Synthesis of Acetyl Salicylic Acid (Aspirin)

Table of Content


The report details the production of Aspirin in a small laboratory, highlighting the esterification reaction between salicylic acid and acetic anhydride. This reaction replaces salicylic acid’s alcohol group with acetic anhydride to form a new compound called acetylsalicylic acid or Aspirin.

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The report provides further details about the procedure and experimental technique employed in the synthesis of aspirin, as well as information on its production. It examines the melting point of the synthesized aspirin in comparison to established values and assesses the yield. Additionally, it investigates the factors that influence both the yield and purity of aspirin during production, which are discussed under the hypothesis heading. As we progress through the text, it becomes evident that these hypothesis inquiries have been answered.

The report examines the dangers and evaluation of risks associated with the chemicals utilized in the experiment. It also covers the safety precautions implemented to lessen these risks. The report includes both initial data and data collected during the experiment, along with detailed explanations, conclusions, and recommendations. All sources mentioned in the report will be cited in its final section.


  1. The following hypothesis will be tested:
  2. What is the actual yield produced in the experiment compared to the theoretical yield?
  3. Why are the reasons for this yield?
  4. What is the melting point of aspirin?
  5. What is the solubility of Aspirin in water?
  6. How is this affected by temperature changes?
  7. What are the major differences between your experimental process and the process most widely used in industry?

Experimental Plan

A laboratory experiment will be performed to synthesize aspirin (Acetylsalicylic acid) using Salicylic acid and acetic anhydride. Following that, the quantity of aspirin produced will be measured. The initial data values will then be examined to determine the theoretical yield based on mole and mass calculations.

To assess the experiment’s quality, it is crucial to compare the theoretical yield and actual yield. Temperature control poses a significant challenge as it greatly impacts the experiment’s quality. Thus, analyzing the disparity between the actual and theoretical yields allows for direct evaluation of how temperature fluctuations influence aspirin production. After obtaining the yield, its melting point will be measured and compared to values provided in chemical textbooks for aspirin.

Firstly, the text will examine the similarities and differences between the yield produced and melting point of a substance. It will also explore how these factors relate to the solubility of Aspirin in different water temperatures. Furthermore, it will compare laboratory experiments with industrial production methods of Aspirin, sourcing information from textbooks and online references for later citation.

Procedure and Experimental Technique

Production Method for Aspirin:

  • Before starting the experiment, read the COSHH analysis sheets for each of the chemicals that are going to be used in the experiments. This way an idea of the safety conditions and the handling of chemicals can be considered.
  • Measure out 50g of salicylic acid with care.
  • Measure out 80ml of acetic anhydride.
  • Using a round-bottomed Quick-fit flask mix the measured Salicylic acid and the acetic anhydride together.
  • Now measure out between (0. 4-0. 5) ml or of concentrated sulphuric acid. Note: (no more then 0. 5ml) ? Shake the mixture very well.
  • Swirl the mixture using a stirring rod before heating.
  • Gently heat the Quick-fit flask mixture for 30 minutes at 70 degrees. (Do not allow temperature to exceed 70 degrees). This is for the reaction to occur while preventing the aspirin from re-crystallizing prematurely
  • Make sure while heating, in equal intervals agitate the mixture carefully to ensure the sulphuric acid is dispersed.
  • If necessary remove the heater and carefully shake the mixture ensuring you do not get burnt or hurt.
  • After 30 minutes of heating leave the flask standing to cool to about 50 degrees. Place the contents into a beaker with around 750 ml of cool water.
  • Measure the mass of a separate beaker in which you are going to use later in the experiment.
  • Then carefully filter the product using the filter paper and filtering equipment such as the vacuumed container.
  • One it has been filtered weight the product with the beaker (that was measured previously). This will be the wet weight.
  • Then place the beaker into a warm and dry place and leave for 24 hours
  • After 24 hours weigh the beaker containing the product again and this will be the dry weight.
  • Calculate the yield.

This can be achieved by subtracting the mass of the beaker from the mass of the dry weight. The process for determining the melting point is as follows:

  • Put a small amount of yield (approximately 0.5-0.7 g) in a very small test tube.
  • Insert the test tube into the melting point apparatus checker.
  • Activate the heater.
  • Carefully observe the aspirin in the test tube. Take note of the temperature when it starts to melt.
  • Continue observing until all of the aspirin has melted. Record this temperature.

By following these steps, you will obtain a temperature range for the aspirin. It is also important to consider hazard and risk analysis.

The report includes the MSDS data sheet and details the precautions taken to minimize the risks associated with hazardous chemicals.

  • PPE (personal protective equipment) was used such as laboratory coats as well as safety goggles. The lab coats were 75% of the length of the apprentice’s height. This ensured that the majority of the apprentice’s clothes and body were protected. Therefore precautions were taken with chemicals such as sulphuric acid that causes severe burns.
  • The safety goggles were used to ensure, chemicals did not come in contact with the eyes or areas near to the eyes. Therefore precautions to chemicals such as Acetylsalicylic acid were taken as it is irritating to the eyes.
  • Salicylic acid is irritating to the skin and sulphuric acid causes severe burns. Gloves were used to ensure chemicals did not come in contact with the skin as chemicals could enter the body through broken skin.
  • Fume cupboards were also used to ensure any dangerous vapour was not inhaled and also to keep the apprentice at a safe distance in case any vigorous reactions took place. For example Acetic Anhydride could be harmful is inhaled in large amounts.
  • Therefore specific safety measures were taken. This was done by providing a safety glass barrier that was placed in front of the fume cupboard to keep a safe distance.

The lab technician was notified of any spillages.

