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Synthesis of Acetyl Salicylic Acid (Aspirin)

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    Date Experiment conducted: 05/02/2009 Date Report Written: 08/02/2009 Synthesis of Acetyl salicylic acid (Aspirin) Abstract Introduction: The following report contains information on how to produce aspirin. The experiment has been carried out on a small laboratory scale. The experiment starts by combining such chemicals such as salicylic acid and acetic anhydride. The synthesis of aspirin is classified as an esterification reaction. This is a substitution reaction where the alcohol group from salicylic acid reacts with ascetic anhydride to form an ester, (acetylsalicylic acid) which is commonly known as Aspirin.

    The report progresses further giving details to the procedure carried out and the experimental technique that has been developed to show how aspirin is produced. The report tests the melting point of the aspirin produced compared to textbook values as tests the amount of yield produced. The report also mentions how there are factors in the production of aspirin and how they affect the yield and purity. These can be found under the hypothesis subheading. As the report progresses the answers to the hypothesis become clear.

    The report then approaches to the hazards and risk analysis of the chemicals involved in the experiment and how precautions are taken to reduce these risks. The original data and obtained data are revealed, and then they are discussed with thorough interpretations along with conclusions made, as well as recommendations. Any information that is included in the report will be referenced at the end. Hypothesis: The following hypothesis will be tested: ? What is the actual yield produced in the experiment compared to the theoretical yield? ? Why are the reasons for this yield? What is the melting point of aspirin? ? What is the solubility of Aspirin in water? ? How is this affected by temperature changes? ? What are the major differences between your experimental process and the process most widely used in industry? Experimental Plan: An experiment will take place producing aspirin (Acetylsalicylic acid) from Salicylic acid and acetic anhydride. Once the aspirin has been produced in the laboratory, its yield will be measured. From analysing the original data values it is possible to calculate the theoretical yield using moles and masses.

    Comparing the theoretical yield with the actual yield produced, the quality of the experiment carried out will become evident. Temperature will be one of the hardest aspects to control; the quality of the experiment heavily lies on this. Therefore the difference in yield from the actual yield produced compared to the theoretical yield will give a direct indication on how temperature changes affects the aspirin produced. As the yield is produced its melting point will be found, and it will be compared to values of aspirin that have been stated in chemical textbooks.

    Then it will be discussed as to why the yield produced are the same or different and also why the melting point are the same or different. Using these ideas it will be deduced as how the temperature of water affects the solubility of the Aspirin. Then a comparison will be made between the experiments carried out in the laboratory and how the production of aspirin is carried out in industry. The information on how aspirin is carried out in industry will be established using various text books and internet sources that will be referenced at a later date. Procedure and Experimental Technique:

    Method of Production of 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 will be done by subtracting the mass of the dry weight by the mass of the beaker. Melting Point Procedure: ? Place a small amount of yield around 0. 5-0. 7 g in a very small test tube. ? Place the test tube in the melting point apparatus checker. ? Turn on the heater ? Look carefully at the aspirin in the small test tube. As you see it starting to melt makes a note of the temperature. ? Wait and observe a little longer until all of the aspirin has melted. As soon as this occurs note the temperature. Therefore you should get a temperature range of the aspirin Hazard and Risk Analysis:

    Included with the report is the MSDS data sheet. The precautions taken to reduce the risk of the hazardous chemicals are the following: ? 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. ? If there were any spillages they were noted to the lab technician. Data: ? 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 ? Starting Melting point temperature of aspirin: 110. 0°C ? Complete Melting point temperature of aspirin = 121. °C ? According to the “Handbook of Chemistry and Physics” the melting point of aspirin is 135°C. [i] ? Mass is measured in grams ? Temperature measures in degrees Celsius Results: The mass of salicylic acid that was provided was 50g. The relative molecular mass of salicylic acid is 138. Therefore we are able to calculate the number of moles of salicylic acid using the equation: m = n/ Mr Moles of acetic anhydride 50/138 = 0. 3623 mol The chemical name for Aspirin is Acetylsalicylic Acid. A balanced equation for the synthesis of Aspirin from Salicylic Acid and Acetic Anhydride is the following:

