.
Acetic anhydride (2) is a colourless clear liquid at room temperature. It is a corrosive liquid with a strong odour which can cause damage to the eyes, skin, lungs and mucous membranes.
Sulphuric acid (1) is a colourless, odourless and non-flammable liquid. This acid can be corrosive in the lungs, skin and eyes and also as an irritant on the skin.
The entire experiment was completed in a fume cupboard. The purpose of the fume cupboard is to allow the fumes from the substances to be removed for a safer working environment. For the substances used, inhalation and skin contact should be avoided at all times to prevent injury. Latex gloves, safety googles and laboratory coats were worn for protection.
If contact was to be made with any of the substances, the part of the body affected should be washed or flushed out immediately and then medical advice should be sought.
Results and Calculations
The mass of the beaker with the product was 167.4500g. The original mass of the beaker was 113.4159g. This