The information:

  • 50g of Salicylic acid
  • 80 ml acetic anhydride
  • 0. 5 ml of sulphuric acid
  • 750 ml of cold water
  • Mass of beaker = 166. 8 g
  • Mass of wet product with beaker = 253. 0g
  • Mass of dry product with beaker = 223. 0g
  • Mass of Product = 56. 2g

The initial melting point temperature of aspirin is:

  • 110. 0°C
  • Complete Melting point temperature of aspirin = 121. °C

Temperature measures in degrees Celsius Results: The given mass of salicylic acid is 50g. The relative molecular mass of salicylic acid is 138. We can use the equation: m = n/ Mr to determine the number of moles of salicylic acid.

Moles of acetic anhydride: 0.3623 mol

The chemical name for Aspirin is Acetylsalicylic Acid. The balanced equation for the synthesis of Aspirin from Salicylic Acid and Acetic Anhydride is as follows:

The reaction between salicylic acid and acetic anhydride results in the production of Acetylsalicylic acid and Acetic acid. The chemical formulas for the reactants and products are as follows:

(C7H6O3) + (C4H6O3) → (C9H8O4) + (C2H4O2)

Both components, 0.3623 mol each, are utilized equally in the reaction.

The mole ratio shown above is 1:1:1:1:1.

The mole quantity of acetylsalicylic acid, also known as aspirin, is 0.3623 mol.

The formula for determining the theoretical mass of aspirin is m = mr * mol. The molar mass (Mr) of acetylsalicylic acid is 180, so when multiplied by 0.3623, it equals 65.22g.

Based on calculations, the projected quantity of aspirin that will be manufactured is approximately 65.22g.

However, it was concluded from the experiment that 56.20g of aspirin was produced.

The formula to calculate the yield percentage is:
Actual yield divided by theoretical yield, multiplied by 100.

Thus, the percentage yield obtained was (56.20/65.22) * 100 = 86.2%.

Despite some flaws in the procedures, the experiment was successful in generating a large amount of aspirin. The results revealed that Acetylsalicylic acid (Aspirin) has a melting point of 121°C, contradicting the information from the “Handbook of Chemistry and Physics” which states it as 135°C.

The melting point value obtained in a previous experiment was different from the value recorded in the “Handbook of Chemistry and Physics.” This difference suggests that there were impurities present in the experimental aspirin, which led to a lower purity level.

Discussion and Interpretation

The experiment successfully obtained 56.6g of aspirin, but the yield was lower than expected. It is important to note that achieving a 100% yield is impossible, but it is possible to increase the yield. The inaccuracies observed during the experiment were influenced by several factors.

Reflux: The experiment employed dated and dilapidated equipment, specifically the reflux apparatus. The reflux apparatus was visibly worn out and contained residue that impeded condensation and diminished efficiency. The presence of residue obstructed proper water circulation within the reflux tube.

If particles were stuck, water couldn’t reach that area and therefore cooling couldn’t occur. This would have allowed vapour or gases formed in the reaction to travel up the reflux tube and escape the system. Although this may seem unlikely, it was still a flaw in the experiment.

Balance: The balance used for calculating the mass of the wet and dry product, as well as the beaker, was significantly outdated. It had scratches on the panel and the figures were difficult to see. It had a disk-shaped scale and was not digital. Hence, the balance lacked precision and would result in a percentage error in the reading.

The reactants: In the experiment, the apprentices did not measure the reactants using the normal procedural method. Instead, they were given predetermined amounts of each substance. The accuracy of these measurements could not be confirmed, so it was assumed that they were correct. This lack of precision in measuring the reactants may have resulted in an inaccurate yield. Another issue in the experiment was heating the reactants to 70 °C at the beginning.

The use of a heater prevented the selection of the desired maximum temperature, resulting in continuous heat input into the system. When the temperature reached 70°C and the heater was turned off, it was noticed that the thermometer reading increased by approximately 10°C afterwards. This caused some burning of the chemicals, potentially affecting the purity of the final Aspirin product. Consequently, this could have caused inaccuracies in the yield and could explain the significant temperature difference observed.

General errors that were unavoidable include losses in transferring substances and solutions, as well as in processes such as filtration and washing. Additionally, human error was considered. Another issue that was encountered was the time factor. Since there was a limited time to complete the experiment, certain parts were rushed and not performed accurately. Consequently, a lack of overall accuracy occurred. It was also uncertain whether the reaction had fully occurred or only partially.

If the reaction is incomplete, the resulting Aspirin will not be pure as it will still contain unreacted substances. This inability to determine completeness may explain the significant difference in melting points of aspirin. Additionally, temperature affects aspirin’s solubility in water; as temperature increases, so does its solubility. At 37°C, one can dissolve 1g of aspirin in 100g of water.

Water has a solubility of 1.0 g of aspirin per gram of water at boiling temperature, but this decreases to only 0.01 g of aspirin per gram of water at 15°C. The solubility increases as the temperature rises because higher temperatures cause molecules to have greater kinetic energy and move faster, resulting in more collisions between them. These increased interactions between molecules lead to an increase in solubility. Consequently, the solubility of aspirin also increases with increasing water temperature due to the increased amount of molecule interactions and collisions.

When the temperature decreases, particularly the water temperature, it affects the ability of aspirin and water to mix due to a decrease in kinetic energy. At very low temperatures like 0 degrees, molecules have very little kinetic energy and become slow-moving. As a result, there is limited interaction between the molecules of both substances, leading to the formation of precipitates or crystals from aggregated aspirin molecules. Generally, solvents that are hot are better at dissolving solids compared to cold solvents.

Cite this page

Synthesis of Acetyl Salicylic Acid (Aspirin). (2018, Feb 16). Retrieved from

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