    Salicylic acid + acetic anhydride –> Acetylsalicylic acid + Acetic acid (C7H6O3) + (C4H6O3) –> (C9H8O4) + (C2H4O2) 0. 3623 mol + 0. 3623 mol 0. 3623 mol + 0. 3623 mol As we can see above the mole ratio is 1:1:1:1:1. Therefore moles acetylsalicylic acid (aspirin) = 0. 3623 mol To calculate the mass of aspirin that should be produced theoretically use the equation: m = mr * mol Mr of acetylsalicylic acid = 180 Therefore 180 * 0. 3623 = 65. 22g The above calculations show that theoretically there should be 65. 22g of aspirin produced.

    However from the experiment that was been done it was concluded that 56. 20g of aspirin was produced. Actual yield / theoretical yield *100 = yield % Therefore the percentage yield produced was (56. 20/65. 22) * 100 = 86. 2%. Overall this shows that the experiment was a success as a large amount of aspirin was produced, however these results also showed that there was major errors or inefficiencies in the experiment. The melting point of the Acetylsalicylic acid (Aspirin) was found to be 121°C according to the experiment carried out. The textbook “Handbook of Chemistry and Physics” showed the melting point of aspirin had a value of 135°C.

    The value of the melting point found in the experiment that was done earlier had a different value that has been recorded in the “Handbook of Chemistry and Physics”. This proves that the aspirin that had been made in the experiment was not 100% pure and contained some impurities. Discussion and Interpretation: Analysing the results obtained it is clear that the experiment was a success. 56. 6g of aspirin was attained. However compared to the theoretical yield it is evident that there was a great loss of aspirin that should have been formed.

    Also bearing in mind it is very impossible to get 100% yield it is still possible to obtain a greater amount of yield. There were many reasons to this. The factors that contributed to the inaccuracy of the experiment are the following: Reflux: The apparatus used in the experiment were quite old. They appeared to look worn out. For example the reflux used in the experiment has some sort of residue contained inside it. As a result the action of condensing was not 100% efficient. The reason for this is because water was not travelling all around the reflux tube as there were residue particles inside it.

    Were the particles could have been stuck would have meant water could not travel to that area therefore cooling was not able to take place here. As a result the vapour or gases formed in the reaction could have travelled up into reflux tube and left the system. Although this sounds far fetched it was still a flaw in the experiment. Balance: The balance used to calculate the mass of the wet and dry product along with the beaker was considerably outdated. It was hard to see the figures and it was old and had scratches on the panel. It was not digital and did had a disk shaped scale.

    Therefore the balance did not have a very good precision and would give a percentage error in the reading. The reactants: In the experiment that was carried out the reactants were not measured by the apprentices. Instead of the normal procedural method, the measured amounts of each substance were given. There was no way to tell weather these had been measured out correctly. As a result it had to be assumed they were correct. This could have been a reason as to why the yield was not very accurate. Heating Another problem found in the experiment was heating the reactants at the start of the experiment to 70 °C.

    As a heater was used it was not possible to select the maximum temperature required. Therefore when heating, heat was constantly being imputed into the system. However when 70°C was reached and the heater was turned off, it was observed that the temperature on the thermometer had risen around 10°C more after this point. As a result the chemicals were a little burnt. This could have affected the purity of the Aspirin formed at the end. Therefore this could also be a reason as to why the yield was not accurate and also explain why there was a significant difference in the temperatures.

    General Other errors that could not be avoided include losses in transferring substances and solutions and also in processes such as the filtration process and washing. Human error was also taken into account Time Other problems also included time factor. As there was a fixed time to complete the experiment, some parts of the experiment were rushed and were not done accurately. Due to this, a lack of accuracy occurred in general overall. As the reaction had taken place there was no possible way of knowing whether the complete reaction had taken place or whether it was partially complete.

    If the reaction has not fully completed then the Aspirin formed would not be pure, as it would contains unreacted reactants. Due to the time factor it was unable to make this judgment. This could be reason as for why the there was a great temperature difference in the melting points of aspirin, The solubility of aspirin in water varies with temperature. For example, in water, the solubility of aspirin increases as temperature increases. At 37°C 1g of aspirin is soluble in 100g of water. [ii] In boiling water, 1. 0 g of aspirin will dissolve in each gram of water. At 15°C, the solubility is only 0. 01 g of aspirin per gram of water.

    The solubility of aspirin in water increases as the temperature increases. The reason for this is due to an increase in kinetic energy. As the kinetic energy increase, molecules move faster and collide with other molecules, therefore there are more interactions. As the temperature of the water increases, the solubility of aspirin increases due to an increased amount of interactions and collisions. However if the temperature decreases, i. e. water temperature decreases, there is less kinetic energy hence the molecules do not interact as much with each other therefore the aspirin and water do not blend very easily together.

    At cooler temperature such as 0 degrees, the kinetic energy is very little as molecules are slowed down and there are little interactions between molecules of two substances, therefore allowing the aspirin molecules to stick together and “fall out” of the solution or crystallise. Overall most solids are more soluble in hot solvents than in cold solvents[iii] There are many major differences in the manufacturing of aspirin in the laboratory compared to major industrial processes. The first major differences are[iv]: ? the quality of the equipment used ? Size of the apparatus ? Quantity of raw materials (reactants) Quantity of Aspirin produced ? Shape of aspirin depending on the size and dosage (in industry) ? Tests such as disintegration tests and friability tests. ? Quality control departments. ? Packaging (in industry) Conclusion and Recommendations Overall the experiment was a success, considering the flaws in the experiment such as the apparatus and time. Although there were many errors it was a surprising to get a yield of around 80%. If the experiment was to be done again the following recommendations would be given: ? Use a precise heating apparatus that gives heat up to a certain degree. Use a digital balance with 2 decimal places. ? Repeat the experiment 3 times and work out an average yield ? Measure out all the substance individually. ? take longer time in completing the experiment ? use better apparatus that are 100% efficient ? Generally take more care with the experiment. Nomenclature List with Units m = Mass (measured in grams) n = Number of Moles (Mol) Mr = relative molecular mass Mol = Number of moles Apparatus: ? Thermometer ? Measuring cylinder 0. 5 +/- ml ? Round bottom Flask (quick fit flask) ? Pipette pump ? Pipette ? Jack/ Lift ? Clamp stand ? Clamp ? Heater Cooler (Cooling Column) ( Reflux apparatus) ? Filtration ? Filter paper ? Beaker 1 +/- 100 ml ? Beaker 2 +/- 100ml ? Stirrer ? Distilled water ? Plastic spatula ? 50g of salicylic acid ? 80ml of acetic anhydride ? 0. 5 ml of concentrated sulphuric acid ? Balance ? Fume cupboard ? Melting point apparatus checker ? Stopper ? Very small test tube Reaction Equations: Salicylic acid + acetic anhydride –> acetylsalicylic acid + acetic acid (C7H6O3) + (C4H6O3) –> (C9H8O4) + (C2H4O2) References: ———————– [i] [ii] Chemicalland: Lifestyle. (2008). ACETYLSALICYLIC ACID [online].

    Korea: Available from: http://chemicalland21. com/lifescience/phar/ACETYLSALICYLIC%20ACID. htm [Accessed 05 MAR 2009] [iii] About. com: (2006). How to Make Aspirin – Acetylsalicylic Acid. [online]. Available from: http://chemistry. about. com/od/demonstrationsexperiments/ss/aspirin_5. htm [Accessed 05 MAR 2009] [iv] How products are made: Volume 1. (2007). Aspirin [online]. Available from: http://www. madehow. com/Volume-1/Aspirin. html [Accessed 05 MAR 2009] Appendices: Appendix A- word processer used The document is word processed using Microsoft ® Word 2003 and is saved in the compatibility mode for word 2007

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